WO2007083717A1

WO2007083717A1 - Color conversion matrix creation method and color conversion method

Info

Publication number: WO2007083717A1
Application number: PCT/JP2007/050725
Authority: WO
Inventors: Yoshifumi Shimodaira; Yoshiyuki Kawagoe
Original assignee: National University Corporation Shizuoka University
Priority date: 2006-01-18
Filing date: 2007-01-18
Publication date: 2007-07-26
Also published as: JPWO2007083717A1

Abstract

An RGB signal value corresponding XYZ of a predetermined gradation is obtained by using a color conversion matrix (step 106). An RGB gradation value corresponding to the RGB signal value is obtained from the normal reproduction characteristic of a display device (step 108). XYZ corresponding to the RGB gradation value is obtained from a device profile of the display device (step 110). Luminance of XYZ of the predetermined gradation is matched with luminance of XYZ of a reference gradation and a color difference between the XYZ of the predetermined gradation and XYZ of the reference gradation is obtained (step 112). If the obtained color difference exceeds a threshold value, a color conversion matrix is created from the XYZ of the predetermined gradation and stored, and the reference gradation is modified to the predetermined gradation (steps 114-118). A process for modifying the predetermined gradation by one gradation (step 122) is executed for all the gradations and each of the RGB primary colors. This enables highly-accurate and high-speed color conversion capable of performing a faithful color reproduction in a display device where color tracking is caused.

Description

Specification

Color conversion matrix creation method and color conversion method

Technical field

The present invention relates to a color conversion matrix creation method and a color conversion method, and in particular, a color conversion matrix creation method when color conversion is performed by matrix calculation and a color conversion created by the color conversion matrix creation method. The present invention relates to a color conversion method for color-converting an input image using a matrix. Background art

Conventionally, there has been a demand for faithful color reproduction in places such as electronic commerce and telemedicine (see, for example, Non-Patent Document 1). However, since existing image systems perform color reproduction that depends on the device, the color displayed on the display appears to vary from device to device.

[0003] To deal with this problem, there is a color management system (CMS) (for example, see Non-Patent Document 2). In CMS, a shaper ZMatri X Model (for example, see Non-Patent Document 4, hereinafter referred to as SMM) using an ICCdnternational Color or Consortium) profile (for example, Non-Patent Document 3) is used for color reproduction of a display.

[0004] For the color reproduction of S. M. M, tristimulus values XYZ with the highest luminance of each primary color are used. In order to perform accurate color reproduction, the chromaticity must be constant with respect to changes in the brightness of each primary color. However, some types of displays, for example, some displays using liquid crystal, cause color tracking that shifts chromaticity in a low-brightness region, so that accurate color reproduction cannot be performed (see, for example, Non-Patent Document 5). Therefore, a method corresponding to color tracking (hereinafter referred to as a faithful color reproduction method) has been reported so far (see, for example, Non-Patent Document 6).

Non-Patent Document 1: Shuichi Kagawa, Hiroaki Sugiura, "Current Status and Future of Color Management Technology", Mitsubishi Electric Technical Report, vol.76, No.ll, pp.739-742, (2002).

Non-Patent Document 2: MD Study Group et al. "Illustration Color Management Practice Rule Book 2005-200 6", MD Study Group, Works Corporation, pp.52-53, (2005). Patent Document 3: International Color Consortium, "ICC Profile Specification Version 3.2", (1995).

Non-Patent Document 4: Dawn Wallner, "Building ICC profiles- the Mechanics and Engineering, (2000).

Non-Patent Document 5: Yuka Uchiumi et al. "Study on luminance dependence of color tone in liquid crystal display", Journal of the Institute of Image Information and Television Engineers, vol.25, No.72, pp.13-18, (2001).

Non-Patent Document 6: Mamoru Shimazu, Masanori Takaya, Gosuke Ohashi, Mifumi Shimohira, "High-fidelity color reproduction method for force tracking in displays", IEICE technical report, vol.103, No.649 , pp.37-40, (2004).

Disclosure of the invention

Problems to be solved by the invention

However, the above-described faithful color reproduction method has a problem that it takes a long time for color conversion because a color conversion matrix is created for each pixel.

[0006] The present invention has been made to solve the above-described problems, and is a color capable of high-precision and high-speed color conversion that enables faithful color reproduction in a display device or the like in which color tracking occurs. It is an object to provide a conversion matrix creation method and a color conversion method.

Means for solving the problem

[0007] In order to achieve the above object, the color conversion matrix creation method according to the present invention creates a color conversion matrix for conversion to RGB signal values of the RGB color system, such as XYZ color system tristimulus values XYZ color. A method for creating a color conversion matrix, comprising: obtaining a RGB signal value corresponding to tristimulus values XYZ of a predetermined gradation using a predetermined color conversion matrix; and an RGB gradation value corresponding to the obtained RGB signal value Determining from the halftone reproduction characteristics of the predetermined display device, determining the tristimulus values XYZ corresponding to the determined RGB gradation values from the device profile of the display device, and determining the tristimulus of the predetermined gradations Obtaining the color difference between the tristimulus value XYZ of the predetermined tone and the tristimulus value XYZ of the reference tone after adjusting the brightness of the value XYZ to the tristimulus value XYZ of the reference tone If the color difference exceeds a predetermined threshold, With the tristimulus values XYZ of the predetermined tone Te based ヽ creating and storing a color conversion matrix, a step of changing the reference gray scale to the predetermined gray level, the predetermined floor A process of repeatedly executing a process including changing a tone by one gradation or a plurality of gradations for all gradations, for each primary color of RGB.

According to the present invention, the tristimulus value XYZ of the predetermined gradation and the reference gradation are obtained after matching the luminance of the tristimulus value XYZ of the predetermined gradation with the luminance of the tristimulus value XYZ of the reference gradation. Find the color difference from the tristimulus values XYZ. When the obtained color difference exceeds a predetermined threshold value, a process of creating and storing a color conversion matrix based on the tristimulus values XYZ of the predetermined gradation is executed for each primary color of RGB. For this reason, a color conversion matrix is created for each primary color for gradations where the color difference exceeds the threshold.

[0009] During color conversion, an optimum color conversion matrix corresponding to the gradation is selected from a plurality of created color conversion matrices and color conversion is performed, so that high-precision and high-speed color conversion can be performed. It becomes possible.

[0010] In the above method, the predetermined display device can be a display device in which color tracking occurs. The present invention is particularly effective when applied to a display device in which such color tracking occurs.

[0011] Further, the color conversion method according to the present invention is a color conversion method for converting an XYZ color system tristimulus value XYZ into an RGB color system RGB signal value, the step of inputting the tristimulus value XYZ; The step of obtaining RGB signal values corresponding to the input tristimulus values XYZ using a predetermined color conversion matrix, and halftone reproduction of the RGB gradation values corresponding to the obtained RGB signal values by a predetermined display device A step of obtaining from the characteristics, a step of selecting a color conversion matrix corresponding to the obtained RGB gradation value from the color conversion matrix created by the color conversion matrix creation method of the above configuration, and the input tristimulus value XYZ And a step of obtaining an RGB signal value corresponding to the obtained RGB signal value from the halftone reproduction characteristic.

[0012] According to the present invention, the color conversion is performed by selecting the optimum color conversion matrix corresponding to the gradation from the plurality of color conversion matrices created by the color conversion matrix creating method having the above-described configuration. And high-speed color conversion becomes possible.

The invention's effect

[0013] According to the present invention, faithful color reproduction can be achieved in a display device or the like in which color tracking occurs. There is an effect that color conversion can be performed with high accuracy and high speed.

Brief Description of Drawings

FIG. 1 is a schematic block diagram of a color conversion device.

FIG. 2 is a diagram showing an example of halftone reproduction characteristics.

FIG. 3 is a flowchart of a color conversion matrix creation process executed by a color conversion matrix creation unit.

FIG. 4 is a flowchart of color conversion processing executed by a color conversion unit.

FIG. 5 is a chromaticity diagram for explaining color tracking.

Explanation of symbols

[0015] 10 ... color conversion device, 12 ... color conversion matrix creation unit, 14 ... storage unit, 16 ... color conversion unit.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic block diagram of a color conversion apparatus 10 to which the present invention is applied. As shown in FIG. 1, the color conversion apparatus 10 includes a color conversion matrix creation unit 12, a storage unit 14, and a color conversion unit 16.

[0018] Although details will be described later, the color conversion matrix creating unit 12 performs color change based on device profiles (colorimetric data), halftone reproduction characteristics (TRC) data, and the like stored in the storage unit 14. A color conversion matrix is created by obtaining a conversion matrix coefficient.

The color conversion unit 16 uses the color conversion matrix created by the color conversion matrix creation unit 12 to convert the input XYZ color space image data (XYZ data) into the RGB color system. Convert to color space image data (RGB data) and output.

[0020] The storage unit 14 is a display device that displays an image based on the RGB data that has been color-converted by the color conversion device 10, and is a device profile of the display device that may cause color tracking, and the display device. Halftone reproduction characteristic data, a color conversion creation processing program executed by the color conversion matrix creation unit 12 described later, a color conversion processing program executed by the color conversion unit 16, and the like are stored in advance.

[0021] Here, the device profile is tristimulus XYZ data corresponding to all RGB gradations. It is obtained as follows. For example, change the RGB gradation value for each primary color in increments of several gradations (for example, in increments of 8 gradations) and input it to the display device, and measure the color output from the display device each time with a colorimeter. Tristimulus values XYZ for each primary color number gradation step are obtained. The tristimulus values XYZ of other gradations are obtained by linear interpolation. As a result, tristimulus values XYZ corresponding to all RGB gradations are obtained. The tristimulus values XYZ corresponding to all RGB gradations may be obtained by colorimetry.

FIG. 2 shows an example of halftone reproduction characteristics of a liquid crystal projector. As shown in the figure, the halftone reproduction characteristic shows the correspondence between the RGB gradation value (input value) and RGB signal value (output value) of the display device. Desired. Halftone reproduction characteristic data is data representing halftone reproduction characteristics as shown in the figure, that is, table data and expressions indicating the correspondence between RGB gradation values and RGB signal values, and is stored in the storage unit 14 for each primary color. Stored in advance.

[0023] Here, conventional color conversion from XYZ color system image data to RGB color system image data in S.M.M will be described. In S. M. M, the input tristimulus values XYZ are converted to RGB signal values (relative values) between 0 and 1 using the following formula.

[Number 1]

Here, the values of the coefficients X, Y, Z, X, Y, Z, X, Y, and Z of the color conversion matrix are

R R R G G G B B B

The tristimulus value repulsive force at the gradation value 255 which is the maximum gradation of each primary color obtained from the vice profile is also a value obtained by subtracting the tristimulus value の of the gradation value 0 which is a bias component. In other words, X, Υ, and Ζ correspond to the tristimulus value 対応 corresponding to R of gradation value 255 to R of gradation value 0.

R R R

The corresponding tristimulus value is the value obtained by subtracting ΧΥΖ, and X, Υ, and Ζ correspond to G with a gradation value of 255.

G G G

The tristimulus value ΧΥΖ is the value obtained by subtracting the tristimulus value 対応 corresponding to G with a gradation value of 0, X, Υ

Β Β

, Ζ is the tristimulus value ΧΥΖ corresponding to Β with a gradation value of 255,

Β

It is a value obtained by subtracting the extreme value ΧΥΖ. In the following, the primary colors obtained from the device profile The tristimulus values XYZ of tone values n (= 0 to 255) of p (= R, G, B), that is, the coefficients of the color conversion matrix are represented by X, Y, Z. For example, to the primary colors R, G, B with gradation value 255 as above

pn pn pn

The corresponding tristimulus values XYZ are X, Υ, Ζ, Χ, Υ, Ζ, Χ, Υ, respectively.

255 R255 R255 G255 G255 G255 Β255

, Ζ.

Β255 Β255

Then, using the halftone reproduction characteristic data representing the halftone reproduction characteristic as shown in FIG. 2, an RGB gradation value is obtained from the RGB signal value. That is, the R tone value of R is obtained using the R halftone reproduction characteristic data, the G signal value force of the G tone value is obtained using the G halftone reproduction characteristic data, Using the halftone reproduction characteristic data for B, obtain the gradation value of the signal value B of B.

[0026] In this way, SMM always uses the tristimulus values XYZ of the highest luminance (maximum gradation) of each primary color for matrix calculation, so the effect of color tracking is not taken into consideration and power error is not considered. In a display device in which tracking occurs, optimal color reproduction cannot be obtained.

In this embodiment, although details will be described later, a plurality of color conversion matrices are created for each primary color according to the gradation value, and at the time of color conversion, a color conversion matrix suitable for the gradation value is selected and color is selected. Convert. This enables high-speed and high-precision color reproduction even in a display device in which color tracking occurs.

Next, the color conversion matrix creation processing executed in the color conversion matrix creation unit 12 will be described with reference to the flowchart shown in FIG.

First, in step 100, the color conversion matrix creating unit 12 sets a reference gradation d to be described later. In the present embodiment, as an example, each primary color is represented by 8-bit data, and 256 gradations from 0 to 255 are set, and 255 which is the maximum gradation is set as a reference gradation.

In step 102, a primary color for which a color conversion matrix is to be created is set. In the present embodiment, a color conversion matrix is created for each of the three primary colors R, G, and B. Therefore, for example, R is initially set.

In step 104, an initial color conversion matrix of a color conversion matrix for converting XYZ color system image data into RGB color system image data is set.

[0032] Here, as an example, the coefficients of the color conversion matrix of the above equation (1) are used as the tristimulus values X, Y, Z, corresponding to the primary colors R, G, B of the gradation value 255 as the reference gradation. X, Y, Z

R255 R255 255 G255 G255 G255 , X, Y, Z These values are stored in the device profile stored in the storage unit 14.

B255 B255 B255

Obtained from Aisle.

In step 106, the sum of tristimulus values XYZ of gradations e of R, G, and B obtained from the device profile is added to XYZ in the above equation (1) to obtain an RGB signal value. In the present embodiment, the first gradation e is 255, which is the maximum gradation. That is, X in the above equation (1) is (X

R255

+ X + X), enter (Y + Y + Y) for Y, and (Z + Z for Z)

G255 B255 R255 G255 B255 255 G255

+ Z)) to obtain the RGB signal value.

B255

In step 108, an RGB gradation value is obtained from the RGB signal value using the halftone reproduction characteristic data of each primary color stored in the storage unit 14. That is, R gradation value is obtained from R signal value using R halftone reproduction characteristic data, G signal value force is also obtained G gradation value using G halftone reproduction characteristic data, Use the halftone reproduction characteristics data for B to find the tone value of the signal value B of B.

In step 110, tristimulus values XYZ corresponding to the RGB gradation values obtained in step 108 are obtained from the device profile stored in the storage unit 14.

[0036] In step 112, the color difference between the tristimulus value XYZ of the gradation e obtained in step 110 and the tristimulus value XYZ of the reference gradation d is obtained. As described above, since the first reference gradation d is 255, which is the maximum gradation, the tristimulus value XYZ corresponding to R of gradation 255 obtained from the device profile is set as the tristimulus value XYZ for comparison. And the color difference from the three-stone intensity XYZ of the gradation e obtained in step 110. When obtaining the color difference, the tristimulus value XYZ of the gradation e is matched to the luminance of the reference gradation d, and then the tristimulus value XYZ of both is converted to Lab color system data. The power also calculates the color difference. That is, by replacing Y of the tristimulus value XYZ of the gradation e with Y of the tristimulus value XYZ of the reference gradation, and further multiplying the X and Z of the tristimulus value XYZ of the gradation e by a predetermined factor, Adjust the brightness of the tristimulus value XYZ of key e to the brightness of the reference gradation d. Here, the predetermined coefficient is a value obtained by dividing Y of the reference stimulus tristimulus value XYZ by Y of the tone e tristimulus value XYZ. Specifically, if the tristimulus values of gradation e are Xe, Ye, Ze and the tristimulus values of reference gradation d are Xd, Yd, Zd, then Xe, = Xe X (Yd / Ye), Ye The color difference between the tristimulus value Xe'YeZe 'and the tristimulus value XdYdZd is obtained as = Yd, Ze' = ZeX (YdZYe). Note that the color difference is obtained by, for example, the CIE2000 color difference formula (for example, see Non-Patent Document 7 below). The

In step 114, it is determined whether or not the obtained color difference exceeds a predetermined threshold value.

Since humans determine whether or not the color reproduction is faithful, the threshold that is a criterion for allowing matrix conversion is, for example, a color difference (a color difference that is perceived by human eyes from two colors ( For example, the following non-patent document 8) is used. As will be described later, the specific threshold value is set to 0.2 in the present embodiment as the relationship between the number of color conversion matrices to be created and the average color difference.

[0038] If the color difference between the tristimulus value XYZ obtained in step 110 and the tristimulus value XYZ of the reference gradation d to be compared exceeds the threshold value, the process proceeds to step 116. If not, go to step 120.

In step 116, the color conversion matrix is updated, and the updated color conversion matrix is stored in the storage unit 14. The color conversion matrix is updated using the coefficients X,,, Z of the current color conversion matrix.

R R R

Is updated to the tristimulus value XeYeZe of the gradation e determined in step 110.

[0040] In step 118, the reference gradation d is changed to the current gradation e. As described above, when the color difference exceeds the threshold, the reference gradation d is changed to the current gradation e, and when the color difference is equal to or less than the threshold, the reference gradation d is not changed and is left as it is.

In step 120, it is determined whether or not the processing in steps 106 to 118 has been completed for all the gradations of the primary color R, specifically, whether or not the gradation e has become zero. Then, when the processing of Steps 106 to 118 is completed for all gradations of the primary color R, the process proceeds to Step 124. Otherwise, the process proceeds to Step 122.

In step 122, the gradation e is lowered by one and the process returns to step 106. In the second step 106, the R component of the tristimulus value XYZ entering XYZ in the above equation (1) is set to a value obtained by lowering the gradation by one. That is, X in the above equation (1) is (X + X + X)

Enter 254 G254 B254, and Y is (Y +

254

Y + Y) and (Z + Z + Z) for Z. And so on

G254 B254 254 G254 B254

The

When this is executed until the gradation e becomes 0, step 120 is affirmed and the routine proceeds to step 124.

[0044] In step 124, it is determined whether or not the processing in steps 102 to 122 has been completed for all primary colors. If it is determined that the process has been completed, the process proceeds to step 126. If the process has been completed, the process proceeds to step 102 and G and B are processed in the same manner as described above.

When the processing of steps 102 to 122 has been completed for all RGB, in step 126, the coefficients of all the created color conversion matrices are output to the color conversion unit 16 and the routine is terminated. The color conversion unit 16 stores the coefficient of the color conversion matrix of each primary color output from the color conversion matrix creation unit 12.

As described above, in the present embodiment, the luminance of the tristimulus value XYZ of the gradation e is matched with the luminance of the tristimulus value XYZ of the reference gradation d, and the color difference between the two is obtained. In the above case, the process of creating a new color conversion matrix is performed for all gradations of all primary colors. As a result, as many color conversion matrices are created as the number of color differences equal to or greater than the threshold value for each primary color. That is, the number of color conversion matrices created is (number of color conversion matrices created for R) X (number of color conversion matrices created for G) X (number of color conversion matrices created for B). In the following, the gradation value where the color difference is greater than or equal to the threshold value, that is, the gradation value for which the color conversion matrix has been created and changed (the gradation value that changes the color conversion matrix during color conversion) is the matrix-changed gradation value. Called.

Next, color conversion processing executed in the color conversion unit 16 will be described with reference to the flowchart shown in FIG.

[0048] First, in step 200, the tristimulus value XYZ is input, and in step 202, this is converted to S. M.

Perform color conversion with M to obtain RGB signal values. In other words, the tristimulus value XYZ is converted to the RGB signal value by the above equation (1). Note that each coefficient X, Y, Z, X of the color conversion matrix here

R R R

, Y, Z, X, Y, Z values are tristimulus values XY with gradation value 255, which is the maximum gradation of each primary color

G G G B B B

The value of z.

[0049] In step 204, using the halftone reproduction characteristic data stored in the storage unit 14, an RGB gradation value is obtained from the RGB signal value. In other words, the tone value of the R signal value scale is obtained using the R halftone reproduction characteristic data, and the G signal value force is also obtained of the G tone value using the G halftone reproduction characteristic data. Using the halftone reproduction characteristic data for B, obtain the gradation value of B for the B signal value.

[0050] In step 206, a color conversion matrix corresponding to the RGB gradation value obtained in step 204 For each primary color. For example, if the R matrix change gradation value is 240, 225, 210, etc., and the R gradation value obtained in step 204 is a value within the range of 255-241, Since this is the gradation before the matrix is changed, a color conversion matrix is selected in which the tristimulus value XYZ value of gradation value 255, which is the maximum gradation of each primary color, is a coefficient. If the R gradation value obtained in step 204 is in the range of 240 to 226, the color conversion matrix created when the matrix change gradation value is 240 is selected. If the R tone value obtained in step 204 is within the range of 225 to 211, the color conversion matrix created when the matrix change tone value is 225 is selected. The same applies to the following, and the same applies to the other primary colors G and B. As a result, the color conversion matrix is changed for each primary color with a gradation value at which the color difference is equal to or greater than the threshold value.

[0051] In step 208, using the selected color conversion matrix, the input tristimulus values XYZ are converted into RGB signal values. That is, the coefficient X, Y of the color conversion matrix selected for R

R

Select the color conversion matrix coefficients X, Y, Z, and B selected for, Z, and G.

R R G G G

Color conversion matrix coefficients X, Y, Z

Color conversion is performed using a color conversion matrix with B B B as coefficients.

In step 210, as in step 204, using the halftone reproduction characteristic data stored again in the storage unit 14, an RGB gradation value is obtained from the RGB signal value and output.

As described above, in this embodiment, for each primary color, the tristimulus value XYZ for each tone value is set after adjusting the brightness of the tristimulus value XYZ to the brightness of the reference tone. And the tristimulus values XYZ of the reference gradation are obtained, and if this color difference exceeds the threshold, a new color conversion matrix is created and stored. During color conversion, color conversion is performed by selecting a color conversion matrix corresponding to the gradation value of each primary color. In other words, since the color conversion matrix having the optimum color conversion matrix is selected for each gradation, color reproduction with high speed and high accuracy is possible even in a display device in which color tracking occurs.

In the present embodiment, the case where the reference gradation to be initially set is set to 255 which is the maximum gradation has been described. However, the present invention is not limited to this, and other gradation values such as an intermediate gradation are used. You can set 128 as the reference gradation. In this case, the coefficients of the initial color conversion matrix are X, Y

R128 R1

, Ζ, Χ, Υ, Ζ, Χ, Υ, Ζ. And for example, from tone value 128

28 R128 G128 G128 G128 B128 B128 B128 The process shown in Fig. 3 while increasing the gradation value one by one, that is, the process of updating the color conversion matrix if the color difference is compared with the threshold value and exceeds the threshold value, is performed up to the gradation value of 255. Thereafter, the same processing may be performed while decreasing the gradation value from the gradation value 127 one by one.

Further, in the present embodiment, the case where the color difference is determined for each gradation while changing the gradation one gradation at a time has been described. However, the present invention is not limited to this. Try to determine the color difference while changing multiple gradations, such as one by one.

[0056] (Example)

Hereinafter, examples of the present embodiment will be described. The present invention is not limited to the following examples.

The present inventors verified the color reproduction accuracy and color conversion time of the color conversion matrix creation method according to the present invention described above and the color conversion method using the color conversion matrix created thereby. . In order to verify the two, a liquid crystal projector was used as the display, and a spectral radiance meter was used as the measuring instrument. The measurement was performed in a dark room, a single color was projected on the screen from a liquid crystal projector, and the measurement point was approximately the center of the screen.

[0058] In order to stabilize the operation of the liquid crystal projector, 3 hours had elapsed since the power was turned on.

Thereafter, profile measurement was started. If the RGB primary color data input to the LCD projector is expressed as (R, G, B), (8, 0, 0), (0, 8, 0), (0, 0, 8), (16, (0, 0), (0, 16, 0), (0, 0, 16) ... (255, 0, 0), (0, 255, 0), (0, 0, 255) This primary color was input to the liquid crystal projector in increments of 8 gradations, a single color was projected on the screen from the liquid crystal projector, and tristimulus values XYZ were measured using a spectral radiance meter. Tristimulus values XYZ between each measurement point were obtained by linear interpolation.

[0059] FIG. 5 shows the chromaticity of all the gradations of each primary color measured in this way. As shown in the figure, the chromaticity of each primary color, that is, the ratio of XYZ is not constant with respect to the change in luminance. In the figure, the chromaticity changes in the green direction as the luminance decreases for both red, green, and blue, confirming that color tracking has occurred.

[0060] Table 1 below shows the luminance L and chromaticity u ′, v ′ of white (red + green + blue) and original white (white) displayed by adding each primary color of the liquid crystal projector. The value is shown.

[table 1] L (cd / m ² ) u 'V,

red + green + blue 3 6 5 .6 0. 1 8 0 0. 4 9 4 whi te 3 6 4 .9 0 .1 8 0 0 .4 9 5

[0061] As apparent from Table 1 above, the values of (red + green + blue) (white) are almost the same, and it can be confirmed that additive color mixing of the liquid crystal projector is established.

[0062] Next, in order to determine a threshold at which matrix conversion is allowed, that is, a color difference threshold for determining the matrix change gradation value (step 114 in FIG. 3), for any 2000 colors, A simulation was performed to compare the color conversion accuracy and the number of color conversion matrices. The results are shown in Table 2 below.

[Table 2]

As apparent from Table 2 above, when the color difference for determining the threshold value is decreased from 0.6, the average color difference of the color conversion results decreases and the number of color conversion matrices increases. However, when 0.2 is changed to 0.1, the average color difference of the color conversion results does not change much and the number of color conversion matrices increases significantly. Therefore, the threshold value is set to 0.2.

[0064] As a result of using a threshold value of 0.2, R10, G35, and B20 were created, and 700,000 color conversion matrices were created. The number of color conversion matrices is (R gradation value number) X (G gradation value number) X (B gradation value number) because gradation values are determined for each primary color.

[0065] Next, SMM, faithful color reproduction method (the method described in Non-Patent Document 6 below), and the three methods of the present invention SHIPP (see Non-Patent Document 10 below) Color Chart of Standard Image 293 Colors After conversion, the colors that fall within the color gamut after conversion (199 colors of the present invention, 11 colors of SM M2 and 186 colors of faithful color reproduction) are each projected onto the screen, and the tristimulus values XY Z are spectrally emitted. Measured with a luminance meter. The color difference between the measured tristimulus value XYZ and the input tristimulus value XYZ was calculated using the CIE2000 color difference formula, and the accuracy was compared. The results are shown in Table 3 below. [Table 3]

As apparent from Table 3 above, according to the color conversion method of the present invention, the average color difference was 0.67, which was about a quarter of S.M.M. It was also confirmed that the accuracy was as high as the faithful color reproduction method. This color difference is a second-class color difference (see Non-Patent Document 8 below), but it is an accuracy that can be recognized as almost the same when both are judged side by side.

[0067] Next, the color conversion time was measured for the above three methods. The images used for the color conversion are 4 3110 ^ standard images (3072 4096). The results are shown in Table 4 below. The color conversion time shown in Table 4 is a relative value when the average color conversion time when each image is color-converted by the method according to the present invention is represented by 1.0.

[Table 4]

[0068] As is apparent from Table 4, in the present invention, the color conversion time can be reduced to about 1/50 of the faithful color reproduction method.

[0069] As described above, as shown in Table 3, color reproduction accuracy equivalent to that of the faithful color reproduction method was obtained by creating a color conversion matrix as in the present invention. In addition, the following non-patent literature

It has been demonstrated that the method based on 9 (hereinafter referred to as the proposed method) can achieve the same color reproduction accuracy as the faithful color reproduction method! RU

[0070] Using this method and the previously proposed method, the same device profile force color conversion matrix was created. Table 5 shows the results of the number of color conversion matrices created for each primary color (number of matrix change gradation values).

[Table 5] R matrix G matrix B matrix Color conversion matrix

Changed gradation value Changed gradation value Changed gradation value Total number

Number of numbers number of

The present invention 1 0 3 5 2 0 7 0 0 0

Previously proposed method 9 8 9 4 1 3 2 8 4 1

As is clear from Table 5 above, in the proposed method, the number of G and B matrix change gradation values is larger and the number of R matrix change gradation values is smaller than in the present invention. The proposed method has increased the number of color conversion matrices due to the influence of luminance on the criteria for determining the gradation value for changing the color conversion matrix. In the present invention, in creating the color conversion matrix, the luminance difference is matched to the reference gradation and the color difference is compared, and the difference only in chromaticity is used as the criterion. As a result, the color reproduction accuracy can be made equal to that of the proposed method, and the number of color conversion matrices can be reduced to about one-fourth.

Thus, according to the color conversion matrix creation method and the color conversion method of the present invention, even in a display device in which color tracking occurs, color reproduction can be performed with high accuracy and color conversion can be performed at high speed. We were able to confirm that it was possible.

[0073] (Non-Patent Document 7) G. Sharma ゝ W. Wu, ENDalal: "The CIEDE2000 Color- Difference r ormula: Implementation Notes, supplementary 1 est Data ^ and Mathematical Obs ervations, ..., Color Research and Application ^ vol.30, No. l (2005).

(Non-patent Document 8) The Japan Society of Color Science: "New Color Science Handbook [2nd edition]", University of Tokyo Press (1998).

(Non-patent literature 9) Kawagoe Yoshiyuki, Shimazu Yasunori, Ohashi Gosuke, Shimohira Mifumi: "High-fidelity color conversion method of display corresponding to color tracking", 11th Symposium on Image Sensing, pp.543-546, (2005) .

(Non-Patent Document 10) The Institute of Image Electronics Engineers of Japan: "SHIPP High-Definition XYZ 'CIELAB' RGB Standard Image" (1997).

Industrial applicability

The present invention can be used as a color conversion matrix creation method and a color conversion method capable of high-accuracy and high-speed color conversion that enables faithful color reproduction in a display device or the like in which color tracking occurs.

Claims

The scope of the claims

[1] A color conversion matrix creating method for creating a color conversion matrix for converting from XYZ tristimulus values XYZ to RGB color system RGB signal values,

Obtaining RGB signal values corresponding to tristimulus values XYZ of a predetermined gradation using a predetermined color conversion matrix;

Obtaining an RGB gradation value corresponding to the obtained RGB signal value from halftone reproduction characteristics of a predetermined display device;

Obtaining tristimulus values XYZ corresponding to the obtained RGB gradation values from the device profile of the display device;

The tristimulus value XYZ of the predetermined gradation is matched with the tristimulus value XYZ of the reference gradation, and the tristimulus value XYZ of the predetermined gradation and the tristimulus value XYZ of the reference gradation are determined. Obtaining the color difference of

When the obtained color difference exceeds a predetermined threshold, a color conversion matrix is created and stored based on the tristimulus values XYZ of the predetermined gradation, and the reference gradation is changed to the predetermined gradation; ,

Changing the predetermined gradation to one gradation or a plurality of gradations;

Execute the process that includes all the gradations and repeat it for each RGB primary color.

A color conversion matrix creation method characterized by the above.

2. The color conversion matrix creating method according to claim 1, wherein the predetermined display device is a display device in which color tracking occurs.

[3] XYZ color system tristimulus values A color conversion method that converts XYZ to RGB color system RGB signal values,

Inputting the tristimulus values XYZ;

Obtaining RGB signal values corresponding to the input tristimulus values XYZ using a predetermined color conversion matrix;

Obtaining an RGB gradation value corresponding to the obtained RGB signal value from halftone reproduction characteristics of a predetermined display device; A step of selecting a color conversion matrix corresponding to the obtained RGB gradation value from the color conversion matrices created by the color conversion matrix creating method according to claim 1 or claim 2;

Obtaining an RGB signal value corresponding to the input tristimulus values XYZ from the selected color conversion matrix;

A step of obtaining an RGB gradation value corresponding to the obtained RGB signal value from the halftone reproduction characteristics,

A color conversion method comprising: