Projection display and method for displaying an overall image for projection
free-form surfaces or tilted projection surfaces
Description
Embodiments of the invention relate to a projection display and a method for displaying an
overall image.
The projection of dynamic image contents on a screen or as a virtual image with a digital
liquid crystal-based imaging system is based, according to the prior art, on projection
devices having a mapping optical channel or three channels whose optical paths unite in
front of the projection optics for realizing color mixing.
In particular, US 2009 323 028 A1 shows pico projectors illuminated by LED in a color
sequential manner. Further, US 2009 237 616 A1 describes a projection display having
three color channels combined in front of the projection optics.
However, if the dimensions of the systems known in the prior art are reduced for realizing
miniaturized pico projectors, luminosity losses of the projected image result.
Miniaturization of known projection systems is only possible in a limited manner due to the
limitation of the transmissible light flux through the small surface of the imaging system
existing in these systems. This connection is determined by the optical principle of
etendue conservation. The etendue or light grasp of a light source

results from its luminous surface A, the half angle of divergence Θ and the refractive index
n and remains constant with an ideal optical mapping. Real optics increase the etendue or
reduce system transmission. Thus, a minimum object surface is necessitated for a source
having a given luminance for a minimum transmissible light flux within a projecting optical
system.
It is a general problem in single-channel projection systems that due to optical laws (e.g.
natural vignetting, mapping errors), together with this surface to be mapped, the system
installation length also increases to the same extent, which makes miniaturization more
difficult.

One solution for this problem is described in DE 102009024894. There, a projection
display having a light source and regularly arranged optical channels is described. Due to
a slightly reduced center pitch of the projection lenses with respect to the imaging
structures, an offset of the respective imaging structure and the respective projection
optics increasing towards the outside from the array center results, so that superposition
of the real individual mappings or images results at a finite distance. Due to the
partitioning into several channels, it is possible to reduce the distance between the
imaging structure and the projection optics, i.e. the installation height, so that
miniaturization is obtained simultaneously with other advantages.
However, problems occur when the above systems are used in connection with curved or
tilted projection surfaces. All the above-described systems are only implemented in
connection with the use of planar projection surfaces. Generally, the problem is the front
projection of an image across greatly changing projection distances or tilted, curved
surfaces, and free-form screen geometries while ensuring high contrast and sharp
mapping. Sharp imaging can be obtained for a tilted planar screen by extensive tilting of
object and projection optics according to the Scheimpflug principle. However, this known
approach fails for curved projection surfaces. Tilting again increases the necessary
installation space. If even adaptivity to different degrees of tilting is to be realized, this
necessitates mechanics for realizing the tilting between imaging structure and projection
optics, which opposes the desired miniaturization and low production costs as well as
robust construction. An increased f-number could solve the problem by increasing the
depth of focus, but such an increased f-number is also accompanied by lower light
intensity causing other problems and additionally also opposing miniaturization, since the
problem would then be shifted to the light source.
Thus, it is the object of the present invention to provide a projection display and a method
of displaying an overall image which overcome the above problems at least partly, i.e.
allow obtaining improved projection quality with the same or a comparable miniaturization
and the same or similar apparatus effort when using projection free-form surfaces or tilted
projection surfaces.
This object is solved by a projection display according to claims 1 or 28 and a method
according to claims 27 or 33.
Embodiments of the present invention provide a projection display having an imaging
system that is implemented to generate individual images in a distribution, such as a two-
dimensional distribution, of sub-areas of an imaging plane of the imaging system, and

multi-channel optics that is configured to map one allocated individual image or allocated
sub-area each of the imaging system per channel, such that the mapping of the individual
images is at least partly superimposed to an overall image in a projection surface, wherein
the projection surface is a non-planar free-form surface, such as a curved surface, and/or
tilted with respect to the imaging plane, and the imaging system is implemented such that
constellations of points in the sub-images, each superimposed in a respective common
point in the overall image by the multi-channel optics, differ depending on what distance
the respective common point in the overall image has to the multi-channel optics.
It is the basic idea of the present invention that higher projection quality can be obtained,
even when using projection free-form surfaces and tilted projection surfaces, with
comparable miniaturization and comparable apparatus effort, when the imaging system is
implemented such that constellations of points in the sub-images, each superimposed in a
respective common point in the overall image due to the multi-channel optics, differ
depending on what distance the respective common point in the overall image has to the
multi-channel optics. Thereby, the differing distance of the points in the projection surface
to the multi-channel optics or the projection display can be corrected. This does not
increase installation height and apparatus effort. Merely the implementation of the imaging
system is changed with respect to an implementation where the projection display is
implemented for projection onto a plane-parallel projection surface. Alternatively, the aim
can be achieved by implementing the imaging system and the multi-channel optics such
that a characteristic of a contribution of each channel to the overall image varies locally
across the overall image depending on what distance the respective common point in the
overall image has to the multi-channel optics, since thereby the channels can be adjusted
to different distances and combined in a suitable manner for superposition.
A passive imaging system, such as a shadow mask, can be used as the imaging system,
or an active imaging system such as a digital imaging system, in which case dynamic
adaptation of the projection display to different projection surfaces is also possible by
changing the sub-areas in the imaging plane and the individual images generated in the
same.
The projection optics of the multi-channel optics of the projection display can have
decentration with respect to the allocated sub-areas of the imaging system so that the
overall image superimposed in the projection surface is real or virtual. By decentration or
central compression or extension between the projection optics and the allocated sub-
areas of the imaging system, in particular, a projection distance of the overall image in the
projection surface can be adjusted.

Further, the multi-channel optics can comprise a downstream overall lens cooperating
with the projection optics of the individual channels, which is implemented to refocus
collimated beams from the projection optics.
In further embodiments of the present invention, the downstream overall lens can be
implemented as optics having a variable focal length, so that an average projection
distance can be adjusted.
Embodiments of the present invention will be discussed below in more detail with
reference to the accompanying figures, where same or equal elements are indicated with
the same reference numbers. They show:
Fig. 1 a schematic block diagram of a projection display according to an
embodiment of the present invention;
Figs. 2a-2b schematic side views of projection displays according to different
embodiments;
Fig. 3 a side view of a projection display according to a further embodiment;
Fig. 4 a side view of a projection display according to a further embodiment;
Fig. 5 a side view of a projection display with a lens vertex decentered with
respect to the aperture of a respective projection optics;
Fig. 6 a side view of a projection display with a grid assembly of light sources;
Fig. 7 a side view of a projection display with a two-dimensional assembly of field
lenses;
Fig. 9 a side view of a projection display having two beam splitters and opposing
light sources for illuminating a reflective imaging system from two sides;
Fig. 9 a side view of a projection display having two beam splitters and a half-
wave plate interposed in the illuminating path;

Fig. 10 a side view of a projection display having a reflective imaging system and
an RGB light source synchronized in a color-sequential manner;
Fig. 11 a side view of a projection display having a filter assembly for generating
color mixing;
Fig. 12 a side view of a projection display wherein mappings of individual images
are superimposed to an overall image having a higher resolution;
Fig. 13 a schematic illustration for illustrating superimposing of pixels to an overall
image;
Fig. 14 a schematic illustration for illustrating superimposing of binary black-and-
white sub-images to an overall image;
Fig. 15 a schematic illustration for illustrating further superimposing of binary black-
and-white sub-images to an overall image;
Fig. 16 a schematic illustration of a projection onto a 40° tilted projection surface
having a projection display according to an embodiment;
Fig. 17 a schematic illustration of processing within a digital imaging system
according to an embodiment; and
Fig. 18 a schematic illustration of a projection to a 40° tilted projection surface with
a projection display according to a further embodiment.
Before the present invention will be discussed in more detail below based on the figures, it
should be noted that in the subsequently illustrated embodiments the same or functionally
equal elements in the figures are provided with the same reference numbers. Thus, a
description of elements having the same reference numbers can be interchanged and/or
applied to different embodiments.
Fig. 1 shows a projection display 100 according to an embodiment of the present
invention. The projection display 100 comprises an imaging system 120 and multi-channel
optics 130. The imaging system 120 is implemented to generate or display individual
images in a distribution of sub-areas 124 of an imaging plane 129 of the imaging system
120. The multi-channel optics 130 is configured to map one allocated sub-area 124 of the

imaging system 120 each per channel, such that the mapping of the individual images is
partly superimposed to an overall image 160 in a projection surface 150.
In Fig. 1, the projection display 100 is exemplarily structured in a four-channel manner, i.e.
the imaging system 120 generates individual images in four sub-areas 124, and the multi-
channel optics 130 is accordingly structured in a four-channel manner with, for example,
one respective projection optics 134 per channel. However, the number is merely
exemplary. The two-dimensional distribution of the sub-areas 124 and the projection
optics 134 is also merely exemplary. The distribution could also be realized along a line.
Additionally, the distribution is not limited to regular two-dimension distributions. As will be
discussed in more detail below, the center pitch of the projection optics 134 is reduced, for
example, with respect to a center pitch of the sub-areas 124 in the imaging plane 129.
Details will be provided below.
The projection display 100 of Fig. 1 is implemented such that the projection surface does
not have to be a planar projection surface parallel to the imaging plane 129. The
projection surface, in which the overall image is generated, where the individual images
are superimposed in a sharply focused manner, i.e. the depth of focus area, can rather be
a free surface or a projection surface 150 tilted with respect to the imaging plane 129, as
is exemplarily shown in Fig. 1.
For compensating the deviation with respect to the plane-parallel orientation of the
projection surface 150 with respect to the imaging plane 129, the imaging system 120 is
implemented such that constellations of points in the individual images, each
superimposed in a respective common point in the overall image 16 due to the multi-
channel optics 130, differ depending on what distance the respective common point in the
overall image has to the multi-channel optics 130. Fig. 1 exemplarily shows two such
common points in the overall image 160, namely one with an x and the other one with an
o. The points in the individual images of the sub-areas 124 corresponding to these points
across the multi-channel optics 130 are accordingly also indicated by an x or an o. The
position of the points o or the position of the points x in the imaging plane 129 respectively
form a constellation together.
The constellation of points o and the constellation of points x differ in order to compensate
for the fact that the distance of the common point x along the optical axis of the projection
display, in Fig. 1 exemplarily the normal direction or z axis to the imaging plane 129, to the
projection display 100 or the multi-channel optics 130 is smaller than the distance of the
common point o. As will be discussed in more detail below, the difference caused by the

different distances in the constellations results mainly in a larger extension in the sense of
a centric extension of the constellation of the points x relative to the constellation of the
points o. However, the constellations can also differ depending on the fact in what solid
angle area, seen from the multi-channel optics 130, for example relative to the optical axis
(here exemplarily z), the respective common point o or x lies in order to compensate
mapping errors of the multi-channel optics 130 or the individual projection optics 134. In
particular, the solid angle area differences can be implemented such that imaging errors
of the multi-channel optics 130 can be compensated individually per channel. The exact
correlations will follow in more detail in the following description.
In other words, the embodiment of Fig. 1 will be discussed again based on a specific
implementation where detailed images of all four channels are exemplarily superimposed
completely or congruently. As has already been mentioned above, this is not absolutely
necessary. A different superposition of the individual images to produce the overall image
160 is also possible.
Thus, the individual images in the sub-areas 124 have essentially the same contents.
They all represent one version of the overall image 160. Possibly, the individual images in
the sub-areas 124 or the sub-areas themselves are distorted with respect to the, for
example rectangular, overall image 160, with a pre-distortion which can be the same for
all individual images. The pre-distortion corrects, for example, the distortion resulting from
the divergence of the optical path of the mappings individual for each channel or the
magnification by the mappings individual for each channel depending on their focal length
and the distance to the projection surface and the resulting dimensional change across
the overall image 160 due to the deviation of the projection surface 150 from the actual
image plane to the multi-channel optics 130, which can be in infinity, for example. The
pre-distortion might not be identical across all channels. In order to address a distortion
(3rd order) exceeding first-order aberrations (trapezoid), it can be advantageous to pre-
distort the individual images or sub-areas 124 differently, as different decentrations of the
respective channels exist. Changing the constellations across the array for tilted projection
surfaces will then be added, as will now be discussed below.
The individual images in the sub-areas 124 pre-distorted with respect to the overall image
160 do differ in order to realize the above-mentioned constellations of points in the sub-
images 124 corresponding to a common point in the overall image 160, such that the
sharpness of the overall image 160 is maintained across the whole lateral extension,
despite the depth variation of the projection surface 150 along the optical axis z of the
projection display 100.

Further differences in the individual images in the sub-areas 124 can be caused by the
above-mentioned correction of mapping errors of the multi-channel optics 130 per
channel, which, however, does not depend on the lateral variation of the distance of the
projection surface to the projection display 100.
In this way, the overall image 160 can be projected onto the projection surface 150 such
that the same appears undistorted and sharp from a specific perspective, such as
perpendicular to the projection surface 150.
The projection display 100 of Fig. 1 can serve different purposes and can be used in
different fields of application. The projection display of Fig. 1 is, for example, one that is
intended to project a predetermined overall image sharply onto a predetermined projection
surface 150 that has a constant and stationary position with respect to the projection
display 100. The projection display 100 could, for example, be provided to project an
overall image 160 representing, for example, an inscription or another content, onto a
sculpture whose external surface forms the projection surface 150, wherein in this type of
application the projection display 100 is intended to be positioned and to remain at a fixed
position with respect to the sculpture. In this case, the imaging system 120 can be a
shadow mask or another finely structured mask which is illuminated, for example, from the
rear opposing the multi-channel optics 130, for example by means of Kohler illumination.
The individual images could be realized in the sub-areas 124 binary-coded, gray-scaled or
even color-coded, either in an analog or continuous or pixelated form. The mask 120
could in particular be a slide or, in the sub-areas 124, individual slides. Coding of image
information could be realized particularly by mapping the image information on a
transmission scale. An example of rear illumination will be discussed in more detail below.
Imaging systems 120 in the form of a mask could, however, also work reflectively to
generate static individual images in the sub-areas 124. Examples of reflective systems will
also be presented below.
Instead of a passive or static imaging system 120, an active imaging system, such as a
digital imaging system 120, can be used. The imaging system can operate in a
transmissive or a reflective manner. However, it is also possible that the imaging system
is self-luminous, such as an OLED or an LED display. In these cases, it is possible that,
as will be discussed in more detail below, the imaging system is, for example, internally
implemented to perform the above-mentioned processes which, from incoming pixel array
data representing the overall image 160, provide the position and the contents, namely
the individual images of the sub-areas 124, at first, in order for them to then be displayed

by the imaging system 120, adapted to a specific relative position of the projection surface
150 to the projection display 100, which also enables in particular an adaptation to other
projection surface geometries is possible by accordingly adapting or re-performing the
pre-processing. This will also be discussed in more detail below.
Finally, it should be noted that the imaging system 120 and the multi-channel optics 130
can be stationary to one another, such as installed in a housing. In particular, the
projection display 100 can be installed in a mobile device such as a mobile phone, a PDA,
a notebook or any other portable computer or the like.
After having described an embodiment for a projection display in general above, different
options will be discussed with reference to Figs. 2a-d as to how the optical or apparatus
part of the projection apparatus 100 can be formed. The embodiments of Figs. 2a-d are
not to be seen as limiting, but represent advantageous implementations.
Fig. 2a shows an implementation of a projection display according to Fig. 1 where the
imaging system 120 operates transmissively or displays the individual images in the sub-
areas 124 by displaying or encoding the luminosity variation or color variation in the
individual images by lateral variation in the transmission. As is shown in Fig. 2a, for
realizing rear illumination, i.e. illumination from a side of the imaging system 120 facing
away from the multi-channel optics 130, the projection apparatus can comprise a light
source 110 and a field lens 115. Preferably, the distance between the sub-images 124
and the field lens 115 is selected to be small in order to realize complete illumination of
the imaging system 120. Preferably, additionally or alternatively, Kohler illumination of the
multi-channel optics 134 is realized, according to which the field lens 115 maps the light
source 110 into the opening of the pupil of the projection optics 130.
Fig. 2b shows that a field lens array 116 could be used instead of a field lens and that
additionally or alternatively instead of a point-shaped light source 110 a planar light source
111 could be positioned on the rear for illumination, i.e. such that the field lens array 116
or the field lens 115 are arranged between the light source 111 and the imaging system
120. Here, also, Kohler illumination can be realized. The planar light source can, for
example, be an array of LEDs with allocated collimation optics for realizing illumination
units that are also structured in a very planar manner.
Fig. 2c shows that a self-luminous imaging system, such as a digital imaging system, can
also be used as the imaging system 120. The illumination technology could be OLED-
based, LED-based, TFT-based or implemented differently.

Fig. 2d shows a reflective structure of the projection display, according to which the
imaging system 120 is a reflective imaging system and a front side illumination is realized
by means of a beam splitter 140 arranged between the multi-channel optics 130 and the
imaging system 120 which is illuminated laterally, for example via a combination of
condenser optics 115 and the light source 110 in order to illuminate the sub-areas 124 of
the imaging system 120. Details will become clear from the following discussion.
The imaging system 120 can, for example, be a reflective LCD imaging system 120, just
as well as the imaging system sensor of the embodiments according to Figs. 2a and 2b
could be a transmissive LCD imaging system.
After having described the basic implementation options of the embodiment of Fig. 1,
possible details of the optical assembly of a projection display will be discussed based on
the following figures. For explaining the optical structure, it is first assumed that the
projection surface 150 is planar and runs parallel to the imaging plane of the imaging
system, However, these statements will also show that the optical structure of the
projection display will accommodate the desire for sharp projection onto a differently
shaped or positioned projection surface in that, due to the multi-channel optical structure,
the optical depth of focus basically exists anyway. Due to the normally very short focal
lengths of, for example, a few millimeters, the depth of focus range of each individual
projector or each channel in the array 132 is very high compared to a conventional single-
channel assembly. These circumstances are utilized according to the embodiments of the
present invention to finally produce the actual sharpness of the projection onto a tilted or
free surface-shaped projection surface by appropriately changing the individual images or
sub-areas with respect to a plane-parallel orientation of the projection surface, which, in
the case of a digital imaging system, merely necessitates, for example, digital image
preprocessing. Only after this description will the case be discussed that the projection
surface is not oriented plane-parallel to the imaging plane or does not have to be and also
the additional measures necessary to react to the deviation according to embodiments of
the present invention.
Fig. 3 shows a side view of a projection display 100 according to an embodiment of the
present invention. The projection display 100 shown in Fig. 1 comprises a light source
110, an imaging system 120, here exemplarily implemented in a reflective manner, a two-
dimensional array or assembly 132 of projection optics 134 as multi-channel optics 130
and a beam splitter 140. Here, the imaging system 120 is implemented to display
individual images in a two-dimensional distribution 122 of sub-areas 124 of the same.

Further, the two-dimensional assembly 132 of projection optics 134 is configured to map
an allocated sub-area 125 of the imaging system 120 along optical axes 103, so that
mappings of the individual images are superimposed to an overall image 160 in the
projection surface 150. Finally, the beam splitter 140 is arranged, on the one hand, in an
optical path between the imaging system 120 and the two-dimensional assembly 132 of
the projection optics, and on the other hand, in the optical path between the light source
110 and the imaging system 120.
In particular, in further embodiments, the beam splitter 140 can have a polarizing effect
and the reflective imaging system 120 can be implemented to display the individual
images in the form of a polarization influence.
The projection display can comprise a regular, two-dimensional assembly of imaging
areas on the imaging system 120, which is implemented, for example, as a liquid crystal
imaging system 121, a beam splitter 140, which is implemented, for example, as a
polarizing beam splitter 142, and the two-dimensional assembly 132 of projection optics
134. As is shown in Fig. 3, light from the light source 110, for example implemented as
LED 112, first passes through a condenser optics 115 and is then guided again to the
polarizing beam splitter 142. From there it is finally reflected in a polarized manner in the
direction of the reflective imaging system 120, which is, for example an LCoS imaging
system (LCoS = liquid crystal on silicon).
Depending on the gray scale of the image point to be displayed, the, for example, digital
imaging system rotates the polarization direction of light reflected at the same and hence
controls the transmission during the second pass through the polarizing beam splitter.
Fast switching of the voltages or crystal rotations per pixel allows the display of dynamic
image contents.
The projection optics 134 shown in Fig. 3 could, for example, be microlenses implemented
in a regular two-dimensional assembly as projection objectives, each mapping a sub-area
125 of the imaging system 120 onto the projection surface 150 or a screen. By using such
a projection assembly, it becomes possible to drastically reduce the installation length of
the overall system with respect to conventional single-channel projectors of the same
image size. While a small installation length of the projection display or projection system
results from focal lengths of the projection optics or lenses of, for example, a few
millimeters, wherein their focal lengths again depend on the dimensions of the beam
splitter, multiplication of the object surfaces or lateral extensions provides a proportional
increase in image luminosity. Thus, compared to miniaturized single-channel projectors,

an installation length exceeding the thickness of the beam splitter by only a few
millimeters is obtained, and this with comparable lateral extension and projection
distances.
In further embodiments, the projection image can be produced by superposing, putting
together or interleaving the mappings of individual channels of the assembly.
In further embodiments, the projection optics 134, as shown exemplarily in Fig. 3, have
decentration 135 with respect to the allocated sub-areas 124.
Generally, decentration can be seen as a central compression or extension with respect to
a central optical axis 101 or as a lateral offset of the projection optics 134 with respect to
the allocated sub-areas 124 of the imaging system 120. Decentering the projection optics
with respect to the allocated individual images on the imaging system is decisive for
projection distance. Due to a large depth of focus of the sub-images, the focus or
sharpness at the projection distance depends only in a limited manner on the screen-side
focusing of the individual projection optics. As has already been mentioned, on the object
side, focusing the projection optics 134, for example relative to the short focal length of
the projection optics, can be adjusted exactly such that the imaging plane 129 is within the
focal length of the projection optics 130. However, this is not compulsory. As has already
been mentioned, for virtual images or very close projection distances, the imaging plane
129 can be shortly in front or behind. Depending thereon, the screen-side focusing is, for
example, in infinity, but the depth of focus area of the individual channels is large due to
the relatively short focal lengths. This circumstance is utilized according to Fig. 1 and also
the following description when the image or projection surface 150 does not run plane-
parallel to the imaging plane 129, but tilts out of the same or varies in another way
according to a free-form surface.
By a slightly reduced center pitch (pitch) of the projection optics or projection lenses to the
imaging structures, an offset 135 of the respective imaging structure and the respective
projection optics increasing towards the outside from the central optical axis 101 of the
two-dimensional assembly 132 of the projection optics 134 or array center (grid center)
results. The resulting slight tilting of the optical axes 103 of external projection optics 134
or projectors with respect to the central optical axis 101 or the central channel results in a
superposition of individual mappings in the image plane or projection surface 150 to the
overall image 160. Here, the image plane or projection surface can here be infinity or at a
finite distance to the projection optics in front of the imaging system or behind the imaging
system. As is shown in Fig. 1, the area in front of the imaging system is defined by the

area 102 on the right or in the optical path after the two-dimensional assembly 132 of
projection optics 134, while the area behind the imaging system is defined by the area 104
on the left of the imaging system 120 or on the side of the imaging system 120 facing
away from the beam splitter 140. The individual mappings can be superimposed to the
overall image, for example on a screen.
Here, no further macroscopic optical elements are necessitated for projection in the
optical path. The projection distance L of the array projection display (i.e. the average
distance L of the projection surface 150 to the two-dimensional assembly 132 of projection
optics 134 perpendicular to the same) which is, in the case of a non-plane-parallel
projection surface 150, an average projection distance, results from the focal length of the
projection optics f, the center pitch of the projection optics pPL and the center pitch of the
images P0BJ- Magnification M of the mappings results from the ratio of the projection
distance L to the focal length of the projection lens f. Here, the following relations apply:

Thus, the ratio of the center pitches of object structures to projection optics or their
difference controls the projection distance. Here, it should be noted that in the case of a
non-plane-parallel projection surface 150 the center pitch of sub-areas 124 P0BJ> for
example, represents the average of all corresponding points in the individual images, or
an average of the distances of the area centers of the sub-areas 124, which can, for
example, be distorted, on the one hand for compensating the optical distortion as
described above with reference to Fig. 1, and on the other hand for local sharpness
readjustment. Details will be discussed below.
If the center pitch of the projection optics is smaller than that of the imaging structures, a
real image results at a defined distance. In the case shown in Fig. 1, the center pitch pPL
of the projection optics 134 is smaller than the center pitch pobj of the allocated sub-areas
124. Thus, in the embodiment in Fig. 1, an overall image 162 superimposing in the
projection surface 150 is real. Fig. 1 is also based on this example.
Fig. 4 shows a side view of a projection display according to a further embodiment. In the
embodiment shown in Fig. 4, the multi-channel optics 134 further comprises an overall
lens 310 which is downstream with respect to the two-dimensional assembly 132 of
projection optics 134 and cooperates with the two-dimensional assembly 132 of projection
optics 134. In this context, downstream means that the overall lens 310 is arranged in the

optical path after the two-dimensional assembly 132 of projection optics 134. In Fig. 4, the
overall lens 310 is implemented in particular to refocus collimated beams 315 from the
projection optics 134 such that the image plane or projection surface 150 of an overall
image 302 lies within a focal plane of the overall lens 310, or the projection surface 150
deviating locally from a plane-parallel arrangement is in the depth of focus area. These
circumstances are illustrated in Fig. 4 such that the multi-channel optics 150 has an
average distance fL to the overall lens 310 where the individual mappings are
superimposed to the overall image 302. Further, the distance dPL of the two-dimensional
assembly 132 of projection optics 134 to the imaging system 120 can be adjusted by the
imaging system 120 such that the same approximately corresponds to the focal length of
the projection optics 134.
In Fig. 4, it can be seen that the projection optics 134 are centered and act in a collimating
manner with respect to the allocated sub-areas 124. This means that in this embodiment
the center pitch pPL of the projection optics 134 is equal to the center pitch POBJ of the
allocated sub-areas 124.
If the structure is modified accordingly, as is exemplarily shown in Fig. 4, by adjusting the
distance dPL of the projection optics to the imaging system such that the individual images
are formed in infinity, the pitch of the sub-images corresponds to the pitch of the projection
optics, and if the overall lens 310 is arranged, for example, in the form of a converging
lens 312 in the optical path after the two-dimensional assembly of projection optics or the
array optics, the overall image 302 is formed in the focal plane of the lens 310. When
using a converging lens, a real image is projected onto a screen. An advantage of the
embodiment shown in Fig. 4 is the reduced vignetting of projection channels 103 remote
from the axis compared with the structure shown in Fig. 3 and the option of adjusting
different average projection distances by using a variable converging or diverging lens, for
example in the form of a zoom objective or a liquid lens.
In particular, the downstream overall lens 310 shown in Fig. 4 can be implemented as
optics having a variable focal length, so that a projection distance can be adjusted. It can
be seen in Fig. 4 that the projection distance L, apart from a longitudinal extension of the
projection optics assembly 130, is essentially given by the focal length fL of the overall
lens 310.
The optical effect of a downstream converging or diverging lens can also be obtained by a
specific implementation of the projection array, as is exemplarily shown in Fig. 5. Fig. 5
shows, in particular, a side view of an inventive projection display 400. In the embodiment

shown in Fig. 5, the two-dimensional assembly 132 of projection optics 134 is
implemented as a projection array 410 or a two-dimensional assembly, wherein each
projection optics 414 of the projection array 410 has a lens vertex 415 decentered with
respect to the aperture of the respective projection optics.
The projection optics 414 of the two-dimensional assembly 410 shown in Fig. 5 essentially
correspond to the projection optics 134 of the two-dimensional assembly 132 shown in
Figs. 3 and 4. In an enlarged representation (circle Z), the individual lens vertexes 415 of
the projection optics 414 can be seen more clearly. Decentration of the lens vertexes 415
can, for example, be implemented such that the projection optics 414 of the two-
dimensional assembly 410 together achieve the same effect as the projection optics
assembly 130 shown in Fig. 4 with the downstream overall lens 310. As is exemplarily
shown in Fig. 5, here a center pitch pLS of the lens vertex 415 is smaller than the center
pitch POBJ of the allocated sub-areas 124. Thus, each lens can effect projection of the
individual image of the respective sub-area 125 onto the projection surface 150. There,
the mappings of the individual images are superimposed to the overall image 160.
If, accordingly, projection lenses having a lens vertex increasingly offset with the distance
to the central optical axis 101 or system axis with respect to the aperture are used, the
optical function of the overall lens, such as a converging lens, can be shifted into the
projection or lens array. It is an advantage of the embodiment shown in Fig. 5 that an
optical component can be saved while maintaining the reduced vignetting of channels
remote from the axis.
Fig. 6 shows the option of using array light sources. Fig. 6 shows an inventive projection
display 500 having a grid assembly 510 of light sources. Here, the grid assembly 510
shown in Fig. 6 essentially corresponds to the light source 110 in Figs. 3 to 5. Further, Fig.
6 shows a condenser optics assembly 515. The condenser optics assembly 515 of Fig. 6
essentially corresponds to the condenser optics 115 in Figs. 3 to 5. As is shown in Fig. 6,
the grid assembly 510 comprises a plurality of light sources 510-1, 510-2 510-5,
wherein a condenser optics of the condenser optics assembly 515 is allocated to each
light source. Particularly, the grid assembly 510 of light sources and the condenser optics
assembly 515 can be implemented such that light from the individual light sources 510-1,
510-2, ..., 510-5 is respectively guided onto allocated sub-areas 124 of the imaging
system 120, as is illustrated in Fig. 6, by illuminating paths 501. It is an advantage of the
embodiment shown in Fig. 6 that by superimposing many individual images, as is also the
case in the assembly described above, normally no specific measures for homogenization
of the illumination need to be taken. A further advantage of the use of array light sources,

such as collimated LED arrays, is the resulting reduced increase of the lateral extension of
the overall assembly.
Fig. 7 shows a side view of a projection display 600 having a two-dimensional assembly
610 of field lenses 612. In the embodiment shown in Fig. 7, the two-dimensional assembly
610 of field lenses 612 is arranged at least in an optical path between the imaging system
120 and the beam splitter 140. Here, each field lens 612 in the two-dimensional assembly
610 is allocated to a projection optics 134 in the two-dimensional assembly 132 of
projection optics 134. By this use of the two-dimensional assembly 610 of field lenses
612, Kohler illumination of each projection optics 134 in the two-dimensional assembly
132 can be obtained.
Particularly, in the projection display 600, a focal length fFi_ of the field lenses 612 can lie
between 1.5 times and 2.5 times of a focal length fPL of the projection optics 134.
In other words, the use of the two-dimensional assembly of field lenses or a field lens
array between the beam splitter and the imaging system shown in Fig. 7 allows Kohler
illumination of the projection optics, whereby the image luminosity can be increased with
simultaneously improved stray light suppression.
In further embodiments, stray light suppression can be further improved by using
absorbing apertures (not shown in Fig. 7) in the plane of the field lens arrays covering the
areas between the lenses. Generally, the use of such an aperture array between imaging
system and polarizing beam splitter is useful even without a field lens array for stray light
suppression.
In further embodiments of the present invention, illumination can also take place from
several sides by respective, for example collimated, light sources. Fig. 8 shows a side
view of a projection display 700 having two beam splitters 730, 740 and opposing light
sources 710, 720 for two-sided illumination of a reflective imaging system. In Fig. 8, the
projection display 700 in particular has first and second light sources 710, 720 and first
and second beam splitters 730, 740 arranged between the imaging system 120 and the
two-dimensional assembly 132 of projection optics. Here, the first beam splitter 730 is
arranged in the optical path between the first light source 710 and a set 750 of sub-areas
of the imaging system 120, and the second beam splitter 740 in the optical path between
the second light source 720 and the second set 760 of sub-areas of the imaging system
120.

As is shown in Fig. 8, a first lateral area 750 of the imaging system 120 is illuminated
essentially by the first light source 710 and an allocated first condenser optics 715, while a
second lateral area 760 of the imaging system 120 is illuminated essentially by the second
light source 720 and an allocated second condenser optics 725. Here, the first and
second light sources 710, 720 and allocated first and second condenser optics 715 and
725 essentially correspond to the light source 110 or the condenser optics 115 of the
above-described embodiments. Contrary to the use of a single beam splitter, the two-
sided illumination with two light sources 710, 720 and two polarizing beam splitters 730,
740 shown in Fig. 8 allows approximately halving the installation length of the projector.
In further embodiments of the invention, the projection optics can also differ in that they
are corrected more for distortion for the respective color spectrum by which the sub-area
mapped by the respective projection optics can be illuminated than for one of the other
color spectra of the different color spectra.
In further embodiments of the invention, in the two-dimensional assembly 132 of
projection optics, the projection optics 134 can be corrected for defocusing and/or
astigmatism and/or coma which increase with increasing distance to the optical axis 101
of the imaging system 120 and the projection optics assembly.
Finally, in further embodiments, the imaging system 120 can be implemented such that a
size of the sub-areas 124 continuously changes with increasing distance to the optical
axis 101 of the imaging system 120 and the projection optics assembly 130, so that the
individual images in the projection surface have the same size.
By such a continuous change in the size of the sub-areas, with increasing distance to the
central optical axis 101 or the central channel, an increasing object distance and hence a
lower magnification of outer projection optics 103 with respect to the central channel in the
case of decentration, as is exemplarily shown in Fig. 1, can be compensated during
projection of the individual images onto the projection surface 150.
Fig. 9 shows a side view of a projection display 800 having two beam splitters 810, 820
and a half-wave plate 830 lying between them in the illuminating path. Apart from a first
beam splitter 810, the projection display of Fig. 9 particularly comprises a second beam
splitter 820 which is arranged, on the one hand, in the optical path between reflective
imaging system 120 and two-dimensional assembly 132 of projection optics, and, on the
other hand, in the optical path between light source 110 and reflective imaging system
120, and a half-wave plate 830 arranged between the first beam splitter 810 and the

second beam splitter 820. Thereby, a polarization direction of a polarization component
(e.g. p) transmitted by the first beam splitter 810 of light (polarization components p, s)
emitted by the light source 110 can be rotated by 90° when passing the half-wave plate
830. Here, the first beam splitter 810 and the second beam splitter 820 are implement to
reflect light from a direction of the light source 110 in the direction of the imaging system
120 by the polarization direction (e.g. s) rotated by 90°. An exemplary illuminating path
with the respective polarization component is illustrated in Fig. 9 by arrows indicated by s,
P-
In other words, if two polarizing beam splitters are used, as is exemplarily shown in Fig. 9,
which are connected in series via the half-wave plate 830 or X/2 plate in the illuminating
path, both polarization components (p, s) of an unpolarized light source, such as an LED,
can be used. Here, the half-wave plate rotates the polarization component (p) transmitted
unused by the first beam splitter by 90°, so that the same is reflected in the following
beam splitter onto the allocated half of the imaging system with the correct polarization
direction (s).
The complete utilization of an unpolarized light source by the described assembly having
two polarizing beam splitters or polarization dividers and a half-wave plate (X/2 plate) can
be supplemented by the above-described two-sided illumination allowing further halving of
the installation length.
With reference to the above embodiments, a projection of outer edges of the first 730, 810
and the second beam splitter 740, 820 on the reflective imaging system 120 can be
formed such that the same does not pass through the sub-areas 124 of the imaging
system 120. Thereby, it can be avoided that the outer edges, when projected, have a
spurious effect in the overall image.
In further embodiments, the projection of a full-color RGB image, as is illustrated
exemplarily in Fig. 10, can be realized by an RGB light source 905. This is possible, for
example, by three LEDs 910, 920, 930 with allocated collimation optics 915, 925, 935 and
a color combiner 940. Here, the RGB light source 905 in the embodiment in Fig. 10
essentially corresponds to the light source 110 of the previous embodiments. In particular,
in the embodiment shown in Fig. 10, the RGB light source 905 and the imaging system
950 operate in a synchronized, color-sequential manner to obtain full-color projection.
In Fig. 10, the reflective imaging system 950 essentially corresponding to the imaging
system 120 of the above embodiments can be implemented to represent identical

individual images 904 of the sub-areas 124 of the imaging system 950 with a sufficiently
high frame rate. Further, the light source 905 can be implemented to pass sequentially
different color components (e.g. red, green, blue) per frame. Via the color-sequential
mode of operation of the imaging system 950 and the individual light sources 910, 920,
930, full-color projection can be realized, wherein the image contents , for example of the
digital imaging system, is identical for all projection channels.
In further embodiments, the light source 110, the beam splitter 140, the projection optics
assembly 130 and the reflective imaging system 120 can be implemented such that
reflected light from at least two sub-areas of the imaging system 120 comprises the same
color spectrum.
Further, in other embodiments, the light source 110 can be arranged such that different
sub-areas of the imaging system 120 are illuminated by different color components. With
reference to Fig. 8, for example the first light source 710 can emit light with a first color
component, which is reflected by the first beam splitter 730 to the first sub-area 750 of the
imaging system 120 after passing through the condenser optics 715, while the second
light source 720 can emit light with a second color component, which is reflected by the
second beam splitter 740 to the second sub-area 760 of the imaging system 120 after
passing through the condenser optics 725. Thus, different sub-areas 750, 760 of the
imaging system 120 can be illuminated with the first and second color component which
can differ from one another.
Fig. 11 shows a side view of a projection display 1000 with a color filter assembly 1020 for
generating a color mix in the projection surface 150. In Fig. 11, the imaging system 1030
essentially corresponding to the imaging system 120 of the previous embodiments is
implemented to display groups 1032-1, 1032-2, 1032-3 of individual images each
representing a gray scale of a color component of an image content. Here, a respective
color filter 1022-1, 1022-2, 1022-3 of the filter assembly 1020 can be allocated to each
group 1032-1, 1032-2, 1032-3 of individual images. In this way, the groups 1032-1, 1032-
2, 1032-3 of individual images can be filtered according to the respective color
component, so that a color mix is presented in the overall image 160 superimposed in the
projection surface 150.
In other words, Fig. 11 presents another option for generating RGB images. By
illuminating with a white light source 1010 and inserting RGB color filters 1022-1, 1022-2,
1022-3 into the mapping light path, a basic color image is generated in each of a number
of projection channels. Normally, one projection channel corresponds to the mapping of a

sub-area of the imaging system by an allocated projection optics onto the projection
surface. Allocating the respective basic color image contents to the respective projection
channels results in RGB projection. An advantage with this type of color generation is the
option of white balance by a number of projection channels for the respective basic color
adjusted to the spectral characteristic of the light source and the color filters.
In further embodiments, a separate light source of a basic color can be allocated to each
projecting channel or a group of projection optics. Color mixing is performed during
superposition into the overall image on the screen or in the virtual image.
With reference to Fig. 8, the light source 110 in the projection system 700 is, for example,
implemented in the form of light sources 710, 720 to illuminate the different groups 750,
760 of sub-areas of the imaging system 120 with a different color spectrum via the beam
splitters 730, 740. Here, within the two-dimensional assembly of projection optics,
projection optics 755, 765 which map sub-areas 750, 760 illuminated with different color
spectra (e.g. red, blue) by the light sources 710, 720 differ from one another.
Further, in further embodiments, the imaging system 120 can be implemented such that a
size of sub-areas 750 that can be illuminated with a first color spectrum of the different
color spectra (e.g. red) differs from a size of sub-areas 760 that can be illuminated with a
second color spectrum (e.g. blue) different to the first one. Thereby, a size of the
individual images in the projection surface can be synchronized.
Here, it should be noted that the display of the color apart from the above-stated direct
color illumination of the sub-areas can also be realized by the color filter assembly
exemplarily shown in Fig. 11, so that different groups of sub-areas contribute to the overall
image with different color spectra.
In further embodiments, the same focal length can be selected for all projection optics
within the two-dimensional assembly of projection optics for all different color channels,
i.e. for optical channels allocated to different color spectra, so that the same magnification
results for all different color channels. If, further, different geometric distances of the
projection optics to the imaging system are adjusted, different optical path lengths due to
a dispersion of the beam splitter (e.g. the first or second beam splitters 730, 740) can be
compensated for the different color channels.
However, in further embodiments, it might be undesirable to arrange the projection optics
within the two-dimensional assembly of projection optics at different installation heights.

Thus, it can be advantageous to maintain the projection optics at the same geometric
distance to the imaging system. In this case, the different optical path lengths due to the
dispersion of the beam splitter can be compensated in that different focal lengths of the
projection optics are selected according to the different optical path lengths for the
different color channels. Here, the different focal lengths have the effect that different
magnifications result for the different color channels in the projection surface. The
respective magnification or the respective mapping dimension can, however, be adapted
again by different sizes of the sub-areas allocated to the different color channels, such as
by software (i.e. computer-controlled).
Further, in other embodiments, the beam splitter might not be implemented in the shape
of a cube but as a plate, so that a difference between the different optical path lengths due
to smaller dispersion is negligible.
Thus, in further embodiments of the invention, by adaptation of the focal lengths of the
projection optics of the basic color array per color group, correction of the longitudinal
color aberrations of the mapping can be performed. Further, by adaptation of the sub-
image sizes of the basic color sub-images per color group, correction of the lateral color
aberration of the mapping can be performed. A further advantage of the present invention
is hence the possibility of aberration correction in the form of correction of color
aberrations, such as longitudinal color aberrations, of the projection optics per channel. If
different mapping dimensions for the basic colors exist, correction of the resulting lateral
color aberration in the overall image is, for example, also possible by different image sizes
of the basic color sub-images.
In further embodiments, by pre-distorting the sub-images, correction of the distortion can
be performed. Further, in other embodiments, correction of defocusing of projection
channels remote from the axis can be performed by a focal length of the projection optics
adapted per channel.
In further embodiments, a projection display can also be characterized in that a correction
of the different mapping dimensions of central channels or channels remote from the axis
resulting from a focal length adaptation is performed by a size and pre-distortion of sub-
images remote from the axis amended per channel. Further, in other embodiments,
correction of astigmatism and coma can be performed with different sagittal and tangential
focal lengths of projection optics remote from the axis adapted per channel.

Similarly to achromatization, correction of monochromic aberrations per channel, such as
the influence of image field curvature for larger object distances of projection channels
remote from the axis or the distortion, together with pre-distortions of the sub-images
depending on the axis distance of the projection optics, allows simple solutions for
improving image quality. While in color correction a differentiation is primarily made
between the three color groups and hence three different, corrected projection optics
result, the correction of monochromic aberrations generally necessitates an adaptation of
the respective projection optics depending on the position of the respective projection
channel relative to the array center. Here, for example, lens arrays having focal lengths
varying continuously across the array, in elliptic microlenses also divided into sagittal and
meridional focal lengths, are useful for correcting astigmatism and coma.
A further option for generating color images is the use of an array light source, such as is
shown, for example, in Fig. 6 in the form of the light source 510 having the respective
condenser optics assembly 515, for example with LEDs of different light colors. The
unique allocation of the individual light sources to groups of sub-images and projection
optics is accomplished advantageously by using a field lens array, as is exemplarily
shown in Fig. 6. Here, the omission of color filters allows a higher system transmission as
compared to the above-described approach.
In further embodiments, the reflective imaging system 120 and the projection optics
assembly 130 can be implemented such that identical individual images from different
sub-areas are superimposed in a pixel-precise manner.
Further, the imaging system 120 or the imaging system array can be implemented to
display different individual images. Their mapping by the allocated projection optics results
in the overall image or projection image.
Fig. 12 shows a projection display 1100, where mappings of individual images are
superimposed in the projection surface 150 to an overall image 1130 having a higher
resolution or displayed number of pixels. In particular, in the embodiment shown in Fig.
12, the reflected imaging system 1110 and the projection optics assembly 1120 can be
implemented such that the mappings of the individual images are superimposed in the
projection surface 150 with a sub-pixel offset. Here, the projection optics 1122 has, in the
two-dimensional assembly 1120, decentration with respect to the allocated sub-areas 124
shown exemplarily in Fig. 12. This results, as is exemplarily shown in Fig. 12, in an overall
image 1130 superimposed in the projection surface 150 which has a higher resolution or
displayed number of pixels than the individual images.

Apart from full-color projection, the use of different sub-images allows further realization
variations. In particular, by joining sub-images, for example according to Fig. 12, a
magnification of the resulting overall image 1130, an increase in the number of pixels in
the resulting overall image or a combination of both is enabled. In the case illustrated
exemplarily in Fig. 11, the overall image 1130 is composed of three joined projected sub-
images 1132-1, 1132-2, 1132-3, each mapped via two projection channels 1101.
Fig. 13 shows a schematic illustration for illustrating a superposition 1200 of pixels to an
overall image 19. The realization illustrated in Fig. 13 is particularly advantageous for
imaging systems having a low pixel fill factor. A pixel 16a, 16b, 16c or 16d of the imaging
system is generally composed of an inactive area 17a, 17b, 17c or 17d and an active area
18a, 18b, 18c or 18d. For the following description, it is assumed that pixel 16a is
controlled white, pixel 16b light gray, pixel 16c dark gray and pixel 16d black. If four
groups (a, b, c, d) of projection channels are formed, each including pixels 16a, 16b, 16c
or 16d in their sub-images at the same respective position, projecting the pixel sub-area or
active area 18a, 18b, 18c and 18d in a clearly resolved manner and comprising a
decentration of the projection optics which allows projection to the overall image offset by
half a pixel pitch (sub-pixel offset), a pixel pattern 11 is obtained at the allocated pixel
position in the overall image 19 which represents the superposition of the four sub-
images. The described assembly hence allows a number of pixels in the overall image
which is higher by the factor 4 with respect to the sub-images.
Fig. 14 shows a schematic illustration for illustrating a superposition 1300 of binary black-
and-white sub-images to an overall image 21. If the imaging system has a high fill factor,
the superposition with sub-pixel offset in the overall image 21 will result in a combination
of an increased number of gray scales and an increase in the number of displayable
pixels. These circumstances are illustrated in Fig. 14 based on the example of a strip
structure. The purely binary black-and-white sub-images 20a, 20b are superimposed to an
overall image 21 having an increased number of gray scales and an increased displayable
number of pixels.
Apart from increasing the number of pixels, increasing the number of displayed gray
stages without an image offset is also possible. Fig. 15 shows a schematic illustration for
illustrating a further inventive superposition 1400 of binary black-and-while sub-images to
an overall image 23. Fig. 14 exemplarily shows purely binary black-and-white sub-images
22a, 22b, whose superposition to the overall image 23 already provides three gray scales.
A further increase in the different binary images increases the number of displayable gray

scales even further. This approach for increasing the number of gray scales can also be
used for not purely binary but generally for sub-images having less gray scaless. The
combination of this approach with the above described procedure for displaying full-color
images accordingly allows an increase in color depth.
Thus, with reference to Figs. 14, 15 the projection display can be implemented to receive
an image to be projected having a first gray/color scale resolution, wherein the ref ective
imaging system 120 is implemented to display the individual images (i.e. the binary black-
and-white sub-images 20a, 20b; 22a, 22b) having a second gray/color scale resolution
that is smaller than the first gray/color scale resolution. In particular, the projection display
can be implemented to control the sub-images depending on a gray/color scale VJ lue of
the image to be projected at a pixel of the image to be projected such that the ind vidual
images in the overall image 21; 23 sum up to a gray/color scale corresponding to the
gray/color scale value at a position corresponding to the pixel.
Now that possible details for apparatus implementations of the projection display of Fig. 1
have been described above according to a reflective variation similar to Fig. :>d for
different embodiments, it should be noted that some of the variations described with
respect to these figures 3-15 can obviously also be applied to the other g9neral
implementations according to Figs. 2a-2c. This applies in particular with respect to the
different options of realizing a colored overall image 160. For realizing a colored overall
image 160, the imaging system 120 can, for example, be a digital imaging system with
pixels of different color channels that are arranged, for example, according to a Bayer
pattern. This applies in particular for self-luminous imaging systems 120 according :o Fig.
2c. It would also be possible to combine a white light source 110 with different color filters
in the channels of the multi-channel optics 134, wherein the filter could not only lie behind
the imaging system 120 in the optical path seen from the light source 110, but also in front
of the same. The considerations with respect to the mapping corrections of the individual
projection optics, such as for taking the respective axis distance of the respective mjipping
channel to the optical main axis of the projection display into account, apply accordingly to
the implementations according to Figs. 2a-2c, wherein, however, consideration Df the
dispersion by the beam splitter 140 can be omitted in the embodiments according tc Figs.
2a-2c. The above considerations also apply with respect to the basic option of add ng an
overall lens in addition to the multi-channel optics. Thus, the multi-channel optics 1C0 can
comprise an overall lens, similar to 310, 312, downstream with respect to the two-
dimensional assembly 132 of projection optics and cooperating with the two-dimensional
assembly 130 of projection optics 134, which is implemented to refocus collimated teams
315 from the projection optics 134 in a focal plane of the overall lens 310, 312, wherein

the projection optics 130 are then centered with respect to the allocated sub-areas 124
and act in a collimating manner, or to focus divergent/convergent beams from the
projection optics 134 in an effective focal plane resulting from decentration between the
projection optics 134 on the one hand and the sub-areas 124 on the other hand and
focusing by the downstream overall lens.
With respect to the field lens 115, it should be noted that the same can be implemented in
the form of a Fresnel lens to reduce the installation height. The mentioned light source
and a possible collimation optics can be implemented in a multi-channel manner to reduce
the structural length, and thus a illumination with R, G or B per channel can be performed
in order to generate an RGB image on the screen.
After these explanations with respect to details of the apparatus structure according to
some embodiments, reference will again be specifically made below to the measures
taken according to embodiments in order to compensate deviations of the projection
surface from a plane-parallel orientation to the imaging plane 129. In the following, these
circumstances will be considered in more detail than in the description above.
As has become clear from the above description, the multi-channel projection principle
allows, by means of multi-channel optics 130, to obtain an increased depth of focus of the
individual channels. Thus, it is basically no problem for the individual channels when the
projection surface 150 has a laterally variable distance to the projection display. Rather, it
is obvious from the above description that the assembly of the sub-areas 124 of the
imaging system 120 takes over the adjustment of the depth of focus. Generally, there is a
dependence of the projection distance on the difference of the center pitches of the
projection optics of the multi-channel optics 130 and the corresponding sub-areas 124 in
the imaging plane 129. As has been described above, the depth of focus adaptation to the
lateral variation of the depth of the projection surface 150 is realized in that the object
structures or individual images within the sub-areas 124 differ from one another by
defined deformation in dependence on their position to the center of the distribution of
sub-areas 124, i.e. in dependence on their distance to the interface of the optical axis of
the projection display 100 with the imaging plane 129. By its distance to the corresponding
point in the individual images of the adjacent projection channels (pitch distance), an
exactly determined projection distance is allocated to each point within an object structure
or an individual image, which takes place, according to the above embodiments, such that
the same coincides with the projection distance to that point in the projection surface 150
to which the respective point is mapped by the multi-channel optics 130.

Fig. 16 exemplarily shows a projection onto a plane tilted exemplarily by 40° to the normal
position around the x axis. In particular, Fig. 16 shows on the left a projection along the z
axis, illustrating here exemplarily the optical axis of the projection display, onto the
imaging plane 12; here, it can be seen that exemplarily regular arrays of projection optics
134 are arranged in rows and columns. As mentioned, the assembly is only exemplary.
Apart from that, on the right in Fig. 16 the assembly of imaging plane 129, multi-channel
optics 130 and projection surface 150 is shown in cross-section. In the projection surface
150, two points in the overall image are highlighted exemplarily, wherein one is marked by
a circle 1 and the other with a cross 2. In the following embodiments, the allocated
parameters of these points will be marked with the respective reference number as index.
In the cross-section on the right in Fig. 16 it is shown which points in the imaging plane
129 the points in the projection plane 150 correspond to in the shown cross-section plane
or in the channels allocated to this cross-section plane. In the left projection mapping, i.e.
the top view, the corresponding points in the imaging plane 129 are also illustrated for the
other channels. Here, the projection display of Fig. 16 exemplarily consists of 11 x 11
project channels arranged in a square manner, but neither the type of the assembly nor
the number of channels is in any way limiting.
Thus, according to the example of Fig. 16, the image to be projected consists, exemplarily
of a cross 2 and a circle 1, corresponding to image points having a different position in the
sub-areas of the imaging plane 129. In the exemplary case of Fig. 16, these are
11x11=121 corresponding points per projection point 1 or 2. Together, they form a
constellation defined, for example, by the mutual distances of the participating points in
the plane 129 to each other.
Starting from the tilt angle a of the projection surface 150, due to the opening angle of the
projection optics, a minimum or maximum projection distance (L^ L2) results, which can
be calculated into two corresponding pitch distances (pi, p2) of these object points by

In the shown example, due to the orientation of the projection surface 150: Lip2 applies. Starting from the array center 3, arrays having 11x11 individual images
each are generated for these two exemplary image points, whose object contents vary
due to the pitch distance difference across the 11 x 11 channels. In an image filling the

whole sub-area surface, this corresponds to a deformation of the individual images in the
sub-areas 124 defined per channel corresponding to an above imaging specification.
Concerning the above-mentioned constellations of points in the plane 129, this means that
these spatial constellations of points in the sub-images, each superimposed by the multi-
channel optics in a respective common point 1 or 2 in the overall image, differ from one
another regarding their distances between the constellation points depending on what
distance the respective common point 1 or 2 in the overall image has to the multi-channel
optics 130. With a continuously changing or constant projection surface, this means a
continuous local distortion, i.e. extension and/or compression, of the individual images
124 depending on where the corresponding projection point is in the projection plane 150,
with an intensity that increases with increasing distance from the interface of the optical
axis of the projection display with the plane 129. If the projection surface has
discontinuities in the dimension of the depth, it can happen that the local distortions at
respective locations in the individual images corresponding to the discontinuity positions
result in ambiguities which could be counteracted by appropriate measures, such as by
averaging or the like.
In this way, the image to be projected can be mapped to screen surfaces of any shape
while maintaining a very good mapping quality across an enlarged distance range, without
having to accept a loss of luminosity resulting from too large f-numbers. This allows the
high-contrast and bright illustration of projection images with
a) very flat projection angles onto plane screen surfaces
b) any angles onto curved screen surfaces or
c) any angles onto free-form screen surfaces
An advantage not to be underestimated is the avoidance of tiltings between the object
plane in the projection optics as would otherwise be necessary to fulfill the Scheimpflug
principle. This allows a significantly simplified system structure.
In the following, based on Fig. 17, the above-mentioned preprocessing in the imaging
system 120 according to an embodiment will be described, wherein the imaging system
120 is a digital imaging system. The starting point of the preprocessing is the incoming
image to be displayed in the form of pixel array data 1200. The pixel array data 1200
represent the image to be displayed, for example as a regular array of pixels 1202 or

sample values in columns and rows. The sample values 1202 can be color values,
grayscale values, black-and-white values or the like. In a first processing step 1204, for
example, the pixel data 1200 are used to form output-individual images 1206 for the
different channels of the multi-channel optics 130. The channel partitioning 1204 can, as
is described above with respect to Figs. 13, 14 and 15, provide partitioning of the
information in the pixel array data 1200 according to color channels, so that, for example,
the output-individual images 1206 each correspond to only one color channel of the pixel
array data 1200, and/or the channel partitioning 1204 comprises spatial sub-sampling of
the pixel array data 1200, etc. The output-individual images 1206 then represent the
starting point for the following processing steps. In particular, in a step 1208 the output-
individual images of the individual channels are arranged in the imaging plane. This
means that the individual images 1206 are distorted and placed in the imaging plane 129
such that the sharp projection of the image 1200 results in an undistorted form in the
projection surface 150 by the multi-channel optics 130. As is shown in Fig. 17, step 1208
can be virtually or actually divided into three sub-steps.
In a first sub-step 1208a, the output-individual images 1206 are, for example, at first in the
imaging plane 129, arranged with respect to each other for example only by translatory
shifting such that they are arranged with respect to the individual channels of the multi-
channel optics 130 as described above, with the difference between the center pitch of the
individual images 1206 in the imaging plane 129 on the one hand and the channel
distance of the multi-channel optics 130 on the other hand also described above, so that
adaptation to an average projection distance L can be performed or the average single
image distance is adjusted depending on the latter. After step 1208a, the individual
images 1206 would, for example, be superimposed accurately or sharply for example in a
plane-parallel area at the average projection distance L, if optical inaccuracies caused, for
example, by the above-mentioned mapping errors of the multi-channel optics or by the
different telecenters of the individual channels are ignored.
In a following step 1208b, the individual images 1206 are subjected to pre-distortion in the
sub-areas 124 in the imaging plane 129, which is, for example, the same for all individual
images 1206. This processing could of course also be performed prior to step 1208 and
even prior to step 1204. In the case of Fig. 16, for example, the pre-distortion 1208
corrects the trapezoid distortion of the individual images due to tilting with respect to the
plane-parallel orientation. In Fig. 17, the pre-distortion of individual images 1206 in the
imaging plane 129 is illustrated in an exaggerated manner. Generally, the pre-distortion
1208b deals with correcting the distortions resulting from the fact that the imaging scale by
which the individual images 1206 are mapped to the projection surface 150 by the multi-

channel optics depends on the distance that the respectively considered location in the
projection surface 150 has to the projection display and accordingly varies across the
overall image.
After the pre-distortion 1208b, the individual images 1206 in the sub-areas 124 of the
imaging plane 129 are then individually distorted per channel in a step 1208c. This step
also performs adaptation of the depth of focus to the projection surface 150 deviating from
the plane-parallel orientation. If one were to take a look at the result of projecting the
individual images 1206' after pre-distortion 1208b, the overall image, i.e. the projected
image according to data 1200, would appear undistorted in the projection surface 150, but
would only be sharp, for example, at the average projection distance. After channel-by-
channel distortion 1208c, the individual images 1206" have been distorted individually for
each channel such that they realize the constellation changes of points corresponding to
each other in the sub-areas 124 discussed according to Fig. 16 due to the different depths
along the optical axis of the projection display in the projection surface 150. Thus, the
position of the projection surface 150 or its deviation from the plane-parallel orientation at
the average projection distance, such as the angle a of Fig. 16, is an influencing
parameter in both steps 1208b and 1208c, in the pre-distortion 1208b in the same way for
all channels and in step 1208c individually for each channel.
In addition to that, the distortion 1208c individual for each channel can also implement the
distortions per channel also mentioned above that are intended to correct the other
deviations existing among the different channels, such as those deviations resulting from
the already mentioned different peripheral distances of the channels, i.e. the different
distances of the sub-areas 124 to the optical axis of the projection display, from possible
individual projection optics errors, and possible deviations due to the different allocation of
the sub-areas to different color channels of the projection display, such as red, green and
blue, and the associated refraction intensities of the otherwise possibly identical projection
optics of the individual channels of the multi-channel optics 130.
With respect to step 1208a, it should be noted that the same possibly considers and
addresses the circumstance that the luminosity of the overall image might vary visibly due
to the locally varying imaging scale across the projection surface. Thus, the imaging
system could be implemented such that, by changing transmissions of corresponding
image points within a constellation or by controlling their number, an adaptation of the
illuminance within the superimposed image takes place. In other words, the number of
contributing image points or contributing channels per constellation could be varied, for
example such that this number is lower for projection points in closer regions of the

projection surface than for those further away. Preferably, contributions from channels
remote from the axis would then be omitted, in order to minimize the optical
disadvantages of these channels in their effect on the overall image. However, only a
luminosity reduction of the constellation points could be applied for constellations whose
points lie in closer projection plane regions. This luminosity reduction could also be
greater for channels remote from the axis than for channels close to the axis. In other
words, the imaging system 120 can be implemented in such a way that for homogenizing
the illuminance, the sum of the luminosity of the points of the constellations in the imaging
plane 129 are varied across the overall image depending on the distance of the respective
common point in the overall image to the multi-channel optics 130 to which the points of
the respective constellations are superimposed by the multi-channel optics, by luminosity
variation of the points and/or variation of the number of sub-images 124 contributing a
respective point to the respective constellation. The luminosity variation of the points
and/or the variation of the number of sub-images 124 contributing a respective point to the
respective constellation can be such that points of sub-images 124 of channels remote
from the axis contribute less to the overall image 160.
It should be noted that the process according to Fig. 17 could also be seen as a process
as to how, from a predetermined image, a mask could be generated for the imaging
system for generating the individual images in the sub-areas 124. This applies also for the
above-mentioned consideration of luminosity leveling. Adaptation of the object image
point size per channel across the individual sub-images, in particular in the case of
applying the process according to Fig. 17 to mask generation, could be performed in step
1208c in order to counteract the superposition of differently extended image points
resulting from possible extensions of the sub-images and hence to avoid blurring.
As has become clear from the above description, the above embodiments could be used
to realize a projection onto different projection surfaces 150. Generally, each free-form
surface can serve as a projection surface 150. The projection surface 150 could also
comprise discontinuity locations.
Further, it should be noted that the projection display could be implemented such that the
projection surface 150 is adjustable, such as by user input or automatically, such that the
projection surface 150 onto which the projection display maps the image to be projected
1200 in a sharp manner, approximates the actual form of a screen or a wall towards which
the projection display is oriented to project the image thereon.

One adjustment option relates, for example, to the average distance L of the projection
surface 150 to the projection display, wherein the average projection distance L influences
step 1208a. The distance could also be detected by the projection display via a respective
distance sensor (not shown). Further, it would be possible that the average projection
distance L can be detected via an iterative process in that a known test image is projected
with different average projection distances, wherein the result of the projection is then
evaluated on the actual screen with respect to sharpness or contrast via a camera (not
shown) of the projection display in order to select, as the adjustment to be used, the one
which maximizes the latter quality measure.
Another adjustment option could be the adjustment of the tilt angle a. The tilt angle a
could be input by the user or could be determined automatically. Automatic determination
could provide for different angle adjustments a to be tested and detected and evaluated
by the above-mentioned camera in order to use the adjustment with the most balanced
contrast across the overall image. The same procedure could be used for the tilt angle
around the axis y. Iteratively projecting the test image with different tilt angles could be
performed in combination with varying the average projection distance.
A further adjustment option could be the adjustment of a radius of curvature of the
projection surface 150 in order to adapt the projection surface 150 in this way to projection
surfaces curved away from the projection display or curved in the direction of the
projection display. Here, a similar procedure could be used, namely projecting a test
image with different radii of curvature and recording a camera image with the previously
mentioned optional camera at the respective adjustments for evaluating at which radius of
curvature the best projection quality results.
The adjustments could obviously also be performed in a user-controlled manner. For the
above-mentioned user adjustment options, for example the keypad of an apparatus could
be used, into which the projection display is installed, such as the keyboard of a mobile
phone or a laptop or the like.
The imaging system (120) could thus be implemented to allow one or several of the
following user adjustment options or automatic adjustment options independent of each
other:
a) changing the sub-images such that a change of an average projection distance of the
projection surface to the multi-channel optics with a respective translatory shift in the
position of the projection surface results,

b) changing the sub-images such that a change of tilting of the projection surface with
respect to the imaging plane results,
c) changing the sub-images such that a change of tilting of the projection surface with
respect to the imaging plane results, by simultaneously adapting a trapezoidal distortion
correction for compensating the distortion of the overall image in the projection surface
due to tilting of the same relative to the imaging plane,
d) changing the sub-images such that a change of bending of the projection surface
relative to a plane-parallel orientation to the imaging plane results, and
e) changing the sub-images such that a change of bending of the projection surface with
respect to the imaging plane results, by simultaneously adapting a distortion correction for
compensating the distortion of the overall image in the projection surface due to local
mapping variations due to the bending of the same relative to the plane-parallel
orientation to the imaging plane.
Similar procedures can obviously be used for any projection surface geometries, for
example by using a respective parameterization, similar to that discussed above. For
example, the center of curvature could be implemented in a laterally shiftable manner. For
example, a line grating could be used as a test image. However, different test images
could also be used for different adjustment or setting parameters.
Thus, in summary, the above embodiments describe a solution for the problem of front
projection of an image across greatly changing projection distances or to tilted, curved
surfaces, free-form screen geometries or the like, such that high contrast and sharp
mapping can be ensured.
Hereby, the above embodiments are characterized by small installation space, high depth
of focus and high luminosity. In particular, no tilted optics is necessitated in the
embodiments. Homogenization of the light source such that the light distribution is equally
distributed starting from the source to the screen or in the image in the projection, thus
preventing vignetting of the image without additional optical components, is possible.
Homogenization can here also mean mixing the input distribution of the light source, such
as the angle and space variable, of luminosity and color values. Additionally, with the
above embodiments, a high depth of focus becomes possible even with a small f-number
or a very open aperture. Thus, the above embodiments represent a simple, compact

system that can project a sharp, bright image on screen geometries that are tilted or have
any shape.
It should again be noted that step 1208c in Fig. 17 changes the individual images in the
sub-areas such that they change across the array, starting from the array center, such
that a high contrast, sharp projection results at several discrete distances or a continuous
distance range. A specific projection distance is allocated to each point within an
individual image of a sub-area, which allows sharply focused projection onto tilted and
optionally curved surfaces. This is performed by a defined pitch distance of points
superimposed on the screen within the distribution of sub-areas. Consequently, position-
dependent distortion of individual images or sub-areas or lateral shift of sub-portions of
the individual images or sub-areas results.
Concerning the above option that the imaging system can also be a stationary, static
mask, it should be noted that the latter could be produced, for example, lithographically.
Further, it should be noted that the optical axis of the projection display has mostly been
assumed as standing perpendicularly on the imaging plane 129, but this does not have to
be the case. Rather, it is possible, for example, for several projection displays according
to Fig. 1 to be used together to again form a larger projection display system. The
projection displays would project their individual overall images, for example attached to
one another, perhaps without overlapping, to a common extended projection surface, in
order to result in an even larger overall image when combined. In this case, the optical
axes of the projection displays could, for example, converge.
In the above embodiments, the different projection distances have been encoded into the
individual images in the projection surface 150. According to the subsequently discussed
alternative embodiments, it is also possible for this encoding to be performed via the
lenses or projection optics of the multi-channel optics, such as for realizing discrete
projection distances. According to such embodiments, each channel preferably does not
project the whole image information, which means overall less transmission or luminance,
but only that corresponding to the corresponding distance to the screen or projection
surface 150. Thus, this is an interleaving of array projectors or channels, wherein each
sub-array is allocated to a distance. Here, focusing the optics can also be adapted, such
as via focal length adaptation of the individual projection optics across the array, if the
optics is within a plane-parallel plane with respect to the imaging system.
According to the embodiments discussed in the previous paragraph, the projection display
of Fig. 1 is implemented, in deviation from the above embodiments, for example in the

following way, wherein, however, it should be noted that, apart from the deviations, all
variation options described above with respect to the above embodiments also apply for
the following ones. Thus, according to the alternative embodiments described below, the
projection display also comprises the imaging system 120 that is implemented to generate
individual images in a distribution of sub-areas 124 of an imaging plane 129 of the
imaging system 120, as well as the multi-channel optics 130 that is configured to map one
allocated sub-area of the imaging system 120 each per channel, such that the mapping of
the individual images is superimposed to an overall image in a projection surface.
However, the constellations do not need to have the above-mentioned dependence on the
projection distance of the allocated projection image points in the surface 150. The
projection surface 150 can again be a non-planar free-form surface or be tilted with
respect to the imaging plane, but as a compensation for this and for obtaining the desired
projection sharpness, the imaging system 110 and the multi-channel optics 130 are
implemented such that an implementation of a contribution of each channel to the overall
image varies locally across the overall image depending on what distance the respective
common point in the overall image has to the multi-channel optics 130. For example, the
imaging system 110 and the multi-channel optics 130 can be implemented such that a
number of superimposed channels vary locally across the overall image depending on
what distance the respective common point in the overall image has to the multi-channel
optics 130.
In particular, it is possible that the imaging system 110 and the multi-channel optics 130
comprise disjunct sets of channels for different projection surface distances. This will be
discussed based on Fig. 18, which is similar to Fig. 16 but clearly shows the differences
with respect to the above embodiments. According to the alternative embodiment, not all
11x11 channels, i.e. the sub-areas 124 with allocated projection optics are responsible for
the overall image. Rather, a first set of channels, here, for example, the bottom 6x11
channels are implemented to limit the superposition to the overall image to a first portion
of the overall image which is at a first interval l2 of distances to the multi-channel optics
130. A second set of channels disjunct to the first, here the top half of 5x11 channels, is
implemented to limit the superposition to the overall image to a second portion of the
overall image which is at a second interval U of distances to the multi-channel optics 130
comprising distances that are larger than all distances of the first interval l2. The intervals
h and l2 are here exemplarily free of overlapping, but this does not have to be the case. In
the case of a discontinuous free-form surface having, for example, only two different
distance ranges, namely U and L2, the intervals do not even have to touch and could be
reduced to individual distances. Thus, the individual images in the sub-areas 124 here
cover individual, but no longer all portions of the overall image. The individual images in

the top sub-areas comprise, among the exemplarily highlighted points 1 and 2, only
corresponding points for point 1, since the same lies within interval l1t and the individual
images in the bottom sub-areas comprise, among the exemplarily highlighted points 1 and
2, only corresponding points for point 2, since the same lies within interval l2.
In order to focus the individual channel to their respective distance interval, the channels
are configured such that constellations of points in the individual images, each
superimposed by the first (bottom) set of channels of the multi-channel optics 130 in a
respective common point 2 in the respective portion l2 in the overall image 160, result
mainly by a centric extension with a first ratio of extension from a constellation of locations
where a projection of aperture centers of the channels of this first set is arranged (namely
in Fig. 18 the centers of the bottom 6x11 circles), while the constellations of points in the
individual images, each superimposed by the second set of channels of the multi-channel
optics (130) in a respective common point 1 in the second portion h in the overall image,
mainly result by a centric extension having a second ratio of extension from a
constellation of locations where a projection of aperture centers of the channels of the
second set is arranged (namely in Fig. 18 the centers of the bottom 6x11 circles), such
that the first ratio of extension is higher than the second ratio of extension. This means
that, compared to the constellation of the channel projection optics centers of the bottom
channels, the constellation of the points corresponding to point 2 is extended further than
the constellation of the points corresponding to point 1 with respect to the constellation of
the channel projection optics centers of the top channels. This can happen in different
ways: by adapting the individual images or sub-areas 124 and/or by providing a different
pitch of the channel projection optics centers of the top channels compared to the pitch of
the channel projection optics centers of the bottom channels.
The multi-channel optics 130 could be implemented such that the channels of the first set
are focused to smaller distances to the multi-channel optics 130 than the channels of the
second set. In this way it becomes possible to cover regions of depth of focus that even
exceed the optical depth of focus of the individual channels.
The above embodiments could now be combined with the variation according to Fig. 18
so that each set of channels is again sharp in its respectively allocated interval across an
extended area of distances. In other words, a combination with coding of the projection
distance across the objects can be used to further increase image quality. This can be
advantageous, for example, for extreme screen geometries if the depth of focus of the
individual channels is not sufficient, for example due to large focal lengths or an f-number
which is too small to cover the whole distance range, i.e. focusing per channel becomes

necessary. Thus, the imaging system 120 can be implemented such that constellations of
points in the individual images, each superimposed by the channels of the first set of the
multi-channel optics 130 in a respective common point 1 in the overall image 160, or
constellations of points in the individual images superimposed respectively by the
channels of the second set of the multi-channel optics 130 in a respective common point 1
in the overall image 160 differ depending on what distance the respective common point 1
or 2 in the overall image has to the multi-channel optics 130.
Here, it should further be noted that coding of the projection distance across the objects
124 does not necessarily have to take place in a continuous manner, but can be realized
discretely. Changing the constellations is thus also possible in discrete steps, which
significantly simplifies the system, in particular for respective projection subjects. As one
example, the image of a keyboard is to be seen as content to be projected, more
accurately the projection of a static keyboard at a very flat angle. Here, for each row of
letters, such as the F row of keys, the row from ' to =, the row from A to ', the row from Z
to M, etc., or for each key a projection distance is calculated and hence only discrete
differences of the constellation are introduced. The same can apply for line patterns to be
projected or generally for subjects that can be discretized, i.e. that are non-continuous.
Generally, with respect to the above description it should be noted that generally the
extension of the projector compared to the projection distance should not be of
importance. This means that the distances of the screen alone with respect to the array
center can be calculated. However, for extreme cases, a change of distance to the screen
per channel can occur, which can then be corrected again per channel.
Possible applications for the above embodiments are in the field of personal
communication and entertainment electronics and data visualization at home and in the
mobile field. A further field of application is in the field of automobiles and aircraft in the
form of a head-up display for projected display of color state information, navigation,
environmental information as driver assistance systems or for entertaining passengers.
Applications in metrology and medical technology are also possible, as well as in display
applications in industrial and production plants. Use of the above projection displays as
illuminating units, front headlights, effect illumination, such as for automobiles, is also
possible.
Further fields of application are in the realization of projection and illumination systems on
tilted and optionally curved surfaces for machine vision, automotive, architecture, home

infotainment (e.g. home communication field - kitchen projection), illumination as well as
ophthalmological and general medical applications (e.g. illuminating the curved retina).
While some aspects have been described in the context of an apparatus, it is obvious that
these aspects also represent a description of the respective method, so that a block or a
device of an apparatus can also be seen as a respective method step or as a feature of a
method step. Analogously, aspects that have been described in the context of one or as a
method step also represent a description of a respective block or detail or feature of a
respective apparatus. Some or all of the method steps can be performed by a hardware
apparatus (or using a hardware apparatus), such as a microprocessor, a programmable
computer or an electronic circuit. In some embodiments, some or several of the most
important method steps can be performed by such an apparatus.
Depending on specific implementation requirements, embodiments of the invention can be
implemented in hardware or in software. The implementation can be made by using a
digital memory medium, for example a floppy disc, a DVD, a Blu-ray disc, a CD, an ROM,
a PROM, an EPROM, an EEPROM or a FLASH memory, a hard disc or any other
magnetic or optical memory on which electronically readable control signals are stored
that can cooperate or cooperate with a programmable computer system such that the
respective method is performed. Thus, the digital memory medium can be computer-
readable.
Thus, some embodiments according to the invention comprise a data carrier comprising
electronically readable control signals that are able to cooperate with a programmable
computer system such that one of the methods described herein is performed.
Generally, embodiments of the present invention can be implemented as a computer
program product with a program code, wherein the program code is effective to perform
one of the methods when the computer program product runs on a computer.
The program code can, for example, be stored on a machine-readable carrier.
Other embodiments comprise the computer program for performing one of the methods
described herein, wherein the computer program is stored on a machine-readable carrier.
In other words, an embodiment of the inventive method is a computer program comprising
a program code for performing one of the methods described herein when the computer
program runs on a computer.

Thus, a further embodiment of the inventive method is a data carrier (or a digital memory
medium or a computer-readable medium) on which the computer program for performing
one of the methods described herein is recorded.
Thus, a further embodiment of the inventive method is a data stream or a sequence of
signals representing the computer program for performing one of the methods described
herein. The data stream or the sequence of signals can be configured such that they can
be transferred via a data communication connection, for example via the Internet.
A further embodiment comprises a processing means, for example a computer or a
programmable logic device configured or adapted to perform one of the methods
described herein.
A further embodiment comprises a computer on which the computer program for
performing one of the methods described herein is installed.
A further embodiment according to the invention comprises an apparatus or a system
implemented to transmit a computer program for performing at least one of the methods
described herein to a receiver. The transmission can be made, for example, electronically
or optically. The receiver can, for example, be a computer, a mobile device, a memory
device or a similar apparatus. The apparatus or the system can, for example, comprise a
file server for transmitting the computer program to the receiver.
In some embodiments, a programmable logic device (for example a field-programmable
gate array, an FPGA) can be used to perform some or all functionalities of the methods
described herein. In some embodiments, a field-programmable gate array can cooperate
with a microprocessor to perform one of the methods described herein. Generally, in
some embodiments, the methods are performed by means of any hardware apparatus.
The same can be a universally usable hardware such as a computer processor (CPU) or
hardware specific to the method, such as an ASIC.
The above-described embodiments present merely an illustration of the principles of the
present invention. It is obvious that modifications and variations of the arrangements and
details described herein will be obvious to other persons skilled in the art. Thus, the
invention is merely limited by the scope of the following claims and not by the specific
details presented together with the description and the discussion of the embodiments.

Claims
1. A projection display (100) comprising
an imaging system (120) that is implemented to generate individual images in a
distribution of sub-areas (124) of an imaging plane (129) of the imaging system
(120); and
a multi-channel optics (130) that is configured to map one allocated sub-area of
the imaging system (120) each per channel, such that the mapping of the
individual images is superimposed to an overall image in a projection surface,
wherein the projection surface is a non-planar free-form surface or tilted with
respect to the imaging plane, and the imaging system (100) is implemented such
that constellations of points in the individual images, each superimposed in a
respective common point in the overall image (160) by the multi-channel optics
(130), differ depending on what distance the respective common point in the
overall image has to the multi-channel optics (130).
2. The projection display according to claim 1, wherein the multi-channel optics
comprises a two-dimensional assembly of projection optics in a projection optics
plane essentially perpendicular to the imaging plane, wherein the projection
optics assembly is configured to map one allocated individual image of the
imaging system each along a respective optical axis in the direction of the
projection surface, such that the mappings of the individual images are
superimposed to the overall image in the projection surface.
3. The projection display according to claim 2, wherein the projection optics (134)
comprises decentration (135) with respect to the allocated sub-areas (124),
wherein a center pitch (pPL) of the projection optics (134) is smaller than a center
pitch (POBJ) of the allocated sub-areas (124), so that the overall image (162)
superimposed in the projection surface is real.
4. The projection system according to claim 2, wherein the projection optics (134)
comprises decentration (137) with respect to the allocated sub-areas (124),
wherein the center pitch (pPL) of the projection optics (134) is larger than or equal

to the center pitch (POBJ) of the allocated sub-areas (124), so that the overall
image (202) superimposed in the projection surface is virtual.
5. The projection display according to claim 2, wherein the projection optics (134) is
centered with respect to the allocated sub-areas (124) and has a collimating
effect.
6. The projection display according to claims 3, 4 or 5, wherein the projection optics
assembly (130) further comprises an overall lens (310, 312) that is downstream
with respect to the two-dimensional assembly (132) of projection optics and
cooperates with the two-dimensional assembly (132) of projection optics (134)
that is implemented to refocus collimated beams (315) from the projection optics
(134) in a focal plane of the overall lens (310, 312), wherein the projection optics
(134) are centered with respect to the allocated sub-areas (124) and have a
collimating effect, or to focus divergent/convergent beams from the projection
optics (134) in an effective focal plane resulting by decentration between the
projection optics (134) on the one hand and the sub-areas (124) on the other
hand and focusing by the downstream overall lens.
7. The projection display according to claim 6, wherein the overall lens (310, 312) is
implemented as optics with variable focal length, so that an average projection
distance can be adjusted.
8. The projection display according to claim 7, wherein the optics with variable focal
length is a zoom objective or a liquid lens.
9. The projection display according to claim 2, wherein each projection optics (414)
comprises a lens vertex (415) decentered with respect to the aperture of the
respective projection optics, wherein a center pitch of the lens vertex (415) is
larger or smaller than the center pitch of the allocated sub-areas (124), so that
the lenses effect a projection of the individual image of the respective sub-area
along optical axes running divergently or convergently.
10. The projection display according to one of claims 2 to 9, wherein a distance
between the sub-areas and the respective projection optics essentially
corresponds to a focal length of the respective projection optics.

11. The projection display according to one of claims 2 to 10, wherein a distance
between the sub-areas and the respective projection optics essentially
corresponds to a focal length of the respective projection optics, but such that the
projection lenses remote from the axis have a larger focal length for correcting a
defocus due to the larger image distance of these channels.
12. The projection display according to one of claims 1 to 11, wherein the imaging
system is further implemented such that the constellations additionally differ
depending on the solid angle region in which, seen from the multi-channel optics
(130), the respective common point lies, in order to compensate mapping errors
of the multi-channel optics (130).
13. The projection display according to claim 12, wherein the imaging system is
further implemented such that the constellations differ additionally depending on
the solid angle region in which, seen from the multi-channel optics, the respective
common point lies such that mapping errors of the multi-channel optics (130) can
be compensated individually for each channel.
14. The projection display according to one of claims 1 to 13, wherein the imaging
system is implemented such that the difference between the constellations
depending on the distance of the respective common point in the overall image to
the multi-channel optics (130) is reflected mainly in a centric extension between
the constellations, so that first constellations of points in the individual images,
each superimposed by the multi-channel optics in a respective common point in
the overall image that is less distant to the multi-channel optics (130) than a
respective common point in the overall image where points of second
constellations in the individual images are superimposed by the multi-channel
optics assembly, are laterally more extended with respect to the second
constellations.
15. The projection display according to one of claims 1 to 14, wherein the imaging
system (120) is implemented, for homogenizing the illuminance across the overall
image, to vary the sum of the luminosities of the points of the constellations in the
imaging plane (129) depending on the distance of the respective common point
in the overall image to the multi-channel optics (130) to which the points of the
respective constellations are superimposed by the multi-channel optics, namely
by luminosity variation of the points and/or variation of the number of sub-areas
(124) contributing a respective point to the respective constellation.

16. The projection display according to claim 15, wherein the imaging system (120) is
implemented such that the luminosity variation of the points and/or the variation
of the number of sub-areas (124) contributing a respective point to the respective
constellation is such that points of sub-areas (124) of channels remote from the
axis contribute less to the overall image (160).
17. The projection display according to one of claims 1 to 16, wherein the imaging
system is implemented to generate the individual images from pixel array data
representing the overall image, namely by pre-distorting the pixel array data so
that distortion of the overall image in the projection surface is corrected due to
tilting the same relative to the imaging plane.
18. The projection display according to one of the previous claims, wherein the image
system is a reflective imaging system or a transmissive imaging system with rear
illumination or a reflective background or an emissive imaging system.
19. The projection display according to one of the previous claims, wherein the image
system is a transmissive imaging system that is implemented to display the
individual images by lateral variation of transmissivity, wherein the projection
display comprises a light source and a field lens or field lens array, and the field
lens is arranged at a distance to the individual images so that Kohler illumination
of the multi-channel optics is realized.
20. The projection display according to claim 19, further comprising a further field
lens for canceling the telecentric illumination.
21. The projection display according to one of the previous claims, wherein at least
part of the imaging system is implemented passively, such as in the form of a
finely structured mask.
22. The projection display according to one of the previous claims, wherein the
imaging system and the multi-channel optics are implemented such that identical
individual images from different sub-areas are superimposed in the projection
surface in a pixel-precise manner.
23. The projection display according to one of the previous claims that is
implemented to receive an image to be projected with a first gray/color scale

resolution, wherein the imaging system is implemented to display the individual
images with a second gray/color scale resolution that is smaller than the first
gray/color scale resolution, wherein the projection display is implemented to
control the sub-areas at an image point of the image to be projected depending
on a gray/color scale value of the image to be projected, such that the individual
images in the overall image (21, 23), at a position corresponding to the image
point, sum up to a gray/color scale corresponding to the gray/color scale value.
24. The projection display according to one of claims 1 to 21, wherein the imaging
system (120) and the projection optics assembly are implemented such that the
mappings of the individual images are superimposed in the projection surface
with a sub-pixel offset so that the overall image (19) superimposed in the imaging
plane (150) has a higher resolution than the individual images.
25. The projection display according to one of claims 1 to 24, wherein the imaging
system (120) allows one or several of the following user adjustment options
independent of one another:
a) changing the sub-images such that a change of an average projection
distance of the projection surface to the multi-channel optics with a respective
translatory shift in the position of the projection surface results,
b) changing the sub-images such that a change of tilting of the projection surface
with respect to the imaging plane results,
c) changing the sub-images such that a change of tilting of the projection surface
with respect to the imaging plane results, by simultaneously adapting a
trapezoidal distortion correction for compensating the distortion of the overall
image in the projection surface due to tilting of the same relative to the imaging
plane,
d) changing the sub-images such that a change of bending of the projection
surface relative to a plane-parallel orientation to the imaging plane results, and
e) changing the sub-images such that a change of bending of the projection
surface with respect to the imaging plane results, by simultaneously adapting a
distortion correction for compensating the distortion of the overall image in the

projection surface due to local mapping variations due to the bending of the same
relative to the plane-parallel orientation to the imaging plane.
26. The projection display according to one of claims 1 to 25, further comprising a
camera and an adjuster, wherein the adjuster is implemented to regulate the
projection surface into which the multi-channel optics superimpose the individual
images to the overall image, in an iterative process and by controlling the imaging
system, so that the same displays a test image, such that the projection surface
is approximated to an actual projection surface.
27. Method for displaying an overall image, comprising:
generating individual images in a distribution of sub-areas (124) of an imaging
plane (129); and
mapping, by one channel of a multi-channel optics (130) each, one allocated sub-
area of the imaging plane (129) each, such that the mapping of the individual
images is superimposed to an overall image in a projection surface,
wherein the projection surface is a non-planar free-form surface or tilted with
respect to the imaging plane, and generation of the individual images is
performed such that constellations of points in the individual images, each
superimposed by the multi-channel optics (130) in a respective common point in
the overall image (160), differ depending on what distance the respective
common point in the overall image has to the multi-channel optics (130).
28. Projection display (100) comprising
an imaging system (120) that is implemented to generate individual images in a
distribution of sub-areas (124) of an imaging plane (129) of the imaging system
(120); and
a multi-channel optics (130) that is configured to map one allocated sub-area of
the imaging system (120) each per channel, such that the mapping of the
individual images is superimposed to an overall image in a projection surface,
wherein the projection surface is a non-planar free-form surface or tilted with
respect to the imaging plane, and the imaging system (110) and the multi-

channel optics (130) are implemented such that a manifestation of a contribution
of each channel to the overall image varies locally across the overall image
depending on what distance the respective common point in the overall image
has to the multi-channel optics (130).
29. The projection display (100) according to claim 28, wherein the imaging system
(110) and the multi-channel optics (130) are implemented such that a number of
superimposed channels vary locally across the overall image depending on what
distance the respective common point in the overall image has to the multi-
channel optics (130).
30. The projection display (100) according to claims 28 or 29, wherein the imaging
system (110) and the multi-channel optics (130) are implemented such that a first
set of channels is implemented to limit the superposition to an overall image to a
first portion of the overall image that is located within a first interval of distances
to the multi-channel optics (130), and a second set of channels disjunct to the
first is implemented to limit the superposition to the overall image to a second
portion of the overall image that is located within a second interval of distances to
the multi-channel optics (130), comprising distances that are larger than all
distances of the first interval, and that constellations of points in the individual
images, superimposed respectively by the first set of channels of the multi-
channel optics (130) in a respective common point in the first portion in the
overall image (160), result essentially by a centric extension having a first ratio of
extension from a constellation of locations where a projection of aperture centers
of the channels of the first set is arranged, and constellations of points in the
individual images, superimposed respectively by the second set of channels of
the multi-channel optics (130) in a respective common point in the second portion
in the overall image (160), result essentially by a centric extension having a
second ratio of extension from a constellation of locations where a projection of
aperture centers of the channels of the second set is arranged, and wherein the
first ratio of extension is larger than the second ratio of extension.
31. The projection display (100) according to claim 30, wherein the multi-channel
optics (130) is implemented such that channels of the first set are focused to
smaller distances to the multi-channel optics (130) than the channels of the
second set.

32. The projection display (100) according to claims 30 or 31, wherein the imaging
system (120) is implemented such that constellations of points in the individual
images, each superimposed by the channels of the first set of the multi-channel
optics (130) in a respective common point in the overall image (160), or
constellations of points in the individual images, each superimposed by the
channels of the second set of the multi-channel optics (130) in a respective
common point in the overall image (160), differ depending on what distance the
respective common point in the overall image has to the multi-channel optics
(130).
33. A method for displaying an overall image, comprising
generating individual images in a distribution of sub-areas (124) of an imaging
plane (129); and
mapping, by one channel of a multi-channel optics (130) each, one allocated sub-
area of the imaging plane (129) each, such that the mapping of the individual
images is superimposed to an overall image in a projection surface,
wherein the projection surface is a non-planar free-form surface or tilted with
respect to the imaging plane, and generation and mapping are performed such
that a manifestation of a contribution of each channel to the overall image varies
locally across the overall image depending on what distance the respective
common point in the overall image has to the multi-channel optics (130).
34. A computer program comprising a program code for performing the method
according to claims 27 or 33 when the program runs on a computer.