KR20180034207A - Image Display Device And Method Of Displaying Image - Google Patents

Abstract

The present invention is to improve the reproducibility of the local luminance of an image even if each dimming block of a local dimming technique does not emit light with the same luminance distribution. An image display device comprises a front LCD panel displaying RGB images, a rear LCD panel displaying gray images, and a backlight unit capable of adjusting the luminance of each of a plurality of blocks. The image display device further comprises: 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; a local luminance value estimator for estimating an emission luminance value of each pixel or each subpixel; 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 gray converter for controlling the luminance level of a gray image displayed on the rear LCD panel based on the luminance level of the subpixel adjusted by the level converter.

Description

Technical Field [0001] The present invention relates to an image display device and an image display method,

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, an HDR (High Dynamic Range) image has been proposed in which the luminance and the contrast ratio are greatly improved. About HDR, ST2084 according to SMPTE (Association of American Cinema Technicians), HLG (Hybrid Log Gamma) method developed by so called Dolby Vision or NHK and British BBC is being standardized. The image display device is required to have display capability according to 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), a backlight is transmitted through an LCD panel to display an image. In particular, a so-called black floating phenomenon occurs in which the gradation characteristic of the black region is 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, for example, about 1,500: 1.

In order to improve the contrast ratio of the LCD image display apparatus, an image display apparatus using two LCD panels has been proposed (see, for example, Patent Document 1). In this image display apparatus, the rear LCD panel (LV: Light Valve) displays a gray image to adjust the transmission amount of the backlight, and the front LCD panel (RGB panel) displays RGB images to improve the contrast ratio.

Patent Document 1: JP-A-2016-118690

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

For example, by applying the local dimming technique of the backlight, the black floating in the dark block is greatly reduced. The local dimming technique is a technique for individually adjusting the brightness of each of a plurality of dimming blocks constituting a screen. Here, the transmissivity of the LCD panel is controlled on the premise that one dimming block emits light with the same brightness distribution. However, in reality, it is difficult to emit one dimming block with the same luminance distribution, so that the local accuracy of the image, in particular, the reproducibility of the luminance may be inferior.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image display apparatus and an image display method capable of enhancing local luminance reproducibility of an image even when local dimming technology is applied and each dimming block does not emit light with the same luminance distribution.

The image display apparatus according to the present invention includes: a front side LCD panel displaying RGB images; a rear side LCD panel disposed behind the front side LCD panel and superimposed on the front side LCD panel to display a gray image; A backlight unit disposed at the rear side and capable of adjusting the luminance of each of a plurality of blocks by irradiating light to the front side LCD panel and the rear side LCD panel, a block luminance value determining unit for determining a desired luminance of each of the blocks from the input RGB image signal, A backlight drive signal generator for driving the backlight unit to adjust the brightness of the block in accordance with a desired brightness of each of the blocks determined by the block brightness value determiner; Based on the desired luminance of each of the blocks, when each block is emitted with the desired luminance, each pixel A local luminance value estimator for estimating the luminance of each subpixel; and a local luminance value estimator for estimating luminance of each of the subpixels based on the luminance of each pixel or each subpixel estimated by the local luminance value estimator, A gray converter for generating a gray image signal for controlling a brightness level of a gray image displayed on the rear side LCD panel based on the brightness level of the subpixel adjusted by the level converter; Respectively.

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 further includes: a storage device for storing typical luminance distribution data in the block and in a block adjacent to the block or in the entire display area when the block is lit only for each block; And an arithmetic unit for calculating the light emission luminance of each pixel or each sub pixel from the data and the desired luminance of each block.

Alternatively, the local luminance value estimator may include a storage device for storing typical luminance distribution data in the block and in a block close to the block or in the entire display area when the block is lighted only in the block, A data interpolator for interpolating and generating detailed luminance distribution data, and an arithmetic unit for calculating luminance of each pixel or each subpixel from the detailed luminance distribution data and a desired luminance of each block.

Alternatively, the local luminance value estimator may include a distribution characteristic generator for generating the typical luminance distribution data in the block and in the entire block or in the entire display area in the block adjacent to the block when the block is lighted for each block using a calculation formula, And an arithmetic unit for calculating the emission luminance of each pixel or each subpixel from the 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 the subpixel as the luminance of each pixel or 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 sub-pixels of each pixel as the luminance level of the gray image of the pixel.

Preferably, the image display apparatus further comprises an RGB gradation converter for correcting the gradation of the RGB image signal whose luminance level is adjusted by the level converter so as to match the output characteristic of the front side LCD panel, The gradation of the RGB image signal is corrected based on the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator.

Preferably, the RGB gradation converter includes a gradation converter corresponding to each color of RGB, and each gradation converter has a number of gradation converters, each of which is smaller than the number of steps of the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator A selector for selecting two of the plurality of lookup tables according to the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator, and a selector for selecting one of the two lookup tables selected by the selector, And an interpolator for obtaining the gradation of the image signal.

Preferably, the RGB gradation converter includes a gradation converter corresponding to each of the RGB colors, and each gradation converter includes a first calculation section, a second calculation section and an interpolator, and each of the first calculation section and the second calculation section includes a plurality of Wherein the coefficient value memory stores a coefficient value in which each coefficient value memory is smaller than half of the number of steps of the luminance of each pixel or each subpixel estimated in the local luminance value estimator, A selector for selecting one coefficient value from each of the plurality of coefficient value memories in accordance with the light emission luminance of each pixel or each subpixel estimated by the luminance value estimator and a selector for selecting one coefficient value from each of the plurality of coefficient value memories based on a plurality of coefficient values selected by the selector Wherein the interpolator comprises: an arithmetic processing result of the conversion operator of the first arithmetic unit; and an arithmetic processing result of the conversion arithmetic unit of the second arithmetic unit And the gradation of the image signal is obtained by interpolating the processing result.

Preferably, the image display apparatus further comprises a gray gradation converter that corrects the gradation of the gray image signal generated by the gray converter to match the output characteristics of the rear LCD panel, and the gray gradation converter converts the local brightness The gradation of the gray image signal is corrected based on the light emission luminance of each pixel or each subpixel estimated by the value estimator.

Preferably, the gray level converter includes: a plurality of lookup tables each of which is smaller than the number of stages of the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator; 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 level converter includes a first calculation unit, a second calculation unit and an interpolator, wherein each of the first calculation unit and the second calculation unit includes a plurality of coefficient value memories, A coefficient value memory for storing a coefficient value smaller than half of the estimated number of steps of the light emission luminance of each pixel or each subpixel; A selector for selecting one coefficient value from each of the plurality of coefficient value memories; and a conversion operator for performing an arithmetic processing based on a plurality of coefficient values selected by the selector, wherein the interpolator performs conversion The arithmetic processing result of the arithmetic unit and the arithmetic processing result of the conversion arithmetic unit of the second arithmetic unit are interpolated to obtain the gradation of the image signal.

The image display method according to the present invention includes: a front side LCD panel displaying RGB images; a rear side LCD panel disposed behind the front side LCD panel and superimposed on the front side LCD panel to display a gray image; And a backlight unit disposed behind the front LCD panel and the rear LCD panel, the backlight unit being capable of adjusting the luminance of each of the plurality of blocks, the image display method comprising: The method comprising the steps of: determining a desired luminance of each of the blocks from the plurality of blocks; driving the backlight unit to adjust the luminance of the blocks according to a desired luminance of each of the determined blocks; On the basis of the luminance, when each block is caused to emit light with the desired luminance, the light emission luminance of each pixel or each sub pixel Adjusting the luminance level of the subpixel of the RGB image signal corresponding to the pixel or the subpixel based on the estimated light emission luminance of each pixel or each subpixel; And generating a gray image signal for controlling the brightness level of the gray image displayed on the rear side LCD panel based on the level of the gray image.

In the present invention, a local dimming technique is applied to an image display apparatus including a front LCD panel for displaying RGB images and a rear LCD panel for displaying gray images, and based on the desired luminance of each block, Pixel, adjusts the luminance level of the subpixel of the RGB image signal corresponding to the pixel or the subpixel, and based on the luminance level of the adjusted subpixel, the luminance of the gray image displayed on the rear side LCD panel Thereby generating a gray image signal for controlling the level. Thus, even if each of the dimming blocks does not emit light with the same luminance distribution, it is possible to enhance the reproducibility of the local luminance of the image.

1 is a schematic side view of an image display apparatus according to an embodiment of the present invention.
2 is a schematic plan view of a backlight unit showing the LED arrangement of the image display apparatus of Fig.
3 is a schematic view showing a relationship between a block, a pixel and a subpixel in the image display apparatus of FIG.
4 is a graph showing the luminance distribution of each block in the image display apparatus of Fig.
5 is a block diagram showing a signal processing unit of the image display apparatus of FIG.
FIG. 6 is a block diagram showing a detailed example of the local luminance value estimator of the signal processing unit of FIG. 5;
7 is a block diagram showing another detailed example of the local luminance value estimator of the signal processing unit of FIG.
8 is a block diagram showing another detailed example of the local brightness value estimator of the signal processing unit of FIG.
9 is a graph showing an example of gradation conversion characteristics according to the RGB gradation converter of the signal processing unit of Fig.
10 is a graph showing an example of gradation conversion characteristics according to the gray gradation converter of the signal processing unit of Fig.
11 is a graph for explaining the operation of the gradation converter.
12 is a block diagram showing details of an example of a gradation converter or a color balance correction parameter generator of the signal processing unit of Fig.
13 is a block diagram showing details of another example of the gradation converter or the color balance correction parameter generator of the signal processing unit of Fig.
14 is a block diagram showing details of another example of the gradation converter or color balance correction parameter generator of the signal processing unit of Fig.
15 is a schematic view showing a result of correcting the viewing angle according to the edge hold circuit of the signal processing unit of FIG.
FIG. 16 is a block diagram showing details of the color balance controller of the signal processing unit of FIG. 5; FIG.
Fig. 17 is an explanatory view of color balance adjustment in an arm portion of an image according to the action of the color balance controller. Fig.
18 is a diagram showing an example of a display image in which the local dimming technique is applied to the image display device having two LCD panels, but the local brightness 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 apparatus having two LCD panels and a local brightness value is estimated according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS 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 the different drawings, the same reference numerals are used to denote the same or functionally similar elements. It is to be understood that the drawings are schematically shown, and that the scale of the drawings is not accurate.

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

The front side LCD panel 2 displays RGB images. The front side 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, and 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 on the front surface of the color filter substrate 20 and the polarizing film 26 is disposed on the rear surface of the TFT substrate 22. [ The driving IC 28 is mounted on the TFT substrate 22 and controls the transmissive state of the liquid crystal of the front side LCD panel 2 for each of the sub pixels (sub-pixels) in accordance with the RGB image signal input to the driving IC 28 do.

The rear side LCD panel 3 is disposed behind the front side LCD panel 2 and superimposed on the front side LCD panel 2 to display a gray image (LV image). The rear side LCD panel 3 includes a glass substrate 30, a TFT substrate 32, a polarizing film 34, and a driving IC 36. The glass substrate 30 corresponds to the color filter substrate 20 in the front side LCD panel 2 and has a common electrode but does not have a color filter unlike the color filter substrate 20. This is because the rear side LCD panel 3 displays a grayscale image, which is expressed only by LV images, that is, 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 driving IC 36 is mounted on the TFT substrate 32 and controls the liquid crystal transmission state of the rear side LCD panel 3 in accordance with the gray image signal inputted to the driving IC 36. [ The front side LCD panel 2 and the rear side LCD panel 3 are bonded 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 side LCD panel 3 and irradiates the front side LCD panel 2 and the rear side LCD panel 3 with light. The backlight unit 4 is directly underneath and includes a substrate 40, a plurality of flat LEDs (Light Emitting Diodes) 42 mounted on the substrate 40, and side walls (44). The LED 42 is provided at a desired distance from the rear side LCD panel 3. The light emission of the LED 42 is controlled by the LED driver 46. The LED driver 46 may be mounted on the substrate 40 or on a substrate different from the substrate 40, for example.

As shown in Fig. 2, the LEDs 42 are assumed to have a rectangular shape, and the gaps between the LEDs 42 are spaced apart from each other so as to be lattice-like. 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 is capable of adjusting 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 the 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 brightness of the plurality of LEDs 42. [ Although not shown, the backlight unit 4 may be provided with a known partition wall, a known lens, and a known flatter described later. By controlling the light emission of the LED 42, the brightness 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, even if it is an edge light type, the backlight unit 4 can be used in the present invention as long as it can perform local dimming in which luminance of each of a plurality of blocks can be adjusted.

3 shows a relationship between a block, a pixel and a subpixel in an image display apparatus. 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 side LCD panel 3, the brightness of each pixel PX of the gray image can be adjusted. In the front side LCD panel 2, the luminance of each subpixel SP of RGB three colors can be adjusted. In this specification, the brightness to be described with respect to the panels 2 and 3 means the transmittance of the panels 2 and 3.

Fig. 4 is a graph showing the luminance distribution in each block of the image display apparatus of Fig. 1. Fig. Fig. 4 (A) shows an ideal distribution state of luminance. In this abnormal state, one dimming block BL emits light of the same luminance distribution, and there is no light leakage from one dimming block BL to the other dimming block BL. Fig. 4 (B) shows the luminance distribution in the case of performing a high-level optical design. In the case where a high degree of optical design is performed, a distribution approximate to Fig. 4 (A) is obtained. Fig. 4 (C) shows the distribution of the luminance in the case where the high optical design is not performed. In a case where a high degree of optical design is not performed, one dimming block BL emits light with an unequal luminance distribution, and there are many light gaps from one dimming block BL to the other dimming block BL.

The high optical design means at least one of a partition for separating the blocks BL from each other, a lens and a platter for uniformly distributing the luminance in the block. However, installing them increases the cost due to the development period and the number of parts. Even if they are installed, it is difficult or impossible to obtain an ideal distribution of luminance.

An embodiment of the present invention aims to improve the reproducibility of local luminance of an image even if each dimming block does not emit light with the same luminance distribution.

5 shows the relationship between the image data supplied to the drive IC 28 of the front side LCD panel 2 of this image display apparatus 1 and the drive IC 36 of the rear side LCD panel 3, And a signal processing unit 5 for generating control data supplied to the LED driving unit 46. [ The signal processing unit 5 is supplied with RGB image signals (R, G, B) having a signal level in linear relationship with the luminance through an EOTF (Electro-Optical Transfer Function).

The signal processing unit 5 includes a block luminance value determiner 50 for determining the desired luminance of each of the dimming blocks from the input RGB image signals R, G, The block brightness value determiner 50 determines the block brightness value of the entire dimming block based on the maximum brightness BLmax among the brightnesses of the respective RGB subpixels in the respective dimming blocks of the input RGB image signals R, G, And determines the luminance. Specifically, for example, the block brightness value determiner 50 may determine the maximum brightness BLmax in each dimming block to be the desired brightness (block brightness value, BLum) of the entire dimming block. In this case, BLum = BLmax.

If the number of steps (n) of the luminance (Lj) controllable with respect to each dimming block of the backlight unit (4) is smaller than the number of luminance steps that can be represented by the RGB image signal, the block luminance value determiner (50) 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 gradation, and that 4096 gradations can be expressed. It is also 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. Thus, the block luminance value determiner 50 determines any one of the luminance that can be controlled for each dimming block to be the block luminance value (BLum).

However, the RGB image signal is not limited to the 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 certain delay time to the block luminance value BLum. The block luminance value (BLum) output from the delay circuit 52 is supplied to an LED drive signal generator (backlight drive signal generator). The LED driving signal generator 54 generates a driving signal for adjusting the brightness of the dimming block in accordance with the block luminance value BLum (i.e., the desired luminance of each of the dimming blocks determined by the block luminance value determiner 50) (BD) for driving the LEDs (4). The LED driving signal BD is supplied to the LED driving unit 46 of the backlight unit 4. [

The LED driving signal generator 54 may control the voltage or current of the LED driving signal BD in such a manner that the luminance of the dimming block is adjusted. The LED drive signal generator 45 may perform the blinking of the LED 42 corresponding to the dimming block by, for example, a PWM (Pulse Width Modulation) method. In this case, the LED driving signal BD is a pulse signal of a constant amplitude whose duty ratio is changed according to a desired luminance of the dimming block.

The signal processing unit 5 further includes a local brightness value estimator 55. [ The local luminance value estimator 55 estimates the luminance value of each dimming block based on the desired luminance (block luminance value, BLum) of each dimming block determined by the block luminance value determiner 50 And estimates the light emission luminance value of the pixel or each sub pixel. The light emission luminance value referred to here is a luminance value when the luminance of the panels 2 and 3 is not adjusted, that is, a luminance value when the transmittance of the panels 2 and 3 is the maximum. Then, the local luminance value estimator 55 outputs the local luminance value PLum showing the emission luminance of each estimated pixel or each sub pixel.

6 to 8 show a detailed example of the local brightness value estimator 55, respectively. In the example shown in Fig. 6, the local luminance value estimator 55 includes a memory (storage device) 55A for storing typical luminance distribution data, typical luminance distribution data stored in the memory 55A, And an arithmetic operation unit 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 the typical luminance distribution data showing the typical luminance distribution in the block adjacent to the block and the typical luminance distribution data in the case where only the block is emitted for each block, And the typical luminance distribution data showing the typical luminance distribution in the entire display region may be stored. The computing unit 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.

Here, α _{[i, j]} (X, Y) is a luminance distribution of the dimming block [i, j] It is a function of the relationship. There is no or no dependence on α _{[i, j]} (X, Y) on the BLum value.

x0 _{[i, j]} and y0 _{[i, j]} are coordinates showing the positions of representative points (or reference points) 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 corner.

BLum [i, j] is a luminance value (BLum) in the dimming block [i, j] and varies according to an image to be displayed.

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

The above formula is determined in consideration of the fact that PLum (x, y) is affected by light from a plurality of dimming blocks, and therefore the sum is found. The range of the dimming block for obtaining the sum can be arbitrarily selected in accordance with the diffusion method of the luminance distribution alpha. For example, if the diffusion of the luminance distribution? Is small, the dimming block for obtaining the sum may be a pixel for which PLum (x, y) is calculated or a dimming block to which a subpixel belongs and a few dimming blocks adjacent thereto. If the diffusion of the luminance distribution? Is large, the dimming block for obtaining the sum may be any dimming block.

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

In order to implement the example of the local luminance value estimator 55 shown in Fig. 6, a luminance distribution? For calculating a local luminance value is obtained in advance for each pixel or each sub pixel of the image display apparatus , And stores the luminance distribution? In the memory 55A.

7, the local luminance value estimator 55 includes a memory (storage device) 55C for storing the typical luminance distribution data, and a luminance distribution data storage unit 55C for interpolating the typical luminance distribution data stored in the memory 55C, A data interpolator 55D for generating data for each pixel or each sub pixel based on the detailed luminance distribution data generated by the data interpolator 55D and the desired luminance (block luminance value, BLum) of each dimming block, And a calculator 55E for calculating the value PLum. The memory 55C may store the typical luminance distribution data showing the typical luminance distribution in the block and the block adjacent to the block when the block is emitted only in that block, The typical luminance distribution data showing the typical luminance distribution in the entire region may be stored.

The computing unit 55E can calculate the light emission luminance value PLum according to the above equation, for example. In the example shown in Fig. 7, the luminance distribution? Is included in the detailed luminance distribution data generated by the data interpolator 55D. The data interpolator 55D obtains the detailed luminance distribution data based on the interpolation equation from the typical luminance distribution data stored in the memory 55C. Therefore, in the example shown in Fig. 7 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? For each pixel or each subpixel is recorded in the typical luminance distribution data, but in the example shown in Fig. 7, for example, The luminance distribution alpha for the pixel (or a subpixel included therein) can be recorded in the typical luminance distribution data. The example shown in Fig. 7 is suitable for a case where the typical luminance distribution in a case where the luminance distribution is not wide is large and can be interpolated with a smaller error, and the memory storage amount is saved and the circuit scale increase is suppressed can do.

In the example shown in Fig. 8, the local luminance value estimator 55 includes a distribution characteristic generator 55F for generating the typical luminance distribution data in each block by using a calculation formula, a typical luminance value generator 55F, And an arithmetic operation unit 55G for calculating the light emission luminance value PLum of each pixel or each sub pixel from the distribution data and the desired luminance (block luminance value, BLum) of each dimming block. The distribution characteristic generator 55F may generate the typical luminance distribution data showing the typical luminance distribution in the block and the block adjacent to the block in the case where only the block is lighted for each block, The typical luminance distribution data showing the typical luminance distribution in the entire display region of the luminance distribution data may be generated.

The computing unit 55G can calculate the light emission luminance value PLum, for example, according to the above equation. In the example shown in Fig. 8, the luminance distribution? 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 is obtained by previously measuring the luminance distribution? For each pixel or each subpixel of the image display device and further calculating the luminance distribution? And the positional coordinates of the pixel or subpixel Of the function. This function may be used as a calculation expression 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, and there is a possibility that the error increases. In the example shown in Fig. 8, The increase in the circuit scale can be suppressed.

Returning to Fig. 5, the signal processing section 5 further includes a level converter 56 and a delay circuit 58. Fig. The level converter 56 converts the RGB image signal R (R) corresponding to the pixel or subpixel based on the light emission luminance (local luminance value, PLum) of each pixel or each subpixel estimated by the local luminance value estimator 55 , G, and B) is adjusted. The delay circuit 58 adds the time required for the determination of the block luminance value (BLum) in the block luminance value determiner 50 and the time required for determination of the block luminance value (BLum) to the RGB image signals (R, G, B) supplied to the signal processing section 5 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 lower the level of the light emission luminance (local luminance value, PLum) of each pixel or each subpixel estimated by the local luminance value estimator 55, The luminance level of the pixel is increased. The level converter 56 adjusts the luminance level of each subpixel of the RGB image signal so that the rate of change of the luminance level of each subpixel is smaller than the level of the local luminance value PLum as the local luminance value PLum is higher Change. The level converter 56 also 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. [

When 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 luminance level of the B subpixel The luminance level of the R subpixel output from the level converter 56 is R1 and the luminance level of the G subpixel output from the level converter 56 is G1 and the output from the level converter 56 is the output The level converter 56 performs level conversion, i.e., 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 that the RGB image signals (R, G, B) can have, for example, 4095 according to the above example (RGB image signal is 12 bit gradation).

The lower the local luminance value PLum, the higher the luminance level of each subpixel of the RGB image signal. However, if the local luminance value PLum is higher, the luminance of the pixel or the subpixel is raised 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. [ Gray converter 60 controls the gray level of the gray image displayed on the rear side LCD panel 3 based on the brightness levels R1, G1, and B1 of the sub pixels adjusted by the level converter 56 Thereby generating the signal W1. More specifically, the gray converter 60 converts the maximum luminance level among the luminance levels (R1, G1, B1) of the plurality of subpixels of each pixel to the luminance of the gray image of the pixel (the pixel to which these subpixels belong) As a level.

The signal processing unit 5 further includes a delay circuit 62 and an RGB gradation converter 64. The delay circuit 62 is supplied with the RGB image signals R1, G1 and B1 outputted from the level converter 56 and the delay circuit 62 supplies a predetermined delay time to the RGB image signals R1, G1 and B1 . The RGB image signals (R1, G1, 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 and B1 whose luminance levels are adjusted by the level converter 56 to match the output characteristics of the front side LCD panel 2. [ For example, the display characteristic of the front side LCD panel 2 is a gamma characteristic represented by a gamma curve, and the RGB gradation converter 64 performs gamma correction on the RGB image signals R1, G1, and B1. However, the display characteristic is not limited to the gamma characteristic, and the correction is not limited to the gamma correction. Further, in this embodiment, the RGB gradation converter 64 converts the RGB image signal (luminance value) of each pixel or each sub pixel estimated by the local brightness value estimator 55 Thereby correcting the gradation.

The signal processing unit 5 further includes a gray-scale converter 66. [ The gray level converter 66 corrects the gray level of the gray image signal W1 generated by the gray converter 60 to match the output characteristics of the rear side LCD panel 3. [ For example, the display characteristic of the rear side LCD panel 3 is the gamma characteristic, and the gray level converter 66 corrects the gray image signal W1 in consideration of the gamma characteristic. However, the display characteristic is not limited to the gamma characteristic, and the correction is not limited to the gamma correction. Further, in this embodiment, the gray-scale level converter 66 calculates the gray level of the gray image signal (luminance value) based on the emission luminance (local luminance value, PLum) of each pixel or each subpixel estimated by the local luminance value estimator 55 Thereby correcting the gradation of the image W1.

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 and outputs R2. The G gradation converter 64G corrects the input signal G1 to G2 and outputs G2, Corrects the input signal B1 to B2, and outputs B2.

Further, the RGB gradation converter 64 obtains the color balance correction parameters (L _R , L _G , and L _B ) used in the color balance controller 70 to be described later from the input RGB image signals (R 1, G 1, It 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. Color balance correction parameter generator (64L _R) is obtained for the color balance correction parameters extracted from the input signal (R1) (L _R) and outputs the color balance correction parameter (L _R), the color balance correction parameter generator (64L _G) are , get the color balance correction parameter (L _G) from the input signal (G1), and outputting the color balance correction parameter (L _G), the color balance correction parameter generator (64L _B), the color from the input signal (B1) balance obtaining a correction parameter (L _B) and outputs the color balance correction parameter (L _B).

FIG. 9 is a graph showing an example of the gradation conversion characteristic according to the RGB gradation converter 64, and FIG. 10 is a graph showing an example of the gradation conversion characteristic according to the gray gradation converter 66 as a solid line. In Figs. 9 and 10, the linear characteristics are shown by broken lines for reference. 9 and 10, the abscissa indicates the input luminance value to the RGB gradation converter 64 or the gray gradation converter 66, and the ordinate indicates the output luminance from the RGB gradation converter 64 or the gray gradation converter 66 Value.

An example of the gradation conversion characteristic according to the RGB gradation converter 64 shown in Fig. 9 is realized by a gamma curve (Y = X ^? ) ^Having ? = 0.5, for example. On the other hand, an example of the gray-scale conversion characteristic according to the gray-scale level converter 66 shown in Fig. 10 corresponds to the case where the two LCD panels 2 , And 3), and the input / output characteristics of the LV are determined so that the final synthesis result is equivalent to the linear luminance characteristic of the natural system and therefore appears natural to humans. The RGB image signal and the gray image signal are suitable for the output characteristics of the front side LCD panel 2 and the rear side LCD panel 3 by the grayscale conversion of the RGB grayscale converter 64 and the gray grayscale converter 66, And is corrected to have a natural luminance gradation in the eyes.

The operation 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 gradation converter 64 and the gray gradation converter 66 will be described with reference to Fig. Explain. 11A shows basic characteristics (characteristics corresponding to Figs. 5 and 6) of the gradation converter. This basic characteristic is a characteristic (characteristic shown in Fig. 11 (E)) when the backlight unit 4 is caused to emit light with the maximum luminance (for example, L4).

If the number of steps n of the controllable luminance Lj of the backlight unit 4 is 4 and Lj ∈ {L1, L2, L3, L4}, the four-stage characteristic shown in Figs. 11B to 11E can be used have. 11B is a characteristic in which the range of the input of Fig. 11A from 0 to L1 is an enlarged view of both the input shaft and the output shaft (that is, both longitudinally and transversely). The characteristic shown in Fig. 11 (C) is a characteristic in which both the input shaft and the output shaft are enlarged in the range from 0 to L2 in Fig. 11 (A). 11 (D) is a characteristic in which the range of the input of FIG. 11 (A) from 0 to L3 is enlarged for both the input shaft and the output shaft. However, the respective curves shown in Fig. 11 are illustrative, and are not limited thereto.

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

Speaking of the input of the basic properties Vinput _org, it can be expressed as 0 ≤ Vinput _org ≤L4, when the output of the basic properties that Voutput _org, can be expressed as _{Voutput org = f (Vinput org)} . f is a function.

Voutput = g (Vinput) = (1 / f (BLum / L4)) < / RTI > where Voutput is the input of other characteristics, f ((BLum / L4) ㅧVinput).

With reference to Figures 12 to 14, a description of each example gradation converter (64R, 64G, 64B, 66 ) and color balance correction parameter generator (64L _{R, G} 64L, 64L _B).

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 steps of the controllable luminance Lj of the backlight unit 4 for local dimming. For example, the number of steps (n) is not limited, but may be four. On the other hand, for example, when the RGB image signal is 12-bit gradation and 4096 gradations can be expressed, the number of steps h of the local luminance value PLum must be equal to the number of luminance gradations 4096 Ideally, this is the number of luminance gradations (4096).

When the gradation conversion is performed by using the multi-level local luminance value PLum as an input, for example, in the look-up table method, the number of count values stored in the lookup table number or count value memory, The number of stages h of the memory cell is large, so that the circuit scale becomes very large. Each example shown in Fig. 12 and Fig. 14 has been studied in order to suppress an increase in circuit scale.

12 is a gray level converter (64R, 64G, 64B, 66 ) and color balance correction parameter generator (64L _{R, G} 64L, 64L _B) a block diagram showing the respective detailed Example. Each of the tone converters or each of the color balance correction parameter generators has a plurality of lookup tables (LUT1, LUT2, ..., LUTk), a selector (80), and an interpolator (81). The number k of the lookup tables LUT1, LUT2, ..., LUTk is an integer larger than the number of stages n of the controllable luminance Lj of the backlight unit 4 for local dimming, It is the number that multiplies by two to a multiple. The number k of steps is smaller than the number of steps of the local luminance value PLum (the number of steps of each pixel or each light-emitting luminance estimated by the local luminance value estimator 55, h). If n is 4 then Lj ∈ {L1, L2, ... , Ln} = {L1, L2, L3, L4}, for example ten lookup tables (LUT1 to LUT10) can be used. However, k is not limited to 10, and may be, for example, 130, 258 or other numbers.

Each look-up table corresponds to any one of the local luminance values PLum. Since h > k, the step of the local luminance value (PLum) corresponding to these lookup tables is discrete, and these steps close to h / (k-2). 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 selects one of the signals (RGB image signal (R1, G1, B1) or gray image signal (W1)) currently input to the gradation converter or the color balance correction parameter generator according to the inputted local luminance value (Plum) Up table (LUT1, LUT2, ..., LUTk) to be used for the lookup table (LUT1, LUT2, ..., LUTk). If the local luminance value PLum is between two stages corresponding to the 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 the lookup table LUT3 corresponding to the step 1023 and the lookup table LUT4 corresponding to the step 1535 if, for example, PLum = 1050, If PLum = 3091, the lookup table LUT7 corresponding to the step 3071 and the lookup table LUT8 corresponding to the step 3583 are selected.

When the local luminance value PLum coincides with one step corresponding to one lookup table, the selector 80 selects the lookup table and the lookup table corresponding to the immediately preceding step. For example, the selector 80 selects the lookup table LUT3 corresponding to the step 1023 and the lookup table LUT4 corresponding to the step 1535 if PLum = 1023, the lookup table LUT7 corresponding to the step 3071 if PLum = 3071, The lookup table LUT8 corresponding to 3583 is selected.

That is, when the step of the luminance value corresponding to one lookup table is L (i), the stage immediately preceding thereto is L (i + 1), and L (i)? PLum? L Selects the values O (i) and O (i + 1) of the two lookup tables corresponding to the 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 gradation of the image signal.

(I)) / (L (i + 1) -L (i)) where Vout = PLum-L (i)

In this manner, the R-to-G converter 64R corrects the input signal R1 by R2 and outputs R2. The G-tone converter 64G corrects the input signal G1 by G2 to output G2, The gray level converter 66 corrects the inputted gray image signal W1 by W2 and outputs W2. In addition, the color balance correction parameter generator (64L _R) is obtained with the color balance correction parameter L _R from the input signal R1 output the color balance correction parameter L _R, and the color balance correction parameter generator 64L _G, the color from the input signal G1 and it obtained the balance correction parameter L _G outputs a color balance correction parameter L _{G, B} color balance correction parameter generator 64L, the color balance correction parameter from an input signal B1 obtained to L _B, and outputs a color balance correction parameter L _B. The content of the look-up table differs depending on the type of the tone converter or the color balance correction parameter generator.

13 is a gray level converter (64R, 64G, 64B, 66 ) and color balance correction parameter generator (64L _{R, G} 64L, 64L _B) a block diagram showing each of other examples in detail. The example of FIG. 13 may be used instead of the example of FIG.

13, each of the gradation converters or each of the color balance correction parameter generators includes a plurality of selectors 82a to 82m and a plurality of coefficient value memories 84a to 84m respectively corresponding to the selectors 82a to 82m, And a conversion operator 86. Each of the count value memories 84a to 84m is configured to have the same number of steps as the number of steps of the local luminance value PLum (the number of steps of the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator 55) (For example, coefficient values A ₁ to A _h ).

Each of the selectors 82a to 82m selects one of the signals (RGB image signals (R1, G1, B1) or gray image signals W1 (G1, G2)) currently input to the gradation converter or the color balance correction parameter generator according to the local luminance value ) From the coefficient value memory corresponding to the selector. For example, the selector 82a selects any _one 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 _h ). The conversion operator 86 uses the coefficient values A (any of A ₁ to A _h ) to M (M ₁ to M _h ) selected by the selectors 82a to 82m to calculate the luminance value .

For example, the conversion operator 86 converts the luminance value Vin of the input signal (RGB image signal (R1, G1, B1) or gray image signal W1) into the output luminance value Vout correction, and obtains the output signals (R2, G2, B2, W1, L _R, L _G, or L _B).

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

Here, m is the number of the selectors 82a to 82m, and is, for example, an integer of 4 or more.

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

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

Here, m is the number of the selectors 82a to 82m, and is, for example, an integer of 4 or more.

Thus, the R gradation converter 64R corrects the input signal R1 by R2 and outputs R2. The G gradation converter 64G corrects the inputted signal G1 by G2 to output G2, and outputs it to the B gradation converter ( 64B corrects the input signal B1 by B2 and outputs the corrected signal B1. The gray level converter 66 corrects the inputted gray image signal W1 by W2 and outputs W2. In addition, the color balance correction parameter generator (64L _R) is obtained with the color balance correction parameter L _R from the input signal R1 output the color balance correction parameter L _R, and the color balance correction parameter generator 64L _G, the color from the input signal G1 and it obtained the balance correction parameter L _G outputs a color balance correction parameter L _{G, B} color balance correction parameter generator 64L, the color balance correction parameter from an input signal B1 obtained to L _B, and outputs a color balance correction parameter L _B. The contents of the selectors 82a to 82m, the coefficient memory 84a to 84m and the conversion operator 86 differ 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 stores the number of steps of the local luminance value PLum (the luminance value of each pixel or each subpixel estimated by the local luminance value estimator 55 The number of steps is the same as the number of steps of h), so that the circuit scale becomes very large. The example shown in Fig. 14 suppresses an increase in circuit scale.

14 is a gray level converter (64R, 64G, 64B, 66 ) and color balance correction parameter generator (64L _{R, G} 64L, 64L _B) a block diagram showing each of other examples in detail. The example of FIG. 14 may be used instead of the examples of FIG. 12 and FIG.

As shown in FIG. 14, each of the gradation converters or each of the color balance correction parameter generators includes a first calculation unit 90, a second calculation unit 91, and an interpolator 98. The first arithmetic section 90 has a plurality of selectors 92a to 92m and a plurality of coefficient value memories 93a to 93m respectively corresponding to the selectors 92a to 92m and a conversion arithmetic operator 96. [ The second arithmetic section 91 has a plurality of selectors 94a to 94m and a plurality of coefficient memory 95a to 95m respectively corresponding to the selectors 94a to 94m and a conversion calculator 97. [

Each of the count value memories 93a to 93m of the first arithmetic section 90 calculates the number of steps of the local luminance value PLum (the step of the luminance of each pixel or each subpixel estimated by the local luminance value estimator 55 (For example, coefficient values A ₁ , A ₃ , ~A _f ). Each of the coefficient memory 95a to 95m of the second calculator 91 also stores a number of coefficient values far less than half the number of steps h of the local luminance value PLum A ₂ , A ₄ , ~ A _{f + 1} ).

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

Each of the selectors 92a to 92m selects one of the signals (RGB image signals (R1, G1, B1) or gray image signals W1 (G1, G2)) currently input to the gradation converter or the color balance correction parameter generator according to the local luminance value ) From the coefficient 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 92m selects one of the count values from the count value memory 93m And selects any one of the coefficient values (M ₁ , M ₃ , and M _f ). Each of the selectors 92a to 92m selects a coefficient value corresponding to the step closest to the local luminance value PLum with 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 And performs arithmetic processing. For example, the conversion operator 96 obtains the calculated value Vcal1 from the luminance value Vin of the input signal (RGB image signal (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

Here, m is the number of the selectors 92a to 92m, and is, for example, an integer of 4 or more.

Alternatively, the conversion operator 96 may obtain the calculated 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 selects a coefficient to be used for the signal currently input to the gradation converter or the color balance correction parameter generator, based on the local luminance value PLum, Select from memory. For example, the selector 94a selects any one of the coefficient values A ₂ , A ₄ , and A _{f + 1} from the coefficient memory 93a, and the selector 94m selects one of the coefficient values stored in the coefficient memory 93m (M ₂ , M ₄ , ..., M _{f + 1} ) is selected from among the coefficient values Each of the selectors 94a to 94m selects a coefficient value corresponding to a step that is larger than the local luminance value PLum and closest to the local luminance value PLum.

The conversion operator 97 selects one of the coefficient values A (A ₂ , A ₄ , to A _{f + 1} ) to M (M ₂ , M ₄ , to M _{f + 1} ) selected by the selectors 94a to 94m ) To perform the arithmetic processing. For example, the conversion operator 97 obtains the calculated value Vcal2 from the luminance value Vin of the input signal (RGB image signal (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

Here, m is the number of the selectors 94a to 94m, and is, for example, an integer of 4 or more.

Alternatively, the conversion operator 97 may obtain the calculated 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 result (calculation value Vcal1) of the conversion calculator 96 of the first calculation unit 90 and the calculation result (calculation value Vcal2) of the conversion calculator 97 of the second calculation unit 91, The gradation of the image signal is obtained.

Thus, the R gradation converter 64R corrects the input signal R1 by R2 and outputs R2. The G gradation converter 64G corrects the inputted signal G1 by G2 to output G2, and outputs it to the B gradation converter ( 64B corrects the input signal B1 by B2 and outputs the corrected signal B1. The gray level converter 66 corrects the inputted gray image signal W1 by W2 and outputs W2. In addition, the color balance correction parameter generator (64L _R) is obtained with the color balance correction parameter L _R from the input signal R1 output the color balance correction parameter L _R, and the color balance correction parameter generator 64L _G, the color from the input signal G1 and it obtained the balance correction parameter L _G outputs a color balance correction parameter L _{G, B} color balance correction parameter generator 64L, the color balance correction parameter from an input signal B1 obtained to L _B, and outputs a color balance correction parameter L _B. The contents of the selectors 92a to 92m and 94a to 94m and the coefficient memory 93a to 93m and 95a to 95m and the conversion operators 96 and 97 differ depending on the type of the gradation converter or the color balance correction parameter generator .

The example shown in Fig. 14 brings about the same result as the example shown in Fig. 13, but the increase in the circuit scale can be suppressed from the example shown in 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 gradation converter 64 are supplied to the color balance controller 70. The gray image signal W2 output from the gray level converter 66 is supplied to the edge hold circuit 68. [

The edge hold circuit 68 performs a 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 driving IC 36 of the rear side LCD panel 3. There is no problem when viewed from the front of the two LCD panels 2 and 3, but when viewed from the diagonal direction, the difference between the display image of the front side LCD panel 2 and the display image of the rear side LCD panel 3 There is a problem that the double image and the color deviation are seen by the position being deviated according to the angle. In order to solve this problem, the edge hold circuit 68 plays a role of correcting the viewing angle of the gray image.

15 is a schematic diagram showing the result of the viewing angle correction (local edge hold processing) performed by the edge hold circuit 68. 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. [ On the other hand, the black circles in Fig. 15 correspond to the luminance values of the pixels subjected to the edge hold processing.

As shown in Fig. 15, by performing the local edge hold processing, the luminance value of the near portion dark pixel is replaced with the luminance value of the bright portion pixel of the image at the boundary (edge) with the dark portion. By performing the correction to improve the luminance of the dark portion pixels adjacent to the bright portion as described above, it is possible to prevent the image from becoming dark when viewed from the diagonal direction.

The specific configuration and specific processing of the edge hold circuit 68 may be those described in Japanese Patent Laid-Open Publication No. 2016-118687. The edge hold circuit 68 is configured so that the difference between the maximum value and the minimum value of the luminance values of a plurality of pixels in the vicinity including the target pixel is higher than the other threshold value The luminance value lower than the luminance value of the target pixel among the luminance values of the plurality of pixels is replaced with the luminance value of the target pixel.

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 receives the RGB image signals R2, G2 and B2 and the color balance correction parameters L _R , L _G and L _B after the gradation conversion by the RGB gradation converter 64 and the edge- Color balance correction is performed on the basis of the color balance correction parameter Lw outputted from the color balance correction parameter Lw. That is, the color balance controller 70 adjusts the color balance using the color balance correction coefficient for each of the subpixels for the RGB image signals (R2, G2, B2) subjected to the gray level conversion, G3, and B3. The RGB image signals R3, G3, and B3 are supplied to the driving IC 28 of the front side LCD panel 2.

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

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

RGB image signals (R 2, G 2, B 2) subjected to tone conversion by the RGB tone converter 64.

The color balance correction parameters (L _R , L _G , L _B ) generated by the RGB gradation converter (64).

The color balance correction parameter (Lw, gray image signal W3) generated in the edge hold circuit 68.

The divider 74R, 74G, 74B calculates the color balance correction coefficient by dividing the color balance correction parameter of the corresponding color by the color balance correction parameter Lw. The multipliers 72R, 72G, and 72B generate RGB (R3, G3, B3) after color balance correction by multiplying the RGB image signal of the corresponding color by the color balance correction coefficient 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 an explanatory diagram of color balance adjustment in the dark part of an image due to the action of the color balance controller 70. Fig. As shown in Fig. 17 (a), a case in which R, G, and B respectively represent mixed colors other than 0 (R> G> B) will be described as an example. As described above, the gray converter 60 converts the maximum luminance level among the luminance levels R1, G1, B1 of the plurality of subpixels of each pixel to the gray image signal W1 of the pixel (the pixel to which these subpixels belong) As a luminance level of the pixel. Accordingly, a gray image having the luminance value of the R sub-pixel which is the maximum value is generated in the rear side LCD panel 3.

In this case, there is a possibility that the backlight for ensuring the luminance of a certain subpixel passes through another subpixel belonging to the same pixel as the subpixel, thereby causing color discrepancy. The luminance of the G and B subpixels becomes larger than the desired luminance due to the light leakage through the pixels PX of the rear LCD panel (LV panel 3) from the backlight unit 4, The color of which is shifted.

This tendency continues after the processing by the gray gradation converter 66 and the RGB gradation converter 64 (Fig. 17 (b)). Therefore, for example, the R light transmitted through the front side LCD panel 2 has a desired luminance, but the color balance is collapsed because the luminance of G and B light 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 sub-pixel as shown in Fig. 17 (c). However, in the rear side LCD panel 3, the luminance of each pixel of the gray image can be adjusted, but the luminance of each sub pixel can not be adjusted. Therefore, in order to obtain a desired synthetic transmittance for each subpixel, it is necessary to adjust the gray level of each subpixel of the front side LCD panel 2.

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

A concrete 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, the original color can be displayed even in the mixed color portion, and the color reproducibility can be improved. Although the case of expressing the dark portion of the image has been described above, the backlight for ensuring the luminance of a certain sub-pixel SP is different from the sub-pixel SP belonging to the same pixel PX And transmits the sub-pixel SP. Therefore, the effect of the color balance controller 70 is exerted not only on the dark portion of the image but also on the list portion.

17, the color balance correction parameters (L _R , L _G , and L _B ) generated in the RGB gradation converter 64 (see FIG. 5) correspond to the RGB image signals (R1, G1, B1) Therefore, in the case of displaying an RGB image only in the front side LCD panel 2, in order to realize the luminance represented by each sub pixel in the panels 2 and 3, if the rear side LCD panel 3 displays different luminance for each RGB sub pixel The luminance of the sub-pixel of the rear LCD panel 3 is supposed to be. The color balance correction parameter generator 64L _R of the RGB gradation converter 64 can generate the color balance correction parameter L _R from only the input signal R 1 and the color balance correction parameter generator 64L _G can generate The color balance correction parameter generator 64LB can generate the color balance correction parameter L _G from only the inputted signal _{G 1} and the color balance correction parameter generator 64L _B can generate the color balance correction parameter L _G from only the input signal _{B 1} , Lt; / RTI >

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

5, the delay circuit 62 is provided to synchronize the processing of the RGB gradation converter 64 and the processing of the gray level gradation converter 66, and the gray image signal (R1, G1, B1) A considerable delay is given to the time required for the processing of the processing unit 60. The delay circuit 52 outputs the LED drive signal BD for driving the backlight unit 4 to the RGB image signals R3, G3 and B3 supplied to the front side LCD panel 2 and the rear side LCD panel 3, G3 and B3 and the gray image signal W3 supplied to the local luminance value PLum supplied from the block luminance value determiner 50. The gray level signal A delay corresponding to the time required for generation of the word line W3. Although the delay circuits 52, 58 and 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, the local dimming technique is applied to the image display apparatus including the front side LCD panel 2 displaying the RGB image and the rear side LCD panel 3 displaying the gray image , The emission luminance of each pixel or each sub pixel is estimated based on the desired luminance of each dimming block to adjust the luminance level of the sub pixel of the RGB image signal corresponding to the pixel or the sub pixel, A gray image signal for controlling the brightness level of the gray image displayed on the rear side LCD panel 3 is generated. Thus, 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 the local dimming technique is applied to an image display apparatus having two LCD panels, but the local brightness value estimation is not performed (luminance variation in the dimming block is not taken into account). 19 shows an example of a display image in which a local dimming technique is applied to an image display apparatus having two LCD panels and a local luminance value estimation (light emission luminance estimation of each pixel) is performed according to an embodiment of the present invention Respectively. For reference, the positions of the dimming blocks for these display images are shown in the lower part of Fig. A square corresponds to the dimming block.

According to the contrast of FIG. 18 and FIG. 19, since the luminance variation in the dimming block (see FIG. 4) is not considered in FIG. 18, the luminance difference is conspicuously visually observed near the boundary of the adjacent dimming block. On the other hand, in FIG. 19, since the luminance of each pixel is estimated in consideration of the luminance variation in the dimming block and the RGB image signal and the gray image signal are adjusted based on the estimated luminance of each pixel, The difference in luminance is not distinguished. 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 the image display apparatus capable of displaying an HDR image, a maximum luminance of 10,000 nits and a contrast ratio of 2,000,000: 1 are realized. Even if a high luminance area and a low luminance area are mixed in one dimming block, . 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.

When an 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 the transmittance of the image display device of one panel It is necessary to increase the brightness of the backlight unit in order to obtain the same display brightness as in the case of one panel. In this case, a considerable power consumption in the backlight unit and installation of the cooling mechanism accompanying the heat generation may become a problem.

However, according to the embodiment of the present invention, by applying the local dimming technique, the backlight unit 4 emits the LEDs 42 corresponding to the necessary dimming blocks with appropriate brightness, so that the backlight unit 4 is compared with the backlight unit not using the local dimming technique So that the power consumption can be greatly reduced, and a large-scale cooling mechanism is not required. Therefore, the cost of the backlight unit 4 according to the embodiment of the present invention can be reduced as compared with the backlight unit not using the local dimming technique.

1: Image display device 2: Front side 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: driving IC
30: glass substrate 32: TFT substrate
34: polarizing film 36: driving IC
40: substrate 42: LED
44: side wall 46: LED driving part
5: signal processing unit 50: block luminance value determining unit
52, 58, 62: delay circuit
54: LED drive signal generator (backlight 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 gradation converter 64B: B gradation converter
64L _R : Color balance correction parameter generator
64L _G : Color balance correction parameter generator
64L _B : Color balance correction parameter generator
66: Gray gradation converter 68: Edge hold circuit
70: color balance controller 80: selector
81: interpolators 82a to 82m: selector
84a to 84m: coefficient value memory 86: conversion operator
90: first calculation unit 91: second calculation unit
92a to 92m, 94a to 94m: selectors 93a to 93m, 95a to 95m: coefficient value memory
96: conversion operator 98: interpolator
72R, 72G, 72B: multipliers 74R, 74G, 74B:

Claims (14)

A front side LCD panel for displaying RGB images;
A rear side LCD panel disposed behind the front side LCD panel and superimposed on the front side LCD panel to display a gray image;
A backlight unit disposed behind the rear LCD panel and capable of adjusting the brightness of each of the plurality of blocks by irradiating light to the front LCD panel and the rear LCD panel;
A block luminance value determiner for determining a desired luminance of each of the blocks from an input RGB image signal;
A backlight driving signal generator for driving the backlight unit to adjust the luminance of the block in accordance with a desired luminance of each of the blocks determined in the block luminance value determiner;
A local brightness value estimator for estimating a light emission luminance value of each pixel or each subpixel in the case where each block is caused to emit light at the desired luminance based on a desired luminance of each of the blocks determined by the block luminance value determiner;
A level converter for adjusting a luminance level of a subpixel of the RGB image signal corresponding to the pixel or the subpixel based on the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator; And
And a gray converter for generating a gray image signal for controlling the brightness level of the gray image displayed on the rear side LCD panel based on the brightness level of the subpixel adjusted by the level converter.
The method according to claim 1,
Wherein 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.
3. The method according to claim 1 or 2,
Wherein the local brightness value determiner comprises:
A storage device for storing typical luminance distribution data in the block in the case where only the block is lighted for each block, in the block adjacent to the block, or in the entire display area,
And an arithmetic unit for calculating the light emission luminance of each pixel or each sub pixel from the typical luminance distribution data and the desired luminance of each block.
3. The method according to claim 1 or 2,
Wherein the local brightness value estimator comprises:
A storage device for storing typical luminance distribution data in the block in the case where only the block is lighted for each block, in the block adjacent to the block, or in the entire display area,
A data interpolator for interpolating the typical luminance distribution data to generate detailed luminance distribution data;
And an arithmetic unit for calculating the light emission luminance of each pixel or each sub pixel from the detailed luminance distribution data and the desired luminance of each block.
3. The method according to claim 1 or 2,
Wherein the local brightness value estimator comprises:
A distribution characteristic generator for generating typical luminance distribution data in the block and in a block adjacent to the block or in the entire display area when light is emitted only in that block for each block using a calculation formula,
And an arithmetic unit for calculating the light emission luminance of each pixel or each sub pixel from the typical luminance distribution data and the desired luminance of each block.
3. The method according to claim 1 or 2,
Wherein the level converter is configured to increase the luminance level of the subpixel of the RGB image signal corresponding to the pixel or the subpixel as the emission luminance of each pixel or each subpixel estimated by the local luminance value estimator is lower, .
3. The method according to claim 1 or 2,
Wherein 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.
3. The method according to claim 1 or 2,
Further comprising an RGB gradation converter for correcting the gradation of the RGB image signal whose luminance level is adjusted by the level converter so as to match the output characteristic of the front side LCD panel,
Wherein the RGB gradation converter corrects the gradation of the RGB image signal based on the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator.
9. The method of claim 8,
Wherein the RGB gradation converter has a gradation converter corresponding to each color of RGB,
Each gradation converter includes a plurality of lookup tables each having a number smaller than the number of steps of the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator and a lookup table for each pixel or each subpixel estimated by the local luminance value estimator And an interpolator for interpolating the values of the two lookup tables selected by the selector to obtain the gradation of the image signal.
9. The method of claim 8,
Wherein the RGB gradation converter includes a gradation converter corresponding to each color of RGB,
Each gradation converter includes a first calculation unit, a second calculation unit, and an interpolator,
The first calculation unit and the second calculation unit, respectively,
A plurality of coefficient value memories each of which stores a coefficient value smaller than half of the number of steps of light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator;
A selector for selecting one coefficient value from each of the plurality of coefficient value memories in accordance with the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator;
And a conversion operator for performing an operation process based on a plurality of coefficient values selected by the selector,
Wherein the interpolator interpolates the arithmetic processing result of the conversion arithmetic unit of the first arithmetic unit and the arithmetic processing result of the conversion arithmetic unit of the second arithmetic unit to obtain the gradation of the image signal.
3. The method according to claim 1 or 2,
And a gray level converter for correcting the gray level of the gray image signal generated by the gray converter so as to match the output characteristic of the rear side LCD panel,
Wherein the gray level converter corrects the gray level of the gray image signal based on the light emission luminance of each pixel or each subpixel estimated by the local brightness value estimator.
12. The method of claim 11,
Wherein the gray gradation converter includes a plurality of lookup tables each of which is smaller than the number of stages of light emission luminances of each pixel or each subpixel estimated by the local luminance value estimator and a plurality of lookup tables each of which is estimated by the local luminance value estimator, And an interpolator for interpolating the values of the two lookup tables selected by the selector to obtain the grayscale of the gray image signal.
12. The method of claim 11,
Wherein the gray level converter includes a first calculation unit, a second calculation unit and an interpolator,
The first calculation unit and the second calculation unit, respectively,
A plurality of coefficient value memories each of which stores a coefficient value smaller than half of the number of steps of light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator;
A selector for selecting one coefficient value from each of the plurality of constant value memories in accordance with the light emission luminance of each pixel or each subpixel estimated by the local luminance value estimator;
And a conversion operator for performing an operation process based on a plurality of coefficient values selected by the selector,
Wherein the interpolator interpolates the arithmetic processing result of the conversion arithmetic unit of the first arithmetic unit and the arithmetic processing result of the conversion arithmetic unit of the second arithmetic unit to obtain the gradation of the image signal.
A front side LCD panel for displaying RGB images,
A rear LCD panel disposed behind the front LCD panel and superimposed on the front LCD panel to display a gray image;
And a backlight unit disposed behind the rear LCD panel and capable of adjusting the luminance of each of the plurality of blocks by irradiating light to the front LCD panel and the rear LCD panel as an image display method executed in an image display apparatus ,
Determining a desired luminance of each of the blocks from an input RGB image signal;
Driving the backlight unit to adjust the brightness of the block according to a desired brightness of each of the determined blocks;
Estimating a light emission luminance value of each pixel or each subpixel in the case where each block is caused to emit light at the desired luminance based on a desired luminance of each of the determined blocks;
Adjusting a luminance level of a subpixel of the RGB image signal corresponding to the pixel or the subpixel based on the estimated light emission luminance of each pixel or each subpixel; And
And generating a gray image signal for controlling a brightness level of the gray image displayed on the rear side LCD panel based on the brightness level of the adjusted subpixel.

Images