DESCRIPTION
Picture Display Apparatus and Method
Technical Field
This invention relates to a picture display apparatus and a picture display
method for displaying an output picture via a liquid crystal display surface.
The present application claims priority rights based on the JP Patent
Application 2005-175550, filed in Japan on June 15, 2005. This patent application
of the earlier filing data is incorporated into the present application by reference.
Background Art
[0002] In a conventional direct-view liquid crystal display, there is produced a
difference in a picture birefringence phase difference (retardation), depending on
the angle of visibility (angle with which the display is viewed), with the result that
the picture displayed on the display appears as if the picture has been changed in
color. This problem is routinely coped with by an optical compensation plate
introduced between the optical compensation plate and the liquid crystal layer to
improve the retardation.
Although sufficient improvement may be achieved in case of displaying
black (lowest luminance) or white (highest luminance), such is not the case with
displaying intermediate luminance. For example, even though the input grayscaleluminance
characteristics are D characteristics shown at P in Fig.30, with the angle
of visibility of 0Q (in case of viewing the display from the front side), the input
grayscale- luminance characteristics in case of viewing the display at an angle of
visibility of 60Q (in case of viewing the display from an angle of 60Q) depart from
the D characteristics, as indicated at Q in Fig.30.
Meanwhile, the processing for improving display characteristics for moving
pictures, termed over-drive processing and black-insertion processing, is used in a
direct-viewing liquid crystal display. The over-drive processing is a technique of
slightly increasing the driving voltage for the liquid crystal, in case a picture is
transitioning, in such a manner as to raise follow-up characteristics of the liquid
crystal. The black-insertion processing is the processing of displaying a black
picture before a picture image transitions to the next picture image to prohibit the
picture image from becoming blurred due to a residual image on the retina of the
human eye.
Disclosure of the Invention
Problem to be solved by the Invention
[0003] It is a technical task of the present invention to provide an apparatus and a
method for improving angle-of-visibility characteristics of the liquid crystal display
and for improving display characteristics of a moving picture.
In one aspect, the present invention provides a picture display apparatus for
displaying a picture corresponding to an input picture signal via a liquid crystal
display surface. The apparatus includes a driving level correction unit for correcting
a driving level based on the input picture signal, a converter for converting the
grayscale level of a signal supplied thereto into a plurality of correction levels for
expressing the grayscale level by synthesis of transmittances of a plurality of
temporally consecutive fields, and a driving unit for driving the liquid crystal
display surface by a driving signal generated via the driving level correction unit
and the converter. The converter generates the correction levels so that each picture
image of the input picture signal includes at least a first field and a second field.
The first field has transmittance converted to a transmittance corresponding to the
grayscale level of the input picture signal added by a positive correction value. The
second field has transmittance converted to a transmittance corresponding to the
grayscale level of the input picture signal added by a negative correction value.
The driving level correction unit performs driving level correction of signal values
of the first field or the second field or both, depending on effective response
characteristics of the liquid crystal driven by the driving unit, in case time changes
of the grayscale level have occurred at the same spatial position of the input picture
signal.
In another aspect, the present invention provides a picture display method for
displaying a picture corresponding to an input picture signal via a liquid crystal
display surface. The method includes a driving level correction step of correcting a
driving level based on the input picture signal, a converting step of converting the
grayscale level of a signal supplied thereto into a plurality of correction levels for
expressing the grayscale level by synthesis of transmittances of a plurality of
temporally consecutive fields, and a driving step of driving the liquid crystal
display surface by a driving signal generated by the driving level correction step
and the converting step. The converting step generating the correction levels so that
each picture image of the input picture signal includes at least a first field and a
second field. The first field has transmittance converted to a transmittance
corresponding to the grayscale level of the input picture signal added by a positive
correction value. The second field has transmittance converted to a transmittance
corresponding to the grayscale level of the input picture signal added by a negative
correction value. The driving level correction step performs driving level correction
of signal values of the first field or the second field or both, depending on effective
response characteristics of the liquid crystal driven by the driving step, in case time
changes of the grayscale level have occurred at the same spatial position of the
input picture signal.
In the apparatus and method for picture display, according to the present
invention, an input picture signal is converted into a corrected picture signal in
which a grayscale level of the input picture signal is expressed by synthesis of
liquid crystal transmittances of a plural number of temporally consecutive fields.
The corrected picture signal includes, for each picture image of the input picture
signal, at least a first field set to transmittance corresponding to a grayscale level
higher than a grayscale level of the input picture signal and a second field set to
transmittance corresponding to a grayscale level lower than the grayscale level of
the input picture signal. In case time changes of the grayscale level are produced at
the same spatial position in the input picture signal, signal values of one or both of
the first and second fields are corrected in level depending on the response speed of
the liquid crystal. By so doing, the angle of visibility characteristics are improved,
while the moving picture may properly be prohibited from becoming blurred in
keeping with response characteristics of the liquid crystal.
Other objects and advantages derived from the present invention will become
more apparent from the following description which will now be made in
conjunction with the accompanying drawings.
Brief Description of the Drawings
Fig.l is a block circuit diagram showing an embodiment of a picture display
apparatus according to the present invention.
Fig.2 is a plan view showing a picture image an upper half of which is a
region represented by 50% transmittance grayscale and a lower half of which is a
region represented by 100% transmittance grayscale.
Fig.3 shows pictures of first and second fields in which the picture image
shown in Fig.2 is improved in grayscale.
Fig.4 shows a pixel column w in the vertical direction in a picture image Wl.
Fig.5 shows a driving example for driving the pixel column w shown in
Fig.4.
Fig.6 is a graph showing the relationship between the grayscale of an input
picture signal and a voltage applied to the first field and the relationship between
the grayscale of an input picture signal and a voltage applied to the second field.
Fig.7 is a graph showing input/output characteristics for angles of visibility
of 0Q and 60e of a liquid crystal panel of a picture display apparatus according to the
present invention.
Fig.8 is a graph showing transmittance of a liquid crystal display panel for
different grayscale levels.
Fig.9 shows time changes of transmittance at different spatial positions in
case the boundary between black and white pictures are moved with time, with the
grayscale of the input picture signal being lower than 166.
Fig. 10 shows time changes of transmittance at different spatial positions in
case the boundary between black and white pictures are moved with time, with the
grayscale of the input picture signal being not lower than 166.
Fig.l 1 shows changes in transmittance at the boundary positions PI to P4
shown in Fig.9.
Fig. 12 shows changes in transmittance at the boundary positions PI to P4
shown in Fig.9.
Fig. 13 is a block circuit diagram showing an example of an over-drive unit.
Fig. 14 shows a first table.
Fig. 15 shows a second table.
Fig. 16 shows a third table.
7
Fig. 17 shows changes in transmittance in case the grayscale of a field is
lower than 166 and the input picture signal is changed over from a dark state to a
light state.
Fig. 18 shows changes in transmittance in case the grayscale of a field is
lower than 166 and the input picture signal is changed over from a light state to a
dark state.
Fig. 19 shows a first example of changes in transmittance in case the
grayscale of a field is lower than 166 and the grayscale is increased monotonously.
Fig.20 shows a second example of changes in transmittance in case the
grayscale of a field is lower than 166 and the grayscale is increased monotonously.
Fig.21 shows a first example of changes in transmittance in case the
grayscale of a field is lower than 166 and the grayscale is decreased monotonously.
Fig.22 shows a second example of changes in transmittance in case the
grayscale of a field is lower than 166 and the grayscale is decreased monotonously.
Fig.23 shows changes in transmittance in case the grayscale of a field is not
lower than 166 and in case Sn+1 is high in grayscale level among three fields.
Fig.24 shows changes in transmittance in case the grayscale of a field is not
lower than 166 and in case Sn+1 is low in grayscale level among three fields.
Fig.25 is a flowchart showing the sequence of an over-drive and an
under-drive.
Fig.26 is a block circuit diagram showing a second embodiment of the
8
picture display apparatus according to the present invention.
Fig.27 shows a liquid crystal panel used in the second embodiment of the
picture display apparatus according to the present invention.
Fig.28 shows a first gamma pattern in the second embodiment of the picture
display apparatus according to the present invention.
Fig.29 shows a second gamma pattern in the second embodiment of the
picture display apparatus according to the present invention.
Fig.30 is a curve showing input/output characteristics for the angle of
visibility of a conventional liquid crystal display panel of 0Q and 60s.
Best Mode for Carrying out the Invention
[0005] As the best mode for carrying out the present invention, a picture display
apparatus for displaying an input picture signal on a liquid crystal display panel will
now be described in detail.
Overall Structure
Referring to Fig.l, a picture display apparatus 10 according to the present
invention includes an interpolator 11, an over-drive unit 12, an angle of visibility
improvement unit 13, a convert-to-A.C. unit 14, a source driver 15 and a liquid
crystal display panel 16. A digital picture signal HI of a picture rate of 60 Hz, for
example, is supplied from outside via an input terminal lOa of the picture display
apparatus 10. Specifically, this digital picture signal HI is supplied via input
terminal lOa to the interpolator 11. The interpolator 11 redoubles the picture rate of
the 60Hz picture signal to 120 Hz by rate conversion. In redoubling the picture
rate of the picture signal, the interpolator 11 generates picture image portions,
which would be insufficient, by interpolation of corresponding picture image
portions from e.g. temporally forward or backward pictures. The method for
interpolation is arbitrary. By this upward rate conversion, it is possible to eliminate
blurring, such as dual image, which tends to be generated when a moving subject is
follow-up viewed.
The picture signal, the picture rate of which has been converted to 120 Hz by
the interpolator 11, is supplied to the over-drive unit 12. The over-drive unit 12
corrects a driving signal to an optimum level signal, in keeping with the response
characteristics of the liquid crystal, in case there is a level change in the input
picture signal. More specified processing contents of the over-drive unit 12 will be
described subsequently.
The angle of visibility improvement unit 13 expresses a sole grayscale level
of the original 60Hz picture signal, by two picture images (fields) arrayed in the
time direction of the picture signal, the picture rate of which has been up-converted
to 120Hz, such as to improve angle-of-visibility characteristics. The specified
processing by the angle of visibility improvement unit 13 will be described
subsequently.
The convert-to-A.C. unit 14 is supplied with the picture signal of the picture
rate of 120 Hz from the angle of visibility improvement unit 13. The converMo-A.C.
unit 14 converts the polarity of the driving of the liquid crystal to alternating
positive and negative polarities. The liquid crystal molecules are oriented in the
same direction in case the direction and the magnitude of the vector of the electrical
field applied remain the same, despite the difference in polarity of 180Q. For this
reason, the driving signal is inverted in polarity at a preset period to convert the
driving signal into an A.C. signal, such as to establish D.C. balance. The
convert-to-A.C. unit 14 takes charge of converting the driving signal into the
corresponding A.C. signal.
It is noted that the convert-to-A.C. unit 14, supplied with the input picture
signal of 120 Hz, inverts the polarity of the driving signal for converting the
polarity of liquid crystal driving to an A.C. signal at 60 Hz for the input 120 Hz
picture signal. The reason the polarity of the driving signal is inverted at 60Hz, even
though the field rate is 120 Hz, is that, since the angle of visibility improvement
unit 13 has performed the processing for expressing a sole grayscale level with two
picture images (fields) neighboring to each other in the time direction, the D.H,
balance would be upset if convert-to-A.C. processing is effected at 120 Hz.
The frequency for polarity inversion is not limited to 60Hz, such that it is
sufficient that polarity inversion is made with a multiple of the period necessary for
expressing a sole grayscale level. For example, the frequency for polarity inversion
for expressing the sole grayscale level may be 120 Hz for a 240Hz picture signal.
The source driver 15 is supplied with a signal having the polarity inverted by
the convert-to-A.C. unit 14. The source driver 15 is responsive to the input signal to
apply a driving voltage to the liquid crystal display panel 16 to drive the liquid
crystal on the pixel-by-pixel basis.
The liquid crystal display panel 16 is driven by the source driver 15 to
display an input moving picture on a panel. The liquid crystal display panel 16
exploits a so-called effective value response type liquid crystal of a twisted nematic
mode, employing the nematic liquid crystal, or a perpendicular orientation mode,
with a relatively slow liquid crystal response speed, in which the transmittance
corresponds to the effective value (mean square) of the voltages applied to the
liquid crystal in the plural fields.
Processing for improving the angle of visibility
The angle of visibility improvement unit 13 will now be described in further
detail.
Meanwhile, each picture of a picture signal, the picture surface display rate
of which has been up-converted to 120Hz, is referred to below as a field. It should
be noted that, although the picture signal is termed a field, it is irrelevant to the field
of the interlaced scanning.
Referring to Fig.l, the angle of visibility improvement unit 13 includes a first
field gamma converter 21, a second field gamma converter 22 and a switching
output unit 23.
Each of the first field gamma converter 21 and the second field gamma
converter 22 is supplied with a picture signal H2 of 120 Hz output from the
over-drive unit 12. The first field gamma converter 21 corrects the level of the
input picture signal to the plus side, while the second field gamma converter
corrects the level of the input picture signal to the minus side.
Meanwhile, the field corrected for level to the plus side is termed a 'first
field', while the field corrected for level to the minus side is termed a 'second
field'.
The switching output unit 23 alternately selects the picture signal, output
from the first field gamma converter 21, and the picture signal, output from the
second field gamma converter 22, on the field-by-field basis, that is, at 120 Hz, to
output the so selected signals.
The angle of visibility improvement unit 13 outputs a picture signal which is
an alternate repetition of fields corrected for level to the plus side (first fields) and
fields corrected for level to the minus side (second fields).
The first field gamma converter 21 and the second field gamma converter 22
convert the levels of the first and second fields so that, when the first and second
fields are averaged, the resultant picture signal will be the picture signal of the same
level as the input 60 Hz picture signal (input picture signal).
Instead of correcting the level of the picture signal on the field-by-field basis,
the input reference voltage pattern, supplied to the source driver of the liquid crystal
display panel, may be switched on the field-by-field basis. The reference voltage
means the voltage applied to the liquid crystal as selected for input data to the
source driver. In this case, the signal is supplied to the source driver without
correction, and the signaHevel-related voltages, applied to the liquid crystal, are
switched on the field-by-field basis.
It is noted that the visual sense of the human eye exhibits integrating
properties in the time direction. Thus, if the field corrected to the plus side (first
field) and the field corrected to the minus side (second field) are alternately
displayed, the image being displayed is perceived as a picture of the averaged level.
Hence, a user viewing the picture displayed on the liquid crystal display panel 16 is
viewing, as it were, a picture signal represented at an averaged level of the first and
second fields. Thus, even though the level conversion has been made in the first
field gamma converter 21 and in the second field gamma converter 22, the user will
feel that he/she is viewing a picture representing the 60 Hz input picture signal.
It is now assumed that a picture image Wl shown in Fig.2 has been supplied
as an input picture signal, and that an upper half region EI and a lower half region
E2 thereof are a region displayed with the grayscale level of 50% transmittance and
a region displayed with the grayscale level of 100% transmittance, respectively.
In this case, the first field becomes an image the entire surface region of
which is represented with the grayscale of 100% transmittance. The second field
becomes an image an upper half surface region of which is represented with the
grayscale of 0% transmittance and a lower half surface region of which is
represented with the grayscale of 100% transmittance. Since these fields, that is, the
first and second fields, are alternately displayed, in the picture display apparatus 10,
the second field displayed is such a picture image the upper half region of which is
perceived as being of, as it were, the transmittance synthesized from 0% and 100%,
or the transmittance of 50%. In actuality, the transmittance corresponds to the
effective value of the voltages sample-held in each field and the above description
is for ease in understanding the principle.
It is noted that, in the representation shown in Fig.3, it may appear as if the
applied voltage to all pixels of the field is switched simultaneously. However, the
actual liquid crystal driving is so-called line-sequential driving in which the driving
timing is shifted depending on vertical positions. For example, the actual liquid
crystal driving timing of a given pixel column w in a given perpendicular direction
on the picture image Wl, expressed as shown in Fig.4, is not the same from one
vertical position to another.
It is also possible to alternately select and scan pixels, not neighboring to one
another in the vertical direction, as shown in Fig.5, in place of selecting and
scanning vertically neighboring pixels by line-sequential driving. In the case of this
driving method, it is possible, by varying the alternately selected pixel positions in
the vertical direction, to set an optional ratio of the time width of the field corrected
in level to the plus side and that of the field corrected in level to the minus side, in
place of setting the two time widths to an equal time width. For example, the
angle-of-visibility improving effect for a low grayscale level may be achieved by
setting the time width of the field, level-corrected to the plus side, so as to be
smaller than that of the field level-corrected to the minus side.
It is now described, in detail, how the correction (viz. level conversion) is
carried out for the first and second fields.
Fig.6 depicts a graph showing a curve A representing the relationship of the
voltage applied to the first field with respect to the grayscale of the input picture
signal (in eight bits), and a curve B representing the relationship of the voltage
applied to the second field with respect to the grayscale of the input picture signal
(in eight bits).
The first field gamma converter 21 computes the applied voltage in
accordance with the curve A shown in Fig.6 to generate a signal corresponding to
the so computed applied voltage. The second field gamma converter 22 computes
the applied voltage in accordance with the curve B shown in Fig.6 to generate a
signal corresponding to the so computed applied voltage.
It is assumed that a voltage in absolute value which is not lower than 0V and
not higher than 4V may be applied to the liquid crystal display panel 16. With the
liquid crystal display panel 16, color density becomes 100% transmittance (white
representation) in case 4V is applied. With the liquid crystal display panel 16, the
color density (transmittance) becomes smaller as the applied voltage is lowered
from 4V, until the color density becomes 0% transmittance (black representation) at
1.5V. The applied voltage from 0V to 1.5V is a so-called non-sensitive region, that
is, the color density is 0% transmittance (black representation) without regard to
voltage values applied.
With the curve A shown in Fig.6 (input grayscale- applied voltage curve for
the first field), the applied voltage is increased monotonously for the grayscale of
the input picture signal of from 0 (8 bits) D 166 (8 bits), with the applied voltage
becoming equal to and fixed at a maximum value (4V) for the grayscale of the input
picture signal of from 166 (8 bits) D 255 (8 bits).
With the curve B shown in Fig.6 (input grayscale- applied voltage curve for
the second field), the applied voltage becomes equal to and fixed at a minimum
value (0V) for the grayscale levels of the input picture signal of from 0 (8 bits) D
166 (8 bits), with the applied voltage increasing monotonously for the grayscale
levels of the input picture signal of from 166 (8 bits) D 255 (8 bits). As for the
voltage applied to the liquid crystal in each field for the input grayscale levels, the
voltage values of the respective fields are alternately applied to the liquid crystal
layer and sample-held at the respective pixels for a field time duration. The
sample-held voltages are changed as from the selected time point due to such
effects as changes in capacitance attendant on changes in the liquid crystal director
or leakage of TFTs and the liquid crystal layer. The voltage value applied to each
liquid crystal in each field for each input grayscale level is set so that an effective
value which takes the above effects into account will be a preset transmittance
corresponding to the input grayscale level.
In the curves A, B shown in Fig.6, either the maximum voltage is applied to
the first field or the minimum voltage is applied to the second field, in all grayscale
levels not lower than 0 and not larger than 255 (8 bits). That is, at least one of the
fields is in the state of maximum transmittance or the state of minimum
transmittance at all times.
Thus, in the picture display apparatus 10 of the present embodiment, the
grayscale is expressed by the first and second fields, and the transmittance of at
least one field is fixed at the smallest value (0% transmittance) or at the largest
value (100% transmittance). The liquid crystal exhibits superior angle of visibility
characteristics for the transmittance of 0% and for the transmittance of 100%. Thus,
by setting the transmittance of one of the fields to a smallest value or to a largest
value, the angle of visibility characteristics may correspondingly be improved.
Specifically, Figs.6 and 7 show 0Q angle of visibility characteristics P and 60Q
angle of visibility characteristics, respectively.
It is seen that the 609 angle of visibility characteristics P are improved, as
apparent from comparison of this Fig.7 to Fig.30 for a prior-art example.
Over-drive processing
The over-drive processing by the over-drive unit 12 will now be described.
The over-drive processing means processing in which, in case of change
from a dark picture to a light picture or from a light picture to a dark picture,
spatial position, the liquid crystal driving voltage is slightly raised or lowered,
respectively, to improve follow-up characteristics of the liquid crystal to prohibit a
moving picture from becoming blurred.
If, in a conventional liquid crystal driving apparatus, a dark grayscale level is
changed to a light grayscale level, a small voltage may be added to the driving
voltage of the dark grayscale level side, whereby the response characteristics may
approach to ideal characteristics to prohibit a moving picture from becoming
blurred.
The picture display apparatus 10 according to the present invention
up-converts the picture rate to a double picture rate, by the angle of visibility
improvement unit 13, to express a picture, which is intrinsically a sole picture, by a
first field of a light grayscale level and a second field of a dark grayscale level. It is
therefore not possible to effect over-drive processing as conventionally. Hence, if
the over-drive processing is to be applied to the picture display apparatus 10
according to the present invention, it is necessary to make contrivance.
Fig.8 shows time changes of transmittance of the liquid crystal in case
various voltages are applied as a combination to the respective fields. Specifically,
Fig.8 shows changes in transmittance through the liquid crystal display panel 16 in
case respective voltages are applied to the first and second fields.
In Fig.8, a curve a shows changes in transmittance in case 3.0V and 0V are
repeatedly applied to the first and second fields, respectively. A curve b in Fig.8
shows changes in transmittance in case 3.4V and 0V are repeatedly applied to the
first and second fields, respectively. A curve c in Fig.8 shows changes in
transmittance in case 3.6V and 0V are repeatedly applied to the first and second
fields, respectively. A curve d in Fig.8 shows changes in transmittance in case 3.8V
and 0V are repeatedly applied to the first and second fields, respectively. A curve e
in Fig.8 shows changes in transmittance in case 4V and 0V are repeatedly applied
to the first and second fields, respectively. A curve fin Fig.8 shows changes in
transmittance in case 4.0V and 1.9V are repeatedly applied to the first and second
fields, respectively. A curve g in Fig.8 shows changes in transmittance in case 4.0V
and 2.4V are repeatedly applied to the first and second fields, respectively. A curve
h in Fig.8 shows changes in transmittance in case 4.0V and 2.8V are repeatedly
applied to the first and second fields, respectively. A curve i in Fig.8 shows changes
in transmittance in case 4.0V and 3.5V are repeatedly applied to the first and second
fields, respectively. A curve j in Fig.8 shows changes in transmittance in case 4.0V
and 4.0V are repeatedly applied to the first and second fields, respectively. The
reason the transmittance is increased and decreased progressively in the first and
second fields, respectively, is that the liquid crystal molecules of the liquid crystal
display panel 16 exhibit characteristics of responding to the effective value of the
applied voltage. The human eye recognizes the average value of the transmittance
as luminance.
The above-described changes in transmittance, shown in Fig.8, are ideal
response characteristics in the liquid crystal display panel 16 in case there is
produced no change in the grayscale level.
Fig.9(A) and Fig.lO(A) show time changes of transmittance (T) at respective
spatial positions in case the boundary line between a black picture (shown hatched)
and an open picture is moved with time. Meanwhile, Fig.9(A) shows a case where
the grayscale level of an input picture signal is smaller than 166 and Fig.lO(A)
shows a case where the grayscale level of an input picture signal is not smaller than
166.
Fig.9(B) and Fig.lO(B) show characteristics of luminance of respective
boundary locations (PI to P4) in case a human eye follows the boundary between
the black picture and the open picture in an effort to track a moving picture.
When a user views the respective boundary locations (PI to P4) between the
black picture and the open picture as he/she follows a moving picture, he/she will
recognize changes in the transmittance in the direction indicated by oblique dotted
lines of Figs.9 and 10. Figs.l 1(A) to (D) show changes in transmittance of the
positions PI to P4, for the case shown in Fig.9(A), and Figs.l2(A) to (D) show
changes in transmittance of the positions PI to P4 for the case shown in Fig.lO(A).
Since the human eye recognizes the average luminance of the respective
positions PI to P4, the luminance of the positions PI to P4 is not clear-cut, as
shown by dotted lines, but is becomes dull, as shown by solid lines in Figs.9(B) and
If desired to render the profile clear-cut, it suffices to correct the change in
transmittance along the direction as indicated by oblique dotted lines in Figs.9 and
10, so that the change in transmittance will approach to transmittance characteristics
for a case where no changes in grayscale are produced (see Fig.8). That is, it
suffices for the over-drive unit 12 to correct the applied voltage so that, even in case
the changes in the grayscale of the input picture signal are produced, the changes in
transmittance shown in Fig.8 will be approached.
The over-drive processing, in which, in carrying out the processing for
improving the angle of visibility characteristics, the ideal characteristics of the
liquid crystal, shown in Fig.8, may possibly be approached, will now be described
in detail.
In the description to follow, the processing for correcting the voltage applied
to the liquid crystal to the plus side (in the direction of increasing the absolute
value) by driving level correction in a direction of increasing the intrinsic signal
level is termed over-drive, and the quantity of the increase is termed an over-drive
quantity. The processing for correcting the voltage applied to the liquid crystal to
the minus side (in the direction of decreasing the absolute value) by driving level
correction in a direction of decreasing the intrinsic signal level is termed
under-drive, and the quantity of the decrease is termed an under-drive quantity.
Fig. 13 is a block circuit diagram showing the over-drive unit 12. This
over-drive unit 12 includes an operation controller 31, a field memory 32 and a
lookup (LUT) memory 33.
The operation controller 31 is supplied with a 120Hz picture signal H2 via
input terminal 3 la. The operation controller 31 performs computing processing for
the over-drive, while exercising input/output control of the picture signal for the
field memory 32 and output control for the downstream side angle of visibility
improvement unit 13. The field memory 32 has stored therein data of three
consecutive fields, which data are sequentially updated at a timing of 120 Hz. Of
the three consecutive fields, stored in the field memory 32, the first field is termed
'field Sn', the second field is termed 'field Sn+1' and the third field is termed 'field
Sn+2'.
Meanwhile, the three field data, stored in the field memory 32, are updated
every two fields, that is, every 60 Hz. Thus, the 'field Sn+2' of a previous time
zone becomes the 'field Sn' in the next time zone.
In the LUT memory 33, there is stored a table in which there is stored an
overdrive quantity or an under-drive quantity for addition to or subtraction from the
original signal level for overdrive or under-drive, respectively. In the LUT memory
33, there are stored three tables, namely a first table, a second table and a third
table.
In the first table, there is stored, for the grayscale levels for the field Sn (8
bits) and for the field Sn+2 (8 bits), an over-drive quantity or an under-drive
quantity to be afforded to the field Sn+1 and the field Sn+2 as well as the field
Sn+2' (field Sn used for the next time zone), as shown in Fig. 14.
In the second table, there is stored, for the grayscale levels for the field Sn (8
bits) and for the field Sn+1 (8 bits), an over-drive quantity or an under-drive
quantity to be afforded to the field Sn+1 and the field Sn+2 as well as the field
Sn+2' (field Sn used for the next time zone), as shown in Fig. 15.
In the third table, there is stored, for the grayscale levels for the field Sn+1 (8
bits) and for the field Sn+2 (8 bits), an over-drive quantity or an under-drive
quantity to be afforded to the field Sn+1 and the field Sn+2 as well as the field
Sn+2' (field Sn used for the next time zone), as shown in Fig. 16.
The over-drive quantity or the under-drive quantity, stored in the each table,
but not shown in Figs. 14 to 16, is found and set at the outset, by referring to test
values, based on the response characteristics of the liquid crystal when the applied
voltage is changed. In the first table, only grayscale levels for 0 to 166 (8 bits) are
shown, because no reference is made to the grayscale levels in excess of 167 (8
bits).
In the over-drive unit 12, the operation controller 31 refers to the three fields,
stored in the field memory 32, and reads out the signal levels of the pixels of the
same spatial position in the respective fields to compare the values of the signal
levels.
As a result of the comparison, one or two necessary tables are specified and
the over-drive quantity or the under-drive quantity of the corresponding grayscale
level stored in the so specified table(s) is read out. If necessary, the over-drive
quantity or the under-drive quantity is further corrected and added to or subtracted
from the signal levels of the pixels associated with the spatial position.
Over-drive sequence
The sequence of the over-drive processing will now be described in detail.
The over-drive unit 12 refers to signal levels in the same spatial position of
the field Sn, field Sn+1 and the field Sn+2 and, based on the relative magnitudes of
the signal levels, calculates in which of the fields the over-drive quantity is to be
added or the under-drive quantity is to be subtracted.
Initially, it is globally determined, by way of case classification, whether the
grayscale levels of all fields Sn, Sn+1 and Sn+2 are smaller than the halftone 166 (8
bits) or the grayscale level of one of the fields Sn, Sn+1 and Sn+2 is larger than the
halftone 166 (8 bits).
Meanwhile, the grayscale level of 166 (8 bits) is such a level for which the
voltage applied to the first field becomes maximum (with transmittance of 100%)
and for which the voltage applied to the second field becomes minimum (with
transmittance of 0%) (see Fig.6 as an example).
(Case where Sn, Sn+1, Sn+2 < 166)
For the grayscale level less than 166, in which the grayscale level before and
after change in lightness of an input picture signal is low, 0V is applied to the
second field. Hence, the picture signal of the second field does not significantly
affect the combined level of the first and second fields. However, the state is similar
to the so-called black insertion state and hence the response is a pulsed optical
response. Thus, the state suffering only little blurring of a moving picture may be
achieved.
In case of switching from the vicinity of the black level threshold to the
halftone in the perpendicular orientation mode, the offset from the stationary state
of the rising waveform of the optical response is smaller for a case where a voltage
higher than the voltage for a stationary state (state of still picture display) is applied
to the pre-change field than for a case where the voltage higher than the voltage for
the stationary state is applied to the post-change field.
Hence, if the grayscale level of each of the fields Sn, Sn+1 and Sn+2 is
smaller than 166 (8 bits), and if the input picture signal is switched from the dark
state (low grayscale level) to the light state (high grayscale level), a voltage equal to
the inherent applied voltage plus an over-drive voltage is applied to Sn+1 (second
field), as shown in Fig. 17.
However, if, in this case, the above voltage is applied only to the second field,
the rising waveform of the optical response is deviated from the stationary state,
under the effect of back-follow of the liquid crystal, and blurring tends to be
produced before switching. Thus, the voltage corresponding to the inherent applied
voltage plus a suitable over-drive value is applied to the post-change Sn+2 (first
Moreover, if the grayscale level is lower in all fields Sn, Sn+1 and Sn+2 than
166 (8 bits), as shown in Fig. 18, and the input picture signal is switched from the
light state (high grayscale level) to the dark state (low grayscale level), a voltage
corresponding to the inherent applied voltage less an under-drive voltage is applied
to the post-change Sn+2 (first field).
The over-drive value and the under-drive value for the case where the gray
sale levels of all fields, that is, Sn, Sn+1 and Sn+2, are smaller than 166 (8 bits), are
computed by the operation controller 31 referring to the first table. In addition, data
for the field Sn+2' of the first table are used if necessary as an over-drive quantity
for the field Sn used during the next time zone.
(Case where one of Sn, Sn+1 and Sn+2 D 166)
The case where the grayscale level of one of consecutive Sn, Sn+1 and Sn+2
is not smaller than the aforementioned halftone 166 (8 bits) will now be described.
In case the grayscale level is not less than 166, an over-drive sequence is
separately determined for each of the four cases, that is, a case where the grayscale
is monotonously increased in the sequence of Sn, Sn+1 and Sn+2, a case where the
grayscale is monotonously decreased in the sequence of Sn, Sn+1 and Sn+2, a case
where Sn+1 is high in grayscale level among the three fields, and a case where
Sn+1 is low in grayscale level among the three fields.
Case where the grayscale is monotonously increased in the sequence of Sn,
In case the grayscale level is monotonously increased in the sequence of Sn,
Sn+1 and Sn+2, an over-drive is applied to Sn+1, as shown in Figs. 19 and 20.
The reason is that Sn+2 has the maximum value of the grayscale level, so
that, if D of the first field is applied to Sn+2, the maximum voltage is applied to the
liquid crystal, and hence there is possibly no allowance for adding the over-drive
quantity.
The over-drive quantity for Sn+1 is found by the following method.
In the second table, an over-drive quantity for Sn < (Sn+1 = Sn+2) is stored.
In the third table, an over-drive quantity for (Sn = Sn+1) < Sn+2 is stored.
The value that may be taken on by Sn+1 is intermediate between these two
conditions. Hence, the optimum over-drive quantity is also a value intermediate
between these two values. Thus, if the grayscale level is monotonously increased in
the sequence of Sn, Sn+1 and Sn+2, the over-drive quantity is found by
interpolating the values of the second and third tables.
For example, the operation controller 31 calculates an over-drive quantity
OD of the fields Sn+1 and Sn+2, in accordance with the following equation (1):
OD = [OD2*(Sn+l - Sn) + OD*(Sn+2 - Sn+l)]/(Sn+2 - Sn) -(1)
where OD2 is the over-drive quantity stated in the second table and OD3 is the
over-drive quantity stated in the third table.
The equation is computed by linear interpolation. However, this method for
interpolation is not restrictive.
28
Meanwhile, if over-drive is applied to Sn+1, there may be cases where the
post-change state is not up to the stationary state, due to e.g. constraints of the
power supply voltage of the source driver. In such case, the over-drive or
under-drive quantity, applied to the next field, may be deviated from an optimum
value. Hence, for possibly avoiding this deviation, the operation controller
computes a predicted value of the picture signal which has reflected the director
state of the liquid crystal, as predicted as the consequence of applying the
over-drive, and sends the so computed field data to the field memory 32 as a
computed quantity for the next time zone.
That is, data of the field Sn+2 is corrected to compute Sn+2' and the so
computed Sn+2' is set as data of Sn used in the next time zone, as shown in Figs. 19
and 20. Sn+2' may be computed by, for example, the next equation (2):
Sn+2' = [Sn+2'(table2)*(Sn+l - Sn) + Sn+2'(table3)*(Sn+2 - Sn+l)]/(Sn+2 - Sn)
-(2)
where Sn+2' (table2) is data of the column of Sn+2' of the second table and
Sn+2'(table3) is data of the column of Sn+2' of the third table.
(Sn+1 = Sn+2) is stored.
In the third table, an under-drive quantity for (Sn = Sn+1) > Sn+2 is stored.
The value that may be taken on by Sn+2 is intermediate between these two
conditions. Hence, the optimum under-drive quantity is also a value intermediate
between these two values. Thus, if the grayscale level is monotonously decreased in
the sequence of Sn, Sn+1 and Sn+2, the under-drive quantity is found by
interpolating the values of the second and third tables.
For example, the operation controller 31 calculates an under-drive quantity
UD of the fields Sn+1 and Sn+2, in accordance with the following equation (3):
UD = [UD2*(Sn - Sn+1) + UD3*(Sn+l - Sn+2)]/(Sn - Sn+2) -(3)
where UD2 is the under-drive quantity stated in the third table and UD3 is the
under-drive quantity stated in the third table.
The equation (3) is computed by linear interpolation. However, this method
for interpolation is given only by way of illustration and is not to be restrictive.
Meanwhile, if under-drive is applied to Sn+2, there may be cases where the
post-change state is not up to the stationary state, because the voltage value applied
to the liquid crystal cannot be made less than 0V. In such case, the over-drive or
under-drive quantity, applied to the next field, may become offset from an optimum
value. Hence, for possibly avoiding the offset, the operation controller 31 computes
a predicted value of the picture signal which has reflected the director state of the
liquid crystal, as predicted as the consequence of applying the over-drive, and sends
the so computed field data to the field memory 32 as a computed quantity for the
next time zone.
That is, data of the field Sn+2 is corrected to compute Sn+2' and the so
computed Sn+2' is set as data of Sn used in the next time zone, as shown in Figs.21
and 22. Sn+2' may be computed by, for example, the next equation (4):
Sn+2' = [Sn+2'(table2) (Sn - Sn+1) + Sn+2'(table3) (Sn+l - Sn+2)]/(Sn - Sn+2)
Case where Sn+1 is high among the three fields>
In case the grayscale level of Sn+1 is high among the grayscale levels of the
three fields, an over-drive is first applied to Sn+1, and under-drive is then applied to
Sn+2.
The over-drive quantity for Sn+1 is computed by having reference to the
second table. The under-drive quantity for Sn+2 is computed by having reference to
the third table.
There is a possibility that the voltage applied to Sn+1 after adding the
over-drive quantity is not up to the stationary value. In this consideration, a
predicted value Sn+1', which takes into account the fact that the voltage applied to
Sn+1 after adding the over-drive quantity is not up to the stationary value is
computed by having reference to the second table, and the predicted value Sn+1' is
substituted for Sn+1 used for determining an under-drive quantity for the next
Moreover, the operation controller 31 computes a predicted value of the
picture signal, which has reflected the state of the director of the liquid crystal, as
predicted as the consequence of applying the under-drive, and sends the so
computed field data to the field memory 32 as a computed quantity for the next
time zone. That is, data of the field Sn+2 is corrected by referring to the third table
to compute Sn+2', and the so computed Sn+2' is used as data of Sn for the next
time zone.

In case Sn+1 is low among the three fields, under-drive is applied to Sn+2. In
addition, over-drive may further be applied to the field next following Sn+2.
In the second table, there is stored an under-drive quantity for the case of Sn
> (Sn+1 = Sn+2). Sn+1 is fixed at a maximum value.
The value that may be taken on by Sn+2 is intermediate between these two
conditions. Hence, the optimum under-drive quantity is also a value intermediate
between these two conditions. Thus, if Sn+1 is low among the three fields, the
under-drive quantity is found by interpolation of the value of the second table and
the maximum possible voltage that may be applied (Hi).
For example, the operation controller 31 computes the under-drive quantity
UD in accordance with the following equation (5):
UD = [UD2*(Sn - Sn+1) + Sn+2(Hi)*(Sn+2 - Sn+l)]/(Sn+2 + Sn-2*Sn+l)]
Moreover, the operation controller 31 computes a predicted value of the
picture signal, which has reflected the state of the director of the liquid crystal, as
predicted as the consequence of applying the under-drive, and sends the so
computed field data to the field memory 32 as a computed quantity for the next
time zone. That is, data of the field Sn+2 is corrected to compute Sn+2', and the so
computed Sn+2' is used as data of Sn for the next time zone.
That is, the data of the field Sn+2 is corrected to compute Sn+2', and the so
computed Sn+2' is set as data of Sn used for the next time zone. This Sn+2' may be
computed by, for example, the following equation (6):
Sn+2' = [Sn+2'(table2)*(Sn+l - Sn) + Sn+2'(table3) (Sn+2 - Sn+l)]/(Sn+2 +
Sn-2Sn+l) -(6)
Processing flow
A processing flow, conforming to the above-described sequence of the
over-drive processing, is shown in Fig.25.
First, the operation controller 31 in step SI verifies whether the grayscale
levels of all fields Sn, Sn+1 and Sn+2 are smaller than the halftone 166 (8 bits). If
the result is affirmative, processing transfers to a step S2 and, if otherwise,
processing transfers to a step S10.
In the step S2, the operation controller 31 verifies whether or not Sn 0 Sn+2.
That is, the operation controller 31 verifies whether or not the dark grayscale level
has been changed over to the light grayscale level.
When the dark grayscale level has been switched to the light grayscale level,
processing transfers to a step S3 where the operation controller 31 refers to the first
table to apply over-drive to Sn+1. Then, in a step S4, the operation controller refers
to the first table to apply over-drive to Sn+2 to finish the processing.
In case a dark grayscale level has been changed over to a light grayscale
level, processing transfers to a step S5, where the operation controller 31 sets Sn+1
to low driving (driving at the minimum voltage). Then, in a step S6, the operation
controller refers to the first table to apply an under-drive to Sn+2 to finish the
processing.
If it is determined in the step SI that the grayscale levels of all fields Sn,
Sn+1, Sn+2 are higher than the halftone 166 (8 bits), processing transfers to a step
S10, where the operation controller 31 verifies whether or not Sn 0 Sn+2 and Sn D
Sn+1 D Sn+2, that is, whether or not the grayscale level is increasing monotonously.
If the grayscale level is increasing monotonously, processing transfers to a step SI 1
and, if otherwise, processing transfers to a step S14.
In the step SI 1, the operation controller 31 refers to the above equation (1) to
apply an over-drive to Sn+1. Then, in a step SI2, the operation controller sets Sn+2
to high driving (driving at the maximum voltage). Then, in a step SI3, the operation
controller refers to the equation (S2) to correct the value of Sn+2 to finish the
processing.
If it has been determined in the step S10 that the grayscale level is not
increasing monotonously, processing transfers to a step SI4. In this step S14, the
operation controller 31 verifies whether or not Sn > Sn+2 and Sn D Sn+1 D Sn+2,
that is, whether or not the grayscale level is decreasing monotonously. If the
grayscale level is decreasing monotonously, processing transfers to a step S15 and,
if otherwise, processing transfers to a step SI8.
In the step SI5, the operation controller 31 sets Sn+1 to low driving (driving
at the minimum voltage). Then, at a step SI6, the operation controller refers to the
above equation (3) to apply an under-drive to Sn+2. Then, in a step S17, the
operation controller refers to the above equation (4) to correct the value of Sn+2 to
finish the processing.
If it has been determined in the step S14 that the grayscale level is not
decreasing monotonously, processing transfers to a step SI8. In this step SI8, the
operation controller 31 verifies whether or not (Sn Sn+1Sn+2, that is, whether
or not Sn+1 is largest. If Sn+1 is largest, processing transfers to a step S19 and, if
otherwise, processing transfers to a step S23.
In the step SI9, the operation controller 31 refers to the second table to apply
an over-drive to Sn+1. Then, in a step S20, the operation controller 31 refers to the
second table to correct the value of Sn+1 and, in a step S21, the operation controller
refers to the third table to apply an under-drive to Sn+2. Then, in a step S22, the
operation controller refers to the third table to correct the value of Sn+2 to finish the
processing.
In a step S23, the operation controller 31 sets Sn+1 to low driving (driving at
the minimum voltage). Then, in a step S24, the operation controller refers to the
equation (5) to apply an under-driving to Sn+2. Then, in a step S25, the operation
controller refers to the aforementioned equation (6) to correct the value of Sn+2 to
finish the processing.
In the above configuration, picture signals of consecutive frames are stored
in a plural number of frame memories, to which reference is made to determine an
optimum over-drive quantity for a field where a positive value for correction is
added to the grayscale level of the input picture signal by way of converting the
transmittance (field 1) or for a field where a negative value for correction is added
to the grayscale level of the input picture signal by way of converting the
transmittance (field 2). However, the above configuration is given only by way of
illustration and is not intended for restricting the invention. Thus, it is also possible
to find corresponding past and future pixels in the same frame, from the moving
vectors of respective pixels, and to calculate the optimum over-drive quantity from
the pixel information, in place of storing past and future picture signals in the frame
memories.
Also, gamma characteristics of an output for input data differ in general for
each of the colors red (R), green (G) and blue (B). A configuration of having
reference to tables of respective colors R, G and B, a configuration of having
reference to an over-drive table following the conversion at the outset to data
having corrected gamma characteristics of R, G and B colors, or a configuration of
correcting gamma characteristics of R, G and B colors in a gamma converter, is
possible. Moreover, if an optimum over-drive is configured for being applied to the
correction levels of the fields 1 and 2, output from the angle of visibility
improvement unit 13, it is possible to correct the signal level supplied to the angle
of visibility improvement unit 13 and to apply the desired over-drive to an
resultantly converted output, while it is also possible not to correct the level of the
signal supplied to the angle of visibility improvement unit 13 but to convert the
signal to the correction levels of the fields 1 and 2 in the angle of visibility
improvement unit 13 and thereafter to convert the level of the output so that the
desired over-drive will be applied depending on an input signal.

With the first sub-pixel, the grayscale level lower than the half-tone is
represented by two fields. The respective fields of the second sub-pixel are each of
a voltage of the black level or the level close to the black level. As for the grayscale
level higher than the halftone, each field of the first sub-pixel is of the grayscale
level of the white level or the level close to the white level and each field of the
second sub-pixel mainly expresses the grayscale level difference.

The grayscale level lower than the halftone is represented by two sub-pixels
of the first field period. A voltage corresponding to the black level or the level close
to the black level is applied to the second field. As for the grayscale level higher
than the halftone, a voltage corresponding to the white level or the level close to the
white level is applied to the first sub-pixel, and the grayscale level difference is
mainly expressed with two pixels during the second field period.
The over-drive processing is carried out on the liquid crystal display
apparatus 50 as well. The over-drive processor may be implemented by setting
optimum values for the respective sub-pixels for the same cases as described above
in connection with the previous embodiment.
Although the present invention has so far been described with reference to
preferred embodiments, the present invention is not to be restricted to the
embodiments. It is to be appreciated that those skilled in the art can change or
modify the embodiments without departing from the scope and spirit of the
invention.

CLAIMS
1. A picture display apparatus for displaying a picture corresponding to an input
picture signal via a liquid crystal display surface, comprising:
a driving level correction unit for correcting a driving level based on said
input picture signal;
a converter for converting the grayscale level of a signal supplied thereto into
a plurality of correction levels for expressing said grayscale level by synthesis of
transmittances of a plurality of temporally consecutive fields; and
a driving unit for driving said liquid crystal display surface by a driving
signal generated via said driving level correction unit and said converter;
said converter generating said correction levels so that each picture image of
said input picture signal includes at least a first field and a second field, said first
field having transmittance converted to a transmittance corresponding to the
grayscale level of said input picture signal added by a positive correction value;
said second field having transmittance converted to a transmittance corresponding
to the grayscale level of said input picture signal added by a negative correction
value;
said driving level correction unit performing driving level correction of
signal values of said first field or said second field or both, depending on effective
response characteristics of the liquid crystal driven by said driving unit, in case time
changes of the grayscale level have occurred at the same spatial position of said
input picture signal.
2. The picture display apparatus according to claim 1 wherein, in case the grayscale
level has been changed at the same spatial position from the light grayscale level to
the dark grayscale level, said driving level correction unit corrects at least the signal
value of the field at said spatial position, the transmittance of which is converted to
a transmittance corresponding to the grayscale level of said input picture signal
added by a negative correction value, to a light grayscale level side.
3. The picture display apparatus according to claim 1 wherein, in case the grayscale
level has been changed at the same spatial position from the dark grayscale level to
the light grayscale level, said driving level correction unit corrects at least the signal
value of the field at said spatial position, the transmittance of which is converted to
a transmittance corresponding to the grayscale level of said input picture signal
added by a positive correction value, to a dark grayscale level side.
4. The picture display apparatus according to claim 1 wherein said driving level
correction unit refers at least to signal values of a plurality of fields representing a
grayscale level at a spatial position, and to a signal value of a first one of another
plurality of fields representing the next grayscale level at said spatial position to
compute the correction value of said driving level.
5. The picture display apparatus according to claim 1 wherein said converter
generates a corrected picture signal at each spatial position so that at least one of a
plurality of fields which represent a grayscale level is of the maximum level or the
minimum level.
6. The picture display apparatus according to claim 5 wherein said driving level
correction unit computes a correction value of a driving level of each of a plurality
of fields representing two or more consecutive grayscale levels at the same spatial
position, based on the magnitudes of two or more consecutive grayscale levels at
the same spatial position, or on relative magnitudes of signal values of said fields
representing said two or more consecutive grayscale levels at the same spatial
position.
7. The picture display apparatus according to claim 6 wherein, in case two
consecutive grayscale levels at the same spatial position are both lesser than a
preset halftone between said maximum level and said minimum level, said driving
level correction unit compares a signal value of a first one of a plurality of fields
representing a temporally previous grayscale level and a signal value of a first one
of the same plurality of fields representing a subsequent grayscale level to compute
a correction value of a driving level.
8. The picture display apparatus according to claim 6 wherein, in case at least each
of signal values of a plurality of fields representing a grayscale level at the same
spatial position or the value of a signal of a first one of another plurality of fields
representing the next grayscale level at said same spatial position is not less than a
preset halftone intermediate between said maximum level and said minimum level,
said driving level correction unit computes a correction value of a driving level
depending on whether the signal levels of at least three fields of the consecutive
grayscale levels are increasing or decreasing monotonously, whether the signal
value of a mid field is high or whether the signal value of said mid field is low.
9. The picture display apparatus according to claim 6 wherein said driving level
correction unit includes a lookup table having stored therein correction values of
driving levels for respective signal values of respective fields and wherein the
correction value is calculated by having reference to said lookup table.
10. The picture display apparatus according to claim 6 wherein, if, in comparing the
relative magnitudes of signal values at the same spatial position of respective fields
representing two consecutive grayscale levels, the correction of the driving level at
said spatial position was made in the past, said driving level correction unit refers to
a signal level equivalent to transmittance reached after correction to compute the
correction value of the driving level for each field.
11. The picture display apparatus according to claim 1 wherein said converter
effects grayscale conversion in such a manner that a grayscale level of said input
picture signal is expressed by a plurality of pixels or by a plurality of sub-pixels of
a pixel neighboring to one another in the spatial direction on a liquid crystal display
surface and, in combination therewith, by liquid crystal transmittances of a plurality
of temporally consecutive fields.
12. The picture display apparatus according to claim 1 wherein said driver includes
a polarity inverter for reversing the polarity of a driving signal for reversing the
polarity of an electrical field to be applied to the liquid crystal on a liquid crystal
display surface; said polarity inverter reversing the polarity at a period n times as
large as the picture period of a plurality of fields used for expressing a grayscale
level, where n is an integer not less than unity.
13. The picture display apparatus according to claim 1 wherein, when said
converter synthesizes liquid crystal transmittances of a plurality of temporally
consecutive fields, the average value of the synthesized liquid crystal transmittances
is the gamma characteristics of the liquid crystal display surface conforming to the
level of an input picture signal.
14. The picture display apparatus according to claim 1 further comprising an
interpolator for increasing a picture rate of said input picture signal and for
interpolating a plurality of picture images corresponding to the increased rate; said
converter performing processing on the input picture signal having the picture rate
increased by said interpolator.
15. A picture display method for displaying a picture corresponding to an input
picture signal via a liquid crystal display surface, comprising:
a driving level correcting step of correcting a driving level based on said
input picture signal;
a converting step of converting the grayscale level of a signal supplied
thereto into a plurality of correction levels for expressing said grayscale level by
synthesis of transmittances of a plurality of temporally consecutive fields; and
a driving step of driving said liquid crystal display surface by a driving signal
generated by said driving level correction step and said converting step ;
said converting step generating said correction levels so that each picture
image of said input picture signal includes at least a first field and a second field,
said first field having transmittance converted to a transmittance corresponding to
the grayscale level of said input picture signal added by a positive correction value;
said second field having transmittance converted to a transmittance corresponding
to the grayscale level of said input picture signal added by a negative correction
value;
said driving level correction step performing driving level correction of
signal values of said first field or said second field or both, depending on effective
response characteristics of the liquid crystal driven by said driving step, in case
time changes of the grayscale level have occurred at the same spatial position of
said input picture signal.
16. The picture display method according to claim 15 wherein, in case the grayscale
level has been changed at the same spatial position from the light grayscale level to
the dark grayscale level, said driving level correction step corrects at least the signal
value of the field at said spatial position, the transmittance of which is converted to
the transmittance corresponding to the grayscale level of said input picture signal
added by a negative correction value, to a light grayscale level side.
17. The picture display method according to claim 15 wherein, in case the grayscale
level has been changed at the same spatial position from the dark grayscale level to
the light grayscale level, said driving level correction step corrects at least the signal
value of the field at said spatial position, the transmittance of which is converted to
the transmittance corresponding to the grayscale level of said input picture signal
added by a positive correction value, to a dark grayscale level side.
18. The picture display method according to claim 15 wherein said driving level
correction step refers at least to signal values of a plurality of fields representing a
grayscale level at a spatial position and to a signal value of a first one of another
plurality of fields representing the next grayscale level at said spatial position to
compute the correction value of said driving level.
19. The picture display method according to claim 15 wherein said converter
generates a corrected picture signal at each spatial position so that at least one of a
plurality of fields which represent a grayscale level is of the maximum level or the
minimum level.
20. The picture display method according to claim 19 wherein said driving level
correction step computes a correction value of a driving level of each of a plurality
of fields representing two or more consecutive grayscale levels at the same spatial
position based on the magnitudes of said two or more consecutive grayscale levels
at the same spatial position or on relative magnitudes of signal values of said fields
representing two or more consecutive grayscale levels at the same spatial position.
21. The picture display method according to claim 20 wherein, in case two
consecutive grayscale levels at the same spatial position are both lesser than a
preset halftone between said maximum level and said minimum level, said driving
level correction step compares a signal value of a first one of a plurality of fields
representing a temporally previous grayscale level and a signal value of a first one
of the same plurality of fields representing a subsequent grayscale level to compute
a correction value of a driving level.
22. The picture display method according to claim 20 wherein, in case at least each
of signal values of a plurality of fields representing a grayscale level at the same
spatial position or the value of a signal of a first one of another plurality of fields
representing the next grayscale level at said same spatial position is not less than a
preset halftone intermediate between said maximum level and said minimum level,
said driving level correction step computes a correction value of a driving level
depending on whether the signal levels of at least three fields of the consecutive
grayscale levels are increasing or decreasing monotonously, whether the signal
value of a mid field is high or whether the signal value of said mid field is low.
23. The picture display method according to claim 20 wherein said driving level
correction step includes a lookup table having stored therein correction values of
driving levels for respective signal values of respective fields and wherein the
correction value is calculated by having reference to said lookup table.
24. The picture display method according to claim 20 wherein, if, in comparing the
relative magnitudes of signal values at the same spatial position of respective fields
representing two consecutive grayscale levels, the correction of the driving level at
said spatial position was made in the past, said driving level correction step refers to
a signal level equivalent to transmittance reached after correction to compute the
correction value of the driving level for each field.
25. The picture display method according to claim 15 wherein said converter effects
grayscale conversion in such a manner that a grayscale level of said input picture
signal is expressed by a plurality of pixels or by a plurality of sub-pixels of a pixel
neighboring to one another in the spatial direction on a liquid crystal display surface
and, in combination therewith, by liquid crystal transmittances of a plurality of
temporally consecutive fields.
26. The picture display method according to claim 15 wherein said driver includes a
polarity inverter for reversing the polarity of a driving signal for reversing the
polarity of an electrical field to be applied to the liquid crystal on a liquid crystal
display surface; said polarity inverter reversing the polarity at a period n times as
large as the picture period of a plurality of fields used for expressing a grayscale
level, where n is an integer not less than unity.
27. The picture display method according to claim 15 wherein, when said converter
synthesizes liquid crystal transmittances of a plurality of temporally consecutive
fields, the average value of the synthesized liquid crystal transmittances is the
gamma characteristics of the liquid crystal display surface conforming to the level
of an input picture signal.
28. The picture display method according to claim 15 further comprising an
interpolating step for increasing a picture rate of said input picture signal and for
interpolating a plurality of picture images corresponding to the increased rate; said
converting step performing processing on the input picture signal having the picture