KR20080061772A - Driving circuit for liquid crystal display device and method for driving the same - Google Patents

Abstract

A device for driving an LCD device and a method for driving the same are provided to embody a peak luminance of a high brightness/achromatic color by generating 4-color conversion data using a compensated value based on a chroma ratio of images. A device for driving an LCD(Liquid Crystal Display) device includes an LCD panel(102), data and gate drivers(104,106), a data converter(110), and a timing controller(108). The LCD panel includes plural unit pixels having red, green, blue, and white sub-pixels. The data and gate drivers supply images and a gate on voltage to respective sub-pixels, respectively. The data converter compensates for a gain value, which is extracted using a gray scale difference of 3-color input data supplied to the respective sub-pixels, according to a chroma ratio of the 3-color input data and converts the 3-color input data into 4-color data using the compensated gain value. The timing controller supplies the 4-color data from the data converter to the data driver and controls the gate and data drivers.

Description

Driving device for liquid crystal display and driving method thereof {Driving circuit for liquid crystal display device and method for driving the same}

1 is a block diagram showing a driving device of a liquid crystal display according to an embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a data converter shown in FIG. 1. FIG.

3 is a block diagram showing a histogram generating unit shown in FIG.

4 is a graph for setting a correction gain value in the gain value correction unit shown in FIG. 2.

FIG. 5 is a configuration diagram illustrating an RGBW generation unit illustrated in FIG. 2.

FIG. 6 is a view showing an image supplied to a data converter shown in FIG. 2; FIG.

7 is a view showing an image displayed by the driving device and driving method of the liquid crystal display device according to the embodiment of the present invention.

<Description of reference numerals for main parts of the drawings>

110: data conversion unit 200: first gamma correction unit

210: gray level detection unit 220: histogram generation unit

230: gain value extraction unit 240: RGBW generation unit

250: second gamma correction unit 260: gain value correction unit

320: color correction unit 330: white data extraction unit

Ak: Correction gain value CR: Color ratio factor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a driving device and a driving method of a liquid crystal display device capable of realizing high brightness / achromatic peak luminance while minimizing color degradation of an RGBW type liquid crystal panel.

Recently, various flat panel display devices that can reduce weight and volume, which are disadvantages of cathode ray tubes, have emerged. Such flat panel displays include a liquid crystal display, a field emission display, a plasma display panel, a light emitting display, and the like.

Among flat panel displays, a liquid crystal display includes a plurality of liquid crystal cells disposed in a region defined by a plurality of data lines and a plurality of gate lines, and a thin film transistor (TFT) as a switch element in each liquid crystal cell. And a color filter substrate on which a color filter is formed are maintained at regular intervals and includes a liquid crystal layer formed therebetween.

Such a liquid crystal display obtains a desired image by forming an electric field in the liquid crystal layer in accordance with the data signal to adjust the transmittance of light passing through the liquid crystal layer. In this case, the polarity of the data signal is reversed on a frame, row, or dot basis in order to prevent deterioration caused by an electric field applied to the liquid crystal layer for a long time.

Such a liquid crystal display device realizes one color image by mixing red light, green light, and blue light from three color dots of red (R), green (G), and blue (B). However, there is a disadvantage in that light efficiency is lowered in a general liquid crystal display device that displays one subpixel with three color dots of red (R), green (G), and blue (B). Specifically, the color filter disposed in each of the red, green, and blue subpixels transmits only about one third of the applied light, thereby reducing the overall light efficiency.

Accordingly, RGBW including white subpixels (W) in addition to the red (R), green (G), and blue (B) subpixels as a method for improving luminance and light efficiency while maintaining color reproducibility of the liquid crystal display device. A type liquid crystal display device has been proposed.

The RGBW type liquid crystal display multiplies each of the three-color input data by a gain value to generate three-color amplified data, and then extracts the data having the minimum gray scale among the three-color amplified data as white data, and extracts the three-color amplified data. Four color data is generated by subtracting the extracted white data.

However, the conventional RGBW type liquid crystal display has a disadvantage in that the luminance of the other area is also darkened when a part of the image of one frame is pure color with high brightness and saturation. Such a four-color data conversion algorithm can realize high brightness without distortion of color in mixed colors, but there is a problem that high brightness achromatic peak luminance cannot be realized when mainly displaying high brightness and high saturation such as a notebook (Note Book). .

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a driving apparatus and a driving method of a liquid crystal display device capable of realizing high brightness / achromatic peak luminance while minimizing color degradation of an RGBW type liquid crystal panel. .

A liquid crystal display device driving apparatus according to an embodiment of the present invention for achieving the above object is a liquid crystal panel comprising a plurality of unit pixels consisting of red, green, blue and white subpixels; A data driver for supplying an image signal to each subpixel; A gate driver supplying a gate-on voltage to each of the subpixels; The gain value extracted by using the gray level difference of the three-color input data supplied to each subpixel is corrected according to the color ratio of the three-color input data, and the three-color input data is adjusted by using the corrected gain value. A data converter converting the color data and outputting the color data; And a timing controller which supplies the four-color data from the data converter to the data driver and controls the gate driver and the data driver.

In addition, the driving method of the liquid crystal display according to the embodiment of the present invention for achieving the above object is a method of driving a liquid crystal display comprising a plurality of unit pixels consisting of red, green, blue and white subpixels. Correcting the gain value extracted using the gray level difference of the three-color input data supplied to each subpixel according to the color ratio of the three-color input data; Converting the three-color input data into four-color data by using the corrected gain value and outputting the four-color data; And converting each of the four color data into the image signal and supplying each of the red, green, blue, and white subpixels.

Hereinafter, a driving apparatus and a driving method thereof of a liquid crystal display according to an exemplary embodiment of the present invention having the above characteristics will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram illustrating a driving device of a liquid crystal display according to an exemplary embodiment of the present invention.

The driving device of the liquid crystal display shown in FIG. 1 includes a liquid crystal panel including liquid crystal cells formed in four subpixel regions defined by n gate lines GL1 through GLn and m data lines DL1 through DLm. 102; A data driver 104 for supplying an image signal to the data lines DL1 to DLm; A gate driver 106 for supplying a gate-on voltage to the gate lines GL1 through GLn; The gain generated according to the gradation difference of the tri-color input data (RGB) is corrected using the coloring ratio of the tri-color input data (RGB), and the tri-color input data (RGB is used using the color correction coefficient and the corrected gain ) A data conversion unit 110 for converting the 4-color data into RGBW; The four-color data RGBW from the data converter 110 is arranged and supplied to the data driver 104, and the data control signal DCS is generated to control the data driver 104 and at the same time the gate control signal GCS. And a timing controller 108 to control the gate driver 106.

The liquid crystal panel 102 includes a thin film transistor formed in a region defined by n gate lines GL1 through GLn and m data lines DL1 through DLm, and a liquid crystal connected to the thin film transistor TFT. With cells. The thin film transistor TFT supplies a data signal from the data lines DL1 to DLm to the liquid crystal cell in response to the gate-on voltages from the gate lines GL1 to GLn. The liquid crystal cell may be equivalently represented as the liquid crystal capacitor Clc since the liquid crystal cell includes a common electrode facing the liquid crystal and a sub pixel electrode connected to the thin film transistor TFT. The liquid crystal cell includes a storage capacitor Cst to maintain the data signal charged in the liquid crystal capacitor Clc until the next data signal is charged.

In the liquid crystal panel 102, red (R), green (G), blue (B), and white (W) subpixels are repeatedly formed in the row direction of the subpixels. In this case, a color filter corresponding to each color is disposed in each of the red (R), green (G), and blue (B) subpixels, whereas a separate color filter is not disposed in the white (W) subpixel. In addition, the red (R), green (G), blue (B), and white (W) subpixels form a stripe structure having the same area ratio or different area ratios. In this case, the red (R), green (G), blue (B), and white (W) subpixels may be arranged in a 2 × 2 matrix form.

The data converter 110 uses the gray level difference of the three-color input data RGB supplied to each of the unit pixels consisting of subpixels of red (R), green (G), and blue (B) input from the outside. A histogram for each gradation difference is extracted. Then, the gain value from the extracted histogram for each gradation difference is corrected according to the saturation ratio of the three-color input data RGB, that is, the color ratio coefficient, and the three-color input data (using the corrected gain value and color correction coefficient) is used. RGB is converted into four-color data RGBW and supplied to the timing controller 108.

The timing controller 108 arranges the four-color data RGBW supplied from the data converter 110 to be suitable for driving the liquid crystal panel 102 and supplies the four color data RGBW to the data driver 104. In addition, the timing controller 108 may control the data control signal DCS and the gate control signal GCS according to a main clock MCLK, a data enable signal DE, horizontal and vertical synchronization signals Hsync, Vsync, and the like input from the outside. ) To control driving timing of each of the data driver 104 and the gate driver 106.

The gate driver 106 sequentially generates a gate-on voltage, that is, a gate high pulse, in response to the gate start pulse GSP and the gate shift clock GSC among the gate control signals GCS from the timing controller 108. Contains registers The thin film transistor TFT is turned on in response to the gate-on voltage.

The data driver 104 converts the four-color image data Data arranged from the timing controller 108 into an image signal, which is an analog signal, in accordance with the data control signal DCS supplied from the timing controller 108, thereby converting the gate line GL1. To GLn) is supplied to the data lines DL1 to DLm for one horizontal line every one horizontal period to which the gate-on voltage is supplied. In other words, the data driver 104 selects a gamma voltage having a predetermined level according to the gray value of the four-color image data Data, and supplies the selected gamma voltage to the data lines DL1 to DLm.

FIG. 2 is a diagram illustrating a data converter illustrated in FIG. 1.

2, the data converter 110 may include a first gamma corrector 200, a gray scale detector 210, a histogram generator 220, a gain value extractor 230, and an RGBW generator. 240, a gain value corrector 260, and a second gamma corrector 250.

Since the first gamma correction unit 200 is a signal in which the three-color input data RGB of each unit pixel of the input image is gamma corrected in consideration of the output characteristics of the cathode ray tube, it is linearized using Equation 1 below. Correct with three-color data (RI, GI, BI).

The gray scale detector 210 compares the primary three-color data (RI, GI, BI) of each unit pixel supplied from the first gamma corrector 200 to each other, and thereby the maximum gray scale value (MAX _RGB ) and the minimum gray scale for each unit pixel. Detect the value (MIN _RGB ). The detected maximum gray value MAX _RGB and the minimum gray value MIN _{RGB are} supplied to the histogram generator 220 and the gain value corrector 260.

As shown in FIG. 3, the histogram generator 220 includes a first subtractor 222, a histogram calculator 224, and a histogram accumulator 226.

The first subtractor 222 subtracts the minimum gray value MIN _RGB from the maximum gray value MAX _RGB for each unit pixel supplied from the gray level detector 210 to reduce the gray level difference per unit pixel (MAX _{RGB to} MIN _RGB ). Obtain Here, the gray level difference per unit pixel (MAX _RGB- MIN _RGB ) is an element that determines the saturation saturation of the pixel when the three-color input data ( _RGB ) is converted into four-color data (RGBW).

The histogram calculator 224 calculates a histogram Hist_s for each gray level difference by counting the number of pixels for each gray level difference (MAX _{RGB to} MIN _RGB ) for each unit pixel supplied from the first subtractor 222.

The histogram accumulator 226 accumulates the histogram Hist_s for each gray level difference from the histogram calculator 224 for each gray level difference, and calculates a cumulative histogram Hist_c for each gray level difference, and calculates the cumulative histogram Hist_c for each gray level difference. It is supplied to the gain value extraction unit 230.

As such, the histogram generator 220 has been proposed by Korean Patent Application No. 10-2005-0126274 filed by the present applicant.

In FIG. 2, the gain value extracting unit 230 accumulates the gray level difference at the time when the gray level histogram Hist_c, which is supplied from the histogram accumulator 226, exceeds the gray level setting value M input from the user. A gain value k is extracted according to Equation 2 below using the histogram-level gradation loss limit value N. The gain value extracting unit 220 supplies the extracted gain value k to the gain value correcting unit 260. Here, although the gain value k may be set to have a range of 1 to 4, only the case where the gain value k is set in the range of 1 to 2 will be described below.

In Equation 2, MAX _gray represents a maximum gray value corresponding to the number of bits of the input data RGB, and becomes '255' when the input data RGB is 8 bits. In order to prevent the denominator from being zero in Equation 2, one gray scale is added to the gray scale loss limit value N.

The saturation saturation setting value M set by the user is a variable for setting the number of saturation allowable pixels of the pixels displayed on the liquid crystal panel 102. The saturation saturation setting value M may be set to '0', '3000', '6000', '10000', etc. according to the user's preference according to the resolution of the liquid crystal panel 102. The saturation saturation setting value M refers to the number of pixels which do not affect visual quality visually even when saturation occurs when generating the four-color data RGBW. For example, the gain value extracting unit 230 has a saturation setting value M of '10000', and a cumulative value of the histogram Hist_s of each gradation difference in the cumulative histogram Hist_c for each gradation difference exceeds 10000. When the maximum and minimum gradation difference (MAX _RGB -MIN _RGB ) is' 135 ', set' 135 'to the gradation loss limit value (N), and add' 1 'to the gradation loss limit value (N) to' By dividing 255 'and' 136 ', a gain value k of' 1.875 'is generated.

The gain value correcting unit 260 detects the chroma ratio per unit pixel, that is, the chroma ratio coefficient per unit pixel, and corrects using the detected chroma ratio per unit pixel CR and the input gain value k. Generate the gain value Ak. In other words, the gain value corrector 260 uses the maximum gray value MAX _RGB and the minimum gray value MIN _RGB for each unit pixel from the gray scale detector 210 to adjust the color ratio coefficient CR for each unit pixel. Detect. Here, the color ratio coefficient CR is calculated by performing a subtraction operation of the maximum gray value MAX _RGB and the minimum gray value MIN _RGB or a division operation of the minimum gray value MIN _RGB and the maximum gray value MAX _RGB . can do. Hereinafter, the color ratio coefficient CR calculated by the division operation of the minimum gray value MIN _RGB and the maximum gray value MAX _RGB will be described using Equation 3 below.

As shown in FIG. 4, the gain value corrector 260 generates a correction gain value Ak based on the color ratio coefficient CR and the gain value k input from the gain value extractor 260, thereby generating RGBW. Supply to the generation unit 240. In detail, the gain value correcting unit 260 performs the upper limit correction gain value Ak_max, the lower limit correction gain value Ak_min, and the maximum value CR_max and the minimum value of the color ratio coefficient CR with respect to the input gain value k. (CR_min) is set, and the coloring ratio coefficient (CR) and the gain are obtained by using a linear equation between the upper limit value (k_max, 2) and the lower limit value (k_min, k) of the gain value k as shown in Equation 4 below. A correction gain value Ak corresponding to the value k is generated. Here, Equation 4 below shows a case where the upper limit value k_max of the gain value k is limited to '2', and the lower limit value k_min of the gain value k is limited to 'k'.

This, gain correction section 260 is set to be when the gain value (k) that is input is below the lower limit of the correction gain value _(MIN Ak_) correction gain value (Ak) is the lower limit correction gain value _(MIN Ak_). And, if the input gain value (k) is higher than the lower limit correction gain value _(MIN Ak_) it is to generate a correction gain value corresponding to the color ratio coefficient (CR) are input (Ak).

FIG. 5 is a configuration diagram illustrating an RGBW generation unit illustrated in FIG. 2.

The RGBW generator 240 illustrated in FIG. 5 includes a multiplier 310, a color corrector 320, a white data extractor 330, and a second subtractor 340.

The multiplier 310 uses the first three-color data (RI, GI, BI) supplied from the first gamma correction unit 200 and the correction gain value Ak supplied from the gain value correction unit 260. As shown in Equation 5, second-order tricolor data Ra, Ga, and Ba are generated. In other words, the multiplier 310 multiplies the correction gain value Ak by each of the primary tricolor data RI, GI, and BI to generate secondary tricolor data Ra, Ga, and Ba.

Ra = RI × Ak

Ga = GI × Ak

Ba = BI × Ak

The color correcting unit 320 supplies second and third color data supplied from the multiplier 310 according to color correcting coefficients of red (R), green (G), and blue (B) appropriately set for the characteristics of the liquid crystal panel 102. (Ra, Ga, Ba) are corrected to generate tertiary tricolor data Rb, Gb, and Bb.

The white data extractor 330 extracts data having the minimum gray level among the third tertiary color data Rb, Gb, and Bb supplied from the color corrector 320 as the white data Wb.

The second subtracting unit 340 may receive the white data supplied from the white data extracting unit 330 in each of the secondary tricolor data Ra, Ga, and Ba supplied from the multiplier 310 as shown in Equation 6 below. Subtract Wb) to generate quaternary tricolor data (Rc, Gc, Bc), and quaternary tricolor data (Rc, Gc, Bc) and white data (Wb) are converted into four-color conversion data (Rc, Gc, Bc). , Wc) to be supplied to the second gamma correction unit 250.

Rc = Rb-Wb

Gc = Gb-Wb

Bc = Bb-Wb

Wc = Wb

In FIG. 2, the second gamma correction unit 250 gamma-corrects four-color conversion data Rc, Gc, Bc, and Wc supplied from the RGBW generation unit 240 as shown in Equation 7 below to display four-color images. Generate data RGBW. In this case, the second gamma correction unit 250 uses the look up table (not shown) to convert the four-color conversion data Rc, Gc, Bc, and Wc into four colors suitable for the driving circuit of the liquid crystal panel 102. The gamma correction is performed on the image data RGBW and supplied to the timing controller 108.

FIG. 6 is a diagram illustrating an image supplied to the data converter illustrated in FIG. 2, and FIG. 7 is a diagram illustrating an image displayed by a driving apparatus and a driving method of a liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 6 and FIG. 7, the driving apparatus and driving method of the liquid crystal display according to the present invention correct the gain value k according to the chroma ratio, i.e., the chroma ratio of each unit of the supplied image. Like the image shown in Fig. 8, a bright image as a whole and high brightness achromatic peak luminance can be realized. In addition, the present invention maintains the same color as that of the RGB type liquid crystal panel even in the RGBW type liquid crystal panel, and has low pure color luminance due to the peak luminance of the high brightness / achromatic portion even in an image having a small gain value (k) for an image of one frame. It can be covered to some extent.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

As described above, the driving apparatus and driving method of the liquid crystal display according to the exemplary embodiment of the present invention have the following effects.

According to the present invention, the peak brightness of high brightness / achromatic color and pure color can be realized by correcting a gain value according to a saturation ratio for each unit pixel of an input image and generating conversion data of four colors using the corrected gain value. In addition, even in an image having a small gain value for an image of one frame, the luminance is higher than that of the original image, and at the same time, the peak luminance is realized in the high brightness / achromatic portion.

Claims (17)

A liquid crystal panel including a plurality of unit pixels including red, green, blue, and white subpixels; A data driver for supplying an image signal to each subpixel; A gate driver supplying a gate-on voltage to each of the subpixels; The gain value extracted by using the gray level difference of the three-color input data supplied to each subpixel is corrected according to the color ratio of the three-color input data, and the three-color input data is adjusted by using the corrected gain value. A data converter converting the color data and outputting the color data; And And a timing controller for supplying the four-color data from the data converter to the data driver and controlling the gate driver and the data driver. The method of claim 1, The data conversion unit And generating a histogram using the three-color input data, and generating the gain value in units of frames by using the histogram and the saturation setting value set by the user. The method of claim 2, The data conversion unit A first gamma correction unit configured to gamma-correct the three-color input data to generate linearized primary three-color data; A gray scale detector for detecting a maximum and minimum gray scale value for each unit pixel of the primary tricolor data; A histogram generator for generating the histogram by using the gray level difference between the maximum and minimum gray values; A gain value extracting unit extracting the gain value using the histogram and the saturation setting value; A gain value correcting unit detecting a coloring ratio of the three-color input data for each unit pixel and extracting a gain value corrected using the detected coloring ratio for each unit pixel and the gain value; An RGBW generation unit for converting the primary 3-color data into 4-color converted data using the corrected gain value, and And a second gamma correction unit configured to gamma correct the four color conversion data to generate the four color data. The method of claim 3, wherein The gain value correction unit The upper and lower limit correction gain values for the gain value and the maximum and minimum values of the coloring ratio are set, and the correction gain values corresponding to the coloring ratio and the gain value are obtained using a linear equation between upper and lower gain values. And a drive device for the liquid crystal display device. The method of claim 4, wherein The gain value correction unit If the gain value is lower than the lower limit correction gain value, the correction gain value is set to the lower limit correction gain value, and if the gain value is higher than the lower limit correction gain value, correction corresponding to the coloring ratio using the linear equation A drive device for a liquid crystal display, characterized by generating a gain value. The method of claim 5, wherein The coloring ratio is And a subtraction operation of the maximum and minimum gray level values for each unit pixel or a division operation value of the minimum and maximum gray level values for each unit pixel. The method of claim 3, wherein The histogram generator A first subtractor configured to subtract the minimum gray value from the maximum gray value to generate a gray level difference between the maximum and minimum gray values; A histogram calculator configured to calculate a histogram for each gray level difference by counting the number of unit pixels corresponding to the gray level difference between the maximum and minimum gray values from the first subtractor; And a histogram accumulator for accumulating the histograms for each gray level to generate a cumulative histogram for each gray level. The method of claim 7, wherein The RGBW generator A multiplier for multiplying the primary tricolor data and the corrected gain value to generate secondary tricolor data; A color correction unit configured to generate the third three-color data by correcting the second three-color data by using the color correction coefficient set according to the characteristics of the liquid crystal panel; A white data extracting unit extracting data having a minimum gray level among the third three-color data as white data; Generating fourth fourth color data by subtracting the white data from each of the second third color data, and supplying the fourth color conversion data having the fourth third color data and the white data to the second gamma correction unit. And a subtraction section. A driving method of a liquid crystal display device comprising a plurality of unit pixels consisting of red, green, blue, and white subpixels, Correcting the gain value extracted by using the gray level difference of the three-color input data supplied to each subpixel according to the color ratio of the three-color input data; Converting the three-color input data into four-color data by using the corrected gain value and outputting the four-color data; And And converting each of the four color data into the image signal and supplying the four color data to each of the red, green, blue, and white subpixels. The method of claim 9, The gain value extraction step Gamma correcting the tricolor input data to generate linearized primary tricolor data; Detecting a maximum and minimum gray level value for each unit pixel of the primary tricolor data; Generating the histogram using the gradation difference between the maximum and minimum gradation values, and And generating the gain value in units of frames by using the histogram and the saturation setting value set by the user. The method of claim 10, The gain value correction step Detecting a color ratio of the three-color input data for each pixel; And extracting a gain value corrected by using the detected color ratio for each unit pixel and the gain value. The method of claim 11, Extracting the corrected gain value Setting an upper limit and a lower limit correction gain value for the gain value and maximum and minimum values of the coloring ratio, and And extracting the corrected gain value corresponding to the color ratio and the gain value by using a linear equation between the upper limit and the lower limit gain values of the gain value. The method of claim 12, The correction gain value extraction step When the gain value is lower than the lower limit correction gain value, the correction gain value is extracted as the lower limit correction gain value, and when the gain value is higher than the lower limit correction gain value, the correction corresponding to the coloring ratio using the linear equation A method of driving a liquid crystal display, characterized by extracting a gain value. The method of claim 13, The coloring ratio is And a subtraction operation of the maximum and minimum gray level values per unit pixel or a division operation value of the minimum and maximum gray level values for each unit pixel. The method of claim 14, The histogram generation step Subtracting the minimum gray value from the maximum gray value to generate a gray level difference between the maximum and minimum gray values; Calculating a histogram for each gray level difference by counting the number of unit pixels corresponding to the gray level difference between the maximum and minimum gray values; And accumulating the histograms for each gray level difference to generate a cumulative histogram for each gray level difference. The method of claim 15, Converting the three color input data into four color data Converting the primary three-color data into four-color converted data using the corrected gain value and a preset color correction coefficient; and And gamma correcting the four color conversion data to generate the four color data. The method of claim 16, Converting the primary three-color data to four-color conversion data Multiplying the primary tricolor data and the corrected gain value to generate secondary tricolor data; Generating tertiary tricolor data by correcting the secondary tricolor data according to the preset color correction coefficient; Extracting data having a minimum gray scale among the third three-color data as white data, and And subtracting the white data from each of the second tricolor data to generate fourth tricolor data.

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