KR101989526B1 - Image Display Device And Method Of Displaying Image - Google Patents

Abstract

An object of the present invention is to improve the reproducibility of local luminance of an image even if each dimming block of the local dimming technique does not emit light with the same luminance distribution.
The image display device includes a front LCD panel displaying an RGB image, a rear LCD panel displaying a gray image, and a backlight unit that can adjust the luminance of each of the plurality of blocks. Furthermore, the image display device includes a block luminance value determiner for determining the luminance of each block from an RGB image signal, a backlight drive signal generator for adjusting the luminance of each block, and a local for estimating the emission luminance value of each pixel or each sub-pixel. A luminance value estimator, a level converter for adjusting the luminance level of the subpixel of the RGB image signal based on the estimated luminance of each pixel or each subpixel, and a rear side based on the luminance level of the subpixel adjusted in the level converter And a gray converter for controlling the luminance level of the gray image displayed on the LCD panel.

Description

Image Display Device And Method Of Displaying Image

The present invention relates to an image display apparatus and an image display method capable of improving the contrast ratio and the reproducibility of local luminance.

In recent years, high dynamic range (HDR) images have been proposed which have greatly improved luminance and contrast ratios. With regard to HDR, standardization is being carried out, such as ST2084 according to SMPTE, the so-called Dolby Vision or HLG (Hybrid Log Gamma) developed mainly by NHK and the BBC. The image display device is required to display in accordance with standardization.

In the organic EL panel, a contrast ratio of about 1,000,000: 1 is realized. However, in the case of a liquid crystal display (LCD), since the image of the backlight is transmitted through the LCD panel, an image is displayed. In particular, a so-called black floating phenomenon occurs in which the gradation characteristics of the black region are poor and the luminance is observed in a bright direction compared to the ideal luminance. Therefore, in the conventional LCD image display device, the contrast ratio is about 1,500: 1, for example.

In order to improve the contrast ratio of an LCD image display apparatus, the image display apparatus using two LCD panels is proposed (for example, refer patent document 1). In this image display device, the rear LCD panel (LV: Light Valve) displays a gray image to adjust the amount of backlight transmission, and the front LCD panel (RGB panel) displays an RGB image to improve the contrast ratio.

Patent Document 1: Japanese Patent Application Laid-Open No. 2016-118690

However, for the LCD image display device, it is desirable to further improve the contrast ratio.

For example, by applying the backlight's local dimming technology, black floating in dark blocks is greatly reduced. The local dimming technique is a technique for individually adjusting the luminance of each of the dimming blocks constituting the screen, in which the transmittance of the LCD panel is controlled under the premise that one dimming block emits light with the same luminance distribution. In reality, however, it is difficult to make one dimming block emit light with the same luminance distribution, so that local accuracy of the image, in particular, reproducibility of luminance may be inferior.

It is therefore an object of the present invention to provide an image display apparatus and an image display method capable of increasing local reproducibility of local luminance of an image while applying a local dimming technique while each dimming block does not emit light with the same luminance distribution.

An image display apparatus according to the present invention includes a front LCD panel displaying an RGB image, a rear LCD panel disposed behind the front LCD panel and superimposed on the front LCD panel to display a gray image, and the rear LCD panel. A backlight unit disposed at a rear side and irradiating light to the front LCD panel and the rear LCD panel, the backlight unit capable of adjusting luminance of each of a plurality of blocks, and a block luminance value for determining a desired luminance of each of the blocks from an input RGB image signal; A determiner, a backlight drive signal generator for driving the backlight unit to adjust the luminance of the block in accordance with the desired luminance of each of the blocks determined by the block luminance value determiner, and determined by the block luminance value determiner On the basis of the desired luminance of each of the blocks, when each block emits light at the desired luminance, A local luminance value estimator for estimating the light emission luminance of each sub pixel and a sub-pixel of the RGB image signal corresponding to the pixel or sub pixel based on the light emission luminance of each pixel or each sub pixel estimated by the local luminance value estimator; A level converter which adjusts the luminance level of the pixel, and a gray converter which generates a gray image signal which controls the luminance level of the gray image displayed on the rear LCD panel based on the luminance level of the subpixel adjusted by the level converter. Equipped.

Preferably, the block luminance value determiner determines the desired luminance of the block based on the maximum luminance among the luminance of the subpixels in each block of the input RGB image signal.

Preferably, the local luminance value estimator is a storage device that stores typical luminance distribution data in the block, in the block adjacent to the block or in the entire display area when light is emitted only from the block for each block, and the typical luminance distribution. You may have a calculator which calculates the luminous luminance of each pixel or each sub-pixel from the data and the desired luminance of each block.

Alternatively, the local luminance value estimator includes a storage device that stores typical luminance distribution data in the block, in the block adjacent to the block, or the entire display area when light is emitted only from the block, and the typical luminance distribution data. A data interpolator for interpolating to generate detailed luminance distribution data, and a calculator for calculating light emission luminance of each pixel or subpixel from the detailed luminance distribution data and the desired luminance of each block may be provided.

Or the local luminance value estimator is a distribution characteristic generator for generating typical luminance distribution data in the block, in the block adjacent to the block, or in the entire display area when light is emitted from only the block for each block using a calculation formula; You may be provided with the calculator which calculates the light emission luminance of each pixel or each sub pixel from typical luminance distribution data and the desired luminance of each block.

Preferably, the level converter increases the luminance level of the subpixel of the RGB image signal corresponding to the pixel or subpixel as the emission luminance of each pixel or each subpixel estimated by the local luminance value estimator is lower. .

Preferably, the gray converter determines the maximum luminance level among the luminance levels of the plurality of subpixels of each pixel as the luminance level of the gray image of the pixel.

Preferably, the image display device further comprises an RGB gray scale converter for correcting the gray level of the RGB image signal whose luminance level is adjusted in the level converter so as to be suitable for the output characteristics of the front LCD panel, wherein the RGB gray scale converter includes: The gray level of the RGB image signal is corrected based on the luminance of light emitted from each pixel or each sub-pixel estimated by the local luminance value estimator.

Preferably, the RGB gradation converter comprises a gradation converter corresponding to each color of RGB, and each gradation converter is a number smaller than the number of steps of emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator. Interpolates a plurality of lookup tables, a selector for selecting two of the plurality of lookup tables according to the emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator, and the values of two lookup tables selected by the selector And an interpolator for obtaining the gradation of the image signal.

Preferably, the RGB tone converter comprises a tone converter corresponding to each color of RGB, and each tone converter includes a first calculator, a second calculator, and an interpolator, and each of the first calculator and the second calculator is a plurality of. A coefficient value memory, wherein each coefficient value memory stores a coefficient value less than half of the number of steps of light emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator, and the local value; A selector for selecting one coefficient value from each of the plurality of coefficient value memories according to the light emission luminances of each pixel or each sub-pixel estimated by the luminance value estimator, and arithmetic processing based on the plurality of coefficient values selected by the selector; And an interpolator, wherein the interpolator includes arithmetic processing results of the arithmetic operation calculator of the first arithmetic unit and arithmetic operation of the arithmetic operator of the second arithmetic unit. The result of the processing is interpolated to obtain the gradation of the image signal.

Preferably, the image display device further includes a gray tone converter for correcting the gray level of the gray image signal generated by the gray converter to be suitable for an output characteristic of the rear LCD panel, wherein the gray tone converter includes the local luminance. The gray level of the gray image signal is corrected based on the light emission luminance of each pixel or each sub pixel estimated by the value estimator.

Preferably, the gray scale converter includes a plurality of lookup tables smaller than the number of steps of the emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator, and each pixel or estimated by the local luminance value estimator. And a selector for selecting two of the plurality of lookup tables according to the light emission luminance of each subpixel, and an interpolator for interpolating the values of the two lookup tables selected by the selector to obtain the gray level of the gray image signal.

Preferably, the gray scale converter includes a first calculating unit, a second calculating unit, and an interpolator, and each of the first calculating unit and the second calculating unit is a plurality of coefficient value memories, and each coefficient value memory is configured in the local luminance value estimator. A plurality of coefficient value memories, each having a coefficient value less than half of the number of steps of the estimated luminance of each pixel or subpixel, and the luminance of each pixel or subpixel estimated by the local luminance value estimator; Therefore, a selector for selecting one coefficient value from each of the plurality of coefficient value memories and a conversion calculator for performing arithmetic processing based on the plurality of coefficient values selected by the selector, wherein the interpolator includes a transform of the first calculation unit. The gray level of the image signal is obtained by interpolating the calculation processing result of the calculator and the calculation processing result of the conversion calculator of the second calculation unit.

An image display method according to the present invention comprises a front LCD panel displaying an RGB image, a rear LCD panel disposed behind the front LCD panel and superimposed on the front LCD panel to display a gray image, and the rear LCD panel. An image display method performed in an image display device which is disposed at a rear side and has a backlight unit that irradiates light on the front LCD panel and the rear LCD panel, and has a backlight unit capable of adjusting luminance of each of a plurality of blocks, the input RGB image signal Determining the desired luminance of each of the blocks from the; and driving the backlight unit to adjust the luminance of the block according to the desired luminance of each of the determined blocks; Luminance luminance of each pixel or each sub-pixel when each block emits light at the desired luminance based on the luminance Estimating, and adjusting the luminance level of the subpixel of the RGB image signal corresponding to the pixel or subpixel, based on the estimated luminance of each pixel or subpixel, and the luminance of the adjusted subpixel. Based on the level, generating a gray image signal for controlling the luminance level of the gray image displayed on the rear LCD panel.

In the present invention, a local dimming technique is applied to an image display device having a front LCD panel displaying an RGB image and a rear LCD panel displaying a gray image, and each pixel or each sub is based on a desired luminance of each block. Estimating the luminance of the pixel, adjusting the luminance level of the subpixel of the RGB image signal corresponding to the pixel or subpixel, and based on the adjusted luminance level of the subpixel, the luminance of the gray image displayed on the rear LCD panel A gray image signal for controlling the level is generated. Thereby, even if each dimming block does not emit light with the same luminance distribution, it is possible to improve the reproducibility of the local luminance of the image.

1 is a schematic side view of an image display device according to an embodiment of the present invention.
FIG. 2 is a schematic plan view of the backlight unit showing the LED arrangement of the image display device of FIG. 1.
FIG. 3 is a schematic diagram showing a relationship between a block, a pixel, and a sub pixel in the image display device of FIG. 1.
4 is a graph showing the luminance distribution of each block in the image display device of FIG. 1.
5 is a block diagram illustrating a signal processing unit of the image display device of FIG. 1.
6 is a block diagram illustrating a detailed example of a local luminance value estimator of the signal processor of FIG. 5.
FIG. 7 is a block diagram illustrating another detailed example of the local luminance value estimator of the signal processor of FIG. 5.
FIG. 8 is a block diagram illustrating another detailed example of the local luminance value estimator of the signal processor of FIG. 5.
9 is a graph illustrating an example of gray scale conversion characteristics of the RGB gray scale converter of the signal processor of FIG. 5.
FIG. 10 is a graph illustrating an example of gray scale conversion characteristics of the gray scale converter of the signal processor of FIG. 5.
11 is a graph for explaining the operation of the gray scale converter.
FIG. 12 is a block diagram illustrating details of an example of a gray scale converter or a color balance correction parameter generator of the signal processing unit of FIG. 5.
FIG. 13 is a block diagram illustrating details of another example of a gray scale converter or a color balance correction parameter generator of the signal processor of FIG. 5.
FIG. 14 is a block diagram illustrating details of another example of a gray scale converter or a color balance correction parameter generator of the signal processor of FIG. 5.
FIG. 15 is a schematic diagram illustrating a viewing angle correction result of an edge hold circuit of the signal processor of FIG. 5.
FIG. 16 is a block diagram illustrating details of a color balance controller of the signal processor of FIG. 5.
It is explanatory drawing about color balance adjustment in the dark part of an image according to the action of a color balance controller.
FIG. 18 is a diagram showing an example of a display image in which an image dimming apparatus including two LCD panels is applied, but local luminance value estimation is not performed.
19 is a diagram showing an example of a display image in which a local dimming technique is applied to an image display device having two LCD panels, and local luminance value estimation is performed in accordance with an embodiment of the present invention.

The objects, advantages and novel features of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. In other drawings, the same reference numerals are used to depict the same or functionally similar elements. It is to be understood that the drawings are schematically depicted and that the scale of the drawings is not accurate.

1 is a schematic side view of an image display device according to an embodiment of the present invention. FIG. 2 is a schematic plan view of the backlight unit showing the LED arrangement of the image display device of FIG. 1. As shown in FIG. 1, the image display device 1 includes a front LCD panel (RGB panel) 2, a rear LCD panel (LV panel) 3, and a backlight unit 4.

The front LCD panel 2 displays an RGB image. The front LCD panel 2 includes a color filter substrate 20, a TFT substrate 22, a polarizing film 24, a polarizing film 26, and a driving IC 28. Although not shown, a liquid crystal is disposed between the color filter substrate 20 and the TFT substrate 22. The color filter substrate 20 has a black matrix and R, G, B color filters, and further has a common electrode. The TFT substrate 22 has a TFT (Thin Film Transistor) and an electrode. The polarizing film 24 is disposed in front of the color filter substrate 20, and the polarizing film 26 is disposed in the rear of the TFT substrate 22. The driver IC 28 is mounted on the TFT substrate 22 and controls the transmission state of the liquid crystal of the front LCD panel 2 for each subpixel (subpixel) in accordance with the RGB image signal input to the driver IC 28. do.

The rear LCD panel 3 is disposed behind the front LCD panel 2 and superimposed on the front LCD panel 2 to display a gray image (LV image). The rear LCD panel 3 includes a glass substrate 30, a TFT substrate 32, a polarizing film 34, and a driving IC 36. Although the glass substrate 30 corresponds to the color filter substrate 20 in the front LCD panel 2 and has a common electrode, unlike the color filter substrate 20, it does not have a color filter. This is because the rear LCD panel 3 displays an LV image, i.e., a gray scale image expressed only in contrast from white to black. Although not shown, a liquid crystal is disposed between the glass substrate 30 and the TFT substrate 32. The TFT substrate 32 has a TFT and an electrode. The polarizing film 34 is disposed on the rear surface of the TFT substrate 32. The driver IC 36 is mounted on the TFT substrate 32 and controls the transmission state of the liquid crystal of the rear LCD panel 3 in accordance with the gray image signal input to the driver IC 36. The front LCD panel 2 and the rear LCD panel 3 are joined by a bonding layer 38 disposed between the polarizing film 26 and the glass substrate 30.

The backlight unit 4 is disposed behind the rear LCD panel 3 and irradiates light to the front LCD panel 2 and the rear LCD panel 3. The backlight unit 4 is a direct type and has sidewalls surrounding the LEDs 42 in cooperation with the substrate 40, a plurality of flat LEDs 42 mounted on the substrate 40, and the substrate 40. 44 is provided. The LED 42 is provided away from a desired distance from the rear LCD panel 3. Light emission of the LED 42 is controlled by the LED driver 46. The LED driver 46 may be mounted on the substrate 40 as a circuit, or may be mounted on a substrate different from the substrate 40.

As shown in FIG. 2, the LEDs 42 are assumed to have a rectangular shape and are spaced apart from each other so that the gaps between the LEDs 42 are in a lattice form. However, the shape, number and arrangement of the LEDs 42 are not limited to those shown. For example, the shape of the LED 42 may be circular.

The backlight unit 4 may adjust the luminance of each of the plurality of blocks so as to perform local dimming. The plurality of LEDs 42 correspond to the plurality of dimming blocks of local dimming, respectively. That is, one LED 42 corresponds to one dimming block. The LED driver 46 independently emits the plurality of LEDs 42 and independently adjusts the luminance of the plurality of LEDs 42. Although not shown, the backlight unit 4 may be provided with a known partition, a known lens, and a known platter. By controlling the light emission of the LED 42, the luminance of the dimming block corresponding to the LED 42 can be adjusted.

However, the backlight unit 4 is not limited to the direct type shown in the drawing. For example, the backlight unit 4 may be used in the present invention as long as it can perform local dimming that can adjust the luminance of each of the plurality of blocks even in the edge light type.

3 shows the relationship between blocks, pixels, and subpixels in the image display device. As described above, one LED 42 of the backlight unit 4 corresponds to one dimming block BL. One dimming block BL includes a plurality of pixels PX. In the rear LCD panel 3, the luminance of each pixel PX of the gray image can be adjusted. In the front LCD panel 2, the luminance of each sub-pixel SP of RGB tricolor can be adjusted. In this specification, the luminance described with respect to the panels 2 and 3 means the transmittance of the panels 2 and 3.

4 is a graph showing the luminance distribution in each block of the image display device of FIG. 1. Fig. 4A shows an ideal distribution state of luminance. In this abnormal state, one dimming block BL emits light with the same luminance distribution, and there is no light leakage from one dimming block BL to another dimming block BL. 4B shows the luminance distribution state in the case of carrying out the advanced optical design. In the case of carrying out an advanced optical design, a distribution close to that of Fig. 4A is obtained. Fig. 4C shows a state of distribution of luminance when no high optical design is performed. When no high optical design is performed, one dimming block BL emits light with an uneven luminance distribution, and there are many light leaks from one dimming block BL to another dimming block BL.

The high optical design provides at least one of a partition wall separating the blocks BL from each other, a lens and a platter for equalizing the luminance distribution in the block. However, installing them incurs increased costs as the development period and parts count increase. Even if these are provided, it is difficult or impossible to obtain an ideal distribution of luminance.

Embodiment of this invention aims at improving the reproducibility of the local luminance of an image, even if each dimming block does not emit light with the same luminance distribution.

5 shows the image data supplied to the drive IC 28 of the front LCD panel 2 of the image display device 1 and the drive IC 36 of the rear LCD panel 3 and the backlight unit 4. The signal processing part 5 which produces | generates the control data supplied to the LED drive part 46 is shown. The signal processing unit 5 is supplied with RGB image signals R, G, and B having a signal level in linear relation with luminance via an EOTF (Electro-Optical Transfer Function).

The signal processing unit 5 includes a block luminance value determiner 50 that determines a desired luminance of each of the dimming blocks from the input RGB image signals R, G, and B. The block luminance value determiner 50 selects the desired luminance of the entire dimming block based on the maximum luminance BLmax among the luminance of each RGB subpixel in each dimming block of the input RGB image signals R, G, and B. Determine the luminance. Specifically, for example, the block luminance value determiner 50 may determine the maximum luminance BLmax in each dimming block as a desired luminance (block luminance value, BLum) of the entire dimming block. In this case, BLum = BLmax.

However, when the number n of steps of controllable brightness Lj for each dimming block of the backlight unit 4 is smaller than the number of steps of brightness that can be represented by the RGB image signal, the block brightness value determiner 50 determines that BLmax? The minimum Lj, which is Lj, is determined as the block luminance value BLum. That is, BLum = Lj ≧ BLmax. For example, it is assumed that the RGB image signal is 12-bit gray scale and 4096 gray scales can be expressed. In addition, it is assumed that the number of steps n of the controllable luminance Lj of the backlight unit 4 is 4 for local dimming. In this case, Lj ∈ {L1, L2,... , Ln} = {L1, L2, L3, L4}. For example, {L1, L2, L3, L4} = {1023, 2047, 3071, 4095}. In this case, if BLmax = 1020, BLum = 1023, and if BLmax = 3000, BLum = 3071. In this way, the block luminance value determiner 50 determines any one of the luminance that can be controlled for each dimming block as the block luminance value BLum.

However, the RGB image signal is not limited to 12-bit gradation, and the number n of steps of the controllable luminance Lj of the backlight unit 4 is not limited to four.

The block luminance value BLum output from the block luminance value determiner 50 is supplied to the delay circuit 52. The delay circuit 52 gives a fixed delay time to the block luminance value BLum. The block luminance value BLum output from the delay circuit 52 is supplied to the LED drive signal generator (backlight drive signal generator 54). The LED drive signal generator 54 adjusts the brightness of the dimming block in accordance with the block luminance value BLum (that is, the desired luminance of each of the dimming blocks determined by the block luminance value determiner 50). An LED drive signal BD for driving (4) is generated. The LED drive signal BD is supplied to the LED driver 46 of the backlight unit 4.

As a method in which the LED drive signal generator 54 adjusts the brightness of the dimming block, the LED drive signal generator 54 may control the voltage or current of the LED drive signal BD. However, the LED drive signal generator 45 may perform blinking of the LED 42 corresponding to the dimming block by, for example, a pulse width modulation (PWM) scheme. In this case, the LED drive signal BD is a pulse signal of a constant amplitude whose duty ratio changes in accordance with the desired luminance of the dimming block.

The signal processing unit 5 further includes a local luminance value estimator 55. When the local luminance value estimator 55 emits each dimming block at a desired luminance based on the desired luminance (block luminance value, BLum) of each dimming block determined by the block luminance value determiner 50, The light emission luminance value of the pixel or each sub pixel is estimated. The light emission luminance value here is a luminance value when the luminance adjustment of the panels 2 and 3 is not performed, that is, a luminance value when the transmittance of the panels 2 and 3 is maximum. The local luminance value estimator 55 outputs a local luminance value PLum showing the light emission luminances of each estimated pixel or each subpixel.

6 to 8 each show a detailed example of the local luminance value estimator 55. In the example shown in FIG. 6, the local luminance value estimator 55 stores a typical luminance distribution data (memory device 55A), typical luminance distribution data stored in the memory 55A, and desired dimming blocks. And a calculator 55B for calculating the light emission luminance value PLum of each pixel or each sub-pixel from the luminance (block luminance value BLum). The memory 55A may store typical luminance distribution data showing typical luminance distribution in the block and in the block adjacent to the block when light is emitted only from the block for each block, or in the case of emitting light only from the block for each block. Typical luminance distribution data showing typical luminance distribution in the entire display area may be stored. The calculator 55B can calculate the light emission luminance value PLum, that is, PLum (x, y), for example, according to the following equation. Where x is the x coordinate of the pixel or subpixel and y is its y coordinate.

Where α _{[i, j]} (X, Y) is the luminance distribution for the dimming block [i, j], where the relative position of the representative point (or reference point) of the dimming block and the pixel or subpixel (x, y) It is a function of the relationship. α _{[i, j]} (X, Y) has no dependence on BLum values or is negligible.

x0 _{[i, j]} and y0 _{[i, j]} are coordinates showing the position of the representative point (or reference point) in the dimming block [i, j]. The representative point (or reference point) is, for example, the center of the dimming block or the position of the upper left angle.

BLum [i, j] is a luminance value BLum in the dimming block [i, j] and changes depending on the image to be displayed.

[Alpha] _{[i, j]} (X, Y), x0 _{[i, j]} , y0 _{[i, j]} are fixed irrespective of the image.

The above formula is determined in consideration of the influence of PLum (x, y) from the light from the plurality of dimming blocks, and thus the sum is obtained. The range of dimming blocks for which the sum is obtained can be arbitrarily selected according to the diffusion method of the luminance distribution α. For example, the dimming block for which the sum is obtained when the spread of the luminance distribution α is small may be a dimming block to which the pixel or subpixel for which PLum (x, y) is calculated and some dimming blocks adjacent thereto. If the spread of the luminance distribution α is large, the dimming block to be summed may be all dimming blocks.

The equation for calculating the single emission luminance value PLum is not limited to the above equation.

In order to implement the example of the local luminance value estimator 55 shown in FIG. 6, the luminance distribution α for calculating the local luminance value is obtained in advance for each pixel or each sub pixel of the image display device by measurement. The luminance distribution α is stored in the memory 55A.

In the example shown in FIG. 7, the local luminance value estimator 55 interpolates the detailed luminance distribution data stored in the memory (memory device 55C) and typical memory distribution data stored in the memory 55C, and stores the detailed luminance distribution. Luminance luminance of each pixel or each subpixel from data interpolator 55D for generating data, detailed luminance distribution data generated by data interpolator 55D, and desired luminance (block luminance value, BLum) of each dimming block. The calculator 55E calculates a value PLum. The memory 55C may store typical luminance distribution data showing typical luminance distribution in the block and in the block adjacent to the block when light is emitted only from the block for each block, or display when the light is emitted only from the block for each block. Typical luminance distribution data showing typical luminance distribution in the entire region may be stored.

The calculator 55E can calculate the light emission luminance value PLum according to the above formula, for example. In the example shown in FIG. 7, the luminance distribution α is included in the detailed luminance distribution data generated by the data interpolator 55D. The data interpolator 55D obtains detailed luminance distribution data from the typical luminance distribution data stored in the memory 55C according to the interpolation formula. Therefore, in the example shown in FIG. 7 rather than the example shown in FIG. 6, the typical luminance distribution data need not be detailed. That is, in the example shown in FIG. 6, the luminance distribution α for each pixel or each sub-pixel is recorded in the typical luminance distribution data. In the example shown in FIG. 7, for example, in the horizontal and / or vertical directions, the luminance distribution α is recorded. Luminance distribution α for a pixel (or a subpixel included therein) can be recorded in the typical luminance distribution data. The example shown in FIG. 7 is suitable for the case where the typical luminance distribution in the case of not bleeding is wide, and can be interpolated with less error, and saves the memory storage amount and suppresses the increase in the circuit scale than the example shown in FIG. can do.

In the example shown in FIG. 8, the local luminance value estimator 55 uses a distribution formula to generate typical luminance distribution data in each block, and the typical luminance generated by the distribution characteristic generator 55F. And an arithmetic unit 55G which calculates the emission luminance value PLum of each pixel or each subpixel from the distribution data and the desired luminance (block luminance value BLUM) of each dimming block. The distribution characteristic generator 55F may generate typical luminance distribution data showing typical luminance distribution in the block and in the block adjacent to the block when light is emitted only from the block for each block, or in the case of emitting light only from the block for each block. Typical luminance distribution data showing typical luminance distribution in the entire display area of may be generated.

The calculator 55G can calculate the light emission luminance value PLum, for example, according to the above formula. In the example shown in FIG. 8, the luminance distribution α is included in the typical luminance distribution data generated by the distribution characteristic generator 55F. The calculation formula used in the distribution characteristic generator 55F obtains the luminance distribution α by measurement in advance for each pixel or each subpixel of the image display device, and furthermore, the luminance distribution α and the position coordinates of the pixel or subpixel are Get a function that matches the relationship of This function may be used as a calculation formula used in the distribution characteristic generator 55F. In the peripheral block of the display area of the image, it is not easy to obtain a matching function due to the reflected light by the side wall 44, so that the error may be large. However, in the example shown in FIG. 8, as compared with the example of FIG. 6 and FIG. An increase in the circuit scale can be suppressed.

Returning to FIG. 5, the signal processing unit 5 further includes a level converter 56 and a delay circuit 58. The level converter 56 is based on the emission luminance (local luminance value, PLum) of each pixel or each sub-pixel estimated by the local luminance value estimator 55, and the RGB image signal R corresponding to the pixel or sub-pixel. , G, B) adjusts the luminance level of each sub-pixel. The delay circuit 58 supplies the RGB image signals R, G, and B supplied to the signal processing unit 5 with time and locality necessary for the determination of the block luminance value BLum in the block luminance value determiner 50. A considerable delay is given to the total time of the time required for estimating the local luminance value PLum in the luminance value estimator 55.

The level converter 56 indicates that the lower the emission luminance (local luminance value, PLum) of each pixel or each sub-pixel estimated by the local luminance value estimator 55 is, the lower each sub-element of the RGB image signal corresponding to the pixel or sub-pixel is. Increase the luminance level of the pixel. However, the level converter 56 adjusts the luminance level of each sub-pixel of the RGB image signal so that the higher the local luminance value PLum is, the smaller the rate of change of the luminance level of each sub-pixel is than the lower local luminance value PLum. Change. In addition, the level converter 56 adjusts the luminance level of each subpixel so that the luminance level of the subpixel output from the level converter 56 is proportional to the luminance level of the subpixel input to the level converter 56.

For example, the luminance level of the R subpixel input to the level converter 56 is R, the luminance level of the G subpixel input to the level converter 56 is G, and the B subpixel input to the level converter 56. The luminance level of is B, the luminance level of the R subpixel output from the level converter 56 is R1, the luminance level of the G subpixel output from the level converter 56 is G1, and is output from the level converter 56. When the luminance level of the B subpixel to be B1, the level converter 56 performs level conversion, that is, adjustment according to the following equation.

R1 = (LMX / PLum) * R

G1 = (LMX / PLum) * G

B1 = (LMX / PLum) * B

Here, LMX is the maximum value of the luminance which the RGB image signals R, G, and B can have, and according to the example (the RGB image signal is 12-bit gradation), for example, 4095.

The lower the local luminance value PLum is, the higher the luminance level of each sub pixel of the RGB image signal is. However, when the local luminance value PLum is high, the luminance of the pixel or sub pixel is increased by the backlight unit 4. According to the above equation, the luminance level of the output subpixel is proportional to the luminance level of the input subpixel. Therefore, even if each dimming block does not emit light with the same luminance distribution, the local luminance of the image can be reproduced in the display image.

The signal processing unit 5 further includes a gray converter 60. The gray converter 60 controls the luminance level of the gray image displayed on the rear LCD panel 3 based on the luminance levels R1, G1, B1 of the subpixels adjusted by the level converter 56. Generate signal W1. More specifically, the gray converter 60 sets the maximum luminance level among the luminance levels R1, G1, and B1 of the plurality of subpixels of each pixel, and the luminance of the gray image of the pixel (the pixel to which these subpixels belong). Decide as a level.

The signal processing unit 5 further includes a delay circuit 62 and an RGB gradation converter 64. The RGB image signals R1, G1, and B1 output from the level converter 56 are supplied to the delay circuit 62, and the delay circuit 62 supplies a predetermined delay time to the RGB image signals R1, G1, and B1. Grant. The RGB image signals R1, G1, and B1 output from the delay circuit 62 are supplied to the RGB gradation converter 64.

The RGB gradation converter 64 corrects the gradation of the RGB image signals R1, G1, B1 whose luminance level is adjusted in the level converter 56 so as to be suitable for the output characteristics of the front LCD panel 2. For example, the display characteristics of the front LCD panel 2 are gamma characteristics represented by gamma curves, and the RGB gradation converter 64 gamma-corrects the RGB image signals R1, G1, and B1. However, this display characteristic is not limited to the gamma characteristic, and the degree of correction is also not limited to gamma correction. In this embodiment, the RGB gradation converter 64 is configured to determine the RGB image signal based on the emission luminance (local luminance value, PLum) of each pixel or each sub-pixel estimated by the local luminance value estimator 55 as described later. Correct the gradation.

The signal processor 5 further includes a gray tone converter 66. The gray tone converter 66 corrects the gray level of the gray image signal W1 generated by the gray converter 60 to suit the output characteristics of the rear LCD panel 3. For example, the display characteristic of the rear LCD panel 3 is a gamma characteristic, and the gray scale converter 66 corrects the gray image signal W1 in consideration of the gamma characteristic. However, this display characteristic is not limited to the gamma characteristic, and the degree of correction is also not limited to gamma correction. In this embodiment, the gray scale converter 66 is a gray image signal based on the emission luminance (local luminance value, PLum) of each pixel or each sub-pixel estimated by the local luminance value estimator 55 as described later. The tone of (W1) is corrected.

The RGB gradation converter 64 has an R gradation converter 64R, a G gradation converter 64G, and a B gradation converter 64B. The R gradation converter 64R corrects the input signal R1 to R2 to output R2, and the G gradation converter 64G corrects the input signal G1 to G2 to output G2, and the B gradation converter 64B. Corrects the input signal B1 with B2 and outputs B2.

Further, the RGB gradation converter 64 obtains, from the input RGB image signals R1, G1, B1, color balance correction parameters L _R , L _G , L _B used in the color balance controller 70 described later. Has a role. Therefore, the RGB gradation converter 64 has a color balance correction parameter generator 64L _R , a color balance correction parameter generator 64L _G , and a color balance correction parameter generator 64L _B. The color balance correction parameter generator 64L _R obtains the color balance correction parameter L _R from the input signal R1, outputs the color balance correction parameter L _R , and the color balance correction parameter generator 64L _G , Obtains the color balance correction parameter L _G from the input signal G1 and outputs the color balance correction parameter L _G , and the color balance correction parameter generator 64L _B receives the color balance from the input signal B1. The correction parameter L _B is obtained and the color balance correction parameter L _B is output.

9 is a graph showing an example of the gradation conversion characteristic according to the RGB gradation converter 64 with a solid line, and FIG. 10 is a graph showing an example of the gradation conversion characteristic according to the gray gradation converter 66 with a solid line. 9 and 10 show linear characteristics by dashed lines for reference. 9 and 10, the horizontal axis represents the input luminance value for the RGB gradation converter 64 or the gray gradation converter 66, and the vertical axis represents the output luminance from the RGB gradation converter 64 or the gray gradation converter 66. Indicates a value.

An example of the gradation conversion characteristic according to the RGB gradation converter 64 shown in FIG. 9 is realized by, for example, a gamma curve Y = X ^{γ in} which γ = 0.5. In contrast, an example of the gradation conversion characteristic according to the gray gradation converter 66 shown in Fig. 10 is that two LCD panels 2 are changed while changing the LV value with respect to the RGB value fixed to cause the result of Fig. 9. And 3), the input and output characteristics of the LV are determined so that the final synthesized result is equivalent to the linear luminance characteristics of the natural system and therefore naturally visible to humans. By the gray scale conversion of the RGB gray converter 64 and the gray gray converter 66, the RGB image signal and the gray image signal are suitable for the output characteristics of the front LCD panel 2 and the rear LCD panel 3, Corrected to have a natural luminance gradation in the eye.

With reference to FIG. 11, operations based on the desired luminance (block luminance value, BLum) of each dimming block determined by the block luminance value determiner 50 according to the RGB gray scale converter 64 and the gray gray scale converter 66 will be described. Explain. Fig. 11A shows the basic characteristics (characteristics corresponding to Figs. 5 and 6) of the gradation converter. This basic characteristic is a characteristic (the characteristic shown in FIG. 11 (E)) when the backlight unit 4 emits light at the maximum luminance (for example, L4).

If the number n of the controllable luminance Lj of the backlight unit 4 is 4 and Lj ∈ {L1, L2, L3, L4}, the four-step characteristics of FIGS. 11 (B) to (E) may be used. have. The characteristic of FIG. 11 (B) is the characteristic which expanded the range from 0 to L1 of input of FIG. The characteristic of FIG. 11 (C) is the characteristic which expanded both the input shaft and the output shaft in the range whose input of FIG. 11 (A) is 0 to L2. The characteristic of FIG. 11 (D) is the characteristic which expanded both the input shaft and the output shaft in the range whose input of FIG. 11 (A) is 0 to L3. However, each curve shown in FIG. 11 is an example and is not limited to these.

Each gray scale converter corrects the gray level of the image signal according to the characteristic of FIG. 11B when the block luminance value BLum is L1, and corresponds to FIG. 11 (B) when the block luminance value BLum is L2, L3 or L4. C) The gradation of the image signal is corrected according to the characteristic of any of (E).

If the input of the basic characteristic is Vinput _org , 0? Vinput _org ? L4, and if the output of the basic characteristic is Voutput _org , Voutput _org = f (Vinput _org ). f is a function.

If the input of the other characteristic is Vinput, it can be expressed as 0 ≤ Vinput ≤ BLum, and if the output is called Voutput, Voutput uses the function gVoutput = g (Vinput) = (1 / f (BLum / L4)) * It can be expressed as f ((BLum / L4) * Vinput).

12 to 14, an example of each of the gradation converters 64R, 64G, 64B, 66 and the color balance correction parameter generator 64L _R , 64L _G , 64L _B will be described.

The number of steps h of the local luminance value PLum supplied to the gradation converters 64 and 66 is much larger than the number n of the controllable luminance Lj of the backlight unit 4 for local dimming. For example, although the number n of steps is not limited, four may be sufficient. On the other hand, for example, when the RGB image signal is 12-bit gray scale and 4096 gray scales can be expressed, the number of steps h of the local luminance value PLum is equal to the number of luminance gray scales 4096 that can be represented by the RGB image signal. Although not necessarily matched, it is ideally the number of luminance gray scales (4096).

When such a multi-level local luminance value PLum is input, for example, gradation conversion is performed by a lookup table method, the conventional idea is that the number of lookup tables or the number of coefficient values stored in the count value memory is the local luminance value PLum. The circuit scale becomes very large because it coincides with the number of steps h). Each example shown in FIG. 12 and FIG. 14 is studied in order to suppress a circuit scale increase.

12 is a block diagram showing details of examples of each of the tone converters 64R, 64G, 64B, 66 and the color balance correction parameter generators 64L _R , 64L _G , 64L _B. Each gradation converter or each color balance correction parameter generator has a plurality of lookup tables LUT1, LUT2, ..., LUTk, a selector 80, and an interpolator 81. The number k of lookup tables LUT1, LUT2, ..., LUTk is an integer greater than the number n of steps of controllable luminance Lj of the backlight unit 4 for local dimming, preferably n This is a multiple of two. The number k of steps is smaller than the number of steps of the local luminance value PLum (the number of steps of the emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator 55, h). If n is 4, Lj ∈ {L1, L2,... , Ln} = {L1, L2, L3, L4}, for example, ten lookup tables LUT1 to LUT10 may be used. However, k is not limited to 10 and may be 130, 258 or other numbers, for example.

Each lookup table corresponds to any one of the local luminance values PLum. However, since h> k, the steps of the local luminance values PLum corresponding to these lookup tables are discrete, and these steps in close proximity are h / (k-2) apart. For example, when h = 4096 and k = 10, the lookup table LUT1 corresponds to the lowest step 0, the lookup table LUT2 corresponds to step 511, the lookup table LUT3 corresponds to step 1023, and the lookup table LUT9 Corresponds to step 4095, and the lookup table LUT10 corresponds to step 4607.

The selector 80 is a signal (RGB image signals R1, G1, B1 or gray image signals W1) currently input to the gradation converter or the color balance correction parameter generator according to the input local luminance value PLum. The two lookup tables to be used for are selected from lookup tables LUT1, LUT2, ..., LUTk. When the local luminance value PLum is between two steps corresponding to two lookup tables, the selector 80 selects these two lookup tables. According to the example where h = 4096 and k = 9, the selector 80 selects, for example, a lookup table LUT3 corresponding to step 1023 and a lookup table LUT4 corresponding to step 1535 when PLum = 1050. If PLum = 3091, the lookup table LUT7 corresponding to step 3071 and the lookup table LUT8 corresponding to step 3583 are selected.

When the local luminance value PLum matches one step corresponding to one lookup table, the selector 80 selects the lookup table and the lookup table corresponding to the immediately above step. For example, the selector 80 selects the lookup table LUT3 corresponding to step 1023 and the lookup table LUT4 corresponding to step 1535 when PLum = 1023, and the lookup table LUT7 corresponding to step 3071 when PLum = 3071, and Select the lookup table LUT8 that corresponds to 3583.

That is, the selector 80 when the step of the luminance value corresponding to one lookup table is L (i), the step immediately above it is L (i + 1), and L (i) ≤ PLum ≤ L (i + 1). ) Selects the values O (i) and O (i + 1) of the two lookup tables corresponding to steps L (i) and L (i + 1), respectively.

The interpolator 81 corrects the luminance value of the input signal in accordance with the selected lookup table. Specifically, the output luminance value Vout of the signal is obtained according to the following interpolation formula, and the luminance value Vout is output. That is, the interpolator 81 interpolates the values of the two lookup tables selected by the selector 80 to obtain the gray level of the image signal.

Vout = (PLum-L (i)) * O (i + 1) + (L (i + 1) -PLum) * O (i)) / (L (i + 1) -L (i))

In this way, the R gray scale converter 64R corrects the input signal R1 to R2 and outputs R2. The G gray scale converter 64G corrects the input signal G1 to G2 to output G2, and the B gray scale converter. 64B corrects the input signal B1 to B2 and outputs it, and the gray-scale converter 66 corrects the input gray image signal W1 to W2 and outputs W2. The color balance correction parameter generator 64L _R obtains the color balance correction parameter L _R from the input signal R1 and outputs the color balance correction parameter L _R , and the color balance correction parameter generator 64L _G receives the color from the input signal G1. The balance correction parameter L _G is obtained and the color balance correction parameter L _G is output, and the color balance correction parameter generator 64L _B obtains the color balance correction parameter L _B from the input signal B1 and outputs the color balance correction parameter L _B. The contents of the lookup table differ depending on the type of the gradation converter or the color balance correction parameter generator.

FIG. 13 is a block diagram showing details of other examples of each of the tone converters 64R, 64G, 64B, 66 and the color balance correction parameter generators 64L _R , 64L _G , 64L _B. The example of FIG. 13 may be used instead of the example of FIG. 12.

As shown in Fig. 13, each gray scale converter or each color balance correction parameter generator includes a plurality of selectors 82a to 82m and a plurality of count value memories 84a to 84m respectively corresponding to the selectors 82a to 82m. And a conversion operator 86. Each of the coefficient value memories 84a to 84m is equal to the number of steps of the local luminance value PLum (the number of steps of the emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator 55, h) The count value is stored (for example, count values A ₁ to A _h ).

Each of the selectors 82a to 82m is a signal (RGB image signals R1, G1, B1) or gray image signal W1 currently input to the gradation converter or the color balance correction parameter generator according to the local luminance value PLum. The coefficient to be used in accordance with)) is selected from the coefficient value memory corresponding to the selector. For example, the selector 82a selects any of the count values A ₁ to A _h from the count value memory 84a, and the selector 82m selects the count values M ₁ to M from the count value memory 84m. _h ). The conversion operator 86 uses the coefficient values A (any of A ₁ to A _h ) to M (any of M ₁ to M _h ) selected by the selectors 82a to 82m to calculate the luminance value of the input signal. Calibrate

For example, the conversion operator 86 converts the luminance value Vin of the input signal (RGB image signals R1, G1, B1 or gray image signal W1) into the output luminance value Vout according to the following equation. Correction is performed to obtain output signals R2, G2, B2, W1, L _R , L _G or L _B.

Vout = A * Vin + B * Vin ² + C * Vin ³ +... + M * Vin ^m

M is the number of selectors 82a-82m, for example, is an integer of 4 or more.

Alternatively, the conversion operator 86 may correct the luminance value Vin of the input signal with the output luminance value Vout according to the following equation to obtain an output signal.

Vout = A * (Vin / BLum) + B * (Vin / BLum) ² + C * (Vin / BLum) ³ +. + M * (Vin / BLum) ^m

M is the number of selectors 82a-82m, for example, is an integer of 4 or more.

In this way, the R gray scale converter 64R corrects the input signal R1 to R2 and outputs R2. The G gray scale converter 64G corrects the input signal G1 to G2 and outputs G2. The B gray scale converter ( 64B) corrects the input signal B1 to B2, and outputs it. The gray scale converter 66 corrects the input gray image signal W1 to W2 and outputs W2. The color balance correction parameter generator 64L _R obtains the color balance correction parameter L _R from the input signal R1 and outputs the color balance correction parameter L _R , and the color balance correction parameter generator 64L _G receives the color from the input signal G1. The balance correction parameter L _G is obtained and the color balance correction parameter L _G is output, and the color balance correction parameter generator 64L _B obtains the color balance correction parameter L _B from the input signal B1 and outputs the color balance correction parameter L _B. The contents of the selectors 82a to 82m, the coefficient value memories 84a to 84m, and the conversion calculator 86 vary depending on the type of the gradation converter or the color balance correction parameter generator.

However, in the example shown in Fig. 13, each of the coefficient value memories 84a to 84m has the number of steps of the local luminance value PLum (emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator 55). The circuit scale becomes very large because the number of steps equal to h) is stored. The example shown in FIG. 14 suppresses the circuit scale increase.

14 is a block diagram showing details of other examples of each of the tone converters 64R, 64G, 64B, 66 and the color balance correction parameter generators 64L _R , 64L _G , 64L _B. You may use the example of FIG. 14 instead of the example of FIG. 12 and FIG.

As shown in Fig. 14, each gradation converter or each color balance correction parameter generator includes a first calculating unit 90, a second calculating unit 91, and an interpolator 98. The first calculation unit 90 includes a plurality of selectors 92a to 92m, a plurality of coefficient value memories 93a to 93m corresponding to the selectors 92a to 92m, and a conversion calculator 96, respectively. The second calculation unit 91 includes a plurality of selectors 94a to 94m, a plurality of coefficient value memories 95a to 95m corresponding to the selectors 94a to 94m, and a conversion calculator 97, respectively.

Each of the coefficient value memories 93a to 93m of the first calculating unit 90 includes the number of steps of the local luminance value PLum (the stage of the light emission luminance of each pixel or each sub-pixel estimated by the local luminance value estimator 55). Much less than half of the number h is stored (for example, count values A ₁ , A ₃ , and A _f ). Each of the coefficient value memories 95a to 95m of the second calculation unit 91 also stores a number of coefficient values much smaller than half of the number of steps h of the local luminance value PLum (for example, the coefficient value). A ₂ , A ₄ , ~ A _{f + 1} ).

Each of these coefficient values corresponds to any one step of the local luminance value PLum. However, since h >> f + 1, the steps of the local luminance values PLum corresponding to these coefficient values are discrete, and these steps in close proximity are h / (k-2) apart. For example, when h = 4096 and k = 9, the count value A ₁ corresponds to the lowest step 0, the count value A ₂ corresponds to step 511, and the count value A ₃ corresponds to step 1023, The count value A _f corresponds to 4095 and the count value A _{f + 1} corresponds to 4607.

Each of the selectors 92a to 92m is a signal (RGB image signals R1, G1, B1) or gray image signal W1 currently input to the gradation converter or the color balance correction parameter generator according to the local luminance value PLum. The coefficient to be used for)) is selected from the coefficient value memory corresponding to the selector. For example, the selector 92a selects any one of the count values A ₁ , A ₃ , and A _f from the count value memory 93a, and the selector 92 m is selected from the count value memory 93 m. One of the coefficient values M ₁ , M ₃ , and M _f is selected. Each of the selectors 92a to 92m selects the coefficient value corresponding to the step closest to the local luminance value PLum equal to or less than the local luminance value PLum.

The conversion operator 96 uses the coefficient values A (any of A ₁ , A ₃ , and A _f ) to M (M ₁ , M ₃ , and M _f ) selected by the selectors 92a to 92m. To perform arithmetic processing. For example, the conversion operator 96 obtains the calculation value Vcal1 from the luminance value Vin of the input signal (RGB image signals R1, G1, B1 or gray image signal W1) according to the following equation. .

Vcal1 = A * Vin + B * Vin ² + C * Vin ³ +... + M * Vin ^m

M is the number of selectors 92a-92m, for example, is an integer of 4 or more.

Alternatively, the conversion operator 96 may obtain the calculation value Vcal1 from the luminance value Vin of the input signal according to the following equation.

Vcal1 = A * (Vin / BLum) + B * (Vin / BLum) ² + C * (Vin / BLum) ³ +. + M * (Vin / BLum) ^m

Similarly, each of the selectors 94a to 94m determines a coefficient to be used for the signal currently input to the gradation converter or the color balance correction parameter generator according to the local luminance value PLum, and a coefficient value corresponding to the selector. Select from memory. For example, the selector 94a selects any one of the count values A ₂ , A ₄ , and ˜A _{f + 1} from the count value memory 93a, and the selector 94m selects the count value memory 93m. Select one of the coefficient values (M ₂ , M ₄ , ~ M _{f + 1} ) from Each of the selectors 94a to 94m selects a coefficient value corresponding to a step larger than the local luminance value PLum and closest to the local luminance value PLum.

The conversion operator 97 selects any of the coefficient values A (A ₂ , A ₄ , ~ A _{f + 1} ) ~ M (M ₂ , M ₄ , ~ M _{f + 1} selected by the selector 94a-94m). To perform arithmetic processing. For example, the conversion operator 97 obtains the calculation value Vcal2 from the luminance value Vin of the input signal (RGB image signals R1, G1, B1 or gray image signal W1) according to the following equation. .

Vcal2 = A * Vin + B * Vin ² + C * Vin ³ +... + M * Vin ^m

M is the number of selectors 94a-94m, for example, is an integer of 4 or more.

Alternatively, the conversion calculator 97 may obtain the calculation value Vcal2 from the luminance value Vin of the input signal according to the following equation.

Vcal2 = A * (Vin / BLum) + B * (Vin / BLum) ² + C * (Vin / BLum) ³ +. + M * (Vin / BLum) ^m

The interpolator interpolates the calculation processing result (operation value Vcal1) of the conversion operator 96 of the first calculation unit 90 and the calculation processing result (operation value Vcal2) of the conversion operator 97 of the second calculation unit 91, The gray level of the image signal is obtained.

In this way, the R gray scale converter 64R corrects the input signal R1 to R2 and outputs R2. The G gray scale converter 64G corrects the input signal G1 to G2 and outputs G2. The B gray scale converter ( 64B) corrects the input signal B1 to B2, and outputs it. The gray scale converter 66 corrects the input gray image signal W1 to W2 and outputs W2. The color balance correction parameter generator 64L _R obtains the color balance correction parameter L _R from the input signal R1 and outputs the color balance correction parameter L _R , and the color balance correction parameter generator 64L _G receives the color from the input signal G1. The balance correction parameter L _G is obtained and the color balance correction parameter L _G is output, and the color balance correction parameter generator 64L _B obtains the color balance correction parameter L _B from the input signal B1 and outputs the color balance correction parameter L _B. The contents of the selectors 92a to 92m, 94a to 94m, the coefficient value memories 93a to 93m, 95a to 95m, and the conversion operators 96 and 97 vary depending on the type of the gradation converter or the color balance correction parameter generator. .

Although the example shown in FIG. 14 has almost the same result as the example shown in FIG. 13, it is possible to suppress an increase in circuit scale than the example shown in FIG. 13.

Returning to FIG. 5, the RGB image signals R2, G2, B2 and the color balance correction parameters L _R , L _G , L _B output from the RGB gray scale converter 64 are supplied to the color balance controller 70. The gray image signal W2 output from the gray scale converter 66 is supplied to the edge hold circuit 68.

The edge hold circuit 68 performs viewing angle correction (local edge hold processing) on the gray image signal W2 after the gray level conversion, and generates the gray image signal W3. The gray image signal W3 is supplied to the drive IC 36 of the rear LCD panel 3. With respect to the two LCD panels 2 and 3, there is no problem when viewed from the front, but due to the panel thickness when viewed from the diagonal direction, the display image of the front LCD panel 2 and the display image of the rear LCD panel 3 are different. There is a problem that a color image shift is seen from a double image by shifting the position along the angle. In order to solve this problem, the edge hold circuit 68 plays a role of performing a viewing angle correction on the gray image.

15 is a schematic diagram showing the results of the viewing angle correction (local edge hold processing) by the edge hold circuit 68. As shown in FIG. Each white circle in FIG. 15 corresponds to the luminance value of each pixel in the output image from the gray scale converter 66. In addition, the dark circle in FIG. 15 corresponds to the luminance value of the edge hold process pixel.

By performing the local edge hold processing as shown in Fig. 15, the luminance value of the dark pixel in the vicinity of the dark pixel is replaced by the luminance value of the pixel of the image at the boundary (edge) with the dark portion. By performing the correction to improve the luminance of the dark pixels adjacent to the light in this manner, it is possible to prevent the image from darkening when viewed from the diagonal direction.

The specific structure and the specific process of the edge hold circuit 68 should just be the content of Unexamined-Japanese-Patent No. 2016-118687. The edge hold circuit 68 has a difference between a maximum value and a minimum value of luminance values of a plurality of pixels in the vicinity including the pixel of interest, which is higher than another threshold value, for a pixel having the luminance higher than a certain threshold (notice pixel). In this case, the luminance value lower than the luminance value of the pixel of interest among the luminance values of the plurality of pixels is replaced with the luminance value of the pixel of interest.

Returning to FIG. 5, the gray image signal W3 output from the edge hold circuit 68 is also supplied to the color balance controller 70 as the color balance correction parameter Lw. The color balance controller 70 includes the RGB image signals R2, G2 and B2 after the gray level conversion by the RGB gray converter 64, the color balance correction parameters L _R , L _G , L _B , and the edge hold circuit ( Based on the color balance correction parameter Lw output from 68, color balance correction is performed. That is, the color balance controller 70 adjusts the color balance with respect to the grayscale-converted RGB image signals R2, G2, and B2 by using the color balance correction coefficients for each subpixel, and corrects the RGB image signals R3, G3, B3). The RGB image signals R3, G3, and B3 are supplied to the driving IC 28 of the front LCD panel 2.

16 is a block diagram showing details of the color balance controller 70. The color balance controller 70 has three multipliers 72R, 72G and 72B and three dividers 74R, 74G and 74B.

The following three signals are input to the color balance controller 70.

RGB image signals R2, G2, and B2 that have been tone-converted by the RGB tone converter 64.

Color balance correction parameters L _R , L _G , L _B generated in the RGB gradation converter 64.

Color balance correction parameter Lw generated by the edge hold circuit 68 (gray image signal W3).

Dividers 74R, 74G, 74B calculate the color balance correction coefficient by dividing the color balance correction parameter of the corresponding color by the color balance correction parameter Lw. Multipliers 72R, 72G, and 72B produce RGB (R3, G3, B3) after color balance correction by multiplying the color balance correction coefficients by the RGB image signals of the corresponding colors according to the following equation.

R3 = R2 * (L _R / L _W )

G3 = G2 * (L _G / L _W )

B3 = B2 * (L _B / L _W )

FIG. 17: is explanatory drawing about color balance adjustment in the dark part of an image by the action of the color balance controller 70. As shown in FIG. As shown in Fig. 17A, a case where RGB expresses a mixed color (R> G> B) other than 0 will be described as an example. As described above, the gray converter 60 sets the maximum luminance level among the luminance levels R1, G1, and B1 of the plurality of subpixels of each pixel, and the gray image signal W1 of the pixel (the pixel to which these subpixels belong). Is determined as the luminance level. Therefore, a gray image having the luminance value of the R sub pixel which is the maximum value is generated in the rear LCD panel 3.

In this case, there is a possibility that the color shifts because the backlight for ensuring the luminance of one subpixel passes through another subpixel belonging to the same pixel as the subpixel. For example, the luminance of the G and B sub-pixels is larger than a desired luminance due to light leakage passing from the backlight unit 4 to the pixels PX of the rear LCD panel (LV panel 3), so that the entire pixel PX Will show a misaligned color.

This tendency continues even after the processing by the gray scale converter 66 and the RGB gray scale converter 64 (Fig. 17 (b)). Thus, for example, the light of R passing through the front LCD panel 2 has a desired brightness, but the color balance is broken because the light of G and B is larger than desired.

In order to obtain desired luminance of G and B, it is preferable to control the rear LCD panel 3 to display different luminance for each RGB subpixel as shown in Fig. 17C. However, in the rear LCD panel 3, although the luminance of each pixel of the gray image can be adjusted, the luminance of each sub-pixel cannot be adjusted. Therefore, in order to obtain a desired composite transmittance for each subpixel, it is necessary to perform gradation adjustment of each subpixel of the front LCD panel 2.

Therefore, as shown in Fig. 17 (d), a color balance correction coefficient for adjusting the gradation of the front LCD panel 2 is obtained by introducing a synthetic transmittance thinking method to obtain a desired synthetic transmittance. It can be seen that the correction may be performed in the same manner as shown in FIG. As a result, as shown in Fig. 17F, R3, G3, and B3 are displayed on the front LCD panel 2, and W3 (= Lw) is displayed on the rear LCD panel 3 to adjust the color balance.

A specific configuration in which the color balance control method according to this principle is implemented is the color balance controller 70 shown in FIG. According to the color balance controller 70, an original color can also be displayed also in a mixed color part, and the color reproducibility can be improved. As mentioned above, although the case where the dark part of an image is represented is represented as an example, even when expressing another image, the backlight for ensuring the brightness | luminance of one subpixel SP belongs to the same pixel PX as the said subpixel SP. Passes through the sub-pixel SP. Therefore, the effect of the color balance controller 70 is exhibited not only in the dark part of the image but also in the roster.

As is apparent from the above description regarding FIG. 17, the color balance correction parameters L _R , L _G , L _B generated by the RGB gray scale converter 64 (see FIG. 5) are added to the RGB image signals R1, G1, B1. Therefore, in the case where the RGB image is displayed only in the front LCD panel 2, in order to realize the luminance represented by each sub pixel in the panels 2 and 3, if the rear LCD panel 3 displays different luminance for each RGB sub pixel, If possible, it is the luminance that the subpixels of the rear LCD panel 3 should have. The color balance correction parameter generator 64L _R of the RGB gradation converter 64 can generate the color balance correction parameter L _R only from the input signal R1, and the color balance correction parameter generator 64L _G The color balance correction parameter L _G may be generated from only the input signal G1, and the color balance correction parameter generator 64L _B may generate the color balance correction parameter L _B from only the input signal B1. Can be generated.

As shown in Figs. 17B and 17C, the color balance correction parameter Lw generated by the edge hold circuit 68 (see Fig. 5) may be the same as the gray image signal W3.

Returning to Fig. 5, the delay circuit 62 is provided for synchronizing the processing of the RGB gradation converter 64 and the processing of the gray gradation converter 66, and the gray converter is connected to the RGB image signals R1, G1, and B1. A considerable delay is given to the time required for the processing of 60. The delay circuit 52 further supplies the LED drive signal BD for driving the backlight unit 4 to the RGB image signals R3, G3 and B3 supplied to the front LCD panel 2 and the rear LCD panel 3. RGB image signals R3, G3 and B3 and gray image signals are provided to synchronize with the gray image signals W3 supplied to the local luminance values PLum supplied from the block luminance value determiner 50. FIG. A delay corresponding to the time required for generation of W3 is given. Although the delay circuits 52, 58, 62 are shown in FIG. 5, other delay circuits may be provided for other purposes.

As described above, in the embodiment of the present invention, a local dimming technique is applied to an image display device having a front LCD panel 2 displaying an RGB image and a rear LCD panel 3 displaying a gray image. Based on the desired luminance of each dimming block, estimating the emission luminance of each pixel or each subpixel, adjusting the luminance level of the subpixel of the RGB image signal corresponding to the pixel or subpixel, and adjusting the adjusted subpixel. Based on the luminance level of, a gray image signal for controlling the luminance level of the gray image displayed on the rear LCD panel 3 is generated. As a result, even if each dimming block does not emit light with the same luminance distribution, the local luminance of the image can be reproduced in the display image.

Fig. 18 shows an example of a display image in which an image dimming apparatus having two LCD panels is applied to the local dimming technique, but the local luminance value estimation is not performed (the luminance variation in the dimming block is not taken into account). Fig. 19 shows an example of a display image in which a local dimming technique is applied to an image display device having two LCD panels, and local luminance value estimation (emission luminance estimation of each pixel) is performed in accordance with an embodiment of the present invention. Illustrated. For reference, the positions of the dimming blocks for these display images are shown in the lower part of FIG. 18. Square cells correspond to dimming blocks.

According to the contrast of FIG. 18 and FIG. 19, in FIG. 18, since the luminance variation in the dimming block (see FIG. 4) is not taken into account, the difference in luminance is noticeably visible near the boundary of the adjacent dimming block. On the other hand, in FIG. 19, since the luminance of each pixel was estimated in consideration of the variation in luminance in the dimming block, and the RGB image signal and the gray image signal were adjusted based on the estimated luminance of each pixel, near the boundary of the dimming block. The difference in luminance is not discernible. As described above, according to the embodiment of the present invention, even if each dimming block does not emit light with the same luminance distribution, the local luminance of the image can be reproduced in the display image.

According to the embodiment of the present invention, in an image display device capable of displaying an HDR image, a maximum luminance of 10,000 nits and a contrast ratio of 2,000,000: 1 are realized, and black floating even if a high luminance region and a low luminance region are mixed in one dimming block. This is avoided. In addition, even if each dimming block does not emit light with the same luminance distribution, the local luminance of the image can be reproduced in the display image.

In addition, in the case where the image display device in which the contrast ratio is greatly improved by using the two LCD panels 2 and 3 is applied to the HDR image display device, the light transmittance of the entire panel is lower than that of the image display device of one panel. In order to obtain the same display brightness as in the case of one panel, it is necessary to make the brightness of the backlight unit higher. In this case, the enormous power consumption in the backlight unit and the installation of the cooling mechanism accompanying the heat generation may be a problem.

However, according to the embodiment of the present invention, by applying the local dimming technology, the backlight unit 4 emits the LED 42 corresponding to the required dimming block at an appropriate brightness, so that the backlight unit without applying the local dimming technology is compared. Therefore, power consumption can be greatly reduced, and furthermore, no large-scale cooling mechanism is required. Therefore, compared with the backlight unit which does not apply a local dimming technique, the cost of the backlight unit 4 which concerns on embodiment of this invention can be reduced.

1: Image display device 2: Front LCD panel (RGB panel)
3: Rear LCD Panel (LV Panel) 4: Backlight Unit
20: color filter substrate 22: TFT substrate
24, 26: polarizing film 28: drive IC
30: glass substrate 32: TFT substrate
34: polarizing film 36: drive IC
40: substrate 42: LED
44 side wall 46 LED driver
5: signal processor 50: block luminance value determiner
52, 58, 62: delay circuit
54: LED drive signal generator (backlit drive signal generator)
55: local luminance value estimator 56: level converter
57: delay circuit 60: gray converter
64: RGB gradation converter 64R: R gradation converter
64G: G Gradient Converter 64B: B Gradient Converter
64L _R : Color Balance Correction Parameter Generator
64L _G : Color Balance Correction Parameter Generator
64L _B : Color Balance Correction Parameter Generator
66: gray scale converter 68: edge hold circuit
70: color balance controller 80: selector
81: interpolator 82a to 82m: selector
84a to 84m: count value memory 86: conversion operator
90: first calculating unit 91: second calculating unit
92a to 92m, 94a to 94m: selector 93a to 93m, 95a to 95m: count value memory
96: conversion operator 98: interpolator
72R, 72G, 72B: Multiplier 74R, 74G, 74B: Divider

Claims (15)

A front LCD panel displaying an RGB image;
A rear LCD panel disposed behind the front LCD panel and superimposed on the front LCD panel to display a gray image;
A backlight unit disposed at the rear of the rear LCD panel and configured to irradiate light to the front LCD panel and the rear LCD panel to adjust brightness of each of the plurality of blocks;
A block luminance value determiner for determining a block luminance value of each block from an input RGB image signal;
A backlight driving signal generator for driving the backlight unit to adjust the luminance of the block according to the block luminance value of each block determined by the block luminance value determiner;
On the basis of the block luminance value of each of the blocks determined by the block luminance value determiner, luminance distributions in the block and in the block adjacent to the block or the entire display area when the light is emitted only from the block for each block are determined. A local luminance value estimator for estimating a local luminance value of each pixel or each sub-pixel when each block emits light at the block luminance value using typical luminance distribution data indicated;
A level converter for adjusting a luminance level of a subpixel of the RGB image signal corresponding to the pixel or subpixel based on the local luminance value of each pixel or each subpixel estimated by the local luminance value estimator; And
And a gray converter which generates a gray image signal for controlling the luminance level of the gray image displayed on the rear LCD panel based on the luminance level of the sub-pixel adjusted by the level converter.
The method of claim 1,
And the block luminance value determiner determines the block luminance value of each of the blocks based on the maximum luminance among the luminance of sub-pixels in each block of the input RGB image signal.
The method according to claim 1 or 2,
The local luminance value estimator,
A storage device for storing the typical luminance distribution data;
And a calculator for calculating the local luminance value of each pixel or each sub-pixel from the typical luminance distribution data and the block luminance value of each of the blocks.
The method according to claim 1 or 2,
The local luminance value estimator,
A storage device for storing the typical luminance distribution data;
A data interpolator for generating detailed luminance distribution data by interpolating the typical luminance distribution data;
And a calculator for calculating the local luminance value of each pixel or each sub-pixel from the detailed luminance distribution data and the block luminance value of each of the blocks.
The method according to claim 1 or 2,
The local luminance value estimator,
A distribution characteristic generator for generating the typical luminance distribution data using a calculation formula;
And a calculator for calculating the local luminance value of each pixel or each sub-pixel from the typical luminance distribution data and the block luminance value of each block.
The method according to claim 1 or 2,
The level converter is configured to increase the luminance level of the subpixel of the RGB image signal corresponding to the pixel or subpixel as the local luminance value of each pixel or each subpixel estimated by the local luminance value estimator is lower. Display device.
The method according to claim 1 or 2,
And the gray converter determines a maximum luminance level among luminance levels of a plurality of subpixels of each pixel as a luminance level of a gray image of the pixel.
The method according to claim 1 or 2,
And an RGB gradation converter for correcting the gradation of the RGB image signal whose luminance level is adjusted in the level converter in consideration of output characteristics of the front LCD panel,
And the RGB gradation converter corrects the gradation of the RGB image signal based on the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator.
The method of claim 8,
The RGB gradation converter includes a gradation converter corresponding to each RGB color,
Each gradation converter comprises a plurality of lookup tables, the number of steps being smaller than the number of steps of the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator, and each pixel or each sub-estimated by the local luminance value estimator. And a selector for selecting two out of a plurality of lookup tables in accordance with the local luminance value of the pixel, and an interpolator for interpolating values of the two lookup tables selected by the selector to obtain the gray level of the image signal.
The method of claim 8,
The RGB gradation converter includes a gradation converter corresponding to each color of RGB,
Each gray scale converter includes a first calculator, a second calculator, and an interpolator,
Each of the first operation unit and the second operation unit,
A plurality of coefficient value memories, wherein each coefficient value memory stores coefficient values less than half of the number of steps of the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator Wow,
A selector for selecting one coefficient value from each of the plurality of coefficient value memories in accordance with the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator;
And a conversion operator configured to perform arithmetic processing based on a plurality of coefficient values selected by the selector,
And the interpolator obtains the gradation of the image signal by interpolating the calculation processing result of the conversion calculator of the first calculation unit and the calculation processing result of the conversion calculator of the second calculation unit.
The method according to claim 1 or 2,
And a gray scale converter for correcting the gray scale of the gray image signal generated by the gray converter in consideration of output characteristics of the rear LCD panel,
And the gray tone converter corrects the gray level of the gray image signal based on the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator.
The method of claim 11,
The gray scale converter may include a plurality of lookup tables smaller than the number of steps of the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator, and each pixel or each estimated by the local luminance value estimator. And a selector for selecting two out of a plurality of lookup tables according to the local luminance value of the subpixel, and an interpolator for interpolating values of the two lookup tables selected by the selector to obtain a gray image signal.
The method of claim 11,
The gray scale converter includes a first calculator, a second calculator, and an interpolator,
Each of the first operation unit and the second operation unit,
A plurality of coefficient value memories, wherein each coefficient value memory stores coefficient values less than half of the number of steps of the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator Wow,
A selector for selecting one coefficient value from each of the plurality of coefficient value memories in accordance with the local luminance value of each pixel or each sub-pixel estimated by the local luminance value estimator;
And a conversion operator configured to perform arithmetic processing based on a plurality of coefficient values selected by the selector,
And the interpolator obtains the gradation of the image signal by interpolating the calculation processing result of the conversion calculator of the first calculation unit and the calculation processing result of the conversion calculator of the second calculation unit.
Front LCD panel for displaying RGB image,
A rear LCD panel disposed behind the front LCD panel, superimposed on the front LCD panel, and displaying a gray image;
An image display method which is disposed in the rear of the rear LCD panel and is provided in the image display apparatus comprising a backlight unit which irradiates light on the front LCD panel and the rear LCD panel and adjusts the luminance of each of the plurality of blocks. ,
Determining a block luminance value of each of the blocks from an input RGB image signal;
Driving the backlight unit to adjust the luminance of the block according to the block luminance value of each of the determined blocks;
On the basis of the block luminance value of each of the determined blocks, typical luminance distribution data indicating luminance distribution in the block, in the block adjacent to the block or in the entire display area when light is emitted only from the block for each block is used. Estimating a local luminance value of each pixel or each sub pixel when each block emits light at the block luminance value;
Adjusting a luminance level of a subpixel of the RGB image signal corresponding to the pixel or subpixel based on the estimated local luminance value of each pixel or each subpixel; And
And generating a gray image signal that controls the luminance level of the gray image displayed on the rear LCD panel based on the adjusted luminance level of the sub-pixel.
The method of claim 1,
And the local luminance value is calculated according to the following equation.

Where PLum (x, y) is the local luminance value of the pixel or subpixel, x and y are the x and y coordinates of the pixel or subpixel, respectively, and α _{[i, j]} (x, y) is dimming Luminance distribution for the block [i, j], x0 _{[i, j]} and y0 _{[i, j]} are the x and y coordinates of the representative point (or reference point) in the dimming block [i, j], respectively. , BLum [i, j] is the block luminance value in the dimming block [i, j].)

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