JPH1084551A - Uneven color correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct an uneven color caused by a liquid crystal panel or a projection optical system. SOLUTION: A video signal input 1 is amplified by an amplifier circuit 2 and a V-T correction section 3 converts a liquid crystal voltage - transmission rate characteristic into a linear characteristic. An uneven color correction signal adder circuit 4 superimposes an uneven color correction signal to the signal subject to V-T correction, An uneven color correction signal generating circuit is made up of a memory and a filter circuit. The memory stores correction amounts for uneven color obtained by dividing a video image display pattern into a plurality of blocks and from a luminance level of each block as digital data. The data in the memory are called by a timing generating circuit 9. The called digital data are converted into an analog signal by a D/A converter 11 and added to the video signal subjected to V-T correction by the uneven color correction signal adder circuit 4 through an amplifier circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device, and more particularly to a color unevenness correction device suitable for use in a three-panel projection type liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal projector in which a color image is projected and displayed on a screen using three liquid crystal panels for displaying R, G, and B images, VT correction is performed. I'm trying to do it. The VT correction has a display characteristic in which the transmittance of the liquid crystal does not linearly change with respect to the amplitude of an input video signal. Say

In a conventional liquid crystal projector, color unevenness occurs due to each liquid crystal panel and a projection optical system. To correct the color unevenness, a color unevenness correction signal is generated and input. It is superimposed on the video signal, and then the VT correction is performed.

[0004] As a conventional color non-uniformity correction device for a liquid crystal projector, for example, there is one described in Japanese Patent Application Laid-Open No. 7-75120. FIG. 9 shows the configuration of the color nonuniformity correction device described in the above publication. According to the above publication, as the cause of the color unevenness, the odd or even number of times that the transmitted light of each liquid crystal panel is reflected by the dichroic mirror of one liquid crystal panel before being projected on the screen is determined by the other two sheets. It is described that color unevenness occurs because the number of reflections of the liquid crystal panel is different from that of the liquid crystal panel. That is, in the three-panel type liquid crystal projector, since one liquid crystal panel has a different driving method from the other two liquid crystal panels, color unevenness occurs.

Next, the driving method will be described. FIG.
0 shows a wiring diagram of the liquid crystal panel. Since the liquid crystal gate wiring is wired for each horizontal line in the horizontal direction of the liquid crystal panel,
The length of the wiring differs depending on the horizontal position of each pixel.
For this reason, the signal output from the gate driver causes a time difference in transmission between the left and right pixels. In other words, a delay occurs in the pixel at point B on the right side of the screen with a long gate line compared to the pixel at point A on the left side of the screen with a short gate line. As a result, B
The time for applying the voltage to the liquid crystal of the pixel at the point is shortened.

FIG. 11 shows a waveform in which a voltage is actually applied to a liquid crystal pixel. While the timing signal generated from the gate driver is at the H level, the source voltage is written to the liquid crystal. There is a delay time between points A and B due to the difference in gate line length. As a result, when the time difference for applying the voltage to the liquid crystal becomes the voltage level difference and the projection display is performed, a difference in luminance occurs between the left and right. In the three-panel liquid crystal projector, only one of the three liquid crystal panels has a different driving direction from the other two due to the difference in the number of reflections. If three images can be displayed in the same driving direction, the brightness may differ between the left and right, but no color unevenness occurs. However, when only one image is driven in the opposite driving direction and projection display is performed using three liquid crystal panels, color unevenness occurs because the left and right colors are different. For example, while the writing time is shortened from the left to the right in the red and blue liquid crystal panels, the opposite is true in the case of the green liquid crystal panel. Therefore, 3
It can be easily understood that when the liquid crystal panels are superimposed and projected, color unevenness occurs in the left-right direction.

Next, the color non-uniformity correction apparatus shown in FIG. 9 will be described. The horizontal synchronizing signal input 61 is integrated by an integrating circuit 65, and a sawtooth waveform gain setting circuit 66 generates a sawtooth waveform.
By adjusting the amplitude of the sawtooth waveform, the inverting amplifier 67,
And 68 provide an inverted waveform and a non-inverted waveform. This waveform is inverted by a polarity inversion circuit 69 in accordance with the characteristics of the liquid crystal, and is superimposed on the video signal of the B signal input 63 via DC bias setting circuits 70 and 71. This signal is used to drive a B liquid crystal panel 73 through a drive circuit 72, thereby correcting color unevenness of an image. In other words, since the time during which the video signal is written to the liquid crystal differs depending on the left and right pixels of the liquid crystal panel, color unevenness occurs. Therefore, the color unevenness correction is performed by raising the applied voltage to the right pixel that has a delay in advance. I have to.

[0008]

The first problem is as follows.
When performing color shading correction, the correction of the black level and white level greatly affects the S / N of the screen.
When the color shading correction signal is superimposed before performing the VT correction,
Focusing on the level near the black level, the gain is several times to several tens times before and after performing the VT correction. This indicates that when the voltage-transmittance relationship, which is a characteristic of liquid crystal, is converted into a linear relationship, a gain of several times to several tens times is required. Therefore, when performing the VT correction after performing the mottling correction for the minute change, if the VT correction is performed after the mottling correction, a noise is included in the mottling correction signal because the gain near the black level of the VT correction is large. In this case, the noise is also amplified at the same time. Therefore, S on the screen
/ N is deteriorated.

As a second problem, in the above-mentioned publication, the unevenness of the number of times that the transmitted light of the liquid crystal panel is reflected by the mirror before being projected on the screen is caused by the unevenness of the other two sheets. It describes that the number of reflections of the liquid crystal panel is different from odd / even, and that color unevenness occurs due to wiring capacitance due to different lengths of left and right gate wirings in the liquid crystal panel. However, actually, the cause of the color unevenness is due to the non-uniformity of the thickness (hereinafter, referred to as a gap) of the liquid crystal sealed between the electrodes facing the pixel electrodes of the liquid crystal panel in addition to the above items. Unevenness caused by unevenness in rubbing, unevenness due to unevenness of the deflecting plate used to align the deflection direction of the liquid crystal panel, unevenness due to optical components such as dichroic mirrors in other projection devices, and uneven light sources There are various factors of color unevenness such as unevenness due to gender.

In the above publication, no consideration is given to the color unevenness of the other items. Therefore, when there is color unevenness other than in the left-right direction, the effect of the color unevenness correction is not sufficient, and conversely, other color unevenness is not sufficient. It is also conceivable to add color unevenness due to factors. Further, if the color unevenness correction described in the above publication is performed before the VT correction, the noise problem described in the first problem will occur.

Accordingly, the present invention solves each of the above problems, improves the S / N degradation due to color unevenness correction, and
It is an object of the present invention to provide a color non-uniformity correction device capable of correcting color non-uniformity due to various factors.

[0012]

According to the present invention, there is provided a correction means for correcting an input video signal in accordance with the display characteristics of a display means to achieve the above-mentioned object, and a correction means for generating a video signal on a display screen of the display means. A correction signal generating means for generating a correction signal for correcting color unevenness, and an adding means for adding a correction signal obtained from the correction signal generating means to the video signal corrected by the correction means are provided.

The correction signal generating means may be configured to generate a correction signal for correcting the luminance level of each block when the display screen is divided into a plurality of blocks to be uniform. The color unevenness correction amount based on the color unevenness correction signal is obtained by measuring the luminance of each block when displaying the video signal corrected by the correction means on the display means, and measuring each measured value and the luminance around each block. May be determined from the luminance difference between

Further, the correction signal may be obtained by performing linear interpolation in horizontal and vertical directions so as to eliminate a luminance difference between the blocks.

The correction signal may include a signal for correcting the DC level of the video signal and a signal for correcting the AC level of the video signal.

Further, as the display means, one including three liquid crystal panels and a screen used in a three-panel projection type liquid crystal display device is used, and the voltage-transmittance characteristic of the liquid crystal is linearly corrected by the correction means. VT correction may be performed.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, after a video signal input 1 is amplified by an amplifier circuit 2, a VT correction circuit 3 converts a voltage-transmittance characteristic of the liquid crystal into a linear characteristic. This VT-corrected signal is supplied to a color shading correction signal adding circuit 4.
In, the color shading correction signal from the amplifier circuit 12 is superimposed on the video signal. Further, the video signal is amplified by an inverting amplifier circuit 5 and a non-inverting amplifier circuit 6, and a video signal is switched to a liquid crystal panel 8 by a polarity switching circuit 7 by switching a video signal in an inversion method suitable for a liquid crystal panel such as field inversion or dot inversion. indicate.

The color unevenness correction signal is generated by a color unevenness correction signal generation circuit 10. The color non-uniformity correction signal generation circuit 10 includes a memory and a filter circuit.
The memory stores digital color unevenness correction data obtained from the luminance level of the projected video signal. In this memory, the image display screen is divided into a plurality of blocks, and the color unevenness correction amount of each block is stored as digital data. The data is called from the memory of the color shading correction signal generation circuit 10 by the H synchronization signal 13 and the V synchronization signal 1.
4 is called by the timing generation circuit 9 based on 4. The called color shading correction data is converted into an analog signal by the D / A converter 11, and is added to the VT corrected video signal by the color shading correction signal adding circuit 4 through the amplifier circuit 12. I have.

Next, the operation of the above configuration will be described. In the case of a three-panel type liquid crystal projector, unevenness in luminance on the display screen of the liquid crystal panel of each color is three.
Since the liquid crystal panels appear as color unevenness when they are overlapped, color unevenness can be reduced by reducing the brightness unevenness of each panel.

In FIG. 1, a single-color video signal is input from a video signal input 1. This signal is amplified by the amplifier circuit 2,
The VT correction circuit 3 performs VT correction suitable for the characteristics of the liquid crystal. By this VT correction, the video signal input to the liquid crystal panel and the transmittance are corrected so as to linearly change. FIG. 3 shows an example of a graph showing the relationship between the transmittance of the normally white liquid crystal and the applied voltage. As shown, when the applied voltage is low, the transmittance is high, and when the applied voltage is gradually increased, the transmittance sharply decreases. When the applied voltage is further increased, the amount of change is small, but the transmittance is reduced.

A liquid crystal panel having such characteristics is referred to as a VT
FIG. 2 is a graph showing a correction curve when the correction is performed.
FIG. 4 shows a graph of the applied voltage and the transmittance after further performing the VT correction. FIG. 4 shows that the relationship between the video input signal and the transmittance becomes linear. That is, when a video signal is projected by the projection device, the relationship between the input video signal level and the luminance level of the projected video can be expressed by a simple linear expression.

In the above state, the state of color unevenness is measured from the projected image. The measuring method divides a screen on which an image is displayed into a plurality of parts in a horizontal direction and a vertical direction, and measures a luminance level at each intersection. FIG. 5 shows a screen obtained by dividing the projection screen showing an example of measurement. The luminance level in each block is measured using a luminance meter or the like. Examples of the measuring means include a method of sequentially measuring each block and collecting data, a method of capturing the entire screen using a camera or the like, and converting the luminance level at each intersection into digital data using a personal computer. The data obtained here indicates a low level or a high level with respect to surrounding intersections when there is color unevenness. Therefore, by adjusting the voltage at the intersection having color unevenness so that the luminance becomes the same as that of the other intersections, the color unevenness is reduced.

When color unevenness correction is performed by superimposing a color unevenness correction signal on a video level, it may not be possible to perform correction by simply superimposing the DC level on the video signal.
The correction can be made even at the AC level. That is,
The state of color unevenness may change between the black level and the white level of an image. The cause may be that the transmittance of the liquid crystal is not constant over the entire screen with respect to the applied voltage. Therefore, in the present embodiment, color unevenness can be corrected at both the DC level and the AC level.

When measuring the state of uneven color, first, a video signal of a black level on the entire surface is displayed. At this time, the luminance difference between the blocks is collected as data. Next, an all white display is performed, and the luminance difference between the blocks at this time is collected as data. Color unevenness correction data is created from these data. When the video signal is displayed in all black and there is a luminance difference in the projected display screen, color unevenness can be corrected by superimposing a DC level signal on the video signal. next,
By changing the AC level of the video signal, that is, the video amplitude level, so as to eliminate the luminance difference when performing all white display, the color unevenness is reduced most. With such a method, it is possible to cope with color unevenness that changes from all black to all white.

The luminance data obtained by the above measurement is stored in the memory of the color unevenness generating circuit 10. The memory is prepared for DC level and AC level to be superimposed on the video signal. As an example, a method of generating a color shading correction signal for each block using 8-bit data will be described. First, the luminance value of black display is subtracted from the measured value of each block at the time of white display on the display screen, and the difference is divided by 8 bits, that is, 256. As a result, a luminance value per 1/256 digital data is obtained. Next, when the all black display is performed, only the shortage of the luminance data compared with the peripheral blocks is stored in the memory.

The data stored in the memory is read by the timing generation circuit 25 when it corresponds to each block. The read data is a D / A converter 1
After being converted into an analog signal by 1, it is superimposed on the VT-corrected video signal by the color shading correction signal adding circuit 4.

Next, an all white display is performed, and a luminance difference on the display screen is measured. If there is a luminance difference at this time, it is necessary to change the video amplitude level. As an example, it is assumed that the luminance is 100 as a result of measuring a certain point on the screen displaying all white. Assuming that there is a luminance around 110, the color unevenness can be corrected by multiplying the image amplitude of the point to be corrected by 1.1 times. Therefore, the video amplitude is set to 1.
The coefficient to be multiplied is stored. As with the DC level, the data stored in this memory is read out by the timing generation circuit 9 when corresponding to each block. The read data is converted into an analog signal by the D / A converter 11 and is superimposed on the video signal by the color shading correction signal adding circuit 4.

If color unevenness correction is performed when the number of points of the measured luminance data is small, the read data has only the data of the measured screen position, and there is a possibility that a luminance difference may be seen for each measurement block. . In particular, if the luminance difference between the blocks is large, the boundary of the luminance may be visible. For this reason, techniques such as taking as many measurement points as possible,
The data between the measurement points uses horizontal interpolation and vertical interpolation in the horizontal direction and the vertical direction, respectively, so that the luminance difference between the blocks is eliminated.

Next, the configuration of the filter is performed by linear interpolation.
FIG. 6 shows an example of the horizontal filter. From FIG. 5, the color unevenness measurement points in the horizontal direction are A and B. Ideally, the data for interpolating between A and B is good for each pixel, but it is difficult to obtain data for each pixel because the horizontal scanning speed of the video signal is high. Therefore, the area between A and B is divided into several points. As an example, in the present embodiment, it is divided into eight. As interpolation data, seven data are created from point A to point B. The values of the interpolation data from point A to point B are denoted by C1 to C7, respectively. The seven data can be obtained by subtracting the data at the point A from the point B and multiplying by a coefficient.

The data from the point A to the point B are sequentially written as A =
A + 0/8 (BA), C1 = A + ／ (BA),
C2 = A + 2/8 (B-A), C3 = A + 3/8 (B-
A), C4 = A + 4/8 (BA), C5 = A + 5/8
(BA), C6 = A + 6/8 (BA), C7 = A +
7/8 (BA), B = A + 8/8 (BA).

Therefore, the configuration of the horizontal filter can be composed of a subtractor, an adder and a switch as shown in FIG. That is, BA uses a subtractor. Coefficient K is from 0/8 to 8/8
The data of 1/8 can be obtained by shifting the data of (BA) by 3 bits. 2/8 data can be obtained by shifting the (BA) data by 2 bits. The 4/8 data can be obtained by shifting the (BA) data by 1 bit data. Other data can be obtained by adding and subtracting the above data combinations. That is, when the coefficient K is 3/8, 3/8 =
It is 1/8 + 2/8. When coefficient K is 5/8, 5 /
8 = 1/8 + 4/8. When the coefficient K is 6/8, 6/8 = 2/8 + 4/8. When the coefficient K is 7/8, 7/8 = 8 / 8-1 / 8. By switching the data using a switch, a filter that has been linearly interpolated can be configured.

Next, the filter in the vertical direction will be described. Since the operation speed is slower in the vertical direction than in the horizontal direction,
It is configured to provide data for each pixel. The data is created in the same manner as in the horizontal direction. However, when a coefficient is provided for each pixel, the circuit scale becomes large if it is constituted by a bit shift, an adder, a subtractor, and a switch. For this purpose, the configuration of the vertical filter is configured as shown in FIG. 7 using a multiplier and a counter circuit. As shown in FIG. 5, if there are 50 pixels between the measurement points A and C, the counter value is incremented by one for each line and multiplied by (AC).
Next, by multiplying the multiplied signal by 1/50, it is possible to obtain data of color unevenness correction. That is, A
At point C, point A = A + 0/50 (AC), C
= A + 50/50 (AC). Assuming that an intermediate point between the points A and C is D25, D25 = A + 25/50 (A−
C). The filter configurations for horizontal interpolation and vertical interpolation have been described above.

The order in which the color unevenness correction data is interpolated is such that vertical interpolation is performed first, and then horizontal interpolation is performed. this is,
According to the horizontal interpolation method, interpolated data between the two data points in the horizontal direction is created, but there is no data at locations other than the measurement points. Therefore, by performing the vertical interpolation first, data capable of performing the horizontal interpolation on all the lines can be obtained. FIG. 8 shows an example of a display screen having color unevenness and a correction waveform.

The read data is transferred to a D / A converter 1
The signal is converted into an analog signal by 1 and is superimposed on the video signal by the color non-uniformity correction signal adding circuit 4 through the amplification circuit 12 so that the color non-uniformity can be corrected. The DC level correction adds a color shading correction signal to the video signal. The AC level is corrected by multiplying the video signal by a color shading correction signal, thereby obtaining DC and AC signals.
Both levels can be corrected.

Next, the video signal subjected to the color shading correction is amplified by the inverting amplifier circuit 5 and the non-inverting amplifier circuit 6, respectively.
The polarity switching circuit 7 switches the signal. The switching timing signal is input from the timing generation circuit 9. The reversal timing is based on a reversal method suitable for the characteristics of the liquid crystal panel. By inputting the switched video signal to the liquid crystal panel 8, it is possible to view a video with reduced color unevenness.

As described above, according to the present embodiment, the VT correction of the liquid crystal panel is first performed, and then the uneven color correction is performed. By dividing the image projected on the screen into a plurality of blocks and measuring the luminance of each block, it is possible to easily grasp the state of color unevenness.
Further, since the relationship between the input voltage and the luminance is proportional to the signal for correcting the color unevenness after the VT correction, the correction level can be obtained by a simple calculation from the luminance level. Further, the S / N ratio can be improved as compared with the conventional case where the uneven color correction is performed before the VT correction.

[0037]

The first effect obtained by the present invention is that V
With the configuration in which the color nonuniformity correction is performed after the correction such as the −T correction or the like, the color nonuniformity can be more accurately improved and the S / N can be improved as compared with the case where the reverse is performed. The reason is that in the case of VT correction, the voltage-transmittance relationship of the characteristics of the liquid crystal is linearly converted.
When the projected image is displayed on the LCD panel, the luminance changes little when the input voltage is at a low level and at a high level,
The change in luminance is large at the intermediate level. Therefore, V-
Performing the T correction means increasing the gain when the input voltage level is low and high, and decreasing the gain at the intermediate level.

For this reason, if the color unevenness correction signal is superimposed before the VT correction, accurate correction cannot be performed because the color unevenness correction level changes depending on the video level. In addition, when performing accurate color unevenness correction, it is necessary to superimpose a color unevenness correction signal corresponding to a video level, so that it becomes difficult to manage the correction signal. Therefore, by performing the color unevenness correction after the VT correction, accurate and simple color unevenness correction can be performed.

Regarding noise, if a minute level of noise is mixed in the color unevenness correction signal, the gain of a signal having a level close to black or white can be increased by several to several tens by performing VT correction. become. At the same time, the noise component was also amplified, so that the S / N deteriorated. However, the above problem can be solved by performing the color unevenness correction after the VT correction.

A second effect is that color unevenness caused by the liquid crystal panel and the projection optical system can be reduced. The reason for the occurrence of color unevenness is considered to be various. Therefore, the color unevenness appearing on the video display screen is not uniform in location and level, but by dividing the display screen into a plurality of blocks and performing color unevenness correction on each block, a fine range can be obtained. It is possible to perform color unevenness correction.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing input / output voltage characteristics of VT correction.

FIG. 3 is a graph showing a voltage-transmittance characteristic of a normally white liquid crystal panel.

FIG. 4 is a graph showing voltage-transmittance characteristics after VT correction.

FIG. 5 is a configuration diagram showing measurement points on a display screen.

FIG. 6 is a configuration diagram of a horizontal filter.

FIG. 7 is a configuration diagram of a vertical filter.

FIG. 8 is a configuration diagram showing color unevenness and a color unevenness correction signal.

FIG. 9 is a block diagram showing a conventional color shading correction apparatus.

FIG. 10 is a configuration diagram showing a cause of color unevenness.

FIG. 11 is a time chart showing a cause of occurrence of color unevenness.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 video signal input 2 amplifying circuit 3 VT correction 4 color shading correction signal adding circuit 5 inverting amplifying circuit 6 non-inverting amplifying circuit 7 polarity switching circuit 8 liquid crystal panel 9 timing generating circuit 10 color shading correcting signal generating circuit 11 D / A Converter 12 amplifying circuit 13 H synchronizing signal 14 V synchronizing signal 61 horizontal synchronizing signal input 62 left / right inversion control signal input 63 B signal input 64 amplifying circuit 65 integrating circuit 66 sawtooth waveform gain setting circuit 67 inverting amplifying circuit 68 inverting amplifying circuit 2 69 Polarity inversion circuit 70, 71 DC bias setting circuit 72 Drive circuit 73 B liquid crystal panel

Claims (6)

[Claims] A correcting means for correcting an input video signal in accordance with a display characteristic of a display means; a correction signal generating means for generating a correction signal for correcting color unevenness generated on a display screen of the display means; An unevenness correction device comprising: an addition unit that adds a correction signal obtained from the correction signal generation unit to the video signal corrected by the correction unit. 2. The apparatus according to claim 1, wherein said correction signal generating means generates a correction signal for correcting the luminance level of each block when the display screen is divided into a plurality of blocks to be uniform. The uneven color correction device described in the above. 3. The color shading correction amount based on the color shading correction signal is obtained by measuring the luminance of each block when the video signal corrected by the correcting means is displayed on the display means, and measuring each measured value and each block. 3. The color non-uniformity correction apparatus according to claim 2, wherein the color difference is obtained from a luminance difference from luminance around the image. 4. The color non-uniformity correction apparatus according to claim 2, wherein the correction signal is obtained by performing linear interpolation in horizontal and vertical directions so as to eliminate a luminance difference between the blocks. 5. The color non-uniformity correction apparatus according to claim 1, wherein the correction signal comprises a signal for correcting the DC level of the video signal and a signal for correcting the AC level of the video signal. 6. The display means includes three liquid crystal panels and a screen used in a three-panel projection liquid crystal display device, and the correction means linearly corrects a voltage-transmittance characteristic of the liquid crystal. The color non-uniformity correction apparatus according to claim 1, wherein the VT correction is performed.