JP2018036402A - Image display device and image display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a contrast ratio, using two pieces of LCD panels, and to improve color reproducibility of a dark part.SOLUTION: An image display device comprises: a first controller that creates RGB image signals having a color balance corrected from input RGB image signals, and supplies the post-corrected RGB image signals to a front surface side LCD panel; and a second controller that applies signal processing to the input RGB image signals to thereby create a grey image signal having the signal processing applied, and supplies the grey image signal having the signal processing applied to a rear surface side LCD panel. An RGB gradation conversion circuit is configured to: apply a first LUT to the input RGB image signals to create RGB image signals having a first gradation converted; and apply a second LUT to the input RGB image signals to create a color balance correction image signal having a second gradation converted. A color balance controller is configured to: multiply an adjustment function by a luminance ratio to be obtained by dividing the color balance correction image signal having the second gradation converted by means of the grey image signal having the signal processing applied to calculate a correction function; and multiply the correction function by the RGB image signals having the first gradation converted.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image display apparatus and an image display method for correcting a color balance as well as improving a contrast ratio.

  In a conventional image display device using a single LCD panel, the input image is corrected by a polygonal line gamma with a panel driver, thereby realizing a linearity characteristic of the visual gradation.

  However, in reality, the luminance is expressed by the backlight illumination passing through the liquid crystal panel, so the gradation characteristics in the black region are particularly bad, and the luminance is observed in the brighter direction than the ideal luminance. The so-called black floating phenomenon occurs.

  This phenomenon occurs because when the LCD panel displays a dark region, the light shielding of the LCD panel is not complete and the backlight illumination light leaks. A conventional CRT has a contrast ratio of about 10,000: 1, and an organic EL panel has a contrast ratio of about 1,000,000: 1. However, due to this phenomenon, in a conventional image display device using a single LCD panel, a contrast ratio of only about 1500: 1 can be realized.

  Thus, in order to improve the contrast ratio of such a single LCD image display device, an image display device using two LCDs has been proposed (see, for example, Patent Documents 1 and 2). Each of the image display devices is configured to use two LCDs, and the contrast ratio is improved by adjusting the backlight transmission amount on the rear LCD and performing RGB display on the front LCD.

JP-A-5-88197 International Publication No. 2007/108183

However, the prior art has the following problems.
As described above, an image display device using a single LCD panel has a problem that a contrast ratio of only about 1500: 1 can be realized. Furthermore, one LCD has a major problem that faithful reproduction of an image cannot be realized due to a decrease in color reproducibility in a dark image or a deterioration in black quality.

  On the other hand, an image display device using two LCD panels as in Patent Documents 1 and 2 has an effect of improving contrast and preventing black float. However, there is no mention of improvement in color reproducibility.

  FIG. 16 is a diagram for explaining a problem in the conventional image display device 100 using two LCD panels. The LCD panel on the rear backlight 103 side is referred to as an LV panel (Light Valve Panel) 102, and the front LCD panel on the side close to a person viewing an image is referred to as an RGB panel 101.

  As shown in FIG. 16, the RGB panel 101 is composed of R, G, and B sub-pixels. On the other hand, the LV panel 102 combines R, G, and B sub-pixels into one pixel. That is, one pixel of the LV panel 102 is common to one pixel in which the sub-pixels of the RGB panel 101 are combined, and has a 1: 1 correspondence.

  Therefore, the luminance of the image that is transmitted through one pixel of the LV panel 102 and then transmitted through the sub-pixels of the RGB panel 101 is collectively adjusted for RGB. For this reason, the following first problem and second problem occur.

First problem: Whitening of the color occurs due to light leakage in the dark part.
For example, in the case of a pure color that shines any one of RGB, there is a problem that when only R is radiated and GB is not shined, the light leaks from GB and R becomes white (becomes whitish).

Second problem: Color balance is lost.
For example, in the case of mixed colors in which all of RGB is lit, the luminance value of the LV pixel corresponding to the original luminance value of RGB, that is, the LV value, is an LV value common to all subpixels. For this reason, there is a problem that the luminance value of RGB after transmission as a multiplication of the transmittance of each of the LV panel and the RGB panel is different from the original RGB, so that the color balance is lost and the color appears to change.

  The present invention has been made in order to solve the above-described problems. By using two LCD panels, the contrast ratio is improved and the color balance is corrected. An object is to obtain an image display apparatus and an image display method that can be improved.

  The image display device according to the present invention is configured by stacking two front side LCD panels and a rear side LCD panel, and backlight light is transmitted in the order of the rear side LCD panel and the front side LCD panel. An image display device for displaying an image, comprising an RGB gradation conversion circuit and a color balance controller, generating an RGB image signal after color balance correction from an RGB image signal based on an input RGB image signal, A first controller that supplies the RGB image signal after the color balance correction to the side LCD panel, and a gray scale after the signal processing by performing signal processing on the RGB image signal based on the input RGB image signal. A second controller that generates an image signal and supplies the gray image signal after the signal processing to the rear LCD panel; The B gradation conversion circuit includes a first lookup table for performing first gradation conversion on the RGB image signal and a second lookup table for performing second gradation conversion on the RGB image signal. Each color is stored separately, and the first gradation conversion is performed by applying the first look-up table to the RGB image signal based on the input RGB image signal, thereby performing the first gradation conversion. An RGB image signal after tone conversion is generated, and the second gradation conversion is performed by applying the second look-up table to the RGB image signal based on the input RGB image signal, thereby performing the second gradation conversion. A color balance correction image signal after tone conversion is generated, and the color balance controller performs signal processing on each of the color balance correction image signals after the second gradation conversion generated individually for RGB. By multiplying the luminance ratio obtained by dividing the gray image signal by an adjustment function whose value range is 0 to 1, RGB correction coefficients are calculated, and the RGB image after the first gradation conversion is calculated. The RGB image signal after the color balance correction is generated by multiplying the signal by the RGB individual correction coefficient.

  In addition, the image display method according to the present invention is configured by stacking two front side LCD panels and a rear side LCD panel, and backlight is transmitted in the order of the rear side LCD panel and the front side LCD panel. An image display method executed by an image display device that performs image display by performing RGB gradation conversion processing and color balance correction processing on an RGB image signal based on an input RGB image signal. A corrected RGB image signal is generated, and signal processing is performed on the RGB image signal based on the input RGB image signal to generate a gray image signal after signal processing. The RGB image signal after the color balance correction is supplied, the gray image signal after the signal processing is supplied to the rear LCD panel, and the RGB gradation In the conversion process, a first lookup table for performing first gradation conversion on the RGB image signal and a second gradation conversion on the RGB image signal, which are individually stored for each color of RGB. The first gradation conversion by applying the first lookup table to the RGB image signal based on the input RGB image signal and performing the first gradation conversion. A second gradation conversion is performed by generating a later RGB image signal and applying the second lookup table to the RGB image signal based on the input RGB image signal to perform the second gradation conversion. After the color balance correction image signal is generated, in the color balance correction process, each of the color balance correction image signals after the second gradation conversion generated individually for RGB is The luminance ratio obtained by dividing by the gray image signal after the signal processing is further multiplied by an adjustment function having a value range of 0 to 1, thereby calculating a correction coefficient for each RGB, and the first gradation conversion The subsequent RGB image signals are multiplied by the RGB individual correction coefficients.

  According to the present invention, the RGB image is subjected to gradation conversion, and an RGB image in which the color balance is corrected in consideration of the gradation conversion result of the LV image is provided. As a result, it is possible to obtain an image display device and an image display method capable of improving color reproducibility particularly in a dark part by using two LCD panels and improving the contrast ratio and correcting the color balance. .

It is a signal processing block diagram of the image display apparatus in Embodiment 1 of this invention. FIG. 2 is a more detailed signal processing block diagram of a bit extension circuit, an RGB controller, and an LV controller included in the image display device in the first embodiment. FIG. 3 is an explanatory diagram of bit extension processing by the bit extension circuit in the first embodiment. FIG. 6 is a diagram illustrating gradation conversion characteristics by LUT (R) in the first embodiment. FIG. 4 is a diagram showing gradation conversion characteristics by LUT (W) in the first embodiment. FIG. 2 is a detailed configuration diagram of an edge hold circuit in the first embodiment. 3 is a flowchart regarding local edge hold processing by the edge hold circuit in the first embodiment. It is the figure which showed the operation result of the local edge hold process by the edge hold circuit in the said Embodiment 1 with the waveform. FIG. 4 is an explanatory diagram for improving the color reproducibility of a dark portion by the action of the LUT and the color balance controller in the first embodiment. FIG. 3 is an explanatory diagram regarding adjustment of color balance in a dark part by the function of the color balance controller in the first embodiment. It is explanatory drawing regarding the correction coefficient in the color balance controller of the said Embodiment 1. FIG. It is explanatory drawing which shows the experimental result of the said Embodiment 1. FIG. It is explanatory drawing which shows the experimental result of the said Embodiment 1. FIG. 3 is a schematic cross-sectional view of a display module using two LCD panels in the first embodiment. FIG. It is explanatory drawing of the adjustment function in the modification of this invention. It is a figure for demonstrating the problem in the conventional image display apparatus using two LCD panels.

  Hereinafter, preferred embodiments of an image display device and an image display method of the present invention will be described with reference to the drawings.

  The image display device according to the first embodiment is configured by stacking two front side LCD panels and a rear side LCD panel, and backlight light is transmitted in the order of the rear side LCD panel and the front side LCD panel in order. An image display device that performs display, includes an RGB gradation conversion circuit and a color balance controller, generates an RGB image signal after color balance correction from an RGB image signal based on an input RGB image signal, A gray image signal after signal processing is generated by performing signal processing on the RGB image signal based on the input RGB image signal and a first controller that supplies the RGB image signal after color balance correction to the panel. A second controller that supplies a gray image signal after the signal processing to the rear LCD panel, and the RGB gradation conversion circuit A first lookup table that performs first gradation conversion on the signal and a second lookup table that performs second gradation conversion on the RGB image signal are stored separately for each color of RGB. The first gradation conversion is performed by applying the first lookup table to the RGB image signal based on the input RGB image signal to generate the RGB image signal after the first gradation conversion, By applying a second lookup table to the RGB image signal based on the input RGB image signal and performing the second gradation conversion, a color balance correction image signal after the second gradation conversion is generated, and the color The balance controller further has a range for the luminance ratio obtained by dividing each of the image signals for color balance correction after the second gradation conversion generated individually for RGB by the gray image signal after the signal processing. By multiplying the adjustment function from 0 to 1, RGB individual correction coefficients are calculated, and after the color balance correction by multiplying the RGB image signal after the first gradation conversion by the RGB individual correction coefficient RGB image signals are generated.

[overall structure]
First, the overall configuration will be described.
FIG. 1 is a signal processing block diagram of the image display apparatus according to the first embodiment. The image display device 10 according to the first embodiment shown in FIG. 1 includes an image display device main body 20 and an LCD module 30.

  Here, the image display apparatus main body 20 is configured to include an image processing engine 21. On the other hand, the LCD module 30 includes an I / F (interface) 31, a bit extension circuit 32, an RGB controller (first controller) 33, an LV (light valve) controller (second controller) 34, an RGB panel (front side LCD panel). 35, and an LV panel (rear LCD panel) 36.

  The image processing engine 21 in the image display device main body 20 generates an RGB image and transmits it to the LCD module 30. On the other hand, the I / F 31 in the LCD module 30 receives the RGB image generated by the image processing engine 21 and transmits it to the bit extension circuit 32 as an input RGB image signal.

  FIG. 2 is a more detailed signal processing block diagram of the bit extension circuit 32, the RGB controller 33, and the LV controller 34 included in the image display apparatus according to the first embodiment.

  The bit expansion circuit 32 performs a bit expansion process to 12 bits on the input RGB 8-bit image. In this bit extension process, the bit length is extended with high accuracy in advance so as not to lower the bit precision in subsequent processing. The bit extension circuit 32 transmits the RGB image after bit extension to each of the RGB controller 33 and the LV controller 34.

  In the bit expansion circuit 32 according to the first embodiment, as shown in FIG. 3A, the 8-bit data 50, that is, the 8-bit image signal is expanded to, for example, 12 bits to form 12-bit data 52. Is assumed. When an analog image signal is quantized to 8 bits, changes below the bit resolution are rounded and discarded. However, since an image has a high correlation between adjacent pixels, it can be restored to some extent by introducing the following method.

  FIG. 3B is an explanatory diagram of the pixel to be processed, that is, the target pixel X5, and FIG. 3C is an example in which the procedure of the bit extension process is expressed in a program format. As shown in FIG. 3, the bit extension circuit 32 relates to the brightness of the target pixel X5 with respect to the eight pixels (X1 to X4, X6 to X9) adjacent to the target pixel X5 with respect to the variable dc initialized to 0. When the value is smaller than the luminance value of each adjacent pixel, +1 is calculated, and when the luminance value of the target pixel X5 is larger than the luminance value of each adjacent pixel, −1 is calculated.

  Further, the bit extension circuit 32 adds the total value, that is, a value obtained by dividing dc by 8 to the pixel of interest X5 as a weight 51 after the decimal point, and rounds the result by multiplying by 16 to obtain 12 bits. Make an extension to

  In general, adjacent pixels of an image have a property that the luminance values are similar. For example, when all the luminance values of surrounding pixels are larger than the luminance value of the target pixel X5, the luminance value of each pixel is The waveform of the analog value that is the original value before being rounded to 8 bits has a continuous concave shape, and the analog value that is the original value of the luminance value of the pixel of interest X5 is data that has been rounded to 8 bits. Is estimated to be greater than

  On the other hand, when the luminance values of the surrounding pixels are all smaller than the luminance value of the target pixel X5, the waveform of the analog value that is the original value before the luminance value of each pixel is rounded to 8 bits is It has a continuous convex shape, and it is estimated that the analog value, which is the original value of the luminance value of the pixel of interest X5, will be smaller than the data rounded to 8 bits. Therefore, the bit extension circuit 32 performs the bit extension process as shown in FIG. 3 based on such a basis.

  Note that a method other than the method described here may be introduced for the bit expansion method.

  Next, processing subsequent to the bit extension circuit 32 will be described. As shown in FIG. 2, the RGB controller 33 includes a delay circuit 331, an RGB gradation conversion circuit 332 having six LUTs (Look Up Tables) 3321, 3322, 3323, 3324, 3325, 3326, and a color balance controller 333. It is prepared for.

  On the other hand, the LV controller 34 includes a gray converter 341, an LV gradation conversion circuit 342 having one LUT 3421, a horizontal edge hold circuit 343, a vertical edge hold circuit 344, an LPF (low pass filter) 345, and a rounding processing unit 346. It is configured with.

  The delay circuit 331 in the RGB controller 33 receives the RGB image after bit extension (RGB image signal based on the input RGB image signal) from the bit extension circuit 32, and for the received RGB image after bit extension, Appropriate delay is applied. This “appropriate delay” is for compensating for the delay of processing by the gray converter 341, the horizontal edge hold circuit 343, the vertical edge hold circuit 344, and the LPF 345 in the LV controller 34.

  In the first embodiment, four types of LUTs, that is, a LUT (R) that is a LUT for subpixel R, a LUT (G) that is a LUT for subpixel G, and a LUT that is a LUT for subpixel B are used. (B) and LUT (W) which is a LUT for gray images is used. The RGB gradation conversion circuit 332 in the RGB controller 33 includes one LUT (R) 3321, LUT (G) 3322, LUT (B) 3323 (first LUT 3321, 3322, 3323) and three LUT (W) 3324. , 3325, 3326 (second LUTs 3324, 3325, 3326). The LV gradation conversion circuit 342 in the LV controller 34 includes an LUT (W) 3421 (third LUT 3421).

The RGB gradation conversion circuit 332 in the RGB controller 33 uses the first and second LUTs 3321, 3322, 3323, 3324, 3325, and 3326 for each color after delay to perform gradation conversion (first and second floors). style conversion) performed, RGB image signal after the first gradation converting R2, G2, B2 and the second image signal for color balance correction of a gradation-converted _{L R, L G,} to generate the _{L B.} Details of the gradation conversion processing by the RGB gradation conversion circuit 332 will be described later with reference to the drawings together with the description of the LV gradation conversion circuit 342 in the LV controller 34.

  On the other hand, the gray converter 341 in the LV controller 34 receives the RGB image after bit extension (RGB image signal based on the input RGB image signal) from the bit extension circuit 32, and applies the received RGB image after bit extension to the received RGB image. Thus, each pixel is converted into a gray image having the maximum value among the three luminance values of RGB as a representative value.

  Usually, in the conversion to gray scale, luminance is often obtained by performing color matrix conversion using a multiplier and an adder. The gray converter 341 in the first embodiment sets the maximum value of the R, G, and B luminance values in each pixel so that the color balance controller 333 in the RGB controller 33 can easily perform RGB color balance correction. The hardware is also simplified by detecting this and outputting it as a representative value.

  Of course, it is needless to say that the color balance correction process can be executed without any problem even when the normal matrix conversion is adopted.

  Next, the LV gradation conversion circuit 342 in the LV controller 34 performs gradation conversion (third gradation conversion) on the gray image using the third LUT 3421. The details of the gradation conversion processing by the LV gradation conversion circuit 342 will be described later with reference to the drawings together with the description of the RGB gradation conversion circuit 332 in the RGB controller 33.

  Further, the horizontal edge hold circuit 343 and the vertical edge hold circuit 344 in the LV controller 34 perform viewing angle correction on the gray image after gradation conversion. In the image after the viewing angle correction, the luminance value of each pixel is adjusted as will be described later, but by applying LPF345 so that the luminance value after the adjustment looks natural as the whole image, the adjacent luminance value is obtained. A gray image (B / W image) is generated by smoothing the change in between.

  The LV controller (second controller) 34 performs the above-described signal processing on the RGB image signal based on the input RGB image signal, and generates a gray image signal after the signal processing.

  The gray image after the signal processing is transmitted to the color balance controller 333 in the RGB controller. The gray image after the signal processing is displayed on the LV panel 36 after the luminance value is rounded to 8 bits by the rounding processing unit 346. Details of the viewing angle correction processing by the horizontal edge hold circuit 343 and the vertical edge hold circuit 344 will be described later with reference to the drawings.

  The color balance controller 333 in the RGB controller 33 is based on the signal after the first and second gradation conversion by the RGB gradation conversion circuit 332 and the signal that has undergone the third gradation conversion by the LV gradation conversion circuit 342. Thus, the color balance is corrected, and the corrected RGB image is displayed on the RGB panel 35 as the RGB image signal after the color balance correction. Details of the color balance correction processing by the color balance controller 333 will be described later with reference to the drawings.

  Next, details of gradation conversion processing using the respective LUTs 3321, 3322, 3323, 3324, 3325, 3326, 3421 by the RGB gradation conversion circuit 332 and the LV gradation conversion circuit 342, horizontal and vertical edge hold circuits 343 The details of the viewing angle correction process by H.344 and the details of the color balance correction process by the color balance controller 333 will be described below in this order.

[Details of gradation conversion processing by RGB gradation conversion circuit 332 and LV gradation conversion circuit 342]
In the prior art, a single LCD panel achieves linear gradation characteristics to the human eye by performing gamma conversion on the input pixel value, but the brightness of dark areas is increased by actual measurement and black floating occurs. I explained that.

  On the other hand, in the conventional method using two LCD panels, an RGB image not subjected to gradation conversion is used for the RGB panel 35, and a gray image is generated by gradation conversion for the LV panel 36. By using the / W image, it is possible to improve the contrast ratio and improve the black float.

  However, in this method, since the LV values are the same for each of the RGB sub-pixels constituting one pixel, as described above, whitening may occur in a pure color, or color balance may be lost in mixed color as described above. there were.

  Therefore, in the first embodiment, in order to facilitate the color balance control in the subsequent stage, an RGB image that has been subjected to gradation conversion using the RGB gradation conversion circuit 332 is also used for the RGB panel 35 and the LV panel. The image for 36 is also subjected to gradation conversion so that it can be continuously used in all value ranges so as not to be clipped to the upper limit in a certain range.

  FIG. 4 is a diagram showing the gradation conversion characteristics by the LUT (R) 3321 according to the first embodiment. The LUT (G) 3322 and LUT (B) 3323 also basically have the same gradation conversion characteristics as the LUT (R) 3321, but the light transmission efficiency in each of the R, G, and B subpixels. The characteristics are slightly different from each other. FIG. 5 is a diagram showing the gradation conversion characteristics by the LUT (W) 3421 in the first embodiment.

  As a result of the experiment, by adopting the gradation conversion characteristics as shown in FIGS. 4 and 5, the black expression in the dark portion and the color reproducibility of the pure color are improved, and the problem of whitening in the pure color is improved. I understood.

The gradation conversion characteristics of the LUT (R) 3321 shown in FIG. 4 are realized by, for example, a gamma curve (Y = X ^γ ) with γ = 0.5. In contrast, the gradation conversion characteristics of the LUT (W) 3421 shown in FIG. 5 are obtained by actually measuring the transmitted light of the two LCD panels while changing the LV values with respect to the RGB values. The input / output characteristics of the LV are determined so that the combined result is γ = 2.2 that matches the human visual characteristics.

[Details of Viewing Angle Correction Processing by Horizontal and Vertical Edge Hold Circuits 343 and 344]
The horizontal edge hold circuit 343 performs local enlargement processing of the edge region of the image. There is no problem with the two LCD panels when viewed from the front, but when viewed obliquely in the horizontal direction, the positions of the display images on the front and rear sides are shifted according to the angle due to the thickness of the panel. There is a problem that a double image and a color shift are visible. In order to solve this problem, the horizontal edge hold circuit 343 plays a role of performing viewing angle correction on the LV image in the horizontal direction.

  FIG. 6 is a detailed configuration diagram of the horizontal edge hold circuit 343 according to the first embodiment. FIG. 7 is a flowchart relating to local edge hold processing by the horizontal edge hold circuit 343 according to the first embodiment.

  In the examples of FIGS. 6 and 7, local edge hold processing with 5 horizontal taps is shown. The luminance value of each pixel of the LV image after gradation conversion input in the horizontal line direction is sequentially stored in the registers X1 to X5.

  The horizontal edge hold circuit 343 detects that the luminance value of the center X3 pixel is a rising edge, that is, the luminance value of the X3 pixel is larger than the luminance value of the left pixel of X3. In this case, a process of replacing the luminance value of the pixel on the left side of X3 with the luminance value of the pixel of X3 is performed. The horizontal edge hold circuit 343 detects that the luminance value of the center X3 pixel is a falling edge, that is, the luminance value of the X3 pixel is larger than the luminance value of the right pixel of X3. In this case, a process of replacing the luminance value of the pixel on the right side of X3 with the luminance value of the pixel of X3 is performed.

  However, the process is limited to the case where X3 is the threshold value 3 or more and the edge size ((X3-X2) or (X3-X4)) is the threshold value 4 or more. That is, the horizontal edge hold circuit 343 performs local edge hold processing when the luminance difference is more than a certain level.

  The registers Y1 to Y5 and selection 1 to selection 5 shown in the lower part of FIG. 6 perform the above-described replacement operation. Further, if the pixel once replaced in the previous operation period is smaller than X3, , X3 is replaced.

  The above control signals for replacement are S1 to S5 in FIG. 6, and the horizontal edge hold circuit 343 does not perform replacement when the control signal is 0, but performs replacement when the control signal is 1.

  FIG. 8 is a diagram showing the operation result of the local edge hold processing by the horizontal edge hold circuit 343 in the first embodiment as a waveform. FIG. 8A shows an input waveform to the horizontal edge hold circuit 343, and FIG. 8B shows an output waveform with respect to the input waveform of FIG. 8A. Each white circle in FIG. 8 corresponds to the luminance value of each pixel in the output image from the LV gradation conversion circuit 342. On the other hand, the black circle in FIG. 8B corresponds to the luminance value of the pixel subjected to the edge hold process.

  As shown in FIG. 8, it can be seen that the local edge hold process is executed to replace the previous or subsequent pixel with the value of the edge pixel. In this way, by performing correction to increase the luminance of adjacent pixels, it is possible to prevent the image from becoming dark when viewed from an oblique direction in the horizontal direction.

  The vertical edge hold circuit 344 performs viewing angle correction in the vertical direction on the LV image. The vertical edge hold circuit 344 can be realized by a configuration similar to that described above with respect to the horizontal edge hold circuit 343.

[Details of Color Balance Correction Processing by Color Balance Controller 333]
In this circuit, the RGB gradation conversion circuit 332 uses the LUT (R) 3321, LUT (G) 3322, and LUT (B) 3323 to perform pixel conversion on the converted RGB image (first gradation conversion). Each time, the color balance is adjusted using the correction coefficient.

As shown in FIG. 2, the following three types of signals are input to the color balance controller 333.
(First input signal) Signals R1, G1, and B1 obtained by bit-extending each of R, G, and B are LUT (R) 3321, LUT (G) 3322, and LUT in the RGB gradation conversion circuit 332, respectively. (B) The first gradation-converted RGB signal (R2, G2, B2) subjected to gradation conversion (first gradation conversion) by 3323
(Second input signal) The signals R1, G1, and B1 are subjected to gradation conversion (second gradation conversion) by three LUTs (W) 3324, 3325, and 3326 in the RGB gradation conversion circuit 332, respectively. In addition, the second gradation conversion RGB signal (L _R , L _G , L _B )
(Third input signal) The third gradation conversion signal L _W generated by the LV controller 34 through the gradation conversion (third gradation conversion) by the LUT (W) 3421.

Color balance controller 333, the following equation (1) as to (3), the second gradation converting RGB signals _{L R,} L G, each of _{L B} is divided by the third gradation conversion signal _{L W} The luminance ratio is calculated, and the RGB signals R3 ′, G3 ′, and B3 ′ are generated by multiplying each of the first gradation-converted RGB signals R2, G2, and B2 by the luminance ratio.
R3 ′ = R2 × (L _R / L _W ) (1)
G3 ′ = G2 × (L _G / L _W ) (2)
B3 ′ = B2 × (L _B / L _W ) (3)

  By displaying the RGB signals R3 ′, G3 ′, and B3 ′ on the RGB panel 35, it is possible to solve the first and second problems described above. However, the color balance controller 333 actually performs the RGB signal R3 generated according to the equations (4) to (6) described later, with further adjustment to the RGB signals R3 ′, G3 ′, and B3 ′. G3 and B3 are output to the subsequent RGB panel 35 as RGB image signals after color balance correction. Here, first, the solution of the first and second problems will be described.

[Description of cause and solution of first problem]
FIG. 9 is an explanatory diagram for improving the color reproducibility of a dark portion by the functions of the RGB gradation conversion circuit 332 and the color balance controller 333 according to the first embodiment. That is, it corresponds to the cause of the first problem and the principle diagram of the solution.

  As shown in FIG. 9A, a method for improving the color reproducibility of a dark part will be described by taking as an example the case of displaying a pixel expressing dark red with an R value of 16, and G and B values of 0. To do. In the conventional method of improving the contrast ratio using only the value of the LV image, it is necessary to set the luminance value of the corresponding pixel of the LV panel 36 to 218, for example.

  In this case, as shown in FIG. 9A, the luminance value of the LV panel 36 is set so that R having the highest luminance among the sub-pixels is properly displayed. Becomes the desired value. However, the luminance of G and B, which should be 0, is large. The amount of light passing through the LV panel 36 from the backlight is large, and G and B emit light due to light leakage of G and B in the RGB panel 35. As whitish (grayish) red.

  On the other hand, for example, as shown in FIG. 9B, the luminance value of R is set to a value larger than the original value (for example, 218), and the value of the LV image is set to a small value of 16, and passes through the LV panel. By reducing the amount of light, R after the combined transmission shows a desired luminance, and G and B show a pure dark red without causing a light leak to be very small and red. be able to.

  By actively utilizing this phenomenon, among LUTs 3321, 3322, 3323, 3324, 3325, 3326 in RGB gradation conversion circuit 332, RGB LUT (R) 3321, LUT (G) 3322, LUT (B) 3323 is set so as to be lifted upward from the linear characteristics, particularly in the dark portion, and correspondingly, the LV LUT (W) 3421 in the LV gradation conversion circuit 342 is set to drop below that of the prior art. This corresponds to the gradation conversion characteristics shown in FIGS.

[Description of cause and solution of second problem]
FIG. 10 is an explanatory diagram relating to the adjustment of the color balance in the dark part by the function of the color balance controller 333 in the first embodiment. That is, it corresponds to the cause of the second problem and the principle diagram of the solution.

  As shown in FIG. 10A, description will be given by taking as an example the case of displaying pixels that express a mixed color (R> G> B) in which RGB is not 0, respectively. As described above, the gray converter 341 generates a gray image as represented by the maximum luminance value of each RGB sub-pixel for each pixel with respect to the RGB image. For this reason, an LV image in which the same luminance value as that of R, which is the sub pixel having the maximum luminance value, is gradation-converted by the LUT (W) 3421 for LV is generated.

  As described above, the LUT (R) 3321, LUT (G) 3322, and LUT (B) 3323 in the RGB gradation conversion circuit 332 increase the luminance values of RGB, and the LV gradation conversion circuit. The LUT (W) 3421 in 342 performs gradation conversion so as to lower the luminance value of LV. FIG. 10B shows the result of gradation conversion in this way with respect to FIG. However, even if such gradation conversion is performed, the desired luminance can be obtained for R after combined transmission, but the luminance of G and B is increased, so that the color balance is lost.

Here, the second gradation conversion RGB signals L _R , L _G , and L _B convert the signals _{R 1} , _G 1, and B 1 using the three LUTs (W) 3324, 3325, and 3326 in the RGB gradation conversion circuit 332. It is generated by doing. In other words, the second gradation converting RGB signals _{L R, L G, L B} in order to obtain the luminance of the original RGB, the pixel value to be displayed at the corresponding pixel of the LV image. This is shown in FIG. 10 (c). That is, in order to obtain the original luminance of G and B, it is necessary to change the luminance value in the LV image for each color of RGB as shown in FIG. However, since one pixel of the LV panel is the size of the three sub-pixels of the RGB panel, each pixel of the LV image cannot be changed for each color of RGB. Therefore, in order to obtain a desired combined transmittance for all colors, it is necessary to adjust the gradation on the RGB panel side.

Therefore, as shown in FIG. 10 (d), the gradation on the RGB panel side is adjusted so that the combined transmittances of the RGB panel before and after the adjustment and the LV panel are equal, and the luminance values R3 and G3 after the adjustment are adjusted. , B3 is derived. For this purpose, as shown in FIG. 10E, L _R / L _W , L _G / L _W , and L _B / L _W are set for each of the first gradation conversion RGB signals R2, G2, and B2. It can be seen that the luminance ratio is multiplied, that is, R3 ′, G3 ′, and B3 ′ may be derived by the above-described equations (1) to (3). As a result, when R3 ′, G3 ′, and B3 ′ are displayed on the RGB panel 35 as shown in FIG. 10 (f), W (= L _W ) is displayed on the LV panel 36, and the color balance Can be adjusted.

  The specific configuration in which the color balance control method based on this principle is implemented is the previous FIG. 2 and FIG. 9, and the original color can be displayed even in the color mixture portion, and the color reproducibility can be improved. It becomes. It goes without saying that this effect is exhibited not only in dark areas but also in bright areas.

[Derivation of RGB image signal after color balance correction]
As described above, in the first embodiment, not the RGB signals R3 ′, G3 ′, and B3 ′ obtained by the equations (1) to (3), but the RGB signals R3 that are further adjusted to the RGB signals R3 ′, B3 ′, G3 and B3 are output to the subsequent RGB panel 35 as RGB image signals after color balance correction. This is due to the following reason.

In the above-described configuration, as described above, the display angle is corrected by the horizontal and vertical edge hold circuits 343 and 344, and the edge that is a portion having a large luminance difference is widened in the dark direction, thereby displaying a bright area. Has been expanded. In this widened edge portion, the third gradation conversion signal L _W being adjusted brightly, based on this, RGB signals R3' color balance by the color balance controller 333 is corrected, G3 ', B3' Has been generated. That is, since the RGB signals R3 ′, G3 ′, and B3 ′ are adjusted to be dark except for the sub-pixel having the maximum luminance value, the RGB image displayed by the RGB signals R3 ′, G3 ′, and B3 ′. Is corrected so as to be partially dark.

The RGB panels 35 and LV panel 36, the corresponding RGB signals R3 ', G3', those output displays the B3' third gradation conversion signal _{L W,} when viewed human from the front, of Since the light passing through the panels 35 and 36 is adjusted as described with reference to FIG. 10, the image has good color reproducibility. However, when viewed obliquely, the RGB signals R3 ′, G3 ′, and B3 ′ are corrected so as to be partially dark, and the area that should originally be displayed brightly is partially darkened. Therefore, side effects such as a double line appearing at the edge portion may occur.

To alleviate this side effect, in the first embodiment, instead of the above formulas (1) to (3), a function F (RGB individual correction coefficient) that reduces the multiplication effect of the luminance ratio is determined in advance. The function F is multiplied with each of the first gradation-converted RGB signals R2, G2, and B2, and is output to the subsequent RGB panel 35 as in the following equations (4) to (6). RGB image signals R3, G3, and B3 after color balance correction are generated.
R3 = R2 × F (L _R , L _W ) (4)
G3 = G2 × F (L _G , L _W ) (5)
B3 = B2 × F (L _B , L _W ) (6)

In the first embodiment, the RGB individual correction coefficient, that is, the function F is an adjustment function (1 obtained by subtracting a predetermined value TH from 1 as shown in the following equations (7) to (9). -TH) is multiplied by the luminance ratio, and further, a predetermined value TH is added.
F (L _R , L _W ) = (L _R / L _W ) × (1−TH) + TH (7)
F (L _G , L _W ) = (L _G / L _W ) × (1−TH) + TH (8)
F (L _B , L _W ) = (L _B / L _W ) × (1−TH) + TH (9)

FIG. 11 is a graph showing the function F when the input is the luminance ratio in the equations (7) to (9). As can be seen from FIG. 11, the function F61 is a luminance ratio multiplied by the first gradation-converted RGB signals R2, G2, and B2 in the expressions (1) to (3) represented by 60 in FIG. Clipping is performed so that L _R / L _W , L _G / L _W , and L _B / L _W have values equal to or greater than a certain value TH. Here, when TH is 0, the luminance ratio itself is used as the function F without clipping the luminance ratio, and the above formulas (1) to (3) are applied as they are. This is a case where the RGB image signals R3, G3, and B3 after the balance correction are generated.

  The value of TH is preferably 0.5 or more and 0.75 or less. Human eyes tend to be more sensitive at intermediate brightness than bright or dark brightness. By setting the TH value as described above, it is possible to display an image so as to suppress side effects such as a double line, particularly with respect to the luminance that the human eye is sensitive to.

Thus, in the first embodiment, color balance controller 333, RGB individually generated second image signal for color balance correction of a gradation-converted L _R, L _G, the respective L _B, signal For the luminance ratios L _R / L _W , L _G / L _W , and L _B / L _W obtained by dividing by the processed gray image signal L _W , an adjustment function (1-TH that has a value range of 0 to 1) ) To calculate the RGB individual correction coefficient F, and the RGB image signals R2, G2, and B2 after the first gradation conversion are multiplied by the RGB individual correction coefficient F to correct the color balance. The subsequent RGB image signals R3, G3, and B3 are generated. In this way, the range of the change in the luminance ratio is suppressed more than in the formulas (1) to (3), so that the luminance ratio does not act excessively, thereby improving the color reproducibility. Effectively suppresses side effects such as double wires.

  The function F can be realized by a circuit having a relatively simple configuration.

The “image display device composed of two LCD panels” in the first embodiment, which organizes the above contents, has technical characteristics in the following circuit configuration and operation.
The input RGB image is bit extended by the bit extension circuit 32 and then supplied to the RGB controller 33 and the LV controller 34.
The LV controller 34 generates one gray image from the RGB maximum value for each pixel from the RGB image after the bit expansion, performs gradation conversion using the LUT (W) 3421 for LV, and then holds the edge hold. An LV image subjected to the viewing angle correction process is generated by the process and displayed on the LV panel.
The RGB controller 33 performs gradation conversion using an RGB LUT, then refers to the LV image data, generates an RGB image by performing color balance correction, and displays the RGB image on the RGB panel.
The color balance controller 333 calculates an individual RGB correction coefficient F by multiplying the luminance ratio by an adjustment function whose value range is 0 to 1, and uses this correction coefficient F to perform RGB after color balance correction. An image signal is generated.

  As a result, side effects such as double lines can be effectively suppressed while realizing improvement in contrast ratio, improvement in black expression capability, and improvement in color reproducibility in a dark part.

  Next, an image display method using the image display apparatus described as the first embodiment will be described with reference to FIGS.

  This image display method is configured by stacking two front side LCD panels and a rear side LCD panel, and performing image display by transmitting backlight light in the order of the rear side LCD panel and the front side LCD panel. An image display method executed by a display device, wherein an RGB image signal after color balance correction is performed by performing RGB gradation conversion processing and color balance correction processing on an RGB image signal based on an input RGB image signal. Generate a gray image signal after signal processing by applying signal processing to the RGB image signal based on the input RGB image signal, and generate the RGB image signal after color balance correction for the front side LCD panel. The gray image signal after the signal processing is supplied to the rear LCD panel. The input RGB image is stored in a first lookup table that performs first gradation conversion on the RGB image signal and a second lookup table that performs second gradation conversion on the RGB image signal. An RGB image signal after the first gradation conversion is generated by applying the first lookup table to the RGB image signal based on the signal and performing the first gradation conversion, and the input RGB image signal is based on the input RGB image signal. By applying the second look-up table to the RGB image signal having been subjected to the second gradation conversion, a color balance correction image signal after the second gradation conversion is generated, and in the color balance correction process, The value range is further reduced from 0 with respect to the luminance ratio obtained by dividing each of the image signals for color balance correction after the second gradation conversion generated individually for RGB by the gray image signal after the signal processing. By multiplying the adjustment function is to calculate the RGB separate correction factors for the RGB image signal after the first gradation conversion, multiplying the RGB separate correction factors.

  First, the bit extension circuit 32 performs bit extension processing on the input RGB image signal to generate an RGB image signal after bit extension. The generated RGB image signal after bit expansion is transmitted to the RGB controller 33 and the LV controller 34 as an RGB image signal based on the input RGB image signal.

The RGB controller 33 receives the RGB image signal after bit expansion, and performs RGB gradation conversion processing on the RGB image signal after bit expansion. Specifically, after the delay circuit 331 applies an appropriate delay, the RGB gradation conversion circuit 332 uses the first and second LUTs 3321, 3322, 3323, 3324, 3325, 3326 for each of the delayed colors. By performing gradation conversion (first and second gradation conversion), RGB signals R2, G2, and B2 after the first gradation conversion and RGB signals L _R , L _G , and L after the second gradation conversion are performed. _B is generated. Each generated signal is transmitted to the color balance controller 333.

The LV controller 34 receives the RGB image signal after bit expansion, and performs signal processing on the RGB image signal after bit expansion in order to adjust the amount of backlight transmission. Specifically, first, the gray converter 341 converts the RGB image after bit expansion into a gray image with the maximum value among the three luminance values of RGB as a representative value for each pixel. Next, the LV gradation conversion circuit 342 performs gradation conversion (third gradation conversion) on the gray image using the third LUT 3421. Further, the horizontal edge hold circuit 343 and the vertical edge hold circuit 344 perform the viewing angle correction on the gray image after the gradation conversion, and then apply the LPF 345. The third gradation conversion signal L _W generated in this way, that is, the gray image signal L _W after the signal processing, is supplied to the LV panel (rear side LCD panel) 36 through the rounding processing unit 346 and is supplied to the LV panel. 36 and transmitted to the color balance controller 333.

Color balance controller 333 by using the gray image signal _{L W} after the signal processing, RGB after color balance correction by performing color balance correction processing on the RGB signals R2, G2, B2 after the first gradation conversion Image signals R3, G3, and B3 are generated. The color balance correction is performed as described above with reference to FIGS. That is, in the color balance correction process, each of the image signals for color balance correction L _R , L _G , and L _B after the second gradation conversion generated individually for RGB is divided by the gray image signal L _W after the signal processing. The luminance ratios L _R / L _W , L _G / L _W , and L _B / L _{W obtained} by multiplying the luminance ratios L _R / L _W , L _B / L _W by an adjustment function (1-TH) whose value range is 0 to 1 The correction coefficient F is calculated, and the RGB image signals R2, G2, and B2 after the first gradation conversion are multiplied by the RGB individual correction coefficients F. The RGB image signals R3, G3, and B3 after color balance correction are supplied to the RGB panel (front LCD panel) 35 and displayed on the RGB panel 35.

A third gradation conversion signal _{L W} displayed on the LV panel 36, signal R3 ', G3', produced by adjusting them based on B3 ', after color balance correction displayed on the RGB panel 35 Since the RGB image signals R3, G3, and B3 basically have the relationship described with reference to FIG. 10F, each RGB sub-pixel is displayed with an appropriate luminance value.

  The image display method described above uses the image display device described as the first embodiment, and it goes without saying that the same effects as those described in the image display device described as the first embodiment can be obtained.

  Next, a specific improvement effect related to suppression of the change range of the luminance ratio, that is, color balance correction using the equations (4) to (6) will be described. FIG. 12 shows the result of simulating the display when an image in which a bright vertical line having a width of 10 pixels is drawn on a dark background is displayed on the image display device having the configuration shown in FIG. It is a photograph. FIG. 12A shows the RGB signals R3 ′, G3 ′, and B3 ′ calculated by the equations (1) to (3) in the color balance controller 333 and displayed on the LV panel 36. It is. In FIG. 12B, the RGB image signals R3, G3, and B3 after color balance correction calculated by the color balance controller 333 according to the equations (4) to (6) are transmitted to the LV panel 36. Is displayed.

  In FIG. 12A, a white area is displayed on the left side of the vertical line across a dark area, and a double line is visible. In FIG. 12B, this double line is thinner than that in FIG. 12A. That is, the color balance controller 333 multiplies the luminance ratio by an adjustment function whose value range is 0 to 1. By doing so, side effects such as double lines are reduced.

  FIG. 13 is a photograph of the result of displaying an image in which a bright grid is drawn on a dark background on an actual machine. FIG. 13A shows the RGB signals R3 ′, G3 ′, and B3 ′ calculated by the equations (1) to (3) in the color balance controller 333 transmitted to the LV panel 36 and displayed. Is a photograph when viewed from the front, and FIG. 13B is a photograph when viewed from an oblique direction. 13C and 13E show the RGB image signals R3, G3, and B3 after the color balance correction calculated by the color balance controller 333 according to the equations (4) to (6) with respect to the LV panel 36, respectively. FIGS. 13 (d) and 13 (f) are photographs of the transmission and display of this displayed when viewed from the front. In FIGS. 13C and 13D, TH in the equations (7) to (9) is set to 0.5, that is, the effect of the luminance ratio is more than in the case of FIGS. 13 (a) and 13 (b). Is also suppressed to 50%. In FIGS. 13E and 13F, TH is set to 0.75, that is, the effect of the luminance ratio is suppressed to 25% as compared with the cases of FIGS. 13A and 13B.

  In FIG. 13B, a white area is displayed on the left side of the vertical line across a dark area, and a double line is visible. In FIG. 13D, this double line is thinner than that in FIG. 13B, that is, the color balance controller 333 multiplies the adjustment function whose value range is 0 to 1 with respect to the luminance ratio. By doing so, side effects such as double lines are reduced. In FIG. 13F, the double line is further thinned.

  FIG. 14 is a schematic cross-sectional view of a display module using two LCD panels in the first embodiment. The display module shown in FIG. 14 includes an RGB panel 35, an LV panel 36, a backlight unit 37, and a lamination 38 that joins the RGB panel 35 and the LV panel 36.

  The RGB panel 35 includes a color filter substrate 35b, a TFT substrate 35c, a polarizing film 35a, and a driving IC 35d. The color filter substrate 35b is a substrate on which a black matrix, R, G, and B color filters are arranged and a common electrode and the like are formed. The TFT substrate 35c is a substrate in which TFTs and electrodes are formed on the liquid crystal side.

  The polarizing film 35 a polarizes the light emitted from the backlight unit 37. The driving IC 35d displays the RGB image processed by the RGB controller 33 on the RGB panel 35 by driving the TFT substrate 35c.

  On the other hand, the LV panel 36 includes a glass substrate 36a, a TFT substrate 36b, a polarizing film 36c, and a drive IC 36d. The glass substrate 36a corresponds to the color filter substrate 35b in the RGB panel 35. However, unlike the color filter substrate 35b, the glass substrate 36a does not have a black matrix or a color filter. This is based on the fact that the LV panel 36 displays an LV image, that is, a grayscale image expressed only by light and darkness from white to black.

  The TFT substrate 36b and the polarizing film 36c are the same as the TFT substrate 35c and the polarizing film 35a of the RGB panel 35. The drive IC 36d displays the LV image processed by the LV controller 34 on the LV panel 36 by driving the TFT substrate 36b.

  The RGB panel 35 and the LV panel 36 are arranged so as to overlap each other so that corresponding pixels are overlapped when viewed from the front.

  The backlight unit 37 includes a light guide panel 37a and a light source 37b. The light source 37b irradiates light to the light guide panel 37a. The light guide panel 37a refracts the light emitted from the light source 37b and irradiates the LV panel 36. The light emitted from the light guide panel 37a passes through the superimposed LV panel 36 and the RGB panel 35 in order, and reaches the eyes of a human viewing the image display device.

  The contrast ratio of each of the RGB panel 35 and the LV panel 36 is 1500: 1 as in the conventional single LCD panel. However, the contrast ratio is improved to 2250,000: 1 by adopting the two LCD panel structure as shown in FIG.

  Further, in the first embodiment, the RGB controller 33 and the LV controller 34 cooperate with each other to perform gradation conversion and color balance control, so that the gradation characteristics of the black region in particular are improved. This eliminates the phenomenon, realizes a tight black expression, and improves the color reproducibility at low luminance (dark area).

As described above, according to the first embodiment, the RGB image is subjected to gradation conversion, and an RGB image in which the color balance is corrected in consideration of the gradation conversion result of the LV image is provided. ing. As a result, the following remarkable effects can be realized.
(Effect 1) Compared with a conventional image display device using a single LCD panel, it is possible to improve the contrast ratio and improve the black expression capability.
(Effect 2) Linearity and color reproducibility at low luminance (dark area) can be improved.
(Effect 3) Since it can be realized with a simple circuit configuration and the added circuit scale is small, there is a high cost performance effect.
(Effect 4) By controlling the range of change in the luminance ratio with the adjustment function, the luminance ratio is prevented from acting excessively, and thereby the side effects such as double lines are effective while exhibiting the above effects. Is suppressed.

[Modification]
Next, a modification of the image display device shown as the first embodiment will be described. In the present modification, the RGB individual correction coefficient, that is, the function F in the color balance controller 333 shown in FIG. 2 is different from that of the image display apparatus shown as the first embodiment.

In this modification, the RGB individual correction coefficients, that is, the function F, are expressed as follows using the adjustment function M (L _W ).
F (L _R , L _W ) = (L _R / L _W ) × M (L _W ) (10)
F (L _G , L _W ) = (L _G / L _W ) × M (L _W ) (11)
F (L _B , L _W ) = (L _B / L _W ) × M (L _W ) (12)

FIG. 15 is a graph showing the adjustment function M (L _W ) in this modification. The adjustment function M (L _W ) receives the gray image signal L _W after the signal processing, and changes the output value depending on the input value. The value range of the adjustment function M (L _W ) is 0 to 1, more specifically, a predetermined value k of about 0.5 and 1 or less.

As can be seen from FIG. 15, the adjustment function M (L _W ) has a shape that gradually decreases as the input value increases from 0 and gradually increases as the input value approaches the maximum value. As described in the first embodiment, side effects such as double line, that the value of the gray image signal L _W after the signal processing is significantly appears tendency intermediate case, in the experiment by simulation or actual equipment Is known. The adjustment function M (L _W ) takes this characteristic into consideration, and prevents the luminance ratio from acting excessively, particularly when the value of the gray image signal L _W after the signal processing is intermediate.

When the input value is expressed by 8 bits, the adjustment function M (L _W ) shown in FIG. 15 monotonously decreases when the input value is 0 or more and 64 or less, and monotonically increases when the input value is 194 or more and 255 or less. Is set to The adjustment function M (L _W ) may be implemented as an LUT on the circuit.

  Needless to say, the image display device having the function F shown as the present modification exhibits the same effects as the image display device shown as the first embodiment.

In particular, the image display device having a function F shown as the modification, in particular for a range of values of the gray image signal L _W after side effects significantly appears signal processing such as double line, excess brightness ratio The other ranges are set so that the effect of the luminance ratio is sufficiently obtained. Accordingly, it is possible to improve the color reproducibility better than the first embodiment while effectively suppressing side effects such as double lines.

  Note that the image display device and the image display method of the present invention are not limited to the above-described embodiments and modifications described with reference to the drawings, and various other modifications can be considered within the technical scope thereof. It is done.

For example, the adjustment function M (L _W ) in the above modification may have a shape different from the shape shown in FIG. If the types of images to be displayed are limited and some common features are provided as properties, the properties are reflected in the adjustment function M (L _W ), for example, when the input value is high May not be monotonously increased.

Further, the adjustment function M (L _W ) in the above modification example monotonically decreases when the input value is expressed by 8 bits, and monotonically increases when the input value is 0 or more and 64 or less, and monotonically increases when the input value is 194 or more and 255 or less. However, the threshold values such as 64 and 194 may be other values.

  In addition to this, the configurations described in the above embodiments and modifications can be selected or changed to other configurations as appropriate without departing from the gist of the present invention.

  DESCRIPTION OF SYMBOLS 10 Image display apparatus, 20 Image display apparatus main body, 21 Image processing engine, 30 LCD module, 31 I / F, 32-bit expansion circuit, 33 RGB controller (1st controller), 331 Delay circuit, 332 RGB gradation conversion circuit, 333 color balance controller, 34 LV controller (second controller), 341 gray converter, 342 LV gradation conversion circuit, 343 horizontal edge hold circuit, 344 vertical edge hold circuit, 345 LPF, 346 rounding processing unit, 35 RGB panel (Front side LCD panel), 35b color filter substrate, 35c TFT substrate, 35a polarizing film, 36 LV panel (rear side LCD panel), 36a glass substrate, 36b TFT substrate, 36c polarizing film, 37 backlight Unit, 37a Light guide panel, 37b Light source, 38 Lamination, 3321, 3322, 3323 First lookup table, 3324, 3325, 3326 Second lookup table, 3421 Third lookup table.

Claims (7)

The image display device is configured by stacking two front side LCD panels and two rear side LCD panels, and performs image display by transmitting backlight light in the order of the rear side LCD panel and the front side LCD panel. And
An RGB gradation conversion circuit and a color balance controller are provided to generate an RGB image signal after color balance correction from an RGB image signal based on the input RGB image signal, and after the color balance correction to the front side LCD panel A first controller for supplying a RGB image signal of
Signal processing is performed on the RGB image signal based on the input RGB image signal to generate a gray image signal after the signal processing, and the gray image signal after the signal processing is supplied to the rear LCD panel. A second controller;
With
The RGB gradation conversion circuit includes a first lookup table that performs first gradation conversion on an RGB image signal and a second lookup table that performs second gradation conversion on the RGB image signal. The first gradation conversion is performed by applying the first look-up table to the RGB image signal based on the input RGB image signal and performing the first gradation conversion. The second gradation conversion is performed by generating the RGB image signal after gradation conversion and applying the second lookup table to the RGB image signal based on the input RGB image signal to perform the second gradation conversion. Generate a color balance correction image signal after gradation conversion,
The color balance controller further includes a luminance ratio obtained by dividing each of the image signals for color balance correction after the second gradation conversion generated individually for RGB by the gray image signal after the signal processing. By multiplying an adjustment function whose value range is 0 to 1, RGB individual correction coefficients are calculated, and the RGB image signal after the first gradation conversion is multiplied by the RGB individual correction coefficients. An image display device that generates an RGB image signal after the color balance correction.   The RGB individual correction coefficients are calculated by multiplying the luminance ratio by the adjustment function obtained by subtracting a predetermined value from 1, and further adding the predetermined value. 2. The image display device according to 1.   The image display device according to claim 2, wherein the predetermined value is not less than 0.5 and not more than 0.75.   The image display apparatus according to claim 1, wherein the adjustment function receives the gray image signal after the signal processing as an input, and an output value changes depending on the input value.   The image display apparatus according to claim 4, wherein the adjustment function gradually decreases as the input value increases from 0, and gradually increases as the input value approaches a maximum value.   6. The image according to claim 4, wherein when the input value is expressed by 8 bits, the adjustment function monotonously decreases when the input value is 0 or more and 64 or less, and monotonically increases when the input value is 194 or more and 255 or less. Display device. Constructed by stacking two front and rear LCD panels, and executed by an image display device that displays images by transmitting backlight light in the order of the rear LCD panel and the front LCD panel. An image display method,
An RGB image signal after color balance correction is generated by performing RGB gradation conversion processing and color balance correction processing on the RGB image signal based on the input RGB image signal,
Generate a gray image signal after signal processing by applying signal processing to the RGB image signal based on the input RGB image signal,
Supply the RGB image signal after color balance correction to the front LCD panel,
Supply the gray image signal after the signal processing to the rear LCD panel,
In the RGB gradation conversion processing, a first lookup table for performing first gradation conversion on the RGB image signal and a first lookup table for the RGB image signal, which are individually stored for each of the RGB colors. By applying the first look-up table to the RGB image signal based on the input RGB image signal by the second look-up table for performing the two-tone conversion, the first tone conversion is performed by applying the first look-up table. An RGB image signal after one gradation conversion is generated, and the second gradation conversion is performed by applying the second lookup table to the RGB image signal based on the input RGB image signal. Generate an image signal for color balance correction after two-tone conversion,
In the color balance correction process, each of the image signals for color balance correction after the second gradation conversion generated individually for RGB is divided by the gray image signal after the signal processing with respect to the luminance ratio obtained. Further, an RGB individual correction coefficient is calculated by multiplying an adjustment function whose value range is 0 to 1, and the RGB image signal after the first gradation conversion is multiplied by the RGB individual correction coefficient. , Image display method.