JP2001312254A - Method for setting icc profile for color liquid crystal display panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ICC(International Color Consortium) profile which suitably corrects a color image of a color liquid crystal display panel. SOLUTION: Values in the gamma curves for a green image and a red image are controlled to be almost equal to each other, while the value in the gamma curve for a blue image is made higher than those of the gamma curves of the green image and the red image in the medium luminance region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color liquid crystal display panel used for a personal computer or the like, for performing color matching of a color image displayed on each color liquid crystal panel.
Used ICC (International Co.)
lor Consortium) profile.

[0002]

2. Description of the Related Art In an information processing system using the Internet or the like, color matching of images between monitors in each terminal device such as a personal computer or color matching of a color image on a monitor and a color image printed out by a printer. Is an important issue.

In a liquid crystal display panel, color matching is usually performed using an ICC profile. The ICC profile converts RGB image data into CIE (Commission) data.
ion International de I'Ec
and a 3 × 3 matrix as a profile, which has a conversion table for converting into an XYZ color system of
RGB image data is processed with this profile and X
It is assumed that the image data is of the YZ color system. The ICC profile of the monitor is defined by the chromaticity, gamma curve, and white chromaticity point of the three primary colors RGB (red, green, blue), and these values are set according to the color liquid crystal display panel.

[0004] The equivalent color temperature of a color liquid crystal display panel varies depending on the input gradation level. In a transmissive color liquid crystal display device that irradiates light from the back of a liquid crystal panel, a change in color temperature occurs depending on the gradation level (Nikkei Microdevices, July 1996, 101-l).
08). However, an effective ICC-compliant color profile that compensates for this change in color temperature has not been proposed.

[0005] Japanese Patent Application Laid-Open No. 11-338443 discloses a CRC as an ICC profile for a color liquid crystal panel.
There is disclosed a method of creating by employing an ICC profile for T. However, this publication does not describe anything about the correction of the color temperature change due to the gradation level. For this reason, in the color liquid crystal panel, even if the colors of the images are adjusted using the ICC profile disclosed in this publication, an image in which the colors match between the color liquid crystal display panels cannot be obtained. For this reason, the present applicant disclosed in Japanese Patent Application No. 11-216015 a conversion table (LUT: Look Up Tab1) in a table conversion device.
By using e), a method of mainly correcting an input signal corresponding to a blue image is proposed.

FIG. 7 shows a color liquid crystal display panel.
An example of the change of the chromaticity point according to the input gradation level is x
This is shown on the y chromaticity diagram. The black square marks in FIG. 7 indicate the 8-bit gradation level values of R (red), G (green), and B (blue) input to the liquid crystal panel {R, G, B} = {255, 25}.
It is measured as an achromatic (white, gray, black) chromaticity point every 16 steps from 5,255 to {R, G, B} = {0, 0, 0}, and the equivalent color temperature Varies from about 6000 degrees in white to 14000 degrees in black. In FIG. 7, the color temperature locus of blackbody radiation is shown by a solid line for comparison.

FIG. 6 shows an example of a correction conversion table (LUT) used in a table conversion device for suppressing a change in chromaticity point (equivalent color temperature) in FIG. The table converter corrects the gray level of the input digital signal and outputs a digital signal having the corrected gray level. The vertical axis and the horizontal axis respectively represent the output value and the input value of the 8-bit digital signal,
Each of the output value and the input value indicates a value normalized by the maximum value of the number of bits. The number of bits is the gradation level (luminance)
, The grayscale level (luminance) increases as both the output value and the input value increase. In the graph of FIG. 6, the conversion table of B (blue) indicated by a black circle is
In the middle luminance area, R (red: black square mark), G (green:
The value is lower than the black triangle mark). This is mainly because the input signal of the blue image is corrected. By using this conversion table for correction, ΔR, G,
From B｝ = {255, 255, 255} to {R, G, B}
FIG. 5 is a graph obtained by correcting the graph of the chromaticity point change profile up to = {0, 0, 0}.

FIG. 5 mainly shows a correction performed on a blue image conversion table (LUT) indicated by a black circle.
This indicates that the color temperature change is suppressed. Although the correction conversion table (LUT) can be calculated even in a low luminance area where the gradation level is low, the effect of the equivalent color temperature correction is as follows.
Conversion table for blue image (LU
T).

FIG. 8 shows a gamma curve of a color liquid crystal display panel using the correction conversion table (LUT) shown in FIG. 6 and suppressing a change in chromaticity point. The ordinate and the abscissa respectively represent the output value and the input value of the 8-bit digital signal, and the output value and the input value respectively indicate values normalized by the maximum value of the number of bits. The number of bits is
Since it corresponds to the gradation level (luminance), as the output value and the input value both increase, the gradation level (luminance) increases.
Will be higher.

As shown in FIG. 8, a gamma curve of a color liquid crystal display panel has different colors of R (red: black square), G (green: black triangle), and B (blue: black circle). Curve. Then, the ICC profile is set using the gamma curve after the chromaticity point correction shown in FIG. However, when an ICC profile is set using such a gamma curve, and color correction of a color liquid crystal display panel is performed based on the set ICC profile, color matching between the color liquid crystal display panels is satisfactorily performed. Cannot be performed, and adverse effects may occur. For this reason, in a color liquid crystal display panel, it may be better not to apply the ICC profile set using the gamma curve after the chromaticity point correction.

The CRT (Cathode Ray)
In the case of a (Tube) image monitor, the curves of the respective colors of R (red), G (green), and B (blue) in the gamma curve after the chromaticity point correction substantially match.

FIG. 9 shows a color reproduction range of sRGB (color space defined in IEC 61966-2-1) as a reference on the xy chromaticity diagram (within a broken line) and a color reproduction range of a conventional color liquid crystal display panel (FIG. An example is shown below. The color reproduction range of the conventional color liquid crystal display panel is based on the standard sRGB
The color reproduction range is narrower than the color reproduction range,
The (blue) chromaticity point is located outside the sRGB color reproduction range. Xy of primary color chromaticity of the color liquid crystal display panel shown in FIG.
The coordinates are blue: B (0.1488,
0.1323), green: G (0.3092, 0.557)
0), red: R (0.5933, 0.3357).
Similarly, x of the primary color chromaticity of the reference sRGB color reproduction range
The y coordinate is blue (0.1500, 0.
0600), green (0.3000, 0.6000) and red (0.6400, 0.3300).

[0013]

As described above, since the color reproduction range of the color liquid crystal display panel is different from the reference sRGB color reproduction range, an ICC profile for the color liquid crystal display panel is required to obtain a satisfactory color correction effect. , It is necessary to appropriately set the primary color chromaticity point and the white chromaticity point.

Further, in the color liquid crystal display panel, since the color temperature changes depending on the gradation level, the setting of the white chromaticity point in the ICC profile is unclear, and
Regarding the chromaticity points of the three primary colors, in the color liquid crystal display panel, the chromaticity point changes depending on the input gradation level, so that it is not easy to set the chromaticity point in the ICC profile.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a method of setting an optimum ICC profile for a color liquid crystal display panel.

[0016]

According to the present invention, there is provided a method for setting an ICC profile for a color liquid crystal display panel, the method comprising: correcting an ICC profile used for correcting a color image displayed on a color liquid crystal display panel for displaying a color image; A setting method, wherein the values of the gamma curves of the green image and the red image in the ICC profile substantially match, and the value of the gamma curve of the blue image is higher than the value of the gamma curve of the green image and the red image in the intermediate luminance region It is characterized by doing.

The white chromaticity in the ICC profile is made substantially equal to the equivalent color temperature at the maximum luminance.

The white chromaticity is made substantially equal to the average equivalent color temperature of the intermediate gradation or higher.

The blue chromaticity point (x, y) in the ICC profile is made substantially equal to (0.15, 0.06).

The green chromaticity point (x, y) in the ICC profile is substantially equal to (0.30, 0.60), and the red chromaticity point (x, y) is (0.64, 0. 33)
About equal to

A green image in the ICC profile,
The gamma value of the gamma curve for the red image is 1.8 to 2.4.
And

A green image in the ICC profile,
The gamma curve for the red image is equal to the gamma curve for the achromatic color.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

ICC color management system (C
In MS), image data is combined in a device-independent color space (for example, an XYZ color space) independent of each device, and inversely converted to a color space of another device.

FIG. 1 shows an example of sRGB (IEC61966-2).
FIG. 1 is a block diagram of a color management system when an image in a color space of (-1 color space) is reproduced on a color liquid crystal display panel. The digital data values in the sRGB color space are converted into RGB values in a linear RGB color space by a one-dimensional conversion table (LUT) 1 for each of the RGB channels, and then 3 × 3 from the RGB color space to the XYZ color space. Is converted by the conversion matrix 2 of Next, this XYZ color space is converted to PCS (Pr
As the file connection space (file connection space) 3, inverse conversion to the color space of the color liquid crystal display panel is performed.
The data value (X, Y, Z) of PCS3 is 3 × 3 determined by the ICC profile of the color liquid crystal display panel.
Are converted into RGB values in an RGB color space by an inverse conversion matrix 4 of the above, and the RGB values in the RGB color space are converted into digital data values by a conversion table (LUT) 5 for correction, so that each color liquid crystal panel Color matching. A gamma curve of an ICC profile is used as the conversion table (LUT) 5 for correcting the RGB values.

Next, the gamma characteristic of the ICC profile will be described below. The gamma characteristic indicates a gradation display characteristic of the color liquid crystal display panel, and the gamma curve indicates a relationship between a gradation level as an input value of the gradation display characteristic and a luminance as an output value.

For example, in an sRGB color space, an 8-bit digital data value (R, G, B) is (128, 12).
8,128) is converted into a linear space by a conversion table (LUT) with a gamma value: γ = 2.2, and becomes (128/255) ^2.2 = 0.219520, which is a data value in the PCS space. (X, Y, Z) is (0.
208632, 0.219520, 0.239035)
Becomes When this data value (X, Y, Z) is used as the ICC profile of the color liquid crystal display panel and converted by a 3 × 3 inverse conversion matrix, the data value becomes 0.21952 for each of the RGB channels.

The data values of the R, G, and B channels of the color liquid crystal display panel are converted into digital data values by the gamma curve of the correction conversion table. When the corrected gamma curve shown in FIG. The subsequent digital data values (R, G, B) are (128, 127, 1).
40), which is different from the first gray and is reproduced as a gray mixed with a blue component. However, by setting the correction curve (correction conversion table) shown in FIG. 6 as the gamma curve of the ICC profile, the converted digital data values (R, G, B) are (128, 128, 10).
4), and the corrected gray can be reproduced on the color liquid crystal display panel. Other digital data values (R, G,
By calculating B) similarly, a gamma curve suitable for the ICC profile of the color liquid crystal display panel can be obtained. FIG. 2 is a gamma curve obtained in this manner.

In the gamma curve shown in FIG. 2, the gamma curves of the green image (black triangles) and the red image (black squares) are almost the same, and the gamma curves of the blue image (black circles) are in the middle luminance region. The output value is higher than the gamma curves of the green image (black triangle) and the red image (black square).

FIG. 3 is an example showing a calculation result of a gamma curve for an ICC profile for a color liquid crystal display panel having another color characteristic. In the gamma curve shown in FIG. 3, the gamma curves of the green image (black triangles) and the red image (black squares) almost match, and the gamma curves of the blue image (black circles) correspond to the green image in the entire luminance region. (Black triangle) and the output value are higher than the gamma curves of the red image (black square). As a common gamma curve of the green image and the red image, a measured achromatic gamma curve or a representative gamma curve of a green image may be used. The gamma curve shown in FIG. 3 is obtained by using the gamma curve of the color liquid crystal display panel itself as described above to obtain a gamma value: γ =
An image in 2.2 sRGB space is reproduced.

Thus, when color reproduction is performed using the color reproduction gamma characteristic of a color liquid crystal display panel, an IC
Gamma value for green image and red image of C profile is γ =
It is about 2.2 ± 0.4.

FIG. 4 shows an I for a color liquid crystal display panel when the gamma values for the green image and the red image are γ = 2.2.
3 shows a gamma curve of a CC profile. FIG. 4 shows a green image (black triangles) and a red image (black squares) as in FIG.
And the gamma curve of the blue image (black circle) has a higher output value than the gamma curves of the green image (black triangle) and red image (black square) in the middle luminance region. Indicates that it is.

As shown in FIG. 2, FIG. 3, and FIG. 4, in each case, the gamma curve has an intermediate luminance area (about 0.3 to 0.7 when the maximum value on the horizontal axis is normalized to 1). Area), the gamma curve of the blue image indicates a value whose output value is higher than the gamma curves of the green image and the red image (approximately 0.04 or more when the vertical axis maximum value is normalized to 1). The gamma curves of the image and the red image are almost identical. In the embodiments shown in FIGS. 2, 3, and 4, the output values of the gamma curves of the blue image are 0.04 to 0.2 compared with the output values of the gamma curves of the green image and the red image. It shows a high value.

Although the color reproduction range of the color liquid crystal display panel changes according to the input gradation level, the chromaticity point of the ICC profile usually uses the primary color chromaticity point having the maximum luminance shown in FIG. . Liquid crystal color reproduction range and sRGB
When the color gamut of the color liquid crystal display panel is compared with the color gamut of sRGB, the green and red chromaticity points of the color liquid crystal display panel are within the sRGB color gamut. Out of range. For this reason, in a color liquid crystal display panel, when reproduction of a blue gradation level is required,
The blue chromaticity point of the CC profile is defined as (X, Y) = (0.1
5,0.06) gives better color reproduction.

Further, the chromaticity points of red and green of the color liquid crystal display panel are within the sRGB color reproduction range.
Is reproduced as the primary color of the color liquid crystal display panel, the red chromaticity point in the ICC profile is set to the sRGB red chromaticity point (x, y) = (0.64, 0.
33) and the green chromaticity point in the ICC profile is the sRGB green chromaticity point (x, y) = (0.30, 0.6)
0) to perform color reproduction.

When the change in the chromaticity point according to the input gradation level for the achromatic color of the color liquid crystal display panel is represented by the equivalent color temperature, as shown in FIG. The equivalent color temperature increases toward black. In FIG. 7, the equivalent color temperature changes from about 6000 degrees to 14000 degrees. To correct this color temperature change,
The gamma curve shown in FIG. 2 is used as a conversion table for correction. The change in color temperature is suppressed by this conversion table for correction, and as shown in FIG. 5, 580 in the range from the maximum luminance to the intermediate luminance (range of digital values from 255 to 64 in an 8-bit image).
The correction is made in the range of 0 degrees or 6300 degrees, and the average equivalent color temperature is about 6200 degrees.

For the correction of the color temperature change, the white chromaticity of the maximum luminance and the chromaticity point of the average equivalent color temperature from the middle luminance to the high luminance or the average chromaticity point are used as the white chromaticity of the ICC profile. May be. In any case, good color reproduction characteristics can be obtained.

[0038]

According to the present invention, an ICC for a color liquid crystal display panel is provided.
The profile setting method is such that the values of the gamma curves of the green image and the red image substantially match, and the value of the gamma curve of the blue image is higher than the value of the gamma curve of the green image and the red image in the intermediate luminance region. With such a setting, it is possible to provide an ICC profile with excellent color correction effect in a color liquid crystal display panel.

[Brief description of the drawings]

FIG. 1 is a block diagram of a color management system.

FIG. 2 is a graph showing an example of a gamma curve set in the ICC profile setting method of the present invention.

FIG. 3 is a graph showing another example of a gamma curve set in the ICC profile setting method of the present invention.

FIG. 4 is a graph showing still another example of a gamma curve set in the ICC profile setting method of the present invention.

FIG. 5 is a graph showing an equivalent color temperature change corrected by a correction conversion table in a color liquid crystal display panel.

FIG. 6 is a graph showing an example of a conversion table used for correcting color characteristics of a conventional color liquid crystal display panel.

FIG. 7 is a graph showing an equivalent color temperature change according to a gradation level input in a conventional color liquid crystal display panel.

FIG. 8 is a graph showing a gamma curve in a color liquid crystal display panel after applying a conventional color conversion table.

FIG. 9 is an xy chromaticity diagram comparing an sRGB color reproduction region with a color reproduction region of a color liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 One-dimensional conversion table 2 3x3 conversion matrix 3 PCS 4 3x3 conversion matrix 5 Correction conversion table

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 5/66 H04N 5/66 A 5C080 9/69 9/69 F term (reference) 2H088 FA11 KA29 KA30 MA05 2H093 NA53 NA79 NC90 ND17 ND24 ND56 5C006 AA22 AF46 BB11 BC16 5C058 AA06 BA05 BA13 BB14 5C066 AA00 CA08 CA17 EA05 EC05 HA03 KE09 KE11 KM13 5C080 AA10 BB05 CC03 DD01 EE29 EE30 JJ02 JJ05

Claims (7)

[Claims] 1. A method for setting an ICC profile used for correcting a color image displayed on a color liquid crystal display panel for displaying a color image, wherein a value of a gamma curve of a green image and a gamma curve of a red image in the ICC profile And setting the value of the gamma curve of the blue image higher than the values of the gamma curves of the green image and the red image in the intermediate luminance region. 2. The method for setting an ICC profile for a color liquid crystal display panel according to claim 1, wherein the white chromaticity in the ICC profile is made substantially equal to an equivalent color temperature at the maximum luminance. 3. The method of setting an ICC profile for a color liquid crystal display panel according to claim 2, wherein the white chromaticity is made substantially equal to an average equivalent color temperature of a halftone or higher. 4. The ICC for a color liquid crystal display panel according to claim 1, wherein the blue chromaticity point (x, y) in the ICC profile is substantially equal to (0.15, 0.06).
How to set up a profile. 5. The green chromaticity point (x, y) in the ICC profile is made substantially equal to (0.30, 0.60), and the red chromaticity point (x, y) is set to (0.64, y). 0.3
2. The method for setting an ICC profile for a color liquid crystal display panel according to claim 1, wherein the setting is made substantially equal to 3). 6. A gamma value of a gamma curve for a green image and a red image in the ICC profile is set to 1.8 to
2. The method for setting an ICC profile for a color liquid crystal display panel according to claim 1, wherein the ICC profile is 2.4. 7. The method of setting an ICC profile for a color liquid crystal display panel according to claim 1, wherein a gamma curve for a green image and a red image in the ICC profile is equal to a gamma curve for an achromatic color.