CN100450144C - Color management method capable of converting pixels with different color gamuts - Google Patents

Abstract

For pigments displayed by devices using different color spaces, color coordinate conversion is performed between devices using different color spaces by finding multiple weights of an intermediate color gamut, so that pixels displayed by different devices have the same color characteristics, thereby achieving color communication across devices.

Description

Color management method that converts pixels of different color gamuts

technical field

The invention relates to a color management method, in particular to a cross-device color management method.

Background technique

An image processing system usually includes an image input device, an image output device, and a color management module (CMM). The image input device outputs the data representing an image to the color management module, the color management module processes the received data, and transmits the processed data to the image output device, and finally generates a color close to the original image on the image output device image. Image input devices may include optical scanners, digital cameras and digital video cameras, etc., image output devices may include various printers, plotters or monitors, etc., and the color management module may be a general-purpose computer. Controls peripherals and performs signal processing.

Different image devices will use different color models. A color model is a three-dimensional color space that represents all colors that can be seen by the human eye. The commonly used color models can be divided into two categories, namely RGB colors (red, green, blue) ) and CMYK colors (cyan, magenta, yellow, black). TVs or computer monitors generally use the RGB color model, which is a color space composed of the three primary colors of red, green and blue in different proportions, while printers or printing devices generally use CMYK colors. Visually, these color spaces are often represented by various solid shapes such as cubes, cones, or polygons. The color gamut (color gamut) represents the range of all colors that an image device can represent. The color spaces of image devices can be roughly divided into two types: Device Dependent Color and Device Independent Color. Because each image device has its own color characteristics, even image devices of the same brand have different display color gamuts. The aforementioned RGB colors and CMYK colors are all device-dependent colors. The device-independent color space (such as CIEXYZ, CIExyz, CIELAB, CIELUV, etc.) belongs to the color coordinate system formulated by the International Color Standards Committee (CIE), and its image color data will not change the color coordinate data due to different devices.

Because the images produced by different devices do not necessarily have the same color signal, even if the devices use the same color space, the same color coordinates will show different color characteristics on different devices because of the device-dependent color characteristics. Therefore, the image processing system needs a color management module to perform color management work, so that different devices can correctly express image data with the same color characteristics, so as to facilitate color communication and color matching between cross-media.

Contents of the invention

The invention provides a color management method to provide color communication and color matching between cross-media.

The present invention discloses a color management method, which includes the following steps: (a) obtaining the color coordinates of a pixel generated by a display device, (b) finding the color closest to the pixel among multiple color coordinates of an intermediate color gamut The color coordinates of the coordinates, (c) generate multiple weights according to the color coordinates obtained in step (a) and the color coordinates of the color coordinates found in step (b), and (d) generate multiple weights for a printing device. A plurality of color coordinates corresponding to the plurality of intermediate color coordinates in the color coordinates, (e) generating a color coordinate according to the plurality of weights and the plurality of color coordinates generated in step (d), and (f) according to step (e ) to print the pixel at the color coordinates produced.

The present invention also discloses a color management method, which includes the following steps: (a) obtaining the color coordinates of a pixel generated by a printing device, (b) finding the color closest to the pixel among multiple color coordinates of an intermediate color gamut The color coordinates of the coordinates, (c) generate a plurality of weights according to a plurality of intermediary color coordinates of the color coordinates obtained in step (a) and the color coordinates found in step (b), (d) generate a plurality of weights for a display device A plurality of color coordinates corresponding to the plurality of intermediate color coordinates in the color coordinates, (e) generating a color coordinate according to the plurality of weights and the plurality of color coordinates generated in step (d), and (f) according to step (e ) produces color coordinates displaying the pixel.

Description of drawings

FIG. 1 is a schematic diagram of a color space of a display device.

FIG. 2 is a schematic diagram of an intermediate color gamut.

FIG. 3 is a schematic diagram of a detailed structure of an intermediate color gamut three-dimensional interpolation table of a display device.

4 to 9 are schematic diagrams of a sub-intermediate color gamut of the intermediate color gamut in FIG. 3 .

FIG. 10 is a schematic diagram of a detailed structure of an intermediate color gamut three-dimensional interpolation table of a printing device.

11 to 16 are schematic diagrams of a sub-intermediate color gamut of the intermediate color gamut in FIG. 10 .

Description of reference symbols

10: Color space

20, 30, 100: 3D interpolation table of intermediate color gamut

pQ1-pQ8, dQ1-dQ8: sub-intermediate color gamut

pT1-pT6, dT1-dT6: Tetrahedral

pP1-pP8, dP1-dP8: vertices

pV1-pV4, dV1-dV4: vector

Detailed ways

Assuming that a display device adopts the RGB color space of device-dependent colors, the color components of a pixel are expressed by R, G, and B coordinates; an intermediate color gamut (such as sRGB color space) uses R", G", and B" coordinates coordinates to express the color component of a pixel; a printing device also uses the RGB color space of the device-dependent color, and expresses the color component of a pixel with the three coordinates of R', G', and B'. Since the RGB color space belongs to the device-dependent color, The same color coordinates will show different color characteristics on the display device and the printing device, so the color management module needs to convert the color coordinates, according to the color coordinates of the pixels to be printed in the color space of the display device, in the color space of the printing device Generate a corresponding color coordinate, so that the printing device can print out pixels with the same color characteristics according to the corresponding color coordinate.

Please refer to FIG. 1 , which represents a color space 10 adopted by a display device. The coordinates of a pre-printed pixel P in the color space 10 are (R, G, B), and the coordinates (R, G, B) represent the red (R), green (G), and blue colors of the pixel P in the color space 10 Color (B) is the composition of the three colors. Please refer to FIG. 2 . FIG. 2 represents the intermediate color gamut three-dimensional interpolation table 20 established by the color space 10 of the present invention. The intermediary color gamut three-dimensional interpolation table 20 is established by the chromaticity measurement process, and its structure is similar to the color space 10, the difference is that the intermediary color gamut three-dimensional interpolation table 20 includes a plurality of reference coordinates, represented by the circle in the figure Point indicates. If the color space 10 belongs to the device-dependent color, the intermediary color gamut three-dimensional interpolation table obtained by different devices using the color space 10 will contain different multiple reference coordinates. For example, if a display device and a printing device also use the color space 10 belonging to the device-dependent color, the three-dimensional interpolation table structure of the intermediary color gamut related to the display device and the printing device obtained through color measurement is the same, but Each of them contains multiple distinct reference coordinates.

The invention converts the color coordinates of a pixel from the color space of a display device to the color space of a printing device. Firstly, the color coordinates (R, G, B) of the pixel P in the color space 10 are mapped to an intermediate color gamut (eg, sRGB color space), and the color coordinates are represented by (iR, iG, iB). According to the color coordinates (iR, iG, iB), find the reference coordinates (R", G", B") closest to the color coordinates (iR, iG, iB) in the intermediary color gamut three-dimensional interpolation table of the display device.

First, how to obtain the color coordinates (iR, iG, iB) is described. Please refer to FIG. 3 to FIG. 9 . FIG. 3 represents a detailed structure of an intermediate color gamut three-dimensional interpolation table 30 of a display device. The three-dimensional interpolation table 30 includes 8 display device sub-intermediate color gamuts dQ1-dQ8 centered on the color coordinates (Rr", Gr", Br"). Figures 4 to 9 illustrate the structure of the sub-intermediate color gamut dQ1. The sub-intermediate The color gamut dQ1 is composed of six tetrahedrons dT1-dT6, as shown in Figure 4 to Figure 9. The color coordinates (iR, iG, iB) may have the following situations:

(1) G>B>R: the color coordinates (iR, iG, iB) correspond to the tetrahedron dT1 in the sub-intermediate color gamut dQ1;

(2) G>R>B: the color coordinates (iR, iG, iB) correspond to the tetrahedron dT2 in the sub-intermediate color gamut dQ1;

(3) R>G>B: the color coordinates (iR, iG, iB) correspond to the tetrahedron dT3 in the sub-intermediate color gamut dQ1;

(4) B>G>R: the color coordinates (iR, iG, iB) correspond to the tetrahedron dT4 in the sub-intermediate color gamut dQ1;

(5) B>R>G: the color coordinates (iR, iG, iB) correspond to the tetrahedron dT5 in the sub-intermediate color gamut dQ1;

(6) R>B>G: The color coordinates (iR, iG, iB) correspond to the tetrahedron dT6 in the sub-intermediate color gamut dQ1.

Please refer to FIG. 4 , assuming that the color coordinates (R, G, B) of the pixel P on the color space 10 of the display device fall within the tetrahedron dT1 in the sub-intermediate color gamut dQ1, the color coordinates (iR, iG, iB) can be obtained by The vectors dV1, dV2, dV3 and dV4 represented by the four vertices dP1-dP4 of the tetrahedron dT1 are represented. Vectors dV1, dV2, dV3 and dV4 are respectively defined by vertices dP1 and dP2, vertices dP2 and dP3, vertices dP3 and dP4, and vertices dP1 and dP4, and contain the components of red, green and blue colors in tetrahedron dT1. The color coordinates (R, G, B) of the pixel P correspond to the color coordinates (iR, iG, iB) of the intermediary color gamut three-dimensional interpolation table 30 and the vector dV1-dV4 has the following relationship:

iR＝w1*R1”+w2*R2”+w3*R3”+w4*R4”

iG＝w1*G1”+w2*G2”+w3*G3”+w4*G4”

iB＝w1*B1”+w2*B2”+w3*B3”+w4*B4”

in,

R1"-R4" respectively represent the proportion of the red component of the vector dV1-dV4 of the tetrahedron dT1 in the three-dimensional interpolation table 30 of the intermediary color gamut of the display device;

G1"-G4" respectively represent the proportion of the green component of the vector dV1-dV4 of the tetrahedron dT1 in the three-dimensional interpolation table 30 of the intermediary color gamut of the display device; and

B1"-B4" respectively represent the proportion of the blue component of the vector dV1-dV4 of the tetrahedron dT1 in the three-dimensional interpolation table 30 of the intermediary color gamut of the display device;

in,

w1-w4 respectively represent the weights when the color coordinates (iR, iG, iB) are represented by vectors dV1, dV2, dV3 and dV4, and w1+w2+w3+w4=1.

According to the color coordinates (R, G, B) of the pixel P in the color space 10, the present invention obtains the color coordinates (iR, iG, iB) corresponding to the intermediate color gamut by the above method, and then finds the intermediate color gamut of the printing device The color coordinates (R ", G ", B ") closest to the color coordinates (iR, iG, iB) among the plurality of color coordinates of the three-dimensional interpolation table 30. Please refer to Fig. 10, Fig. 10 represents the intermediate color of a printing device Detailed structure of the three-dimensional interpolation table 100. The intermediary color gamut three-dimensional interpolation table 100 of the printing device includes eight sub-intermediate color gamuts pQ1-pQ8 centered on the color coordinates (R", G", B"), and each sub-intermediate The color gamut is composed of 6 tetrahedrons pT1-pT6, which are defined by 4 of the 8 vertices pP1-pP4 that define each sub-intermediate color gamut. The structure of the tetrahedron pT1-pT6 is shown in Figure 11 to Figure 16 . The present invention takes the color coordinates (R", G", B") of the intermediate color gamut 100 of the printing device as the search starting point, and obtains a plurality of weights α1-α4 by a trial and error method, so that the color coordinates (iR, iG, iB ) can be expressed by the following formula:

iR＝α1*R1”+α2*R2”+α3*R3”+α4*R4”

iG＝α1*G1"+α2*G2"+α3*G3"+α4*G4"

iB=α1*B1"+α2*B2"+α3*B3"+α4*B4"

in,

R1"-R4" respectively represent the proportion of the red component of the vector pV1-pV4 of the tetrahedron pT1 in the three-dimensional interpolation table 100 of the intermediary color gamut of the printing device;

G1"-G4" respectively represent the proportion of the green component of the vector pV1-pV4 of the tetrahedron pT1 in the three-dimensional interpolation table 100 of the intermediary color gamut of the printing device;

B1"-B4" respectively represent the proportion of the blue component of the vectors pV1-pV4 of the tetrahedron pT1 in the three-dimensional interpolation table 100 of the intermediate color gamut of the printing device; and

α1-α4 respectively represent the weights when the color coordinates (iR, iG, iB) are represented by vectors pV1, pV2, pV3 and pV4, and α1+α2+α3+α4=1.

For R1"-R4", G1"-G4" and B1"-B4", the corresponding values in the color space of a printing device are R1'-R4', G1'-G4' and B1'-B4', Together with the weights α1-α4 generated in the previous steps, the target color coordinates (R′, G′, B′) of the pixel P can be generated in the color space of the printing device. The target color coordinates (R', G', B') represent the color coordinates (R, G, B) of the pixel P on the color space 10 of the display device corresponding to the color coordinates on the color space of the printing device, which can be expressed by the following formula:

R'=α1*R1'+α2*R2'+α3*R3'+α4*R4'

G'＝α1*G1'+α2*G2'+α3*G3'+α4*G4'

B'＝α1*B1'+α2*B2'+α3*B3'+α4*B4'

Among them, α1+α2+α3+α4=1

Finally, the corresponding color coordinates are generated in the color space of the printing device, and together with the weights α1-α4 generated in the previous steps, the pixel P can be generated from the color space 10 of the display device to the target color in the color space of the printing device Coordinates (R', G', B').

The intermediary color gamut three-dimensional interpolation tables 30 and 100 shown in Fig. 3 and Fig. 10 are sRGB color spaces, and the present invention also can adopt other color spaces as the intermediary color gamut three-dimensional interpolation tables 30 and 100, such as RGB, Photo YCC, Color spaces such as Adobe RGB.

In addition, the present invention can also convert the color coordinates of a pixel from the color space of a printing device to the color space of a display device. For the color coordinates (Rr', Gr', Br') of the pixel P' on the color space of a printing device, the present invention corresponds the color coordinates (Rr', Gr', Br') to the intermediate color of the printing device in the aforementioned method Gamut three-dimensional interpolation table 100 to obtain the corresponding color coordinates (iRr', iGr', iBr'), and then find the closest color coordinates (iRr', iGr', iBr') color coordinates (Rr", Gr", Br").

As shown in FIG. 3 , the intermediary color gamut three-dimensional interpolation table 30 of the display device includes 8 sub-intermediate color gamuts dQ1-dQ8 centered on the color coordinates (Rr", Gr", Br"), and each sub-intermediate color gamut is composed of 6 sub-intermediate color gamuts. Four tetrahedrons dT1-dT6 are formed, defined by 4 vertices among the 8 vertices dP1-dP4 of each sub-intermediate color gamut. The present invention uses color coordinates (Rr", Gr", Br ") as the display device intermediary The starting point of the search in the color gamut is to judge the position of the color coordinates (Rr', Gr', Br') corresponding to the color coordinates (iRr', iGr', iBr') of the intermediate color gamut three-dimensional interpolation table 30 by trial and error . Assuming that the color coordinates (iRr', iGr', iBr') are located in the tetrahedron dT1 within the sub-intermediate color gamut dQ1, the color coordinates (iRr', iGr', iBr') can be determined by the four vertices dP1-dP4 of the tetrahedron dT1 represented by vectors dV1, dV2, dV3 and dV4. Vectors dV1, dV2, dV3 and dV4 are respectively defined by vertices dP1 and dP2, vertices dP2 and dP3, vertices dP3 and dP4, and vertices dP1 and dP4, and contain the components of red, green and blue colors in tetrahedron dT1. The present invention obtains multiple weights α1-α4 with the method of trial and error, so that the color coordinates (iRr', iGr', iBr') can be represented by the following formula:

iRr’＝1*R1”+2*R2”+3*R3”+4*R4”

iGr’＝1*G1”+2*G2”+3*G3”+4*G4”

iBr'＝1*B1"+2*B2"+3*B3"+4*B4"

in,

R1"-R4" respectively represent the proportion of the red component of the vector dV1-dV4 of the tetrahedron dT1 in the three-dimensional interpolation table 30 of the intermediary color gamut of the display device;

G1"-G4" respectively represent the proportion of the green component of the vector dV1-dV4 of the tetrahedron dT1 in the three-dimensional interpolation table 30 of the intermediary color gamut of the display device; and

B1"-B4" respectively represent the proportion of the blue component of the vector dV1-dV4 of the tetrahedron dT1 in the three-dimensional interpolation table 30 of the intermediary color gamut of the display device;

in,

1-4 respectively represent the weights when the color coordinates (iRr', iGr', iBr') are represented by vectors dV1, dV2, dV3 and dV4, and 1+2+3+4=1.

For R1"-R4", G1"-G4" and B1"-B4" generate corresponding R1-R4, G1-G4 and B1-B4 in the color space of a display device, together with the weights generated in the previous steps 1-4, the target color coordinates (Rr, Gr, Br) of the pixel P' can be generated in the color space of the display device. The target color coordinates (Rr, Gr, Br) represent the color coordinates (R, G, B) of the pixel P' in the color space of the printing device corresponding to the color coordinates on the color space of the display device, which can be expressed by the following formula:

Rr＝1*R1+2*R2+3*R3+4*R4

Gr＝1*G1+2*G2+3*G3+4*G4

Br＝1*B1+2*B2+3*B3+4*B4

Among them, 1+2+3+4=1

The target color coordinates (Rr, Gr, Br) obtained by the present invention are the color coordinates corresponding to the color space of the pixel P' from the color space of the printing device to the color space of the display device, and the display device can be based on the target color coordinates (Rr, Gr , Br) Displaying the pixel P', the color characteristics of the obtained image can match the color characteristics of the pixel P' on the printing device.

To sum up, the present invention provides a color management method. By finding multiple weights of an intermediate color gamut, color coordinate conversion is performed between devices using different color spaces, so that different devices can correctly express the same Image data of color characteristics to achieve color communication and color matching across media.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (8)

1. A color management method capable of converting pixels of different color gamuts, comprising the following steps: (a) obtaining color coordinates of pixels generated by a display device; (b) finding the color coordinate closest to the color coordinate of the pixel among the plurality of color coordinates of an intermediate color gamut; (c) generating multiple weights according to multiple intermediate color coordinates of the color coordinates obtained in step (a) and the color coordinates found in step (b); (d) generating a plurality of color coordinates corresponding to the plurality of intermediate color coordinates among the plurality of color coordinates of a printing device; (e) generating a color coordinate according to the plurality of weights and the plurality of color coordinates generated in step (d); and (f) Printing the pixel according to the color coordinates generated in step (e). 2. The method of claim 1, further comprising a step (g) occurring between steps (b) and (c): finding a plurality of intermediate color coordinates to the color coordinate found in step (b). 3. The method of claim 3, wherein step (g) is finding a plurality of intermediate color coordinates of the color coordinates found in step (b) by trial and error. 4. The method of claim 2, wherein step (g) is finding 4 intermediate color coordinates of the color coordinates found in step (b). 5. A color management method capable of converting pixels of different color gamuts, comprising the following steps: (a) obtaining color coordinates of pixels generated by a printing device; (b) finding the color coordinate closest to the color coordinate of the pixel among the plurality of color coordinates of an intermediate color gamut; (c) generating multiple weights according to multiple intermediate color coordinates of the color coordinates obtained in step (a) and the color coordinates found in step (b); (d) generating a plurality of color coordinates corresponding to the plurality of intermediate color coordinates among the plurality of color coordinates of a display device; (e) generating a color coordinate according to the plurality of weights and the plurality of color coordinates generated in step (d); and (f) Displaying the pixel according to the color coordinates generated in step (e). 6. The method of claim 5, further comprising step (g) occurring between steps (b) and (c): finding a plurality of intermediate color coordinates to the color coordinate found in step (b). 7. The method of claim 6, wherein step (g) is finding a plurality of intermediate color coordinates of the color coordinate found in step (b) by trial and error. 8. The method of claim 6, wherein step (g) is finding 4 intermediate color coordinates of the color coordinates found in step (b).

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