DOUBLE STACKED PROJECTION
BACKGROUND OF THE INVENTION
Modern super high resolution 4K digital cinema projectors designed for normal sized
cinema screens have a resolution ideal also for very large screens but lack the
brightness needed for these. Double stacking projectors are an effective way of in¬
creasing brightness, but traditional double stacking is difficult at such high resolu¬
tions because the tolerance in the alignment of projected images becomes very
small and is hard to meet during presentations due to thermal induced movements
in the mechanical and optical parts and vibrations from the audio system. In other
applications like temporary projection set-ups, home cinemas etc., alignment of
double stacked projectors may be difficult to maintain even when working at much
lower resolutions.
"Double stacking" of projectors, i.e. overlaying the images of two projectors project
ing the same image, is a well known way to increase brightness. However, it is also
well known that traditional double stacking requires high maintenance of the align
ment of the projectors to maintain image quality.
In 4K projection, traditional double stacking is not considered an option, because it
would be impossible to keep the sharpness and detail on par with that of a single 4K
projector throughout a presentation. This is unfortunate for giant screen theatres,
because while 4K projectors lend themselves well to giant screens in terms of resolution,
available projectors generally do not have enough light for giant screens, so
stacking would seem desirable to double the light output.
OBJECT OF THE INVENTION
An object of the invention is to present a double stacking system that overcomes the
above mentioned difficulty and presents other advantages. Exemplary applications
may be giant screen cinemas, simulators, conference presentations, staging, exhibits,
outdoor projection, traditional cinemas, home cinemas, and other applications
where brightness of a projected image is a consideration.
An object of the present invention is also to present a novel image processing systern
for double stacked projector configurations that overcomes the above men
tioned maintenance difficulties and provides for a high quality, low-maintenance
double stacking system even for 4K projection.
SUMMARY OF THE INVENTION
An image processing circuit comprising thresholding limiters and constrained
smoothing filters splits a source image into two images, which, when projected over
laid on a projection surface by a pair of double-stacked projectors, together form an
image essentially identical to the source image, but where one image has significantly
less high frequency components. The invention presents advantages over
traditional double stacking in aspects of projector alignment, content copy protec
tion, banding artefacts and equipment costs.
GENERAL DESCRIPTION
The above objects are according to a first aspect of the present invention met by a
method for producing a first output image and a second output image for being pro
jected by a first projector and a second projector, respectively, the method compris
ing:
(a) providing a source image comprising a plurality of pixels, each pixel
having an source value,
(b) providing a threshold value for each pixel of the plurality of pixels,
in a first alternative
(d) generating a temporary image comprising a temporary value for each
pixel of the plurality of pixels, the temporary value being generated in a process
equivalent to: (i.i) determining a first maximum value as the maximum of the
source value and its corresponding threshold value for each pixel, (i.ii) determining
an intermediate value by subtracting the corresponding threshold value from the first
maximum value for each pixel, (i.iii) generating the temporary value from the inter
mediate value for each pixel;
or in a second alternative
(c) providing an inverted threshold value for each pixel of the plurality of
pixels, each inverted threshold value being an inversion of its corresponding thresh
old value,
(d) generating a temporary image comprising a temporary value for each
pixel of the plurality of pixels, the temporary value being generated in a process
equivalent to: (i.i) determining an intermediate value as the minimum of the source
value and its corresponding inverted threshold value for each pixel, (i.ii) generating
the temporary value from the intermediate value for each pixel;
or in a third alternative
(c) providing an inverted threshold value for each pixel of the plurality of
pixels, each inverted threshold value being an inversion of its corresponding threshold
value,
(d) generating a temporary image comprising a temporary value for each
pixel of the plurality of pixels, the temporary value being generated in a process
equivalent to: (i.i) determining a first maximum value as the maximum of the
source value and its corresponding threshold value for each pixel, (i.ii) determining a
first difference value by subtracting the corresponding threshold value from the first
maximum value for each pixel, (i.iii) determining a first minimum value as the mini
mum of the source value and its corresponding inverted threshold value for each
pixel, (i.iv) determining an intermediate value as the minimum of the first difference
value and the first minimum value for each pixel, (i.v) generating the temporary
value from the intermediate value for each pixel;
or in a fourth alternative
(c) providing an inverted threshold value for each pixel of the plurality of
pixels, each inverted threshold value being an inversion of its corresponding thresh
old value,
(d) generating a temporary image comprising a temporary value for each
pixel of the plurality of pixels, the temporary value being generated in a process
equivalent to: (i.i) determining a first maximum value as the maximum of the source
value and its corresponding threshold value for each pixel, (i.ii) determining a first
difference value by subtracting the corresponding threshold value from the first
maximum value for each pixel, (i.iii) determining a first minimum value as the mini
mum of the source value and its corresponding inverted threshold value for each
pixel, (i.iv) determining an intermediate value from a first range of values comprising
values between the first difference value and the first minimum value for each pixel,
(i.v) generating the temporary value from the intermediate value for each pixel;
and in all alternatives
(e) generating the first output image comprising a first output value for each
pixel of the plurality of pixels, the first output value being generated from the temporary
value and the source value for each pixel, and
(f) generating the second output image comprising a second output value
for each pixel of the plurality of pixels, the second output value being generated
from the temporary value.
The method according to the first aspect of the present invention may further com
prise in the first alternative:
(c) providing an inverted threshold values for each pixel of the plurality of
pixels, each inverted threshold value being an inversion of its corresponding thresh
old value.
The threshold value for each pixel of said plurality of pixels may be limited to be
within an interval having a maximum threshold value and a minimum threshold
value for each pixel. Each inverted threshold value being an inversion of its corre
sponding threshold value may be understood as equivalent to the inverted threshold
value being equal to or approximately equal to the maximum threshold value minus
the threshold value for each pixel.
The process of generating the temporary value may further comprise in all alterna¬
tives: (i.vi) smoothing the intermediate value for each pixel; and in the third and
fourth alternatives: (i.vi) smoothing the first difference value and/or the first minimum
value.
Smoothing the intermediate value of a pixel is here understood to involve the inter
mediate value of at least one other pixel, for example a neighbouring pixel. Smoothing
the first difference value of a pixel is here understood to involve the first differ¬
ence value of at least one other pixel, for example a neighbouring pixel. Smoothing
the first minimum value of a pixel is here understood to involve the first minimum
value of at least one other pixel, for example a neighbouring pixel. The smoothing
may comprise a spline filter, a membrane filter, and/or an envelope filter.
The smoothing may be adapted for limiting the intermediate value to a value from
the first range of values subsequent to the smoothing. The smoothing may comprise
a first dilation operation comprising a first dilation radius. The first dilation radius
may be 4 pixels, or approximately 0.3% of the width of the temporary image. The
smoothing may comprise a first blur operation. The first dilation operation may be
performed prior to the first blur operation. The first blur operation may comprise a
first blur radius approximately equal to or smaller than the first dilation radius. The
first blur operation may comprise a first Gaussian blur operation. The first Gaussian
blur operation may have a standard deviation approximately equal to a third of the
first blur radius, or approximately equal to or smaller than 4/3 pixels, or approxi
mately 0.1% of the width of the temporary image. The first blur operation may com¬
prise a first mean filtering operation.
The process generating the temporary value may further comprise: (i.vii) determin¬
ing a second minimum value as the minimum of the intermediate value and the in
verted threshold value for each pixel, (i.viii) generating a second smoothed value by
smoothing the second minimum value for each pixel, and (i.ix) generating the tem
porary value from the second smoothed value for each pixel.
Smoothing the second minimum value of a pixel is here understood to involve the
second minimum value of at least one other pixel, for example a neighbouring pixel.
The smoothing of the second minimum value may comprise a spline filter, a mem
brane filter, and/or an envelope filter.
The smoothing of the second minimum value may comprise a second dilation op¬
eration comprising a second dilation radius. The second dilation radius may be 2
pixels, or approximately 0.17% of the width of the temporary image. The second
dilation radius may be variable. The second dilation radius may be variable in a
second range of values including zero. The smoothing of the second minimum value
may comprise a second blur operation. The second dilation operation may be per
formed prior to the second blur operation. The second blur operation may comprise
a second blur radius approximately equal to or smaller than the second dilation ra¬
dius. The second blur radius may be variable. The second blur radius may be vari
able in a third range of values including zero. The second blur radius and the sec¬
ond dilation radius may be coupled such that one changes as a function of the
other.
The second blur operation may comprise a second Gaussian blur operation. The
second Gaussian blur operation may have a standard deviation approximately equal
to a third of the first blur radius, or approximately equal to or smaller than 2/3 pixels,
or approximately 0.055% of the width of the temporary image.
The second blur operation may comprise a second mean filtering operation.
Providing the source image may comprise: (ii.i) providing a gamma encoded source
image encoded by a first gamma encoding, (ii.ii) generating a gamma decoded
source image by performing a first gamma decoding of the gamma encoded source
image, the gamma decoding corresponding to the first gamma encoding, and (ii.iii)
outputting the gamma decoded source image as the source image.
The method according to the first aspect of the present invention may further comprise:
(g) performing a second gamma encoding of the first output image, the
second gamma encoding corresponding to a second gamma decoding of the first
projector.
The method according to the first aspect of the present invention may further com¬
prise:
(h) performing a third gamma encoding of the second output image, the
third gamma encoding corresponding to a third gamma decoding of the second pro
jector.
The process of generating the temporary value may further comprise in all alterna¬
tives: (i.x) performing a first colour correction of the intermediate value for each
pixel, and in the third and fourth alternatives: (i.x) performing a first colour correction
of the intermediate and/or the first difference value for each pixel.
In all alternatives the first colour correction may be adapted for correcting the inter¬
mediate value to obtain approximately the same first hue as the corresponding
source value and in the third and fourth alternative the first colour correction being
adapted for correcting the first difference value and/or the intermediate value to ob¬
tain approximately the same first hue as the corresponding source value. The first
colour correction may comprise a process equivalent to: (iii.i) calculating a constant
K for each pixel, K being equal to the maximum of R 11/R6, G 11/G6, and B 1/B6;
R6, G6, and B6 are the pixel colours of the source image; and R 11, G11, and B 1
are the pixel colour values subsequent to determining the first intermediate value for
each pixel, (iii.ii) correcting the intermediate value by replacing it with the source
value multiplied with the constant K for each pixel.
The method according to the first aspect of the present invention may further com
prise: (i) lowering the spatial resolution of the second output image and/or perform
ing a blur operation on the second output image. The method according to the first
aspect of the present invention may further comprise: (j) encrypting the first output
image. The method according to the first aspect of the present invention may further
comprise: (k) recording the first output image on a first recording medium. The
method according to the first aspect of the present invention may further comprise:
(I) extracting the first output image from the first recording medium. The method according
to the first aspect of the present invention may further comprise: (m) re¬
cording the second output image on a second recording medium. The method ac¬
cording to the first aspect of the present invention may further comprise: (n) extract¬
ing the second output image from the second recording medium.
The method according to the first aspect of the present invention may further com
prise: (o) performing a geometric correction of the second output image, the geo
metric correction being adapted for aligning an image projected by the second pro¬
jector with an image projected by the first projector.
The process of generating the temporary value may further comprise: (i.xi) perform
ing an erosion operation, preferably a grey scale erosion operation having a radius a
half pixel, a full pixel, 0.04% of the width of temporary image, or 0.08% of the width
of temporary image, on the intermediate value for each pixel of the plurality of pixels.
In the fourth alternative, the source value may be excluded from the first range of
values for each pixel. In the fourth alternative, the first range of values may further
comprise the first difference value and the first minimum value.
The first output value may be generated for each pixel in a process equivalent to:
(iv.i) determining a second difference value by subtracting the temporary value from
the source value for each pixel, and (iv.ii) generating the first output value from the
second difference value.
The first output value may be generated for each pixel in a process equivalent to:
(iv.i) determining a second difference value by subtracting the temporary value from
the source value for each pixel, (iv.ii) generating a first ratio by dividing the second
difference value by the threshold value for each pixel, and (iv.iii) generating the first
output value from the first ratio for each pixel.
The second output value may further be generated from the inverted threshold
value. The second output value may be generated for each pixel in a process
equivalent to: (v.i) generating a second ratio by dividing the temporary value by the
inverted threshold value for each pixel, and (v.ii) generating the second output value
from the second ratio for each pixel.
The threshold value for each pixel of the plurality of pixels may represent the frac¬
tion of the total illumination intensity which the first projector contributes to at the
corresponding position on the projection surface in a projection of a uniform and
maximum intensity image from the first projector and the second projector, or in a
projection of a uniform and maximum intensity image from each the first projector
and the second projector, or in a projection of a uniform and maximum intensity im
age from the first projector, or in a projection of a uniform and maximum intensity
image from the second projector.
The threshold value for each pixel of the plurality of pixels may be derived by divid¬
ing the total illumination intensity, which the first projector contributes to at the co r
responding position on the projection surface by the combined total illumination in
tensity from each of the first projector and the second projector at the corresponding
position in a projection of a uniform and maximum intensity image.
The method according to the first aspect of the present invention may further com
prise:
(p) adjusting the temporary image to include an alignment pattern.
The method according to the first aspect of the present invention may further com
prise:
(q) providing the alignment pattern,
(r) adjusting the temporary image by adding the alignment pattern to the
temporary image,
(s) adjusting the temporary image by a process equivalent to: (vi.i) deter¬
mining a fourth minimum value as the minimum of the temporary value and its cor
responding source value for each pixel, and (vi.ii) adjusting the temporary value to
the fourth minimum value for each pixel.
The alignment pattern may comprise a grid, a mesh, a barcode, and/or a semacode,
and alternatively or additionally the alignment pattern comprising a regular pattern of
elements, and/or an irregular pattern of elements, and alternatively or additionally
the alignment pattern comprising a regular pattern of dots and/or cross hairs, and/or
an irregular pattern of elements of dots and/or cross hairs.
The above objects are according to a second aspect of the present invention met by
a method for double stacking a first output image and a second output image on a
projection surface by a first projector and a second projector, the method compris
ing:
(aa) positioning and orienting the first projector and the second projector for
overlaying the first output image and the second output image on the projection sur
face,
(ab) producing the first output image and the second output image by the
method according to the first aspect of the present invention,
(ac) supplying the first output image and the second output image to the first
projector and the second projector, respectively, and
(ad ) projecting the first output image and the second output image by the
first projector and the second projector, respectively.
The first projector and the second projector may generate a superimposed image on
the projection surface. The method according to the second aspect of the present
invention may further comprise:
(ae) recording a first captured image of the superimposed image,
(af) determining a first contribution of the first projector to the first captured
image,
(ag) generating a first feedback image from the first contribution,
(ah) generating a first set of misalignment vectors from the first feedback
image and the first output image by a feature tracking and/or feature matching,
(ai) generating a first warped image of the first captured image by a first
warping comprising the first set of misalignment vectors,
(aj) generating a second feedback image by subtracting the first output im¬
age from the first warped image,
(ak) generating a second set of misalignment vectors from the second feed¬
back image and the second output image by a feature tracking and/or feature
matching,
(al) generating a third set of misalignment vectors from the first set of mis¬
alignment vectors and the second set of misalignment vectors, and
(am) deriving a first geometric correction of the first output image and/or the
second output image from the third set of misalignment vectors.
Determining the first contribution of the first projector may comprise a high pass f il
tering of the first captured image.
The above objects are according to a third aspect of the present invention met by a
method for deriving a correction of a double stacking of a first output image and a
second output image on a projection surface by a first projector and a second pro¬
jector, the method comprising:
(ba) positioning and orienting the first projector and the second projector for
overlaying the first output image and the second output image on the projection surface,
(bb) producing a first output for a first source image, the first output compris
ing the first output image and the second output image produced by the method ac
cording to an example of the first aspect of the present invention including an align
ment pattern for the first source image,
(be) supplying the first output image and the second output image of the first
output to the first projector and the second projector, respectively, and
(bd ) projecting the first output image and the second output image of the first
output by the first projector and the second projector, respectively, on the projection
surface,
(be) recording a first captured image comprising the first output image and
the second output image of the first output projected on the projection surface,
(bf) detecting a contribution of the misalignment pattern of the first output in
the first captured image
(bg) deriving a geometric correction for the second output image from the
detected contribution of the misalignment pattern of the first output.
The method according the second aspect of the present invention may further com¬
prise:
(bh) producing a second output for a second source image for being dis¬
played subsequent to the first source image, the second output comprising the first
output image and the second output image produced by the method according to an
example of the first aspect of the present invention including an alignment pattern
for the second source image,
(bi) supplying the second output image and the second output image of the
second output to the first projector and the second projector, respectively, and
(bj ) projecting the second output image and the second output image of the
second output by the first projector and the second projector, respectively, on the
projection surface,
(bk) recording a second captured image comprising the first output image
and the second output image of the second output projected on the projection sur
face,
(bl) detecting a contribution of the misalignment pattern of the second output
in the second captured image,
(bm) deriving a geometric correction for the second output image from the
detected contribution of the misalignment pattern of the second output.
The method according the second aspect of the present invention may further comprise:
(bh) producing a second output for a second source image for being d is
played subsequent to the first source image, the second output comprising the first
output image and the second output image produced by the method according to an
example of the first aspect of the present invention including an alignment pattern
for the second source image,
(bi) supplying the second output image and the second output image of the
second output to the first projector and the second projector, respectively, and
(bj ) projecting the second output image and the second output image of the
second output by the first projector and the second projector, respectively, on the
projection surface,
(bk) recording the first captured image comprising the first output image and
the second output image of the second output projected on the projection surface,
(bl) detecting a contribution of the misalignment pattern of the first output in
the first captured image further comprising detecting a contribution of the misalign
ment pattern of the second output in the first captured image,
(bm) deriving a geometric correction for the second output image from the
detected contribution of the misalignment pattern of the first output and the second
output.
Detecting a contribution of the misalignment pattern of the first output in the first
captured image and detecting the contribution of the misalignment pattern of the
second output in the second captured image may further comprise a time averaging
of the first captured image and the second captured image. Detecting of a contribu
tion of the misalignment pattern of the first output and the second output may com
prise high pass filtering.
The misalignment pattern of the first output and the misalignment pattern of the
second output may be the same. The misalignment pattern of the first output and
the misalignment pattern of the second output may be different. The misalignment
pattern of the second output may be generated from the misalignment pattern of the
first output. The misalignment pattem of the second output and the misalignment
pattern of the first output may be generated by a cyclic function, the cyclic function
being periodic as a function of time.
The above objects are according to a fourth aspect of the present invention met by a
method for producing a first output image and a second output image of a first colour
for being projected by a first projector and a second projector, and for producing
a first output image and a second output image of a second colour for being pro
jected by the first projector and the second projector, the method comprising:
(ca) producing the first output image and the second output image of the first
colour by the method according to the first aspect of the present invention, and
(cb) producing the first output image and the second output image of the
second colour by the method according to the first aspect of the present invention.
The above objects are according to a fifth aspect of the present invention met by a
method for producing a first output image and a second output image of a first col
our for being projected by a first projector and a second projector for projecting the
first colour, and for producing and a first output image and a second output image of
a second colour for being projected by a first projector and a second projector for
projecting the second colour, the method comprising:
(ca) producing the first output image and the second output image of the first
colour by the method according to the first aspect of the present invention, and
(cb) producing the first output image and the second output image of the
second colour by the method according to an example of the first aspect of the pre
sent invention including an alignment pattern.
The first colour and the second colour may represent the left and right colours of
stereoscopic image. The first colour and the second colour may represent two colours
of a colour model, for example the RGB colour model.
In the fourth and fifth aspects of the present invention, the producing of the first o ut
put image and the second output image of the first colour may be performed by the
method according to an example of the first aspect of the present invention including
an alignment pattern. The first colour may represent shorter light wavelengths than
the second colour. The first colour may represent blue and the second colour may
represent green, yellow, or red.
The producing of the first output image and the second output image of the second
colour may be performed by the method according to an example of the first aspect
of the present invention including an alignment pattern the alignment pattern in pro
ducing the first output image and the second output image of the first colour and the
alignment pattern in producing the first output image and the second output image
of the second colour may have the same or approximately the same shape. The
alignment pattern in producing the first output image and the second output image
of the first colour and the alignment pattern in producing the first output image and
the second output image of the second colour may have the same or approximately
the same dimensions.
The method according to the fourth aspect of the present invention may further be
adapted for producing a first output image and a second output image of a third co l
our for being projected by the first projector and the second projector, the method
may further comprise:
(cc) producing the first output image and the second output image of the
third colour by the method according to the first aspect of the present invention.
The first colour, the second colour, and the third colour may represent three colours
of a colour model, for example the RGB colour model.
The method according to the fourth and fifth aspect of the present invention may
further be adapted for producing a first output image and a second output image of
a third colour for being projected by a first projector and a second projector for projecting
the third colour, the method may further comprise:
(cc) producing the first output image and the second output image of the
third colour by the method according to the first aspect of the present invention.
A first source value of a first pixel of the source image may represent the first colour,
a second source value of a second pixel of the source image may represent the
second colour, and a third source value of a third pixel of the source image may rep
resent the third colour, the colours of the first, second and third pixels may define a
second hue; a first intermediate value may be the intermediate value of the first
pixel, a second intermediate value may be the intermediate value of the second
pixel, and a third intermediate value may be the intermediate value of the third pixel
defining a third hue, the method may further comprise:
(cd) subjecting the first, second, and third intermediate values to a colour
adjustment.
The colour adjustment may be adapted for adjusting the first, second, and third in
termediate values to define the third hue being equal to or approximately equal to
the second hue. The colour adjustment may be equivalent to: (vii.i) calculating a first
fraction as the first intermediate value divided by the first source value, (vii.ii) calculating
a second fraction as the second intermediate value divided by the second
source value, (vii.iii) calculating a third fraction as the third intermediate value d i
vided by the third source value, (vii.iv) calculating a second maximum value as the
maximum of the first, second, and third fractions, (vii.v) replacing the first intermediate
value by the first source value multiplied by the second maximum value, (vii.vi)
replacing the second intermediate value by the second source value multiplied by
the second maximum value, and (vii.vii) replacing the third intermediate value by the
third source value multiplied by the second maximum value.
The above objects are according to a sixth aspect of the present invention met by a
system for producing a first output image and a second output image for being pro
jected by a first projector and a second projector, respectively, the system compris
ing a computer and/or one or more circuits for performing the method according to
the first aspect of the present invention. The system according to the sixth aspect of
the present invention may further comprise an image source for providing the
source image according to the first aspect of the present invention.
The above objects are according to a seventh aspect of the present invention met
by a system for double stacking a first output image and a second output image, the
system comprising a first projector, a second projector, and a computer and/or one
or more circuits for performing the method according to the second aspect of the
present invention. The system according to the seventh aspect of the present inven
tion may further comprise an image source for providing the source image according
to the second aspect of the present invention. The system according to the seventh
aspect of the present invention may further comprise a camera for recording the first
captured image of the superimposed image the second aspect of the present inven
tion.
The above objects are according to an eighth aspect of the present invention met by
a system for deriving a correction of a double stacking of a first output image and a
second output image, the system comprising a first projector, a second projector,
and a computer and/or one or more circuits for performing the method according to
the third aspect of the present invention, the system further comprising a camera for
recording the second captured image of the superimposed image.
The above objects are according to an ninth aspect of the present invention met by
a system for producing a first output image and a second output image of a first co l
our for being projected by a first projector and a second projector and a first output
image and a second output image of a second colour for being projected by the first
projector and the second projector, the system comprising a computer and/or one or
more circuits for performing the method according to the fifth and/or the sixth aspect
of the present invention.
The above objects are according to a tenth aspect of the present invention met by a
system for producing a first output image and a second output image of a first colour
for being projected by a first projector and a second projector for projecting the first
colour and a first output image and a second output image of a second colour for
being projected by a first projector and a second projector for projecting the second
colour, the system comprising a computer and/or one or more circuits for performing
the method according to the fifth aspect of the present invention.
The above objects are according to an eleventh aspect of the present invention met
by a projection system comprising a first projector and a second projector, the first
projector comprising: a first lamp, a first integrating rod having an input end and an
output end, the first integrating rod being configured for receiving light from the first
lamp through the input end and generate a uniform illumination at the output end, a
first projector filter configured to filter the uniform illumination at the output end of the
integrating rod, a first spatial light modulator chip, a first illumination system for im¬
aging the first projector filter on the light modulator chip, a first exit pupil through
which light from the a first spatial light modulator chip exits the first projector; the
second projector comprising: a second integrating rod having an input end and an
output end, the second integrating rod being configured for receiving light from the
second lamp through the input end and generate a uniform illumination at the output
end, a second projector filter configured to filter the uniform illumination at the output
end of the integrating rod, a second spatial light modulator chip, a second illumination
system for imaging the second projector filter on the light modulator chip, a sec
ond exit pupil through which light from the a second spatial light modulator chip exits
the second projector, the first projector filter being configured to wavelength shift the
light exiting through the first exit pupil, and the second projector filter being configured
to wavelength shift the light exiting the through the second exit pupil.
The first projector filter may define a first pass band and a first guard band, and the
second projector filter may define a second pass band not overlapping the first pass
band, and a second guard band may overlap the first guard band.
The first projector filter may define a first band stop and the first projector may fur
ther comprise: a first auxiliary filter configured to filter the uniform illumination from
the output end of the first integrating and defining a first pass band and a first guard
band, and the first band stop may match or approximately match the first guard
band; and the second projector filter may define a second pass band not overlap¬
ping the first pass band and a second guard band overlapping the first guard band.
The first projector filter may define a first band stop and the first projector may fur
ther comprise: a first auxiliary filter configured to filter the uniform illumination from
the output end of the first integrating and defining a first pass band and a first guard
band, and the first band stop may match or approximately match the first guard
band, and the second projector filter may define a second band stop; and the sec
ond projector may further comprise: a second auxiliary filter configured to filter the
uniform illumination from the output end of the second integrating and defining a
second pass band not overlapping the first pass band and a second guard band
overlapping the first guard band, and the second band stop may match or approxi
mately match the second guard band.
The second auxiliary filter may be flat and may have a second uniform thickness.
The first auxiliary filter may be flat and may have a first uniform thickness.
The first projector filter may define a first uniform thickness and/or the second pro¬
jector filter may define a second uniform thickness. The first projector filter may have
a first varying thickness and/or the second projector filter may have a second vary¬
ing thickness. The first projector filter may define a first curvature and/or the second
projector filter may define a second curvature. The first projector filter may define a
first flat area in a first central portion of the first projector filter, and/or the second
projector filter may define a second flat area in a second central portion of the sec
ond projector filter. The first projector filter may define a first curved shape in a first
peripheral portion of the first projector filter, and/or the second projector filter may
define a second curved shape in a second peripheral portion of the second projector
filter. The first projector filter may rest on a first transparent substrate, preferably a
first glass substrate, and/or the second projector filter may rest on a second trans¬
parent substrate, preferably a second glass substrate. The first projector filter may
be dichroic, and/or the second projector filter may be dichroic.
The first projector filter may be located at the output end of the first integrating rod
and/or the second projector filter may be located at the output end of the second
integrating rod. The first integrating rod may defining a first aperture having a first
width at the output end and the first projector filter may define a first spherical sur
face having a first radius equal to or approximately equal to the first width, and/or
the second integrating rod may define a second aperture having a second width at
the output end and the second projector filter may define a second spherical surface
having a second radius equal to or approximately equal to the second width.
The above objects are according to an twelfth aspect of the present invention met
by a system for producing a series of three-dimensional images comprising: a computer
and/or one or more circuits for producing left output comprising first output
images and second output images by repeatedly applying the method according to
the first aspect of the present invention, and the computer and/or the one or more
circuits further being adapted for producing right output comprising first output im
ages and second output images by repeatedly applying the method according to the
first aspect of the present invention, the left output representing left perspective im¬
ages of the series three-dimensional images and the right output representing co r
responding right perspective images of the series three-dimensional images; a pro¬
jection screen; a left perspective first projector coupled to the computer and/or one
or more circuits and configured for projecting the first output images of the left out¬
put on the projection screen; a right perspective first projector coupled to the com
puter and/or one or more circuits and configured for projecting the first output im
ages of the right output on the projection screen; and a left/right perspective second
projector coupled to the computer and/or one or more circuits and configured for
alternatingly projecting the second output images of the left output and the second
output images of the right output on the projection screen.
The above objects are according to an twelfth aspect of the present invention met
by a system for producing a series of three-dimensional images comprising: a com
puter and/or one or more circuits for producing left output comprising first output
images and second output images by repeatedly applying the method according to
the first aspect of the present invention, and the computer and/or the one or more
circuits further being adapted for producing right output comprising first output images
and second output images by repeatedly applying the method according to the
first aspect of the present invention, the left output representing left perspective im
ages of the series three-dimensional images and the right output representing cor
responding right perspective images of the series three-dimensional images; a p ro
jection screen; a left perspective first projector coupled to the computer and/or one
or more circuits and configured for projecting the first output images of the left o ut
put on the projection screen; a right perspective first projector coupled to the com
puter and/or one or more circuits and configured for projecting the first output im
ages of the right output on the projection screen; a left perspective second projector
coupled to the computer and/or one or more circuits and configured for projecting
the second output images of the left output the projection screen; and a right per¬
spective second projector coupled to the computer and/or one or more circuits and
configured for projecting the second output images of the right output on the projec
tion screen.
In the twelfth aspect and/or thirteenth aspect the left perspective first projector may
comprise a left polarization filter for polarizing light projected by the left perspective
first projector and the right perspective first projector may comprise a right polariza¬
tion filter for polarizing light projected by the right perspective first projector.
The left polarization filter and the right polarization filter may have orthogonal or ap
proximately orthogonal polarization directions. The left polarization filter and the
right polarization filter may have opposite circular polarization directions. The projec
tion screen may be being non-depolarizing. The systems according the twelfth aspect
and/or thirteenth aspect may further comprise a temporal varying polarization
unit.
BRIEF DESCRIPTION OF THE FIGURES
A multitude of embodiments of the different aspects of the present invention are de¬
picted in the figures, where:
Fig. 1 illustrates an example of the prior art,
Fig. 2 illustrates a preferred embodiment of the present invention,
Fig. 3 illustrates details of the preferred embodiment,
Figs. 4-7 illustrate different pixel values generated in the preferred embodiment.
Figs .8-9 illustrate examples of different outputs of the preferred embodiment,
Figs. 10-12 illustrate alternative embodiments of the present invention,
Fig. 3 illustrates an immersive stereoscopic projection configuration,
Figs. 14-17 illustrate a preferred embodiment of a projection system according to
the present invention,
Fig. 8 illustrates an alternative embodiment of the present invention, and
Fig. 19 illustrates the processing and output of the alternative embodiment de¬
scribed in relation to fig. 18.
DESCRIPTION OF THE INVENTION
The present invention is described below in terms of exemplary configurations but is
not intended to be regarded as limited to those. For the sake of explanation, greyscale
projection systems are used to describe the present invention, whereas the
configurations described may as well be applied to each of the colour planes of a tristimulus
(for example RGB) colour projection system, and, using standard colour
space conversion techniques, further be used for projection systems using other
colour spaces (for example YPbPr). Further, colour correction circuits for adapting
for example hue adjustment, black points and white points etc. between source im
age signals and projectors may obviously be included. Still, image projection sys
tems are used in several descriptions, whereas the described configurations may as
well operate on a sequence of still images constituting a moving image. Monoscopic
projection systems are used in the description, but the invention may as well apply
to a set of projection systems used for stereoscopic applications or to active stereo
scopic projectors with separate left eye and right eye inputs or with double frame
rate inputs. Pixel values are described as being in the range from 0 to 1, whereas in
practical implementations other ranges will likely be chosen. Operations are de
scribed as being performed by separate circuits, whereas in practical implementa
tion they will likely be implemented as software algorithms, lookup tables etc. in
computer memory or graphics card memory. Further modifications, additions and
alternative configurations obvious to a person skilled in the art are intended to be
included in the scope of the invention.
Fig. 1 shows a schematic view of a configuration of prior art, a traditional double
stacking comprising essentially identical projectors, a first projector 1 and a second
projector 2, each projecting an image onto a projection surface 3 and each having a
decoding gamma function corresponding to the encoding gamma of an image gen
erator 4 , which is outputting a source image signal comprising an array of pixel val¬
ues. The connecting lines in the schematic view illustrate image signal paths. The
output of the image generator is supplied to the input of the first projector 1 and to
the input of a warping circuit 5. The output of the warping circuit 5 is supplied to the
input of the second projector 2. The warping circuit 5 performs a geometrical correc¬
tion of the image projected by the second projector 2 to align it with the image pro
jected by projector 1 and compensate for mechanical misalignment between projected
images. Repeated re-calibrations may be needed to compensate for move¬
ments in mechanical and optical parts due to thermal variations etc.
Fig. 2 shows a schematic view of a first embodiment of the invention. To the con¬
figuration of Fig. 1 has been added an image splitting function comprising a gamma
decoding circuit 6 , a first gamma encoding circuit 7, a second gamma encoding cir
cuit 8, an image buffer 9, a lightening image limiter 10, a first image subtraction cir¬
cuit 11, a darkening image limiter 12, a second image subtraction circuit 13, a first
constrained smoothing filter 14, a second constrained smoothing filter 15, an image
inversion circuit 16, a first image division circuit 101 and a second image division
circuit 102, all connected as shown in the figure.
The gamma decoding circuit 6 is matched to the encoding gamma of the image
generator 4 , the first gamma encoding circuit 7 is matched to the decoding gamma
of the second projector 2 and the second gamma encoding circuit 8 is matched to
the decoding gamma of the first projector 1. Thus, all operations in the circuit be
tween the output of gamma decoding circuit 6 , the first gamma encoding circuit 7
and the second gamma encoding circuit 8 are performed at a gamma of unity,
meaning that pixel values represent linear intensities, and the resulting superim¬
posed illumination intensity in a point of the projection surface 3 is a function of the
sum of the corresponding pixel values in the images being input to the first gamma
encoding circuit 7 and to the second gamma encoding circuit 8.
The image buffer 9 stores a threshold image T which holds for each pixel value a
representation of the fraction of illumination intensity which the first projector 1 is
contributing to the corresponding position on the projection surface 3 when both pro
jectors are supplied uniform, maximum intensity images to their inputs. Since in this
embodiment the first projector 1 and the second projector 2 are essentially identical,
the first projector 1 contributes half the illumination intensity in all positions, and all
pixel values in T are 0.5. In an alternative configuration of this embodiment, the pro¬
jectors are not identical but have different spatial distribution of their maximum illu
mination intensities; hence T is an image having pixels with varying values between
0 and 1.
The content T of the image buffer 9 and the output of the gamma decoding circuit 6
are supplied to the lightening limiter 10. The lightening image limiter 10 calculates
an image that in every pixel position is the higher of the two inputs and it outputs the
result to the first image subtraction circuit 11, which subtracts T and supplies the
result to a lower bound image input LB of the constrained smoothing filter 14. The
pixel values of this image represents the amount of intensity that the first projector 1
is not capable of reproducing alone, hence the minimum intensity the second projec¬
tor 2 should contribute in the corresponding pixel position.
The content T of the image buffer 9 is supplied to the image inversion circuit 16 and
the output of the image inversion circuit 16 is supplied to the darkening image limiter
12. Further, the output of the gamma decoding circuit 6 is supplied to the darkening
image limiter 12. The darkening image limiter 12 calculates an image that in every
pixel position is the lower of the two inputs and outputs the result to an upper bound
image input UB of the constrained smoothing filter 14. This image represents the
maximum intensity the second projector 2 should contribute, i.e. the desired result
ing pixel intensities limited by the maximum intensity the second projector is able to
contribute in the corresponding pixel position.
The first constrained smoothing filter 14 calculates a generally smooth, blurry output
image with only few high frequency components and where the output image is e s
sentially constrained in any pixel position to have a pixel value in the range from the
corresponding pixel value in the lower bound image LB and the corresponding pixel
value in the upper bound image. Fig. 3 shows a process flowchart of an exemplary
configuration of the constrained smoothing filter 14. The constrained smoothing filter
14 performs a greyscale dilation operation with a dilation radius r 1 on the lower
bound input image LB followed by a blur operation with a blur radius r smaller than
or equal to r1 on the result of the greyscale dilation operation, followed by a darkening
image limiting operation with the upper bound input image UB on the result of
the blur operation, limiting pixel values in the result of the blur operation to be
smaller than or equal to the corresponding pixel values in the upper bound input
image UB and the result of the darkening image limiting operation is the output of
the first constrained smoothing filter. Alternatively, the darkening image limiting op
eration may be omitted and the result of the blur operation may be the output of the
first constrained smoothing filter. The dilation radius r 1 may be 4 pixels and the blur
radius r1' may be equal to r 1 . Alternatively, the dilation radius r1 may be 1/300 h of
the width of the lower bound input image LB and the blur radius r1' may be equal to
r . The blur operation may be a Gaussian blur operation which may have a standard
deviation of 1/3 * r1' or the blur operation may be a mean filtering operation. In a l
ternative configurations, the first constrained smoothing filter 14 may comprise a
spline based or membrane based envelope filter or a glow effect filter.
The output of the first constrained smoothing filter 14 is supplied to a lower bound
input of a second constrained smoothing filter 15 and the output of the image inver
sion circuit 16 is supplied to an upper bound input of the second constrained
smoothing filter 15. The second constrained smoothing filter 15 may perform an op
eration similar to that of the first constrained smoothing filter 14 with a dilation radius
r2 and a blur radius r2'. The dilation radius r2 may be 2 pixels and the blur radius r2'
may be equal to r2. Alternatively the dilation radius r2 may be 1/600 h of the width of
the lower bound input image of the second constrained smoothing filter 15 and the
blur radius r2' may be equal to r2. In an alternative configuration the second con¬
strained smoothing filter 15 may be substituted by a blur filter. The dilation radius r2
of the second constrained smoothing filter 15 may be adjustable and the blur radius
r2' may be set to follow r2 when adjusted. It is noted that when r2=0 and r2'=0, the
output of the second constrained smoothening filter 15 is equal to the lower bound
input, i.e. equal to the output of the first constrained smoothing filter 14.
The output of the gamma decoding circuit 6 and the output of the second con¬
strained smoothing filter 15 are supplied to an image subtraction circuit 13 which
calculates an image by subtracting the output of the second constrained smoothing
filter 15 from the output of the gamma decoding circuit 6 . The result of the subtraction
is supplied to a first input of the first image division circuit 101 . The output im
age T from the image buffer 9 is supplied to a second input of the first image div i
sion circuit 101. The first image division circuit 101 divides the first input by the sec
ond input and the result of the division is supplied to the input of the second gamma
encoding circuit 8. Hence, the first image division circuit 101 scales pixel values in
the output image of the second image subtraction circuit 3, which will be in the
range from 0 to the corresponding pixel values of T, by dividing with the pixel values
in T, so the resulting output pixel values are scaled to be in the range 0 to 1.
The output image of the second constrained smoothing filter 15 is further supplied to
a first input of the second image division circuit 102 and the output of the image in
version circuit 16 is supplied to a second input of the second image division circuit
102. The second image division circuit 102 divides the first input by the second input
and the result of the division is supplied to the input of the first gamma encoding
circuit 7. Hence, the second image division circuit 102 scales pixel values in the
output image of the second constrained smoothing filter 15, which will be in the
range from 0 to the inverse of the corresponding pixel values of T, by dividing with
the inverse of the pixel values in T, so the resulting output pixel values are scaled to
be in the range 0 to 1.
The output of the first gamma encoding circuit 7 is supplied to the input of the warp
ing circuit 5 and the output of the warping circuit 5 is supplied to the input of the
second projector 2. The output of the second gamma encoding circuit 8 is supplied
to the input of the first projector 1.
In an alternative, simplified configuration of the first embodiment, the darkening im¬
age limiter 12 may be omitted and a uniform, maximum intensity image may be
supplied to the upper bound input of the first constrained smoothing filter 14.
Fig. 4 shows graphs of values in an example section of a row of pixels at different
stages of the processing, the first graph in Fig. 4 shows the output of the gamma
decoding circuit 6, the second graph shows the output of the darkening limiter 12
and the third graph shows the output of the first image subtraction circuit 1.
Fig. 5 shows three graphs of values in the example section of a row of pixels at d if
ferent stages of an operation of the constrained smoothing filter 14 with a dilation
radius r 1 of 3 pixels and a blur radius r1' essentially equal to r 1. In the first graph in
fig. 5 the result of the dilation operation is indicated as a black line with the lower
bound input indicated in dark gray and the upper bound input indicated in light gray.
The second graph shows in a similar manner the result of the blur operation and the
third graph shows the result of the darkening operation.
Fig. 6 shows 3 example graphs of the values in a row of pixels, the first graph in fig.
6 shows the output of the second constrained smoothing filter 15 when r 1=3 pixels
and r2=0 and r1' is essentially equal to r 1 and r2' is essentially equal to r2. The sec
ond graph shows the output of the image subtraction circuit 13 and the third graph
shows summed values of the output of the second constrained smoothing filter 15
and the image subtraction circuit 13, which summed values, as noted above, trans
late directly to the resulting illumination intensity in the corresponding row of pixels
on the projection surface 3 when alignment of the projected images is essentially
perfect, because the operations are performed in a gamma of unity. When r2=0 as
in this example, summation of the input images to the gamma encoding circuits is
equal to the output of the gamma decoding circuit 6 , which is the gamma decoded
source image, hence, with perfect alignment of the projected images, the resulting
image on the projection surface 3 corresponds essentially perfectly to the output of
the image generator 4 , a condition that can be referred to as a "perfect reconstruc
tion". In an alternative configuration of this embodiment working in the "perfect reconstruction"
condition only, the second constrained smoothing filter 15 may be
omitted.
As the first graph in fig. 6 shows, the amount of high spatial frequencies in the out
put of the second constrained smoothing filter 15 is significantly less than in the output
image of the gamma decoding circuit 6, resulting in a generally smoother,
blurred image being projected by the second projector 2 than in a traditional double
stacking configuration.
A first advantage of the invention is that the smoother image of the second projector
2 reduces the visible artefacts introduced by a smaller misalignment of the projected
images. In many cases, a misalignment of a full pixel or more is not noticeable,
which in a traditional double stacking configuration would have introduced highly
visible artefacts.
However, as can be seen on the first graph in fig. 6 , the output of the second con¬
strained smoothing filter 15 is not completely eliminated high frequency compo¬
nents. At high contrast edges in the source image where the contrast is close to or
above the contrast reproduction capability of the first projector 1, the upper bound
and lower bound inputs to the first constrained smoothing filter 14 get so close, so it
may not always be possible to create a smooth "curve" (or rather: surface) between
them, and these areas of the projected image will be the most sensitive to mis¬
alignment. Setting r2 to a value higher than 0 will enforce a smoothing also in these
areas, reducing spatial frequency components further and increase the misalign
ment tolerance. The cost of this increased misalignment tolerance is losing the abil
ity of achieving "perfect reconstruction" and introducing small artefacts even at per
fect alignment of the projected images, in the form of faint haloes around edges in
the source image with a contrast higher than the first projector 1 is capable of reproducing.
Hence, adjusting r2 defines a compromise between "perfect reconstruction"
and "high misalignment tolerance".
Fig. 7 is equivalent to fig. 6 , except that the dilation radius r2 is 2 pixels here and the
blur radius r2' is essentially equal to r2. The dilation radius r 1 is still 3 pixels and the
blur radius r1' is still essentially equal to r1 . The faint halo artefact is visible in the
summed graph at the bottom just to the left of the highest peak. Fortunately, these
artefacts may be unrecognizable for the Human Visual System in a projected image
due to lateral inhibition in the neural response system on the retina (lateral mask¬
ing), when r2 is below a limit determined by the overall projection system on-screen
contrast, hence theoretical "perfect reconstruction" is not necessarily needed. De
termining a good value for r2 for a given type of projection system may be per¬
formed by having a critical group of observers located in the front rows look at a test
pattern containing maximum contrast edges and switch between random values of
r2 and ask the group members to rate the images in terms of edge sharpness and
then selecting the value of r2 where nobody notices the reduction of edge sharp
ness. It is noted that the reason for selecting the second constrained smoothing filter
5 also for the second filtering pass, as opposed to for example selecting a standard
lowpass filter, is that this configuration preserves illumination intensity in small areas
of highlights like reflections in water or leafs, which may be important visual clues
that are not subject to suppression by lateral inhibition.
Fig. 8 shows printed images of an output of the second constrained smoothing filter
15 together with the output of the image subtraction circuit 13 and a simulation of
the resulting projected overlaid image calculated by adding the output of the second
constrained smoothing filter 15 and the output of the image subtraction circuit 13.
(The images have here been applied a gamma so they are watchable on print).
Fig. 9 shows similar simulations of an enlarged section of an image projected with a
2 pixel misalignment. The upper image is a simulation of a projection with traditional
double stacking and the lower image is a simulation of a projection with the first em
bodiment of the invention.
A second advantage of the invention is that the output image of the second con
strained smoothing filter 15 will generally not be watchable and not hold enough de¬
tail information to be manipulated into a watchable image without additional informa
tion being supplied, meaning, that in copy-protected projection systems, where s ig
nal paths and image storages are subject to encryption and physical anti-tampering
requirements, the whole signal path from the output of the second constrained
smoothing filter 15 including the warping circuit 5 and the second projector 2 may
not need to be encrypted or physically secured. Fig. 10 shows an example of includ
ing the first embodiment in a digital cinema server. An anti-tampering protective
housing 18 encompasses the indicated components. The output of the second
gamma encoding circuit 8 is supplied to an encryption circuit 17 and the first projec
tor 1 is a digital cinema projector capable of decrypting the input image signal. Fig.
11 shows an example of including the first embodiment in a digital cinema projector.
The image generator 4 may be a digital cinema server outputting an encrypted image
signal, a decryption circuit 19 decrypts the signal and the anti-tampering hous
ing 8 encompasses the indicated components. Fig. 12 shows an example of the
first embodiment included in a stand-alone unit with an image decryption circuit 18
decrypting the encrypted output of the image generator 4 which may be a digital
cinema server and an image encryption circuit 7 encrypting the image signal and
outputting the encrypted signal to a digital cinema server capable of decrypting the
image signal and the anti-tampering housing encompassing the indicated compo¬
nents. In the configurations of figs. 9, 10 and 11, the first gamma encoding circuit 7,
the warping circuit 5 and the second projector 2 are outside the anti-tampering
housing and process unencrypted signals, making the practical implementation rela
tively uncomplicated.
In an alternative configuration of the first embodiment, a resampling circuit may be
included, which resamples the output image from the first gamma encoding circuit 7
to a lower spatial resolution and supplies the resulting resampled image to the warp
ing circuit 5 and where the warping circuit and the second projector 2 have lower
spatial resolution than the first projector 1. Since the output of the first gamma en
coding circuit 7 contains little high frequency components, this may have only little
or no effect on the resulting image quality.
Hence, a third advantage of the invention is that upgrade costs may be reduced and
investments in existing equipment protected, for example in a theatre with a single
2K projector wishing to upgrade to 4K and increased brightness. In general, the re
laxed requirements to the second projector 2 opens up possibilities for asymmetric
configurations where the second projector 2 may be a completely different projec
tion system than the first projector 1, having limitations that would not make it useful
for traditional double stacking but are less significant in a configuration of the first
embodiment, like lower resolution, slightly visible blending edges or brightness d if
ferences of a tiled system, not supporting encryption etc., but having other relevant
advantages, such as good black level, being already installed or being optimised to
serve specialized applications when not used as part of the first embodiment, such
as conference presentations, planetarium star field projection etc.
In yet an alternative configuration of the first embodiment, an image erosion circuit is
inserted between the output of the first constrained smoothing filter 14 and the lower
bound input of the second constrained smoothing filter 15, where said image e ro
sion circuit performs a greyscale erosion operation on the image signal received
from the first constrained smoothing circuit 14. The radius R3 of the greyscale ero
sion operation may be 0.5 pixel or 1 pixel. This configuration presents the advan
tage that errors in actual on-screen pixel intensities due to misalignment may be
shifted into brighter regions, where the same linear intensities will be less noticeable
to the human eye due to the non-linear nature of the human visual system.
In yet an alternative configuration of the first embodiment, a colour correction circuit
is inserted between the output of the first image subtraction circuit 1 and the lower
bound input of the first constrained smoothing filter 14. Said colour correction circuit
is further connected to the output of the gamma decoding circuit 6 and it adds to the
pixel values in the image received from the first image subtraction circuit 11 in a way
so that the pixels in the output to the first constrained smoothing filter 14 have es
sentially the same hue as the corresponding pixels in the image signal received
from the gamma decoding circuit 6. This operation may be performed by, for each
pixel calculating a constant K = Max(R1 1/R6, G 11/G6, B 11/B6), where (R6,G6,B6)
is the pixel colour value of the output of the gamma decoding circuit 6 and
(R1 1,G1 1,B1 1) is the pixel colour value of the output of the first image subtraction
circuit 11 and where Max(x,y,z) denotes a function returning the highest of the val
ues x , y and z, and by calculating the output pixel colour values R'=K* R6, G'=K*G6
and B'=K* B6, and outputting (R'.G'.B') to the lower bound input of the first constrained
smoothing filter 14. In this configuration, pixel hues in the images projected
from both projectors will be the same, which may in some images reduce the visibil¬
ity of misalignment artefacts further.
In yet an alternative configuration of the first embodiment, the output signal from the
first gamma encoding circuit 7 or from the resampling circuit is recorded on a first
medium and the output of the second gamma encoding circuit 8 is encrypted and
recorded on a second medium, and the first medium and the second medium are
played back synchronously with the output of the first recording medium being supplied
to the warping circuit 5 which is calibrated for alignment of the images and
supplies the warped output to the second projector 2 and the output of the second
medium being supplied to projector 1.
A fourth advantage of the invention is that it may reduce banding artefacts intro¬
duced by a traditional double stacking configuration, because it may have higher
dynamic contrast resolution compared to that of a traditional double stacking sys¬
tem, since more different resulting intensities on said projection surface 3 is possi
ble. In a traditional double stacking configuration where each projector has discrete
intensity steps matched to the Just Noticeable Differences of the Human Visual Sys
tem, the resulting overlaid image on the projection surface 3 may have discrete in
tensity steps exceeding the Just Noticeable Differences, which may result in visible
banding.
A fifth advantage of the invention is that an automatic re-alignment system based on
a digital image capturing system taking pictures of resulting superimposed image
projected on the projection surface 3 may separate a captured image into compo
nents originating from each projector and perform recalibration of the warping circuit
without the need for iterations over a sequence of frames in a public presentation or
using special iterating training sequences. For example, a high frequency filtering of
a captured image may create an image that is related only to the image being pro
jected by the first projector 1 making it possible to do feature matching or tracking,
identify a first set of misalignment vectors from the captured image with respect to
the input image to the first projector 1 and warp the captured image so it is aligned
with the first projector 1, and then subtract a gamma decoded version of the image
being input to the first projector 1 from a gamma corrected and gain-corrected ver
sion of the captured image, resulting in an image that is related only to the image
being projected by the second projector 2, so feature matching or tracking is possi
ble and a second set of misalignment vectors between the captured image and the
image being projected by the second projector 2 can be calculated, and from the
first and second set of misalignment vectors calculate a third set of misalignment
vectors, which is the misalignment vectors between the image being projected by
the first projector 1 and the image being projected by the second projector 2 and
from the third set of misalignment vectors perform a re-calibration of the warping
circuit 5. Alternatively, in an RGB projection system, a single alignment image may
be constructed which in one colour plane contains a geometric pattern, for example
a grid, which has only pixel values above the values in the threshold image T and
where another colour plane contains the same geometric pattern but with pixel val
ues below the values in the threshold image T, thus for each pixel position it is pos
sible to obtain relative misalignment vectors between the projectors and perform a
re-calibration of the warping circuit 5 .
Additionally, the first embodiment may be switchable to a single projector mode, in
which one of the projectors is simply being supplied the source image. This single
projector mode may act as fall-back operation in case of a projector failure and may
be activated automatically by a detection system capable of detecting a projector
failure, where the detection circuit may be an integrated part of the projector or
where the detection circuit may be based on a digital image capture system taking
pictures of the resulting superimposed image being projected on the projection sur
face 3 , resulting in a degree of redundancy, where, for example in the case that a
lamp blows, the system will continue to project correct images albeit with less
brightness.
Fig. 18 shows yet an alternative configuration of the first embodiment, supporting an
especially advantageous re-alignment procedure, where an image buffer 103 hold
ing an alignment pattern, an image addition circuit 104 and a darkening limiter 105
are added. The output of the image buffer 103 is supplied to one input of the image
addition circuit 104 and the output of the constrained smoothing filter 15 is supplied
to another input the image addition circuit 104, and the output of the image addition
circuit 104 is supplied to one input of the darkening limiter 105 and the output of the
gamma correction circuit 6 is supplied to another input of the darkening limiter 105
and the output of the darkening limiter is supplied to one input of the image division
circuit 102 and to one input of the image subtraction circuit 13, as shown in the f ig
ure. The output of the image buffer 103 may be switchable between a black picture
and the alignment pattern, so the alignment pattern can effectively be switched off,
when alignment detection is not requested. The effects of these added circuit elements
on the projected images are that the image projected by projector 2 will be
added a constrained alignment pattern, which is the output of the image buffer 103
being constrained, so that the result of the addition in each pixel position is still
equal to or lower than the intensities of the corresponding pixel values in the source
image, and the image projected by projector 1 will be subtracted the constrained
alignment image, so when the two images are superimposed on the projection sur¬
face 3 with perfect alignment, the alignment pattern will be cancelled out and be
come invisible, so only the source image is visible. However, when a misalignment
is introduced, the alignment pattern becomes visible as pattern sections of lower
and higher intensities than the surrounding pixels. This enables easy and precise
visual detection of any present misalignment. The position of lower and higher in
tensities indicates in which direction the misalignment is oriented. For example, if a
section of an alignment pattern is visible as lighter pixel values compared to the sur¬
roundings, i.e. a lighter pattern imprint, and the same section of the alignment pattern
is visible as darker pixel values compared to the surroundings, i.e. a darker pat
tern imprint, and the dark imprint is located to the right and below the light imprint,
this indicates that projector 1 is displaced to the right and towards the lower edge
relative to the position in which perfect alignment occurs. In this way, detection of
misalignment can be executed during operation of the projection system, and even
correction may be performed by adjusting the warping circuit 5. The alignment pat
tern may be designed, so it is not very noticeable to a general audience, though still
useful for a projectionist, for example by comprising small graphic elements with
regular spacing.
The alignment pattern may be a grid, a mesh or any regular or irregular pattern of
elements which may be dots, cross hairs or other graphic elements and it may con
tain barcodes, semacodes or other identifiers.
Fig. 19 shows example signals of the configuration of fig. 8, where the first image
is the output the darkening limiter 105 with the added alignment pattern visible, the
second image is the output of image subtraction circuit 13 with the subtracted
alignment pattern visible, the third image is the resulting superimposed image on the
projection surface 3 with perfect alignment and the fourth image is an example of a
resulting superimposed image on the projection surface 3 when misalignment is
present.
In a colour image projection system comprising multiple configurations of the first
embodiment each projecting a colour plane of the image, a first colour plane may be
projected with an alignment pattern by the configuration shown in fig. 18 and the
other colour planes may be projected without alignment patterns. When the colour
planes are projected by the same physical projectors, the mechanical misalignment
of projectors and projection optics will affect the colour planes essentially identical,
so the misalignment information observed from the first colour plane can be used to
detect and correct the misalignment of all colour planes. This will further reduce the
visibility of the alignment pattern to a general audience, especially if the colour plane
with the alignment pattern is the blue colour plane, whereas the projectionist can
observe the image through an optical filter having essentially the same colour as the
colour plane with alignment image, thereby increasing the visibility of the alignment
image to the projectionist.
Alternatively to having a projectionist observing the image manually, a camera may
record the image on the projection surface 3 and an image processing system may
detect and correct misalignment. The image processing system may perform feature
matching or feature tracking, for example scale invariant feature tracking, to perform
recognition of the alignment pattern or alignment pattern sections. Further, the cam
era may have a long exposure time, so that several different projected images, for
example subsequent frames of a moving picture, are integrated in the image capturing
element over one exposure, thereby blurring all non-static picture elements, but
preserving the static alignment pattern for easier recognition of alignment pattern or
alignment pattern sections. For example, the alignment pattern or alignment pattern
sections may be separated from the integrated and blurred image by a high pass
filtering. A sequence of images to be projected may be pre-processed, to increase
the blurring of other elements than the alignment pattern when later integrated in the
camera's image capturing element, for example a slow, cyclic motion may be int ro
duced to static scenes of a sequence of a moving picture, or one of the colour
planes, for example the blue colour plane, may be blurred in one or more or all of
the frames of the moving picture.
In a colour image projection system comprising multiple configurations of the first
embodiment each projecting a colour plane of the image, an additional colour co r
rection circuit may be comprised, which adds to the pixel values in the colour chan
nels of the outputs of the first constrained smoothing filters 14 in a way so that the
hue of the pixels in the output of the first constrained smoothing filters 14 are essen
tially identical to the hues of the corresponding pixels in the output of the gamma
decoding circuit 6. The additional colour correction circuit may perform an operation,
where it for each pixel calculates a fraction value, which is the pixel value of the out
put of the first constrained smoothing filter 14 divided by the corresponding pixel
value of the output of the gamma decoding circuit 6, then the additional colour co r
rection circuit identifies the greatest of the fraction values for each of the colour
planes, i.e. for each of the multiple configurations of the first embodiments, and for
each of the colour planes, a new pixel value is calculated by multiplying the output
of the gamma decoding circuit 6 with the fraction value for the colour plane, and the
resulting pixel value is supplied to the input of the second constrained smoothing
filter 15. The advantage of this colour projection system is that the hues projected
from the first projector 1 and from the second projector 2 will for each pixel be es
sentially identical, which may further decrease visible artefacts resulting from mis
alignment.
In a specially advantageous configuration, a 3D system is comprising two image
processing circuits according to the first embodiment, a first image processing circuit
according to the first embodiment being supplied a left perspective image of a 3D
image and a second image processing circuit according to the first embodiment be
ing supplied a left perspective image of said 3D image and three projectors, two sta¬
tionary polarization filters, a temporal varying polarization unit, such as the RealD
ZScreen or the RealD XL polarizing beam splitter arrangement with ZScreens, a
non-depolarizing projection screen and eyewear with polarizers. A first projector is
supplied the output of the second gamma encoding circuit 8 of said first image proc¬
essing system and has a first polarization filter inserted in the optical path between
the light source of said first projector and said projection screen, a second projector
is supplied the output of the second gamma encoding circuit 8 of said second image
processing system and has a second polarization filter inserted in the optical path
between the light source of said second projector and said projection screen, said
first polarization filter and said second polarization filter having essentially orthogo
nal polarization directions or opposite circular polarization direction, and where a
third projector is projecting alternately the output of the first gamma encoding circuit
or the resampling circuit of said first image processing system and the output of the
first gamma encoding circuit or the resampling circuit of said second image processing
system. In other words, two separate projection systems, one for a left eye im
age and one for a right eye image, use each one projector for the high frequency
image and share a time multiplexed projector for the low frequency image.
The advantage of this configuration is that the third projector projects alternately the
overlay images of the left and right perspective images that have low amounts of
high frequency components, therefore the requirements to the performance of this
projector in terms of resolution are relaxed, again allowing to optimize the projector
for brightness on the cost of some resolution or image sharpness, for example utiliz
ing a polarizing beam splitter with image combiner, such as for example the RealD
XL adapter, which essentially doubles the light output of the projector, but at the
cost of limiting the maximum obtainable resolution in practical implementations. This
way, the same amount of light reaching the screen as with four projectors can be
achieved using just three projectors. For example, a 3D projection system compris
ing three projectors with a 7KW Xenon lamp each could result in the same brightness
as that of a system comprising four projectors with 7KW lamps each, which
could be adequate for illuminating 3D giant screens. Such a system could rival exisiting
filmbased 3D projection systems for giant screens in both image resolution,
brightness, image stability, contrast, dynamic range and frame rate.
Fig. 13 shows an immersive, stereoscopic projection configuration with a total of
four overlaid projectors, a first left projector 121 , a second left projector 122, a first
right projector 123 and a second right projector 124, where the first left projector 121
and the second left projector 122 are parts of a configuration according to the first
embodiment and are projecting a left view of a stereoscopic image and where the
first right projector 123 and the second right projector 124 are parts of a conf igura
tion according to the first embodiment and are projecting a right view in an immer
sive giant screen theatre where the projection surface 3 may be a domed screen or
a big flat screen located close to the audience so a large portion of the field of view
of the members of the audience located in the theatre seats 125 is filled with image
and where the audience members are wearing stereoscopic eyewear. The projec
tors may be located off-axis close to the edge of the domed screen and may com
prise wide angle or fisheye projection optics. The projection optics may be constructed
so that pixel density is higher in an area, a "sweet spot", in front of the au
dience, as is well known in the art of immersive projection. The projection optics
may further comprise anamorphic adaptors, which stretch the image in the vertical
direction to fill a larger area of the dome. Additional warping circuits may be com¬
prised, which performs a geometrical correction of the left eye source image and the
right eye source image. The warping circuits may operate individually on each of the
colour planes of the source images so they can be calibrated to further compensate
for chromatic aberration in the projection optics. Alternatively to including image
splitting circuits according to the first embodiment in the configuration, a playback
system may be included, capable of synchronously reproducing previously recorded
outputs from an image splitting circuit according to the first embodiment stored on at
least one storage medium and supplying the reproduced outputs to the projectors.
The storage medium may comprise at least one hard disk containing a first set of
assets comprising a first signal for the first left projector 1, where the first signal is
the recorded output of the second gamma encoding circuit 8 when the left source
image was supplied to the input of the gamma decoding circuit 6 and a second s ig
nal for the first right projector 1, where the second signal is the recorded output of
the second gamma encoding circuit 8 when the right source image was supplied to
the input of the gamma decoding circuit 6, and further containing a second set of
assets comprising a third signal for the second left projector, where the third signal
is the recorded output of the first gamma encoding circuit 7 when the left source im
age was supplied to the input of the gamma decoding circuit 6, and a fourth signal
for the second right projector, where the fourth signal is the recorded output of the
first gamma encoding circuit 7 when the right source image was supplied to the input
of the gamma decoding circuit 6 . The first set of assets may be stored on the
hard disk in the format of a stereoscopic Digital Cinema Package and the second
set of assets may be stored on the hard disk in the format of a stereoscopic Digital
Cinema Package. The first set of assets may be stored in an encrypted form and the
playback system may be able to supply an encrypted signal to the input of the first
left projector and an encrypted signal to the input of the first right projector. Further,
a first warping circuit may be comprised located in the signal path from the playback
system to the second left projector and a second warping circuit may be comprised
located in the signal path from the playback system and the second right projector
where the first warping circuit and the second warping circuit are calibrated for
alignment of the images.
The projectors in the configuration of fig. 2 may use spectral separation for sepa
rating the left and right eye views, where members of the audience wear eyewear
with dichroic spectral separation filters and where the projectors comprise dichroic
spectral separation filters. The separation filters of the first left projector 121 and the
second left projector 122 may be essentially identical and the left eye separation
filter in the eyewear may be matched to the separation filters of the first left projector
121 and the second left projector 122 and the separation filters of the first right projector
123 and the second right projector 124 may be essentially identical and the
right eye separation filter in the eyewear may be matched to the separation filters of
the first right projector 123 and the second right projector 124. Spectral separation
stereoscopic projection has the advantage of not requiring a special projection sur¬
face which is attractive in many immersive cinema applications, and it has very good
image quality and stereoscopic reproduction in a central part of the field of vision,
but it has the disadvantage of introducing artefacts outside of the central part of the
field of vision, because the filters in the eyewear differ from their nominal perform
ance for incident light with angles not normal (perpendicular) to the filters, a phe
nomenon which is inherent in the nature of dichroic filters. For these reasons, an
improved system for spectral separation stereoscopic projection shall be proposed
below.
Fig. 14 shows an example of prior art. A lamp 20 in a first projector emits light into
an integrating rod 2 1 which creates a uniform illumination at the output end. A first
projector filter 23, being a dichroic spectral separation filter resting on a glass sub
strate 22, is located adjacent to the output of the integrating rod 2 1, essentially in a
focal plane of the illumination system 24, so an image of the first projector filter 23 is
essentially focused on the spatial light modulator chips 25 of the projector. A second
projector (not shown) is configured equivalently but with a second projector filter (not
shown), which is mutually exclusive to the first projector filter 23. The first projector
filter 23 and the second projector filter have mutually exclusive pass bands and in
between there are spectral ranges called guard bands where both the first projector
filter 23 and the second projector filter have little transmittance. The left eye separa
tion filter in the eyewear may be a dichroic filter having a set of pass bands encom
passing the pass bands in the first projector filter 23 and the right eye separation
filter in the eyewear may be a dichroic filter having a set of pass bands encompassing
the pass bands in the second projector filter. The separation filters in the eye
wear may be slightly curved to partly compensate for the non-normal (nonperpendicular)
angle of incident light from pixels in the peripheral areas of the image
as observed by a member of the audience positioned with her head directed essen
tially straight forward with her nose towards the screen, because light with a nonorthogonal
angle of incidence travels a longer distance between the dichroic layers
of the separation filters, hence is subject to a filtering where the pass bands have
been spectrally shifted compared to the filtering of light from pixels in the middle
area of the image with essentially normal (perpendicular) angle of incidence, which
would otherwise cause the match with the projector filters to be reduced beyond the
tolerances provided by the guard bands in the projector filters, giving rise to colour
artefacts and artefacts of crosstalk between left and right projection systems
("ghosting") in the peripheral parts of the image. It is normally not practical to use
separation filters that are curved enough to completely compensate for the angles of
incident light from different parts of the image for aesthetic reasons regarding the
eyewear design and because the distance between eyes varies significantly in a
population of different ages. The experience of the remaining artefacts in the pe¬
ripheral parts of the image may be described as having a sheet of slightly coloured,
semi-transparent, semi-reflective material with two fuzzy holes in front of your eyes
attached to your head, the holes not completely covering the image, resulting in a
sense of "tunnel vision". Therefore, further means to reduce the artefacts in the pe
ripheral parts of the image are usually adopted comprising pre-wavelength shifting
the projector filters, increasing the width of the guard bands at the cost of reduced
brightness and further comprising reducing the size of the eye openings in the eye¬
wear limiting the range of possible angles of incident light, thereby introducing a
sharp and psychologically better accepted border of your field of view but obviously
at the cost of a restricted field of view. However, for an immersive cinema applica¬
tion, artefacts in the peripheral field of vision will not be completely eliminated.
Fig. 15 shows an alternative configuration of the system in fig. 14 where the colour
and ghosting artefacts in peripheral parts of the image are compensated by modify
ing the first projector filter 23 and the second projector filter so the spectrally filtered
light at the exit pupils of the projectors becomes wavelength shifted as a function of
the angle of emission. The first projector filter 23 and the second projector filter are
curved with essentially identical curves, so that light focused on pixels in the periph
eral parts of the light modulator chips traverse longer distances between the dichroic
layers than light focused on the central parts of the light modulator chips, hence light
focused on the peripheral parts of the light modulator chips is wavelength shifted
with respect to light focused on the central parts of the light modulator chips and
therefore light emitted from pixels in the peripheral parts of the projected image is
wavelength shifted with respect to light emitted from pixels in the central parts of the
projected image, resulting in a better match of the filtering by the projector filters and
the filtering of the eye filters for pixels in the peripheral parts of the image, and in
more pixels in the peripheral parts of the image being filtered by the eye filters so
that the pass bands of the eye filters encompass the pass bands of the projector
filters when observed by a member of the audience in a target observation position.
Other members of the audience located at other positions may observe a slightly
undercompensated or overcompensated image, but still observe a better image
than without compensation. The curve of the first projector filter 23 and the second
projector filter may be spherical with radii equal to the width of the aperture of the
integrating rod 2 1. An electronic colour correction is normally applied to the source
image to compensate for a slight hue changes as perceived by the Human Visual
System in the filters, which cannot be avoided completely for manufacturing rea
sons. This colour correction is normally spatially uniform over the image area. In the
case of using curved filter, this colour correction may instead be spatially non
uniform, so as to achieve projected images that are perceived as uniform in hue to
the Human Visual System. Alternatively to comprising curved filters, dichroic filters
with varying thickness of the dielectric layers may be comprised.
The experience of watching an image compensated with curved filter is hard to de¬
scribe, but appears somewhat more pleasing than the "uncompensated experience".
It can be described as enlargening the fuzzy holes in the slightly coloured, semitransparent,
semi-reflective sheet so the full image can be seen through them when
your face is oriented forwards towards the screen, but the sheet is now detached
from your head, though still close, so when you move your head away from the
straight looking forward orientation, the edges of the fuzzy holes enter your field of
vision, like gazing through a pair of holes in thin drapes.
Fig. 6 shows an alternative configuration, where the first projector filter 23 and the
second projector filter may each have a flat area in a central region and only have a
curved shape in the peripheral areas of the image where the tolerance by above the
mentioned other means of reducing the artefacts in peripheral areas of the image do
not suffice. The optimal curve of the projector filters is a function of the distance
from the member of the audience to the screen, the curve of the eye filters, the focal
length of the relay lenses of the illumination system of the projectors, subjective aes¬
thetic preferences and other factors. A compromise between the "tunnel vision" and
"gazing through a pair of holes" may be desirable.
Fig. 17 shows yet an alternative configuration equivalent to the configuration of fig.
14, but where a first curved notch filter 27 resting on a first glass substrate 26 is
added located in front of the first projector filter 23 in the left projector and a second
curved notch filter resting on a second glass substrate are added correspondingly in
the second projector, and where the notch filters have notches essentially matching
the guard bands, so the width of the guard bands are being widened as a function of
the emission angle of light exiting the exit pupils of the projectors, hence reducing
artefacts in the peripheral field of vision and eliminating ghosting artefacts in the
central field of vision in the case where the observer turns her head to a large angle
that may occur in the configurations according to figs 14, 15 and 16, although at the
cost of reducing the brightness in the peripheral parts of the projected images. The
notch filters may have a flat area in a central part of the image.
The invention is additionally or alternatively characterized by an image processing
circuit separating an input image into a first image, being the input image clamped to
a threshold, and a second image, being the remainder. The second image is
smoothened by moving fractions of pixel values from the first image to the darker
areas around edges, reducing the content of high-frequency components in the
second image, keeping the sum of the two images identical to the input image. Scal
ing and gamma corrections are performed at the input and outputs, ensuring that
actual luminance superposition applies to the calculations. With perfect alignment,
the projected overlaid image will correspond exactly to the input image, whilst the
second image will have less high frequency components than the first image.
A first advantage is that the system significantly reduces the perceived artefacts
arising from minor misalignment, since the human visual system is less sensitive to
errors in low frequency components than in high frequencies. Only where there are
edges having a contrast higher than one projector can "drive" alone, the second im
age will contain high frequency components. However, the human visual system
exhibits a lower spatial resolution close to edges of contrasts of 150:1 and above,
due to the so called spatial masking effect, so misalignment artefacts at high contrast
edges will also be reduced in visibility. A low-pass filtering of the second image,
moderate enough to be invisible due to the masking effect of the first image's high
frequency components, may help masking misalignment artefacts at high contrast
edges further.
A second advantage is that a camera-based automatic alignment system can peri¬
odically perform realignment throughout a film projection, based on the images in
the film, with no need for special calibration sequence runs. Because the projectors
do not project identical images, it is possible to separate the first and the second
image from the recorded on-screen image, and from those calculate misalignment
information, which in turn may be used for electronic re-alignment by geometric cor¬
rection (warping).
A third advantage is that a single-projector 2K system can be upgraded to increased
brightness and 4K resolution, by adding a 4K projector. Since an invisible moderate
low pass filtering of the second image is possible, it results in that it is possible to
use a lower resolution projector for the second image, maintaining the appearance
of the full high resolution of the first projector (only brighter). A fourth advantage is
that the resulting luminance resolution of the system is higher than that of a single
projector, which could be of significance to high dynamic range projection systems.
The invention is additionally or alternatively characterized by the points:
1. An image projection system comprising two image projectors, a first projector and
a second projector, where said first projector and said second projector project over
laid images onto a projection surface, resulting in a superimposed image, further
comprising a first image processing circuit, which separates an input image into two
images: a first projector image being input to said first projector and a second projector
image being input to said second projector, so that when said first projector is
projecting said first projector image and said second projector is projecting said
second projector image, the overlaid image formed on the projection surface essen
tially corresponds to said input image, and where the amount of high spatial fre
quencies is lower in said second projector image than in said first projector image.
2 . An image projection system according to point 1, where colour correction circuits
are added to both of said projector's inputs, calibrated so that the resulting projector
transfer functions between pixel values and projected colour plane luminances be
come essentially linear and identical, so that the resulting projected colour plane
luminances at a point on the display surface is essentially a function of the sum of
the corresponding pixel values of said first projector image and the corresponding
pixel values of said second projector image, when said corresponding pixel values
of said first projector image is within the range 0 to B1 and said corresponding pixel
values of said second projector image is within the range 0 to B2, where B1 is the
pixel value corresponding to the maximum colour plane luminance of said first pro
jector and B2 is the pixel value corresponding to the maximum colour plane lumi¬
nance of said second projector, and where the calculation of said second projector
image comprises, for each pixel value of essentially all pixels in the input image,
calculating the value that exceeds B 1, and where said first projector image is calcu
lated by subtracting said second projector image from said input image, and where
the pixel values of said input image is within the range 0 to B, where B=B1+B2 is the
pixel value corresponding to maximum colour plane luminance of the resulting superimposed
image.
3. An image projection system according to point 2 , where said calculation of said
second projector image further comprises a smoothing process, adding amounts to
pixel values in said second projector image in a way, so that high frequency components
in said second projector image are reduced, and where said amounts are lim
ited to be within zero and the corresponding pixel values in said first projector im
age.
4. An image projection system according to point 3, where said smoothing process
comprises adding halos to edges in said second projector image, where the halos
extend into the darker side of the edges gradually fading with increasing distance
from the edges.
5. An image projection system according to point 3 or 4, where said smoothing
process comprises a weighted greyscale dilation applied to each of the colour
planes of said second projector image, where said weighted greyscale dilation is
defined as a greyscale dilation with a structuring element D and where the input pix
els are first multiplied by the elements of a filtering kernel F.
6. An image projection system according to points 1-5, further comprising a
low-pass filter with a convolution kernel L or other smoothening filter inserted be
tween said first image processing circuit and said second projector.
7. An image projection system according to points 1-6, where said second projector
has a lower spatial resolution than said first projector.
8. An image projection system according to points 5-7, where the greyscale dilation
structuring element D is a disc shaped element with a radius of 0.2 % of the image
width, the filtering kernel F is a distance function with a radius of 0.2 % of the image
width and the convolution kernel L is a Gaussian kernel with a radius of 0.1 % of the
image width.
9. An image projection system according to points 1-8, further comprising an auto
matic alignment system comprising at least one camera capable of recording im
ages of said resulting projected image on said projection surface and a second im
age processing circuit, capable of isolating a first set of features originating from
said first projector image in an image recorded by said camera(s) and isolating a
second set of features originating from said second projector image in said image
recorded by said camera(s) and capable of spatially correlating said first set of fea
tures and said second set of features to features of said input image and from said
correlations calculating spatial misalignment information, further comprising a third
image processing circuit, capable of geometrically correcting at least one of said first
projector image and said second projector image, based on said misalignment in
formation, so said first projected image and said second projected image become
geometrically aligned.
10. An image projection system according to point 9, where said second image
processing circuit comprises a colour correction circuit, producing from said re¬
corded image a conformed recorded image, calibrated so that the transfer function
between pixel values and colour plane luminances of the overlaid image on said
display surface is essentially identical to said projector transfer functions, and where
said second image processing circuit seeks to identify at least one low-luminance
area(s) in which all pixel values of said conformed recorded image are below a
threshold T, where T is less than or equal to B 1, and performs a first set of feature
matching operations with said first projector image in at least one feature matching
area(s) within said low-luminance area(s) resulting in a first set of offset vectors, and
where said second image processing circuit can perform a geometrical correction of
said conformed recorded image based on said first set of offset vectors, so that the
geometrically corrected, conformed recorded image is aligned with said input image
and where said second image processing circuit subtracts said first projector image
from said geometrically corrected, conformed recorded image and on the resulting
image performs a second set of feature matching operations in at least one area(s)
with said second projector image resulting in a second set of offset vectors, and
where said third image processing circuit is capable of geometrically correcting at
least one of said second projector image and said second projector image based on
said first set and said second set of offset vectors, so said first projected image and
said second projected image become essentially geometrically aligned, and where
said feature matching operations may be template matching operations, scale in
variant feature tracking operations or any other feature tracking operations known in
the art.
1. An image projection system according to points 9 and 10, where said automatic
alignment system perform repeated cycles during presentation of a moving picture,
a live transmission, a still image or other content, to reduce geometric misalignment
arising during projection.
12. An image projection system according to points 1-1 1, where more than two pro¬
jectors are projecting overlaid images, said first image processing circuit outputting
more than two images, each having different amounts of spatial frequencies and
where said second image processing circuit is capable of isolating features in said
recorded image originating from each of said projectors.
13. An image projection system according to points 1-12, further comprising any
modifications and configurations included in the technical description or evident to a
person skilled in the art.
The invention is additionally or alternatively characterized by the additional points:
. An image projection system comprising an essentially hemispheric, dome shaped
projection surface and at least one image projector located near the edge of said
domed shaped projection surface, where said image projector projects an image
onto the inside of said dome shaped projection surface and where the projected im¬
age covers at least 70% of said dome shaped projection surface, comprising a wide
angle projection objective, a fish-eye projection objective, a wide-angle conversion
lens, a wide-angle conversion mirror, an inverse afocal optical system or a retrofocus
optical system or a combination of any of these, further comprising a first image
processing circuit which performs a geometrical correction of an input image and
sends a corrected output image to the input of said projector.
2. An image projection system according to the additional point 1 further comprising
an anamorphic adaptor comprising at least one prism located in the light path be¬
tween the image forming element and the screen, where said anamorphic adaptor is
stretching said image in one direction.
3. An image projection system according to additional points 1 or 2, where said first
image processing circuit is calibrated, so that said projected image essentially has
the same geometry as a projected image from a fish-eye projector located essen
tially at the center of said hemispheric, dome shaped projection surface, when said
input image is being input to said fish-eye projector.
4. An image projection system according to additional points 1-3, where said first
image processing circuit is able to perform separate geometrical corrections of each
of the colorplanes of said input image, and where said first image processing circuit
is calibrated so that said geometrical corrections compensates for chromatic aberrations
in the optical elements of said image projection system.
5. An image projection system according to additional points 1-4, where at least one
area located in said dome shaped projection surface has a higher spatial resolution
than the average spatial resolution of said projected image, and where said input
image has a higher spatial resolution than said corrected output image, and where
said image processing circuit essentially preserves as much spatial resolution from
said input image to said output image as possible.
6 . An image projection system according to additional points 1-5, further comprising
a second image processing circuit able to calculate from said corrected output im
age a reflection-error image, where said reflection-error image is an estimate of the
total reflected light that will be received at each position on the display surface from
other parts of the display surface by scattering, if said input image were to be pro
jected onto the display surface by said projector, where said reflection-error image
may be calculated based on a set of screen measurements and where said ref lec
tion-error image may be calculated by radiosity calculations, and where said image
processing circuit essentially subtracts said reflection error image from said input
image (negative values being set to zero) resulting in a compensated image, which
may be sent to the input of said projector.
7. An image projection system according to additional point 6 , where local contrast
enhancement is applied to areas of said compensated image, where full cancellation
of reflected light is not achieved by the subtraction of said reflection-error im
age.
8. An image projection system according to the additional point 7, where a remain¬
der-error image is calculated as the difference between said reflection-error image
and the result of a subtraction of said compensated image from said corrected o ut
put image, and where a contrast enhanced compensated image is calculated from
said compensated image by local contrast enhancement and where said remain
der-error image is low-pass filtered and then used as a key in a keying operation
between said compensated image and said contrast enhanced compensated image,
and where the resulting image of the keying operation is sent to the input of said
projector.
9. An image projection system according to additional points 7 or 8 , where said local
contrast enhancement is an unsharp mask operation or a local tone mapping operation.
10. An image projection system according to additional points 1-9, further compris
ing any modifications and configurations included in the technical description or evi¬
dent to a person skilled in the art.
CLAIMS
1. A method for producing a first output image and a second output image
for being projected by a first projector and a second projector, respectively, said
method comprising:
(a) providing a source image comprising a plurality of pixels, each pixel
having an source value,
(b) providing a threshold value for each pixel of said plurality of pixels, and
in a first alternative
(d) generating a temporary image comprising a temporary value for each
pixel of said plurality of pixels, said temporary value being generated in a process
equivalent to:
(i.i) determining a first maximum value as the maximum of said
source value and its corresponding threshold value for each pixel,
(i.ii) determining an intermediate value by subtracting the
corresponding threshold value from said first maximum value for each
pixel,
(i.iii) generating said temporary value from said intermediate
value for each pixel;
or in a second alternative
(c) providing an inverted threshold value for each pixel of said plurality of
pixels, each inverted threshold value being an inversion of its corresponding
threshold value,
(d) generating a temporary image comprising a temporary value for each
pixel of said plurality of pixels, said temporary value being generated in a process
equivalent to:
(i.i) determining an intermediate value as the minimum of said
source value and its corresponding inverted threshold value for each
pixel,
(i.ii) generating said temporary value from said intermediate
value for each pixel;
or in a third alternative
(c) providing an inverted threshold value for each pixel of said plurality of
pixels, each inverted threshold value being an inversion of its corresponding
threshold value,
(d) generating a temporary image comprising a temporary value for each
pixel of said plurality of pixels, said temporary value being generated in a process
equivalent to:
(i.i) determining a first maximum value as the maximum of said
source value and its corresponding threshold value for each pixel,
(i.ii) determining a first difference value by subtracting the
corresponding threshold value from said first maximum value for each
pixel,
(i.iii) determining a first minimum value as the minimum of said
source value and its corresponding inverted threshold value for each
pixel,
(i.iv) determining an intermediate value as the minimum of said
first difference value and said first minimum value for each pixel,
(i.v) generating said temporary value from said intermediate
value for each pixel;
or in a fourth alternative
(c) providing an inverted threshold value for each pixel of said plurality of
pixels, each inverted threshold value being an inversion of its corresponding
threshold value,
(d) generating a temporary image comprising a temporary value for each
pixel of said plurality of pixels, said temporary value being generated in a process
equivalent to:
(i.i) determining a first maximum value as the maximum of said
source value and its corresponding threshold value for each pixel,
(i.ii) determining a first difference value by subtracting the
corresponding threshold value from said first maximum value for each
pixel,
(i.iii) determining a first minimum value as the minimum of said
source value and its corresponding inverted threshold value for each
pixel,
(i.iv) determining an intermediate value from a first range of
values comprising values between said first difference value and said
first minimum value for each pixel,
(i.v) generating said temporary value from said intermediate
value for each pixel;
and in all alternatives
(e) generating said first output image comprising a first output value for
each pixel of said plurality of pixels, said first output value being generated from said
temporary value and said source value for each pixel, and
(f) generating said second output image comprising a second output value
for each pixel of said plurality of pixels, said second output value being generated
from said temporary value.
2 . The method according to claim 1, characterized by further comprising:
in said first alternative
(c) providing an inverted threshold value for each pixel of said
plurality of pixels, each inverted threshold value being an inversion of its
corresponding threshold value.
3 . The method according to any of the claims 1 to 2, characterized by said
process of generating said temporary value further comprising:
in all alternatives
(i.vi) smoothing said intermediate value for each pixel,
and in said third and fourth alternative
(i.vi) smoothing said first difference value and/or said first
minimum value.
4 . The method according to claim 3, characterized by said smoothing
comprising a spline filter, a membrane filter, and/or an envelope filter.
5 . The method according to any of the claims 3 to 4, characterized by said
smoothing being adapted for limiting said intermediate value to a value from said
first range of values subsequent to said smoothing.
6 . The method according to any of the claims 3 to 5 characterized by said
smoothing comprising a first dilation operation comprising a first dilation radius.
7 . The method according claim 6, characterized by said first dilation radius
being 4 pixels, or approximately 0.3% of the width of said temporary image.
8 . The method according to any of the claim 3 to 7, characterized by said
smoothing comprising a first blur operation.
9 . The method according to claim 8 and any of the claims 6 to 7,
characterized by said first dilation operation being performed prior to said first blur
operation.
10 . The method according to any of the claims 8 to 9 and any of the claims
6 to 7, characterized by said first blur operation comprising a first blur radius
approximately equal to or smaller than said first dilation radius.
11. The method according to any of the claims 8 to 10 characterized by
said first blur operation comprising a first Gaussian blur operation.
12 . The method according to claim 11, characterized by said first Gaussian
blur operation having a standard deviation approximately equal to a third of said first
blur radius, or approximately equal to or smaller than 4/3 pixels, or approximately
0.1 % of the width of said temporary image.
13 . The method according to any of the claims 8 to 12, characterized by
said first blur operation comprising a first mean filtering operation.
14. The method according to any of the claims 1 to 13, characterized by
said process generating said temporary value further comprising:
(i.vii) determining a second minimum value as the minimum of
said intermediate value and said inverted threshold value for each pixel,
(i.viii) generating a second smoothed value by smoothing said
second minimum value for each pixel, and
(i.ix) generating said temporary value from said second
smoothed value for each pixel.
15 . The method according to claim 14, characterized by said smoothing of
said second minimum value comprising a spline filter, a membrane filter, and/or an
envelope filter.
16 . The method according to any of the claims 14 to 15, characterized by
said smoothing of said second minimum value comprising a second dilation
operation comprising a second dilation radius.
17 . The method according claim 16, characterized by said second dilation
radius being 2 pixels, or approximately 0.1 7% of the width of said temporary image.
18 . The method according to any of the claim 14 to 17, characterized by
said second dilation radius being variable.
19 . The method according to claim 18, characterized by said second
dilation radius being variable in a second range of values including zero.
20. The method according to any of the claim 14 to 19, characterized by
said smoothing of said second minimum value comprising a second blur operation.
2 1. The method according to claim 20 and any of the claims 16 to 19,
characterized by said second dilation operation being performed prior to said
second blur operation.
22. The method according to any of the claims 20 to 2 1 and any of the
claims 16 to 19, characterized by said second blur operation comprising a second
blur radius approximately equal to or smaller than said second dilation radius.
23. The method according to claim 22, characterized by said second blur
radius being variable.
24. The method according to any of the claim 23, characterized by said
second blur radius being variable in a third range of values including zero.
25. The method according to any of the claims 22 to 24, characterized by
said second blur radius and said second dilation radius being coupled such that one
changes as a function of the other.
26. The method according to any of the claims 20 to 25, characterized by
said second blur operation comprising a second Gaussian blur operation.
27. The method according to claim 26, characterized by said second
Gaussian blur operation having a standard deviation approximately equal to a third
of said first blur radius, or approximately equal to or smaller than 2/3 pixels, or
approximately 0.055% of the width of said temporary image.
28. The method according to any of the claims 20 to 27, characterized by
said second blur operation comprising a second mean filtering operation.
29. The method according to any of the claims 1 to 28, characterized by
providing said source image comprising:
(ii.i) providing a gamma encoded source image encoded by a
first gamma encoding,
(ii.ii) generating a gamma decoded source image by performing
a first gamma decoding of said gamma encoded source image, said gamma
decoding corresponding to said first gamma encoding, and
(ii.iii) outputting said gamma decoded source image as said
source image.
30. The method according to any of the claims 1 to 29, characterized by
further comprising:
(g) performing a second gamma encoding of said first output image, said
second gamma encoding corresponding to a second gamma decoding of said first
projector.
3 1. The method according to claim any of the claims 1 to 30, characterized
by further comprising:
(h) performing a third gamma encoding of said second output image, said
third gamma encoding corresponding to a third gamma decoding of said second
projector.
32. The method according to any of the claims 1 to 3 1, characterized by
said process of generating said temporary value further comprising:
in all alternatives
(i.x) performing a first colour correction of said intermediate
value for each pixel, and
in the third and fourth alternatives
(i.x) performing a first colour correction of said intermediate
and/or said first difference value for each pixel.
33. The method according to claim 32, characterized by in all alternatives
said first colour correction being adapted for correcting said intermediate value to
obtain approximately the same first hue as the corresponding source value and in
the third and fourth alternative said first colour correction being adapted for
correcting said first difference value and/or said intermediate value to obtain
approximately the same first hue as the corresponding source value.
34. The method according to any of the claims 32 to 33, characterized by
said first colour correction comprising a process equivalent to:
(iii.i) calculating a constant K for each pixel, K being equal to the
maximum of R 1 1/R6, G 11/G6, and B 11/B6; R6, G6, and B6 are the
pixel colours of said source image; and R 11, G 11, and B 11 are the pixel
colour values subsequent to determining said first intermediate value for
each pixel,
(iii.ii) correcting said intermediate value by replacing it with said
source value multiplied with said constant K for each pixel.
35. The method according to any of the claims 1 to 34, characterized by
further comprising:
(i) lowering the spatial resolution of said second output image and/or
performing a blur operation on said second output image.
36. The method according to any of the claims 1 to 35, characterized by
further comprising:
(j) encrypting said first output image.
37. The method according to any of the claims 1 to 36, characterized by
further comprising:
(k) recording said first output image on a first recording medium.
38. The method according to claim 37, characterized by further comprising:
(I) extracting said first output image from said first recording medium.
39. The method according to any of the claims 1 to 38, characterized by
further comprising:
(m) recording said second output image on a second recording medium.
40. The method according to claim 39, characterized by further comprising:
(n) extracting said second output image from said second recording
medium.
4 1. The method according to any of the claims 1 to 40, characterized by
further comprising:
(o) performing a geometric correction of said second output image, said
geometric correction being adapted for aligning an image projected by said second
projector with an image projected by said first projector.
42. The method according to any of the claims 1 to 4 1, characterized by
said process of generating said temporary value further comprising:
(i.xi) performing an erosion operation, preferably a grey scale
erosion operation having a radius a half pixel, a full pixel, 0.04% of the
width of temporary image, or 0.08% of the width of temporary image, on
said intermediate value for each pixel of said plurality of pixels.
43. The method according to any of the claims 1 to 42, characterized by, in
said fourth alternative, said source value being excluded from said first range of
values for each pixel.
44. The method according to any of the claims 1 to 43, characterized by, in
said fourth alternative, said first range of values further comprises said first
difference value and said first minimum value.
45. The method according to any of the claims 1 to 44, characterized by
said first output value being generated for each pixel in a process equivalent to:
(iv.i) determining a second difference value by subtracting said
temporary value from said source value for each pixel, and
(iv.ii) generating said first output value from said second
difference value.
46. The method according to any of the claims 1 to 45, characterized by
said first output value being generated for each pixel in a process equivalent to:
(iv.i) determining a second difference value by subtracting said
temporary value from said source value for each pixel,
(iv.ii) generating a first ratio by dividing said second difference
value by said threshold value for each pixel, and
(iv.iii) generating said first output value from said first ratio for
each pixel.
47. The method according to any of the claims 1 to 40, characterized by
said second output value further being generated from said inverted threshold value.
48. The method according to any of the claims 1 to 47, characterized by
said second output value being generated for each pixel in a process equivalent to:
(v.i) generating a second ratio by dividing said temporary value
by said inverted threshold value for each pixel, and
(v.ii) generating said second output value from said second ratio
for each pixel.
49. The method according to any of the claims 1 to 48, characterized by
said threshold value for each pixel of said plurality of pixels representing the fraction
of the total illumination intensity which said first projector contributes to at the
corresponding position on the projection surface in a projection of a uniform and
maximum intensity image from said first projector and said second projector, or in a
projection of a uniform and maximum intensity image from each of said first
projector and said second projector, or in a projection of a uniform and maximum
intensity image from said first projector, or in a projection of a uniform and maximum
intensity image from said second projector.
50. The method according to any of the claims 1 to 49, characterized by
further comprising
(p) adjusting said temporary image to include an alignment pattern.
5 1. The method according to claim 50, characterized by said adjusting of
said temporary image to include an alignment pattern comprising:
(q) providing said alignment pattern,
(r) adjusting said temporary image by adding said alignment pattern to said
temporary image,
(s) adjusting said temporary image by a process equivalent to:
(vi.i) determining a fourth minimum value as the minimum of said
temporary value and its corresponding source value for each pixel, and
(vi.ii) adjusting said temporary value to said fourth minimum
value for each pixel.
52. The method according to any of the claims 50 to 5 1, characterized by
said alignment pattern comprising a grid, a mesh, a barcode, and/or a semacode,
and alternatively or additionally said alignment pattern comprising a regular pattern
of elements, and/or an irregular pattern of elements, and alternatively or additionally
said alignment pattern comprising a regular pattern of dots and/or cross hairs,
and/or an irregular pattern of elements of dots and/or cross hairs.
53. A method for double stacking a first output image and a second output
image on a projection surface by a first projector and a second projector, said
method comprising:
(aa) positioning and orienting said first projector and said second projector
for overlaying said first output image and said second output image on said
projection surface,
(ab) producing said first output image and said second output image by the
method according to any of the claims 1 to 52,
(ac) supplying said first output image and said second output image to said
first projector and said second projector, respectively, and
(ad ) projecting said first output image and said second output image by said
first projector and said second projector, respectively.
54. The method according to claim 53, characterized by said first projector
and said second projector generating a superimposed image on said projection
surface, said method further comprising:
(ae) recording a first captured image of said superimposed image,
(af) determining a first contribution of said first projector to said first
captured image,
(ag) generating a first feedback image from said first contribution,
(ah) generating a first set of misalignment vectors from said first feedback
image and said first output image by a feature tracking and/or feature matching,
(ai) generating a first warped image of said first captured image by a first
warping comprising said first set of misalignment vectors,
(aj) generating a second feedback image by subtracting said first output
image from said first warped image,
(ak) generating a second set of misalignment vectors from said second
feedback image and said second output image by a feature tracking and/or feature
matching,
(al) generating a third set of misalignment vectors from said first set of
misalignment vectors and said second set of misalignment vectors, and
(am) deriving a first geometric correction of said first output image and/or
said second output image from said third set of misalignment vectors.
55. The method according to claim 54, characterized by determining said
first contribution of said first projector comprises a high pass filtering of said first
captured image.
56. A method for deriving a correction of a double stacking of a first output
image and a second output image on a projection surface by a first projector and a
second projector, said method comprising:
(ba) positioning and orienting said first projector and said second projector
for overlaying said first output image and said second output image on said
projection surface,
(bb) producing a first output for a first source image, said first output
comprising said first output image and said second output image produced by the
method according to any of the claims 50 to 52 for said first source image,
(be) supplying said first output image and said second output image of said
first output to said first projector and said second projector, respectively, and
(bd ) projecting said first output image and said second output image of said
first output by said first projector and said second projector, respectively, on said
projection surface,
(be) recording a first captured image comprising said first output image and
said second output image of said first output projected on said projection surface,
(bf) detecting a contribution of said misalignment pattern of said first output
in said first captured image
(bg) deriving a geometric correction for said second output image from said
detected contribution of said misalignment pattern of said first output.
57. The method according to claim 56, characterized by further comprising:
(bh) producing a second output for a second source image for being
displayed subsequent to said first source image, said second output comprising said
first output image and said second output image produced by the method according
to any of the claims 50 to 52 for said second source image,
(bi) supplying said second output image and said second output image of
said second output to said first projector and said second projector, respectively,
and
(bj ) projecting said second output image and said second output image of
said second output by said first projector and said second projector, respectively, on
said projection surface,
(bk) recording a second captured image comprising said first output image
and said second output image of said second output projected on said projection
surface,
(bl) detecting a contribution of said misalignment pattern of said second
output in said second captured image,
(bm) deriving a geometric correction for said second output image from said
detected contribution of said misalignment pattern of said second output.
58. The method according to 56, characterized by further comprising:
(bh) producing a second output for a second source image for being
displayed subsequent to said first source image, said second output comprising said
first output image and said second output image produced by the method according
to any of the claims 50 to 52 for said second source image,
(bi) supplying said second output image and said second output image of
said second output to said first projector and said second projector, respectively,
and
(bj ) projecting said second output image and said second output image of
said second output by said first projector and said second projector, respectively, on
said projection surface,
(bk) recording said first captured image comprising said first output image
and said second output image of said second output projected on said projection
surface,
(bl) detecting a contribution of said misalignment pattern of said first output
in said first captured image further comprising detecting a contribution of said
misalignment pattern of said second output in said first captured image,
(bm) deriving a geometric correction for said second output image from said
detected contribution of said misalignment pattern of said first output and said
second output.
59. The method according to any of the claims 57 to 58, characterized by
detecting a contribution of said misalignment pattern of said first output in said first
captured image and detecting said contribution of said misalignment pattern of said
second output in said second captured image further comprising a time averaging of
said first captured image and said second captured image, and/or said detecting of
a contribution of said misalignment pattern of said first output and said second
output comprising high pass filtering.
60. The method according to any of the claims 57 to 59, characterized by
the misalignment pattern of said first output and said misalignment pattern of said
second output being the same.
6 1. The method according to any of the claims 57 to 59, characterized by
the misalignment pattern of said first output and said misalignment pattern of said
second output being different.
62. The method according to any of the claims 57 to 59, characterized by
the misalignment pattern of said second output being generated from said
misalignment pattern of said first output.
63. The method according to any of the claims 57 to 59, characterized by
the misalignment pattern of said second output and said misalignment pattern of
said first output being generated by a cyclic function, said cyclic function being
periodic as a function of time.
64. A method for producing a first output image and a second output image
of a first colour for being projected by a first projector and a second projector, and
for producing a first output image and a second output image of a second colour for
being projected by said first projector and said second projector, said method
comprising:
(ca) producing said first output image and said second output image of said
first colour by the method according to any of the claims 1 to 52, and
(cb) producing said first output image and said second output image of said
second colour by the method according to any of the claims 1 to 52.
65. A method for producing a first output image and a second output image
of a first colour for being projected by a first projector and a second projector for
projecting said first colour, and for producing a first output image and a second
output image of a second colour for being projected by a first projector and a second
projector for projecting said second colour, said method comprising:
(ca) producing said first output image and said second output image of said
first colour by the method according to any of the claims 1 to 49, and
(cb) producing said first output image and said second output image of said
second colour by the method according to any of the claims 50 to 52.
66. The method according to any of the claims 64 and 65, characterized by
said producing of said first output image and said second output image of said first
colour being performed by the method according to any of the claims 50 to 52.
67. The method according to claim 66 characterized by said first colour
representing shorter light wavelengths than said second colour.
68. The method according to any of the claims 66 to 67, characterized by
said first colour representing blue and said second colour representing green,
yellow, or red.
69. The method according to any of the claims 66 to 68, characterized by
said producing of said first output image and said second output image of said
second colour being performed by the method according to any of the claims 50 to
52.
70. The method according to claim 69, characterized by said alignment
pattern in producing said first output image and said second output image of said
first colour and said alignment pattern in producing said first output image and said
second output image of said second colour having the same or approximately the
same shape.
7 1. The method according to any of the claims 69 to 70, characterized by
said alignment pattern in producing said first output image and said second output
image of said first colour and said alignment pattern in producing said first output
image and said second output image of said second colour having the same or
approximately the same dimensions.
72. The method according to claim 64 and any of the claims 66 to 7 1,
characterized by further being adapted for producing a first output image and a
second output image of a third colour for being projected by said first projector and
said second projector, said method further comprising:
(cc) producing said first output image and said second output image of said
third colour by the method according to any of the claims 1 to 52.
73. The method according to any of the claims 64 to 7 1, characterized by
further being adapted for producing a first output image and a second output image
of a third colour for being projected by a first projector and a second projector for
projecting said third colour, said method further comprising:
(cc) producing said first output image and said second output image of said
third colour by the method according to any of the claims 1 to 52.
74. The method according to any of the claims 72 to 73, characterized by a
first source value of a first pixel of said source image representing said first colour,
a second source value of a second pixel of said source image representing said
second colour, and a third source value of a third pixel of said source image
representing said third colour defining a second hue; a first intermediate value being
the intermediate value of said first pixel, a second intermediate value being the
intermediate value of said second pixel, and a third intermediate value being the
intermediate value of said third pixel defining a third hue, said method further
comprising:
(cd) subjecting said first, second, and third intermediate values to a colour
adjustment.
75. The method according to claim 74, characterized by said colour
adjustment being adapted for adjusting said first, second, and third intermediate
values to define said third hue being equal to or approximately equal to said second
hue.
76. The method according to any of the claims 74 to 75, characterized by
said colour adjustment being equivalent to:
(vii.i) calculating a first fraction as said first intermediate value
divided by said first source value,
(vii.ii) calculating a second fraction as said second intermediate
value divided by said second source value,
(vii.iii) calculating a third fraction as said third intermediate value
divided by said third source value,
(vii.iv) calculating a second maximum value as the maximum of
said first, second, and third fractions,
(vii.v) replacing said first intermediate value by said first source
value multiplied by said second maximum value,
(vii.vi) replacing said second intermediate value by said second
source value multiplied by said second maximum value, and
(vii.vii) replacing said third intermediate value by said third source
value multiplied by said second maximum value.
77. A system for producing a first output image and a second output image
for being projected by a first projector and a second projector, respectively, said
system comprising a computer and/or one or more circuits for performing the
method according to any of the claims 1 to 52.
78. A system according to claim 77, further comprising an image source for
providing said source image according any of the claims 1 to 52.
79. A system for double stacking a first output image and a second output
image, said system comprising a first projector, a second projector, and a computer
and/or one or more circuits for performing the method according to any of the claims
53 to 55.
80. A system according to claim 79, further comprising an image source for
providing said source image according any of the claims 53 to 55.
8 1. A system according to any of the claims 79 to 80, further comprising a
camera for recording said first captured image of said superimposed image
according to claim 54.
82. A system for deriving a correction of a double stacking of a first output
image and a second output image, said system comprising a first projector, a
second projector, and a computer and/or one or more circuits for performing the
method according to any of the claims 56 to 63, said system further comprising a
camera for recording said second captured image of said superimposed image.
83. A system for producing a first output image and a second output image
of a first colour for being projected by a first projector and a second projector and a
first output image and a second output image of a second colour for being projected
by said first projector and said second projector, said system comprising a computer
and/or one or more circuits for performing the method according to any of the claims
64 to 76.
84. A system for producing a first output image and a second output image
of a first colour for being projected by a first projector and a second projector for
projecting said first colour and a first output image and a second output image of a
second colour for being projected by a first projector and a second projector for
projecting said second colour, said system comprising a computer and/or one or
more circuits for performing the method according to any of the claims 65 to 76.
85. A projection system comprising a first projector and a second projector,
said first projector comprising:
a first lamp
a first integrating rod having an input end and an output end, said first
integrating rod being configured for receiving light from said first lamp through said
input end and generate a uniform illumination at said output end,
a first projector filter configured to filter said uniform illumination at said
output end of said integrating rod,
a first spatial light modulator chip,
a first illumination system for imaging said first projector filter on said
light modulator chip,
a first exit pupil through which light from said a first spatial light
modulator chip exits said first projector,
said second projector comprising:
a second integrating rod having an input end and an output end, said
second integrating rod being configured for receiving light from said second lamp
through said input end and generate a uniform illumination at said output end,
a second projector filter configured to filter said uniform illumination at
said output end of said integrating rod,
a second spatial light modulator chip,
a second illumination system for imaging said second projector filter on
said light modulator chip,
a second exit pupil through which light from said a second spatial light
modulator chip exits said second projector,
said first projector filter being configured to wavelength shift the light exiting through
said first exit pupil, and
said second projector filter being configured to wavelength shift the light exiting said
through said second exit pupil.
86. The projection system according to claim 85, characterized by said first
projector filter defining a first passband and a first guard band, and said second
projector filter defining a second passband not overlapping said first passband and
a second guard band overlapping said first guard band.
87. The projection system according to claim 85, characterized by said first
projector filter defining a first band-stop and said first projector further comprising:
a first auxiliary filter configured to filter said uniform illumination from
said output end of said first integrating and defining a first passband and a first
guard band, and said first band-stop matching or approximately matching said first
guard band, and
and said second projector filter defining a second passband not overlapping said
first passband and a second guard band overlapping said first guard band.
88. The projection system according to claim 85, characterized by said first
projector filter defining a first bandstop and said first projector further comprising:
a first auxiliary filter configured to filter said uniform illumination from
said output end of said first integrating and defining a first passband and a first
guard band, and said first bandstop matching or approximately matching said first
guard band, and
said second projector filter defining a second bandstop and said second projector
further comprising:
a second auxiliary filter configured to filter said uniform illumination from said output
end of said second integrating and defining a second passband not overlapping said
first passband and a second guard band overlapping said first guard band, and said
second bandstop matching or approximately matching said second guard band.
89. The projection system according to claim 88, characterized by said
second auxiliary filter being flat and having a second uniform thickness.
90. The projection system according to any of the claims 88 to 89,
characterized by said first auxiliary filter being flat and having a first uniform
thickness.
9 1. The projection system according to any of the claims 85 to 90,
characterized by said first projector filter defining a first uniform thickness and/or
said second projector filter defining a second uniform thickness.
92. The projection system according to any of the claims 85 to 90,
characterized by said first projector filter having a first varying thickness and/or said
second projector filter having a second varying thickness.
93. The projection system according to any of the claims 85 to 92,
characterized by said first projector filter defining a first curvature and/or said
second projector filter defining a second curvature.
94. The projection system according to any of the claims 85 to 93,
characterized by said first projector filter defining a first flat area in a first central
portion of said first projector filter, and/or said second projector filter defining a
second flat area in a second central portion of said second projector filter.
95. The projection system according to any of the claims 85 to 94,
characterized by said first projector filter defining a first curved shape in a first
peripheral portion of said first projector filter, and/or said second projector filter
defining a second curved shape in a second peripheral portion of said second
projector filter.
96. The projection system according to any of the claims 85 to 95,
characterized by said first projector filter resting on a first transparent substrate,
preferably a first glass substrate, and/or said second projector filter resting on a
second transparent substrate, preferably a second glass substrate.
97. The projection system according to any of the claims 85 to 96,
characterized by said first projector filter being dichroic, and/or said second projector
filter being dichroic.
98. The projection system according to any of the claims 85 to 97,
characterized by said first projector filter being located at said output end of said
integrating rod.
99. The projection system according to any of the claims 85 to 98,
characterized by said first integrating rod defining a first aperture having a first width
at said output end and said first projector filter defining a first spherical surface
having a first radius equal to or approximately equal to said first width, and/or said
second integrating rod defining a second aperture having a second width at said
output end and said second projector filter defining a second spherical surface
having a second radius equal to or approximately equal to said second width.
100. A system for producing a series of three-dimensional images
comprising:
a computer and/or one or more circuits for producing left output
comprising first output images and second output images by repeatedly applying the
method according to any of the claims 1 to 52, and said computer and/or said one or
more circuits further being adapted for producing right output comprising first output
images and second output images by repeatedly applying the method according to
any of the claims 1 to 52, said left output representing left perspective images of
said series three-dimensional images and said right output representing
corresponding right perspective images of said series three-dimensional images,
a projection screen,
a left perspective first projector coupled to said computer and/or one or
more circuits and configured for projecting said first output images of said left output
on said projection screen,
a right perspective first projector coupled to said computer and/or one
or more circuits and configured for projecting said first output images of said right
output on said projection screen, and
a left/right perspective second projector coupled to said computer
and/or one or more circuits and configured for alternatingly projecting said second
output images of said left output and said second output images of said right output
on said projection screen.
10 1. A system for producing a series of three-dimensional images
comprising:
a computer and/or one or more circuits for producing left output
comprising first output images and second output images by repeatedly applying the
method according to any of the claims 1 to 52, and said computer and/or said one or
more circuits further being adapted for producing right output comprising first output
images and second output images by repeatedly applying the method according to
any of the claims 1 to 52, said left output representing left perspective images of
said series three-dimensional images and said right output representing
corresponding right perspective images of said series three-dimensional images,
a projection screen,
a left perspective first projector coupled to said computer and/or one or
more circuits and configured for projecting said first output images of said left output
on said projection screen,
a right perspective first projector coupled to said computer and/or one
or more circuits and configured for projecting said first output images of said right
output on said projection screen,
a left perspective second projector coupled to said computer and/or one
or more circuits and configured for projecting said second output images of said left
output said projection screen, and
a right perspective second projector coupled to said computer and/or
one or more circuits and configured for projecting said second output images of said
right output on said projection screen.
102. The system according to any of the claims 100 to 10 1, characterized by
said left perspective first projector comprising a left polarization filter for polarizing
light projected by said left perspective first projector and said right perspective first
projector comprising a right polarization filter for polarizing light projected by said
right perspective first projector.
103. The system according to any of the claims 100 to 102, characterized by
said left polarization filter and said right polarization filter having orthogonal or
approximately orthogonal polarization directions.
104. The system according to any of the claims 100 to 102, characterized by
said left polarization filter and said right polarization filter having opposite circular
polarization directions.
105. The system according to any of the claims 100 to 104, characterized by
said a projection screen being non-depolarizing.
106. The system according to any of the claims 100 to 105, characterized by
further comprising a temporal varying polarization unit.