JP2014038117A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method capable of effectively performing calibration for four primary colour panel.SOLUTION: A manufacturing method of a liquid crystal display device including a liquid crystal panel having a plurality of pixels composed of sub-pixels in four colours different to each other includes: a first step of measuring chromaticities of the respective four primary colour displays; a second step of adjusting, for tristimulus values X, Y, Z of an XYZ colorimetric system, a difference ΔZ between an input value of Z of blue component to the liquid crystal panel and a measured value measured in the first step; and a third step of adjusting, after the second step, a difference ΔX or ΔY between an input value of X or Z of colour component other than the blue component to the liquid crystal panel and the measured value measured in the first step.

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that performs display with four primary colors.

  The liquid crystal display device has advantages such as light weight, thinness, and low power consumption, and is used not only as a small display device such as a display unit of a mobile phone but also as a large television. Unlike a self-luminous panel such as a cathode ray tube (CRT) or a plasma display panel (PDP), the liquid crystal panel does not emit light. For this reason, in general, a liquid crystal display device performs display using light of a backlight disposed on the back surface of a liquid crystal panel.

  In recent years, unlike general liquid crystal display devices of three primary colors, liquid crystal display devices that additively mix four or more primary colors have been proposed. Such a liquid crystal display device is also called a multi-primary color liquid crystal display device. In general, in a multi-primary color liquid crystal display device, another primary color is added to three primary colors (that is, red, green, and blue), and the color reproduction range is expanded. Further, in a multi-primary color liquid crystal display device, display is performed by converting the gradation level of an input video signal that can be displayed by a general three-primary color display device into gradation levels of four or more primary colors (for example, patents). Such a conversion is also called multi-primary color conversion.

  Patent Document 3 proposes an algorithm and a calibration method for converting a color (target color) to be reproduced and displayed into four color components of a display panel in a display device having four or more primary colors. This will be described below.

In a general display panel, that is, a three-primary color display composed of three sub-pixels, a three-color component R that realizes tristimulus values X, Y, and Z of the XYZ color system in order to reproduce a specific color. A combination of G and B may be calculated. In this case, one solution can be obtained by calculating the inverse matrix of the _{3 × 3} regular matrix M _{3 × 3} from the following equation (1).

  On the other hand, in a display panel in which one pixel is composed of four color sub-pixels of four color components R, YG, B, and EG, the following expression (2) is established.

In this case, since an inverse matrix of the matrix M _{3 × 4} cannot be calculated, it is necessary to obtain a _{4 × 3} matrix N _{4 × 3} that satisfies the following expression (3).

Then, when obtaining the matrix N _{4 × 3} , the display panel color reproduction area is divided into a plurality of parts in order to lower the order, and N _{4 × 3} of each divided area is calculated to obtain four color components. Realization of conversion and calibration.

JP-T-2004-529396 International Publication No. 2007/032133 JP 2010-217516 A

  As described above, when the panel is calibrated, the process of approaching the target point with the increased degree of freedom compared to the three primary color display becomes complicated. In order to use multi-primary color displays in a wide range of applications, including monitors and TV applications, guidelines for efficiently performing this calibration process are required. In Patent Document 3, calibration is performed efficiently by dividing the area (the operation matrix is switched for each area). However, in this method, when adjustment is performed so that the boundary is crossed at the time of calibration, there is a problem that if the calculation matrix is different for each boundary, the calibration may diverge discontinuously.

  The present invention has been made in view of the above problems, and an object thereof is to provide a method for efficiently performing calibration in a four-primary color display.

  The method for manufacturing a liquid crystal display device according to the present invention includes a first step of measuring chromaticity of each primary color display of the four colors in a liquid crystal display device including a liquid crystal panel in which a plurality of pixels are composed of four different sub-pixels. For the tristimulus values X, Y, Z of the XYZ color system, the second step of adjusting the difference ΔZ between the input value to the liquid crystal panel and the measured value measured in the first step for the blue component Z, After the two steps, there is a third step of adjusting the difference ΔX or ΔY between the input value to the liquid crystal panel and the measured value measured in the first step for X or Y of a color other than the blue component.

  Since the method according to the present invention does not divide the region during calibration and performs the same processing over the entire region, it is possible to obtain a stable calibration result while maintaining continuity.

  The liquid crystal display device according to the present invention enables calibration in a four-primary color display and can be performed efficiently.

1 is a schematic diagram of a liquid crystal display device and a calibration system in an embodiment of the present invention. It is a schematic diagram of the pixel in the embodiment of the present invention. FIG. 2 is a schematic diagram of an internal configuration of a four primary color conversion circuit 30 shown in FIG. 1. It is a flowchart figure of the calibration method in embodiment of this invention. It is a calibration result shown to the specific example of embodiment of this invention.

  Hereinafter, embodiments of a liquid crystal display device according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.

  Embodiments according to the present invention will be described below. FIG. 1 shows a schematic diagram of a liquid crystal display device 100 and a system for performing calibration. The liquid crystal surface device 100 includes a liquid crystal panel 10, a backlight (not shown), and a four primary color conversion circuit 30. The liquid crystal panel 10 has a plurality of pixels. The plurality of pixels are arranged in a matrix of a plurality of rows and a plurality of columns. Each pixel is defined by four subpixels. The liquid crystal panel 10 and the liquid crystal display device 100 are also referred to as a 4-primary color panel and a 4-primary color display device, respectively.

  In FIG. 2, the schematic diagram of the pixel P in the liquid crystal panel 10 is shown. The pixel P has four or more subpixels. Four or more sub-pixels display different colors. The pixel P is also called a color display pixel. Here, the pixel P has a red sub-pixel R, a green sub-pixel G, a blue sub-pixel B, and a yellow sub-pixel Ye.

  In FIG. 2A, the red sub-pixel R, the green sub-pixel G, the blue sub-pixel B, and the yellow sub-pixel Ye are shown in a line along the row direction, but as shown in FIG. The red sub-pixel R, the green sub-pixel G, the blue sub-pixel B, and the yellow sub-pixel Ye may be arranged in a 2 × 2 matrix. In FIG. 2, the areas of the red sub-pixel R, the green sub-pixel G, the blue sub-pixel B, and the yellow sub-pixel Ye are shown to be equal to each other, but the red sub-pixel R, the green sub-pixel G, and the blue sub-pixel B The areas of the yellow sub-pixel Ye may be different. If the average area of the red subpixel R, the green subpixel G, the blue subpixel B, and the yellow subpixel Ye is called a subpixel average area, the area of the red subpixel R is larger than the subpixel average area. Highly bright red can be fully expressed. Moreover, since the area of the blue subpixel B is larger than the average area of the subpixels, it is possible to suppress a decrease in the light emission efficiency of the backlight. For this reason, the areas of the red sub-pixel R and the blue sub-pixel B are preferably larger than the areas of the green sub-pixel G and the yellow sub-pixel Ye.

  The four primary color conversion circuit 30 converts input color information such as XYZ or xvYCC into four primary color signals R, G, B, and Ye, and supplies them to the liquid crystal panel 10. Although there are many means for the four-color conversion algorithm, in the present embodiment, R, G, B, and so on can be reproduced faithfully with respect to color information such as XYZ or xvYCC for simplification of description. Consider a four-color conversion circuit that selects a combination of Ye. The chromaticity of the screen displayed by this four-color conversion should ideally match the XYZ values assumed by the input signal. However, in an actual liquid crystal panel, a difference from an ideal XYZ value occurs due to a problem inherent in the panel. Calibration is required to correct this difference.

  In this embodiment, theoretical values when displaying combinations of four primary color signal theoretical values (R, G, B, Ye) for realizing a certain chromaticity point X, Y, Z, and measured values on an actual panel Calibration is performed for the error. Since the calculation of the target point and the like is performed with a theoretical value, it is preferable to perform calibration with a panel after gamma correction in accordance with the calculation. By performing gamma correction, each primary color exhibits characteristics close to the theoretical value. Other possible causes of the panel error include crosstalk between sub-pixels and a decrease in saturation near the low gray level seen in a low contrast panel. Such correction can be compensated (calibrated) before gamma correction, that is, in the four-color conversion unit.

FIG. 3 shows an example of the internal configuration of the four primary color conversion circuit 30. After the color information input by the 4-primary color conversion algorithm circuit 1 is converted into 4-primary color signals R ₀ , G ₀ , B ₀ , Ye ₀ , the gamma correction circuit 2 performs gamma correction, and the 4 primary color signals R _out , G _out , B _out , Ye _out are output.

Calibration is performed by the following method. The colors displayed on the four primary color panels are measured by the chromaticity measuring device 200, and the measurement results are fed back to the feedback circuit 300. The theoretical values R ₀ , B ₀ , G ₀ , Ye of the actually used four color gradations are measured. Differences from ₀ are recognized as ΔX, ΔY, and ΔZ, adjustments using blue primaries and red, green, and yellow primaries are performed, and the adjusted combination of the four primary colors is fed back to the four-primary system. If the chromaticity deviation does not fall within the arbitrarily set allowable range, the same operation is repeated again.

  A flowchart of calibration is shown in FIG. In step 1, first the gamma value of the panel is adjusted. Since the following calculation is performed using theoretical values, it is necessary to correct gamma in the color display of the actual panel (for example, gamma = 2.2). In step 2, a combination of four target colors to be calibrated is determined. Various algorithms are conceivable for the four-color conversion, but here the conversion algorithm is not specified because the theoretical value is calculated from the four-color combination after conversion. In step 3, tristimulus values XYZ are obtained. Since it is a theoretical value, the XYZ values that are created with four colors according to the corrected gamma are obtained using the primary chromaticities of the four primary colors (Table 1 below). Further, the amount of change in X, Y, and Z when a small amount of gradation is shifted from each gradation for each primary color is calculated in advance, and the behavior of each color is defined. In step 4, four color gradations are actually displayed and measured. In step 5, the blue primary color difference that minimizes ΔZ out of the error from the target value is obtained. In step 6, the difference between the red, green, and yellow primary colors that can minimize the remaining ΔX and ΔY is obtained. In step 7, the difference between the resulting chromaticity point and the target point is confirmed. If the difference is larger than the arbitrary chromaticity deviation allowable range, the process returns to step 3.

  As can be seen from Table 1 above, the X component is composed of similar proportions for each primary color with respect to the overall components, and the Y component also enters the green pixel and the yellow pixel in proportion, but as an order There is not much difference. However, only the proportion of the blue primary color in the Z component is orders of magnitude. This means that the Z component of the color displayed by color mixing in this panel is almost the influence of the blue primary color. Therefore, in the color adjustment, the error of the Z component can be adjusted efficiently using the blue primary color. Thereafter, the X and Y components are adjusted using the remaining red, green, and yellow primary colors. By using this adjustment method, one of the degrees of freedom of the four primary colors can be fixed, so that the solution is difficult to diverge and can be a practical method.

  The gradation determination and color difference determination in step 6 and step 7 will be further described. Adjustment is performed using red, green, and yellow pixels according to the amount of change obtained in step 6. It is not preferable from the viewpoint of errors to make adjustments to bring them closer to the ideal values as they are. In particular, when the amount of error is large, there is a possibility of deviating from the ideal value. Therefore, by defining the maximum value F of one adjustment amount, it is approximated to the ideal value in several times. Among the variation amounts r, g, and ye of R, G, Ye obtained in step 6, the maximum absolute value is A_MAX, and the suppression coefficient C = A_MAX / F is introduced. However, C = 1 when A_MAX <F. By introducing this coefficient, the color balance (calibration direction) of gradation change can be maintained to some extent while suppressing the amount of change. Note that the final change amount is (r / C, g / C, ye / C) (however, the required change amount is an integer). Reflecting this amount of change, the color difference from the target value is calculated for XYZ finally obtained. An allowable value of color difference is set (for example, 0.0003), and when this is not satisfied, the trial is repeated.

  Hereinafter, a specific example will be described. The input (target chromaticity point) gradation is a combination of four colors as shown in Table 2 below.

  The tristimulus values XYZ at this time are as shown in Table 3 below.

In this tone, for example, if the tone of the red primary R, and the X component X _R primary ^{_{color, ΔX R = ((R +}} 1) / 255) 2.2 - (R / 255) 2.2) X R As follows, the effect on the tristimulus value derived from the primary color point when one gradation is changed is defined. The slight change amount is calculated for each color and XYZ component. The results are shown in Table 4 below.

  The measured values when displayed on the panel are as shown in Table 5 below.

Here, ΔZ is adjusted with the blue primary color. Comparing the Z component of the target value and the measured value, the adjustment amount of blue primary colors is obtained by [Delta] Z / [Delta] Z _B. In this case, as shown in Table 6 below, it can be seen that the amount of change in B is approximately minus 3.

  Table 7 below shows XYZ that has been changed by adjusting the blue primary color, and the difference from the target point is defined again.

  When ΔX and ΔY are expressed by mathematical formulas based on changes due to differences between the red, green, and yellow primary colors, the following formulas (4) and (5) are obtained.

  Here, r, g, and ye are gradation changes in red, green, and yellow.

In the above equations (4) and (5), in order to minimize ΔX and ΔY, change amount ((ΔX) ² + (ΔY) ² ) ^1/2 is defined, and r and g that minimize this are defined. , Ye are selected.

  The amount of change selected in the above process is shown in Table 8 below.

However, a very large change is not preferable in the calibration process (the above calculation is performed on the assumption of a small change). Therefore, the maximum gradation F that is moved at a time is defined. In this example, F = 5. Of the change amounts of R, G, and Ye above, the absolute value A _MAX of the maximum value is 15. From here, the suppression coefficient C = A _MAX / F is defined. However, C = 1 when A _MAX <F. Here, C = 15/5 = 3. Table 9 shows the result obtained by dividing the change amount by the suppression coefficient.

  This value is output as the final change amount. Therefore, in the first calibration, the following table 10 is obtained.

  As a result, the tristimulus values XYZ are as shown in Table 11 below.

  It was shown that the color difference Δu′v ′ = 0.0085 from the initial target is approaching 0.0066. If the allowable value of the color difference is 0.0003, it has not yet been reached, so the trial is repeated. As a result of four trials, the color difference was acceptable.

  FIG. 5 shows a chromaticity change process by calibration according to this embodiment. The respective display gradations RGBYe after trials 1 to 4 are shown in Table 12 below.

  Table 3 below shows the tristimulus values XYZ and the color difference Δu′v ”from the target points after trials 1 to 4 are performed.

  In this example, paying attention to the fact that only the blue primary color has the dominant influence on Z among the four primary colors, the adjustment of Z using the blue primary color is performed first, reducing the degree of freedom of adjustment, and calibration. It has been shown that it has succeeded in streamlining the process. This calibration method will be an effective adjustment method when the application range of the four primary color panels is expanded to the design and industrial fields.

  The liquid crystal display device according to the present invention can display a wide color reproduction range with low power consumption.

DESCRIPTION OF SYMBOLS 1 4 primary color conversion algorithm circuit 2 Gamma correction circuit 10 Liquid crystal panel 30 4 Primary color conversion circuit 100 Liquid crystal display device 200 Chromaticity measuring device 300 Feedback circuit

Claims (1)

In a method of manufacturing a liquid crystal display device including a liquid crystal panel in which a plurality of pixels are composed of different four color sub-pixels,
A first step of measuring the chromaticity of each of the four primary color displays;
For the tristimulus values X, Y, Z of the XYZ color system, the second step of adjusting the difference ΔZ between the input value to the liquid crystal panel and the measured value measured in the first step with respect to Z of the blue component,
A third step of adjusting the difference ΔX or ΔY between the input value to the liquid crystal panel and the measured value measured in the first step for X or Y of a color other than the blue component after the second step;
A method for manufacturing a liquid crystal display device.