KR100416231B1 - Method and apparatus for extending gamut of color devices - Google Patents

Abstract

The present invention relates to a linear gamut widening device and a method of a color device, and in particular, the color coordinates of red (R), green (G), and blue (B) are input from a device of a small color gamut, and luminance (L *), Input color coordinate conversion unit converts saturation (C *), color (h) into color coordinates, and color coordinates of luminance (L *) and saturation (C *) by linear expansion formula. A gamut width extension unit for expanding and converting, a gamut width preserving unit for controlling color attribute information of luminance and saturation extended in the gamut width expansion unit to prevent the device from a large color gamut from going out of the gamut, and a gamut width extension unit And an output color coordinate conversion unit which inversely converts the color attribute information of the luminance, saturation, and color into the color coordinates of red (R), green (G), and blue (B), and delivers them back to a device of a large color gamut. Therefore, the present invention can improve the image quality by linearly extending the gamut width when the relatively narrow gamut of the display and printing equipment of the small color gamut is converted to the wide gamut of the large gamut display.

Description

Linear color gamut expansion device and method thereof for color devices {METHOD AND APPARATUS FOR EXTENDING GAMUT OF COLOR DEVICES}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color conversion apparatus of a color device, and in particular, when a relatively narrow color gamut of a small color gamut display and a printing apparatus is converted into a wide color gamut of a large color gamut display and outputted. An apparatus and method for extending a linear gamut width of a color device capable of eliminating mismatches and improving image quality.

In the field of color reproduction, the use of color devices such as color scanners, monitors, and printers is increasing.

On the other hand, Korean Patent Application Publication No. 2001-64277, "Nonlinear color gamut compression device and method using multiple convergence points," which has been patented in Korea by the applicant, is disclosed on July 9, 2001. . This technology relates to a color display and a compression device and method for converting color gamut between input and output color printing equipment.

1 is a view showing a color conversion apparatus of color devices according to the prior art. As shown in FIG. 1, the conventional color conversion apparatus 30 is a device of a large color gamut, for example, from red (R), green (G), and blue (B) from a display 10 and a printing apparatus 20. The color coordinates are received and converted and output to the device of the small color gamut, for example, the display 40.

Therefore, in the conventional color conversion apparatus 40, the relatively wide color gamut of the device 10 and the printing equipment 20 of the large color gamut is used to print a small color gamut with a nonlinear compression mechanism using multiple convergence points. It is compressed and printed in the narrow color gamut of the equipment 40. This corrects for color gamut mismatches between devices as much as possible to adapt to human viewing characteristics.

However, such a prior art is capable of color conversion of a large color gamut device to a device of a small color gamut, but cannot be used to color convert a small color gamut device and printing equipment to a device of a large color gamut. That is, when a relatively narrow color gamut of a display and a printing apparatus of a small color gamut is converted into a wide color gamut of a large color gamut display and output, there is a problem in that image quality cannot be solved because the color gamut width cannot be resolved.

Accordingly, an object of the present invention is to linearly expand the gamut width when a relatively narrow gamut of a display of a small color gamut and printing equipment is converted to a wide gamut of a large gamut display in order to solve the problems of the related art. It is to provide a linear color gamut expansion device of a color device that can improve the image quality.

Another object of the present invention is to linearly extend from the narrow gamut of a small color gamut display or printing equipment to the wide gamut of a large gamut display equipment, thereby reproducing a portion of the color gamut between color devices that cannot be expressed due to color gamut mismatch. To provide a linear gamut extension method of.

In order to achieve the above object, the present invention provides a color conversion apparatus that receives color coordinates of red (R), green (G), and blue (B) from a device of a small color gamut, converts the color coordinates, and outputs them to a device of a large color gamut. Input color coordinate conversion that receives color coordinates of red (R), green (G), and blue (B) from the device of small color gamut and converts them into color coordinates of luminance (L *), saturation (C *), and color (h). A color gamut extension unit for converting the color coordinates transmitted from the input color coordinate conversion unit by expanding the color attributes of luminance (L *) and saturation (C *) by a linear expansion formula; And a color gamut preserving unit for controlling color attribute information of saturation from going out of the gamut in a device of a large color gamut, and red and green (R) and green ( G), inversely converted into color coordinates of blue (B) And a color coordinate conversion unit outputs to the transmission device of a large color gamut.

In order to achieve the above object, the present invention relates to a color conversion method of receiving color coordinates of red (R), green (G), and blue (B) from a device of a small color gamut, converting the color coordinates, and outputting the color coordinates to a device of a large color gamut. And receiving color coordinates of red (R), green (G), and blue (B) from devices of a small color gamut, and converting them into color coordinates of luminance (L *), saturation (C *), and color (h). And expanding and converting the color attributes of luminance (L *) and saturation (C *) from the color coordinates according to the linear expansion formula, and converting the extended luminance, saturation, and color attribute information of the colors into red (R) and green (G). ), And inversely transforming it into the color coordinates of blue (B) and passing it back to the device of the large color gamut.

1 is a view showing a color conversion apparatus of a color device according to the prior art,

2 is a view showing a linear gamut widening apparatus of color devices according to the present invention;

3 is a diagram illustrating an example of an input color coordinate conversion unit of the linear gamut widening device illustrated in FIG. 2;

4 is a diagram illustrating an example of a color gamut extension unit of the linear gamut widening unit shown in FIG. 2;

5 is a flowchart illustrating a method for expanding a linear gamut width of color devices according to the present invention;

6 is a graph illustrating the linear luminance extension of the present invention;

7 is a graph illustrating the linear saturation expansion of the present invention;

FIG. 8 is a diagram illustrating an example of an output color coordinate conversion unit of the linear gamut widening device illustrated in FIG. 2. FIG.

<Description of the code | symbol about the principal part of drawing>

100: small color display 110: small color printing equipment

200: color conversion device 210: input color coordinate conversion unit

220: gamut width expansion unit 230: gamut width storage unit

240: output color coordinate conversion unit 300: large color display

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

2 is a view showing a linear gamut width expansion device of color devices according to the present invention. Referring to FIG. 2, the present invention is composed of a device of a small color gamut, a linear gamut width expansion device 200, and a device of a large color gamut. In this embodiment, the device of the small color gamut is the small color display 100 and the printing equipment 110 and the device of the large color gamut is the large color display 300.

Meanwhile, the linear gamut widening device 200 according to the present invention includes an input color coordinate conversion unit 210, a gamut width expansion unit 220, a gamut width preserving unit 230, and an output color coordinate conversion unit 240. .

Here, the input color coordinate conversion unit 210 is a tri-stimulus value of the color coordinate input variables of the image red (R), green (G), blue (B) of the small color display 100 and the printing equipment 110 used by the user Luminance (L *), saturation (C *), and hue (L *), saturation (C *), and color (CIE X, Y, Z) and the LIE, a *, b * color coordinate system of the Commission Internationale de lCleriage (hereinafter referred to as CIE). h *) to color coordinates.

The color gamut width expansion unit 220 expands and converts the color coordinates transmitted from the input color coordinate conversion unit 210 by expanding the color attributes of the luminance L * and the saturation C * by the linear expansion formula.

The gamut width preserving unit 230 controls the color attribute information of the luminance and saturation extended by the gamut width expansion unit 220 not to go out of the gamut in the large color display 300.

The output color coordinate conversion unit 240 inversely converts the color attribute information of the luminance and saturation extended by the color gamut extension unit 220 into color coordinates of red (R), green (G), and blue (B) to display a large color display ( To 300).

FIG. 3 is a diagram illustrating an example of an input color coordinate conversion unit of the linear gamut widening device illustrated in FIG. 2. Referring to FIG. 3, the input color coordinate conversion unit 210 includes three look-up tables (LUTs) as follows. That is, the luminance (L *) lookup table (luminance_LUT) 212, the saturation (C *) lookup table (saturation_LUT, 214), and the hue (h) lookup table (color_LUT, 216).

These tables 212, 214, and 216 provide the color coordinates of the red (R), green (G), and blue (B) inputs from the small color display 100 and the printing equipment 110 using the following formula. The color coordinate system is converted into CIE (Commission de l'Cleriage) XYZ coordinates and converted into luminance (L *), saturation (C *), and color (h) information.

log Tr = C1r log [(1- C2r) D + C2r]

log Tg = C1g log [(1- C2g) D + C2g]

log Tb = C1b log [(1- C2b) D + C2b]

Luminance (L *) = 116 * (Y / Yn) ^1/3 -16.0 (Y / Yn> 0.008856)

Luminance (L *) = 903.3 * (Y / Yn) ^1/3 (Y / Yn <= 0.008856)

a * = 500 * [(X / Xn) ¹ / ^3- (Y / Yn) ^1/3 ]

b * = 200 * [(Y / Yn) ¹ / ^3- (Z / Zn) ^1/3 ]

Saturation (C *) = (a * × a * + b * × b *) ²

Color (h) = Actan (b * / a *)

Here, xr, yr, and zr are chromaticity values when a signal of 255 is given to a red gun, 0 to a green gun, and 0 to a blue gun in a display device. , xg yg, zg are the color measurements when the red signal is 0, the green color is 255, and the blue color is 0 on the display device, and xb, yb, zb is 0, green on the display device. Is a measurement of color when 0 is given to the signal and 255 is given to the blue item. In addition, C1r, C2r, C1g, C2g, C1b, and C2b are Optimization Coefficients of functions related to the corresponding red, green, and blue guns.

FIG. 4 is a diagram illustrating an example of a gamut extension unit of the linear gamut extension device illustrated in FIG. 2. Referring to FIG. 4, the gamut width expansion unit 220 of the present invention includes a luminance (L *) color gamut width expansion unit 222, a saturation (C *) color gamut width expansion unit 224, and a gamut width information storage unit. 226.

Herein, the luminance L * gamut width expansion unit 222 expands the received luminance L * information according to Equation 2 below.

bL * = (L * × 1.02)-4.44

Here, bL * indicates extended luminance information and L * indicates input luminance information.

The saturation (C *) gamut width expansion unit 224 expands the received saturation (C *) information according to Equation 3 or Equation 4 below. In this case, the saturation (C *) gamut width expansion unit 224 converts the input saturation (C *) value differently according to the reference value t or less and the reference value t.

When the input saturation value (C *) is below the reference value (t)

bC * = C *

When the input saturation value (C *) exceeds the reference value (t)

bC * = 1.48 × (C *-t) + t

Here, bC * is an extended saturation value, C * is an input saturation value, and t is a reference value (for example, 23).

In addition, the color gamut information storage unit 226 provides color gamut width information necessary for the luminance (L *) color gamut width expansion unit 222 and the saturation (C *) color gamut width expansion unit 224. ) And binary data of a gamut width that can be represented to the maximum by the printing equipment 110 is stored. Therefore, it is transmitted as marginal gamut boundary information necessary for the luminance gamut width extension 222 and the chroma gamut width extension 224.

3 and 4, the linear gamut widening device 200 of the present invention linearly expands the luminance L * and the saturation C * by the following method. However, the color (h) information is not expanded. Detailed description thereof will be made with reference to FIGS. 5 to 7. 5 is a flowchart illustrating a linear color gamut expansion method of color devices according to the present invention. 6 is a graph for explaining the linear luminance expansion of the present invention, Figure 7 is a graph for explaining the linear saturation expansion of the present invention.

First, the input color coordinate conversion unit 210 of the present invention receives the color coordinates of red (R), green (G), and blue (B) from the small color display 100 and the printing equipment 110, and receives luminance / saturation / color. The lookup table converts the color coordinates of luminance (L *), saturation (C *), and hue (h), respectively (S100).

First, the color gamut extension unit 220 linearly adjusts the color property of the luminance L * as shown in bL * = (L * × 1.02)-4.44 of Equation 2 through the luminance gamut width expansion unit 222. (S102) Referring to the graph shown in Fig. 6, the horizontal axis represents the input luminance L * value and the vertical axis represents the extended luminance bL * value being processed. Therefore, it can be seen that the expanded luminance bL * value increases linearly (thick lines) like an equivalent straight line (thin line).

The color gamut extension unit 220 determines whether the color attribute of the saturation C * is greater than 0.5 through the chroma gamut extension unit 224 (S104). If large, the color gamut width expansion unit 224 receives the color gamut information of the display 300 of the large color gamut from the color gamut information storage unit 226. (S106) On the other hand, the chroma (C *) value is 0.5. In the following case, the extended luminance (bL *) information and the input saturation (C *) value are transmitted to the output color coordinate conversion unit 240 as expanded saturation (bL *) information (see Equation 3).

If the chroma gamut width expansion unit 224 determines that the chroma (C *) value is 90% or less of the maximum gamut that can be displayed in the large color display 300 transmitted from the color gamut information storage unit 226. (S108)

As a result of the determination in S108, when the saturation (C *) value is 90% or less of the color gamut width for the large color display 300, the color attribute of the saturation (C *) is left as in Equation 3 above, or Equation 4 Linearly expands (bC *), such as bC * = 1.48 × (C *-t) + t. (S110) Referring to the graph shown in FIG. 7, the horizontal axis is the input saturation value and the vertical axis is processed. Outgoing extended saturation value. Therefore, it can be seen that the expanded saturation (bL *) value increases linearly (thick line) like an equivalent straight line (thin line).

The luminance (bL *) and chroma (bC *) information expanded through the color gamut extension unit 220 in S102 and S110 are transmitted to the output color coordinate conversion unit 240 (S112).

On the other hand, when the result of the determination in S108 is that the saturation (C *) value is less than 90% of the color gamut width for the large color display 300, the expanded luminance (bL *) information and the input saturation (C *) value are expanded. The information is transmitted to the output color coordinate conversion unit 240 as (bL *) information (see Equation 3).

8 is a diagram illustrating an example of an output color coordinate conversion unit of the linear gamut widening device illustrated in FIG. 2. Referring to FIG. 8, the output color coordinate conversion unit 240 includes three lookup tables (LUTs) as follows. That is, the red lookup table R_LUT 242, the green lookup table G_LUT 244, and the blue lookup table B_LUT 246. Through the three lookup tables 242, 244, and 246, the color attribute information of the luminance (bL *), the saturation (bC *), and the color (h) is expanded into red (R), green (G), and blue (B). Inversely converted to the color coordinate of the () is transmitted to the large color display (300).

Therefore, the present invention can linearly expand and convert the color gamut width of the color image between the color gamut devices of the small color gamut and the color gamut of the large gamut, thereby displaying the color gamut to be adapted to the human viewing characteristics as much as possible.

As described above, the present invention provides luminance and saturation information that cannot express colors due to inconsistency of color gamut of large color gamut color display equipment from a narrow gamut width of a small gamut color display or printing equipment based on human viewing characteristics. By expanding according to the linear equation, the color of the image reproduced on the large display equipment can be converted to the color best suited to human viewing characteristics, thereby improving the image quality of the large display. In addition, the present invention can be used as an application library of a color management system that minimizes color gamut inconsistency between information providers and end users in a high-speed information communication network.

On the other hand, the present invention is not limited to the above-described embodiment, various modifications are possible by those skilled in the art within the spirit and scope of the present invention described in the claims to be described later.

Claims (9)

In the color conversion apparatus that receives the color coordinates of the red (R), green (G), blue (B) from the device of the small color gamut, converts it and outputs the color coordinates to the device of the large color gamut, Input color coordinate conversion that receives color coordinates of red (R), green (G), and blue (B) from the device of the small color gamut and converts the color coordinates of luminance (L *), saturation (C *), and color (h) into color coordinates. part; A color gamut width expansion unit for converting the color coordinates transmitted from the input color coordinate conversion unit by expanding the color attributes of luminance (L *) and saturation (C *) by a linear expansion formula; A gamut width preserving unit for controlling color attribute information of luminance and saturation extended by the gamut width expansion unit not to go out of the gamut in the large color gamut device; And An output color coordinate that inversely converts the luminance, saturation, and color attribute information of the color, which are expanded in the gamut width extension part, into color coordinates of red (R), green (G), and blue (B), and transfers them back to the device of the large color gamut; An apparatus for expanding a linear gamut width of a color device, comprising: a conversion unit. The apparatus of claim 1, wherein the input color coordinate conversion unit comprises a luminance (L *) lookup table, a saturation (C *) lookup table, and a color (h) lookup table. The luminance gamut width extension unit of claim 1, wherein the color gamut width extension unit expands the received luminance (L *) information according to a linear expansion equation and converts the received chroma (C *) information into the linear extension equation. And a gamut width information storage unit for providing the gamut width information necessary for the chroma (C *) gamut width expansion unit to be expanded according to the luminance (L *) gamut width expansion unit and the chroma (C *) gamut width expansion unit. Linear color gamut expansion device for color devices. 4. The apparatus of claim 3, wherein the luminance (L *) gamut width expansion unit expands the input luminance (L *) information by the following equation. bL * = (L * × 1.02)-4.44 Here, bL * indicates extended luminance information and L * indicates input luminance information. The color gamut of the saturation (C *) gamut width expansion unit converts the input saturation (C *) value by each of the following equations according to a reference value (t) or less and a reference value (t). Linear color gamut extender for devices. When the input saturation value (C *) is below the reference value (t) bC * = C * When the input saturation value (C *) exceeds the reference value (t) bC * = 1.48 × (C *-t) + t Here, bC * is an extended saturation value, C * is an input saturation value, and t is a reference value. The gamut width information storage unit of claim 3, wherein the gamut width information storage unit stores binary data of a gamut width that can be represented by a device of the large color gamut at a maximum, and is required for the luminance gamut width expansion unit and the chroma gamut width expansion unit. An apparatus for extending linear gamut of a color device, characterized in that it is transmitted as marginal gamut boundary information. In the color conversion method of receiving a color coordinate of red (R), green (G), blue (B) from a device of a small color gamut, converts it and outputs it to a device of a large color gamut, Receiving color coordinates of red (R), green (G), and blue (B) from the device of the small color gamut, and converting them into color coordinates of luminance (L *), saturation (C *), and color (h); Expanding and converting color attributes of luminance (L *) and saturation (C *) from the color coordinates according to a linear expansion formula; And And inversely converting the extended luminance, saturation, and color attribute information of the color into color coordinates of red (R), green (G), and blue (B), and transmitting the inverse to the device of the large color gamut. Linear color gamut expansion method for color devices. The method of claim 7, wherein the step of expanding and converting the color attributes of the luminance (L *) and the saturation (C *) comprises: Expanding the color attribute of the luminance L * by the following equation; Determining whether the color attribute of the saturation (C *) is greater than 0.5; If the color attribute of the saturation (C *) is greater than 0.5, the gamut width information of the device of the large color gamut is input and the saturation (C *) value is the maximum of the gamut width that can be represented by the device of the large color gamut. Determining whether it is 90% or less, If the saturation (C *) value is equal to or less than 90% of the color gamut, expanding the color attribute of the saturation (C *) by the following equation. Luminance expansion bL * = (L * × 1.02)-4.44 Saturation (C *) Expansion bC * = 1.48 × (C *-t) + t Here, bL * is extended luminance information, L * is input luminance information, bC * is an extended saturation value, C * is an input saturation value, and t is a reference value. 9. The apparatus of claim 8, wherein the extended luminance information and the input chroma (C *) value are respectively extended when the saturation (C *) value is 0.5 or less, or when the saturation (C *) value is less than 90% of the color gamut width. And transmitting the color saturation information to a color gamut.