JP2014093617A - Color video signal processing device, processing method, and processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform color signal conversion taking full advantage of a color gamut by having an input-side color gamut and an output-side color gamut determined in advance.SOLUTION: A color saturation ratio calculation unit 108 calculates, as a function of brightness and hue, a color saturation ratio obtained by the output-side color saturation calculated by a color saturation/hue calculation unit 107 by an input-side color saturation calculated by a color saturation/hue calculation unit 106. An abmagnification determination unit 105 calculates a magnification of chromaticity a, bin the chromaticity diagram of an Labcolorimetric system by using the color saturation ratio, as well as a color saturation Cand a hue h supplied from a hue/color saturation calculation unit 104. An abexpansion unit 109 expands the color gamut of actual video by multiplying each coordinate value of the chromaticity a, bin the chromaticity diagram of the Labcolorimetric system by the magnification determined by the abmagnification determination unit 105. By having an input-side color gamut and an output-side color gamut determined in advance, it is possible to determine a magnification for color gamut expansion according to the brightness and hue of an input color video signal.

Description

  The present invention relates to a color video signal processing apparatus, processing method, and processing program, and more particularly to a color video signal processing apparatus, processing method, and processing program for performing color signal conversion between color video systems having different color expression ranges.

  A conventional general color video system is designed on the premise of displaying colors in accordance with the international standard sRGB (standard RGB) standard. On the other hand, in order to improve the performance of recent color video system devices (displays, personal computers, color printers, digital cameras, etc.), the color expression range (hereinafter also referred to as “color gamut”) tends to expand. .

  For example, liquid crystal display devices using liquid crystal panels that use light emitting diodes (LEDs) with high color purity as the backlight, projectors using laser light sources, etc., have a considerably wider color gamut than conventional ones. doing. On the other hand, in response to this situation, a color space far wider than sRGB such as Adobe RGB corresponding to a wide color gamut has been proposed, and color video system equipment complying with the standard is also used.

  In this way, in the situation where color video system devices conforming to standards with different color gamuts (color spaces) are mixed, the appearance of the color image expressed between devices with different color gamuts changes, so conventionally, A color signal conversion method for converting color data so that the appearance of these color images does not change has been proposed (see, for example, Patent Documents 1 and 2). A color signal conversion method for expanding the color gamut has also been proposed (see, for example, Patent Document 3).

JP 2000-165692 A JP 2002-359748 A JP 2003-153027 A

  However, the color signal conversion methods described in Patent Documents 1 and 2 are methods for converting color data of a wide color gamut into color data of a narrow color gamut so that the appearance of a color image does not change. Cannot be converted into color data of a wide color gamut.

  On the other hand, in the color signal conversion method described in Patent Document 3, color signal conversion for expanding the color gamut is performed, but in the color gamut expansion, the color gamut expansion is linearly expanded depending on values of saturation and output color gamut width. There is no process for changing the degree of expansion according to lightness or hue. Therefore, if it is attempted to control the color gamut width that does not cause color saturation for all lightness and all hues by the color signal conversion method described in Patent Document 3, the color gamut that can be expanded cannot be expanded. It is difficult to use the color gamut sufficiently effectively.

  The present invention has been made in view of the above points, and color video signal processing capable of performing color signal conversion using the color gamut sufficiently by preliminarily determining the input side color gamut and the output side color gamut. An object is to provide an apparatus, a processing method, and a processing program.

  In order to achieve the above object, a color video signal processing apparatus according to the present invention includes a first polygon having a first color gamut serving as a basis of a color video signal before color signal conversion in a CIE xy chromaticity diagram. For each of a plurality of division points on each side, input side saturation / hue calculation means for calculating saturation and hue for a plurality of lightness values and constituting input side saturation as a function of the lightness and hue; , In the CIE xy chromaticity diagram, a plurality of division points on each side of the second polygon forming the second color gamut that is the basis of the color video signal after the color signal conversion wider than the first color gamut. For each, output saturation and hue calculation means for calculating the saturation and hue for a plurality of brightness values, and constituting the output saturation as a function of their brightness and hue, and the output saturation for the input side saturation Saturation ratio calculation means to calculate the saturation ratio divided by degrees, and input Hue / saturation calculation means for calculating the hue and saturation of the color video signal in the first color gamut in units of pixels, hue and saturation calculated by the hue / saturation calculation means, and saturation ratio calculation means Multiplying the magnification determined based on the saturation ratio calculated by the chromaticity of the color video signal for which hue and saturation were calculated by the hue / saturation calculation means, and expanding the color gamut of the color video signal Color gamut expansion means for outputting a color signal, and output conversion means for converting the color gamut expansion color signal into an output color video signal of the second color gamut and outputting it.

  In order to achieve the above object, the color video signal processing method according to the present invention includes a first multi-color that forms a first color gamut that is a basis of a color video signal before color signal conversion in the CIE xy chromaticity diagram. Calculate the saturation and hue for each of the multiple division points on each side of the square and calculate the saturation and hue for the brightness and configure the input saturation as a function of the brightness and hue. In the CIE xy chromaticity diagram, a plurality of division points on each side of the second polygon forming the second color gamut that becomes the color video signal base after color signal conversion wider than the first color gamut For each of the above, the saturation and hue calculation steps for calculating the saturation and hue for a plurality of brightness values, and constituting the output saturation as a function of those brightness and hue, and the output saturation for the input side Saturation ratio calculation that calculates saturation ratio by dividing by saturation A hue / saturation calculation step for calculating the hue and saturation of the input color video signal of the first color gamut in units of pixels, and the hue and saturation calculated by the hue / saturation calculation step; Multiply the magnification determined based on the saturation ratio calculated in the saturation ratio calculation step by the chromaticity of the color video signal for which the hue and saturation are calculated by the hue / saturation calculation means, and obtain the color image. A color gamut expansion step of outputting a color gamut expansion color signal of the signal; and an output conversion step of converting the color gamut expansion color signal into an output color video signal of the second color gamut and outputting the signal.

In order to achieve the above object, a color video signal processing program of the present invention is stored in a computer.
In the CIE xy chromaticity diagram, for each of a plurality of division points on each side of the first polygon forming the first color gamut that is the basis of the color video signal before the color signal conversion, the chromaticity for a plurality of brightness values is represented. In the CIE xy chromaticity diagram, a color signal wider than the first color gamut in the input side saturation / hue calculation function that calculates the degree and hue and constitutes the input side saturation as a function of their brightness and hue For each of a plurality of division points on each side of the second polygon that forms the second color gamut that forms the basis of the color video signal after conversion, the saturation and hue for a plurality of brightness values are calculated, and these are calculated. Output-side saturation / hue calculation function that configures output-side saturation as a function of brightness and hue, and saturation ratio calculation function that calculates saturation ratio by dividing output-side saturation by input-side saturation, Calculates the hue and saturation of the input color video signal in the first color gamut in units of pixels. The hue / saturation function, the hue and saturation calculated by the hue / saturation calculation function, and the magnification determined by the saturation ratio calculated by the saturation ratio calculation function. A color gamut expansion function for outputting the color gamut expansion color signal of the color video signal by multiplying the chromaticity of the color video signal whose hue and saturation are calculated by the calculation means, and the color gamut expansion color signal as the second color signal. An output conversion function for converting and outputting to an output color video signal of a color gamut is realized.

  According to the present invention, the input side color gamut and the output side color gamut are determined in advance, whereby the magnification of the color gamut expansion can be determined according to the brightness and hue of the input color video signal. It is possible to perform color signal conversion that fully utilizes the above.

1 is a block diagram of an embodiment of a color video signal processing apparatus of the present invention. FIG. It is a flowchart for operation | movement description of embodiment of FIG. It is a CIE xy chromaticity diagram showing an example of an input side color gamut and an output side color gamut. It is explanatory drawing of the magnification determined by FIG.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of a color video signal processing apparatus according to the present invention. The configuration of the color video signal processing apparatus shown in FIG. 1 can be realized by a central processing unit (CPU) of an arbitrary computer, a memory, and other large-scale integrated circuits (LSI) in terms of hardware. This is realized by a program loaded on the computer. In FIG. 1, functional blocks realized by such cooperation are depicted. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  The color video signal processing apparatus 100 shown in FIG. 1 is roughly classified into a signal processing unit that obtains a wide color gamut color video signal by performing actual signal processing on an input color video signal in a narrow color gamut to be signal processed. A and an input / output saturation ratio calculation unit B that calculates and prepares in advance an input / output saturation ratio used for the color gamut expansion in the signal processing unit A. Here, a case where three primary color video signals (hereinafter referred to as RGB video signals) in the sRGB color space under the D65 light source are used as input color video signals in a narrow color gamut will be described as an example. Further, a case where an RGB video signal in the Adobe RGB color space is used as an output color video signal in a wide color gamut will be described as an example.

The signal processing unit A includes an RGB → linear RGB conversion unit 101, a linear RGB → CIE XYZ conversion unit 102, a CIE XYZ → L ^* a ^* b ^* conversion unit 103, a hue / saturation calculation unit 104, and a ^* b ^* magnification determination. Part 105, a ^* b ^* enlargement part 109, L ^* a ^* b ^* → CIE XYZ conversion part 110, CIE XYZ → linear RGB conversion part 111, and linear RGB → RGB conversion part 112.

The RGB → linear RGB conversion unit 101 is supplied with an RGB video signal, which is an input color video signal in a narrow color gamut to be processed, and performs normalization and gamma correction for digital processing on the RGB video signal. To convert to a linear RGB signal. The linear RGB → CIE XYZ conversion unit 102 converts the linear RGB signal into a color signal in a CIE XYZ color space (hereinafter also referred to as a color system) formulated by the International Lighting Commission (CIE). The CIE XYZ color space is used as an intermediate work color space when the sRGB color space is converted into another color space (here, for example, L ^* a ^* b ^* color space). The CIE XYZ → L ^* a ^* b ^* conversion unit 103 converts a color signal in the CIE XYZ color space into a color signal in the L ^* a ^* b ^* color space. The hue / saturation calculation unit 104 calculates the color signal of the L ^* a ^* b ^* color space supplied from the CIE XYZ → L ^* a ^* b ^* conversion unit 103 using an L ^* a ^* b ^* table according to a known calculation formula. The saturation C ^* and hue h of the color system are calculated.

The a ^* b ^* magnification determination unit 105 is a block that forms a main part of the present embodiment, and is supplied from a saturation ratio supplied from a saturation ratio calculation unit 108 and a hue / saturation calculation unit 104 described later. Using the saturation C ^* and the hue h, the magnification of the chromaticity a ^* and b ^* in the chromaticity diagram of the L ^* a ^* b ^* color system is calculated. Note that chromaticity a ^* and b ^* indicate hue and saturation. The a ^* b ^* enlargement unit 109 converts the magnification determined by the a ^* b ^* magnification determination unit 105 to the coordinate values of the chromaticities a ^* and b ^* of the chromaticity diagram of the L ^* a ^* b ^* color system. The color gamut expansion of the actual video (that is, the input RGB video signal) is performed by multiplication.

The L ^* a ^* b ^* → CIE XYZ conversion unit 110 converts the color signal of the L ^* a ^* b ^* color space whose color gamut has been expanded by the a ^* b ^* expansion unit 109 into the CIE XYZ that is an intermediate work color space. Convert to color signal of color space. The CIE XYZ → linear RGB conversion unit 111 performs a predetermined operation on the color signal in the CIE XYZ color space to convert it into a linear RGB signal. The linear RGB → RGB conversion unit 112 performs a predetermined operation on the linear RGB signal and converts it to an RGB signal. The RGB signal after the conversion is a video signal whose color gamut is expanded with respect to the input video signal.

In the present invention, the hue / saturation calculation unit 104 constitutes hue / saturation calculation means for calculating the hue and saturation of the input color video signal of the first color gamut in units of pixels. In the present invention, the a ^* b ^* magnification determination unit 105 and the a ^* b ^* enlargement unit 106 are determined based on the hue and saturation calculated by the hue / saturation calculation unit and a saturation ratio described later. Multiplying the obtained magnification by the chromaticity of the color video signal for which the hue and saturation are calculated by the hue / saturation calculation means, and constituting a gamut expansion means for outputting the color gamut expansion color signal of the color video signal . In addition, the L ^* a ^* b ^* → CIE XYZ conversion unit 110, the CIE XYZ → linear RGB conversion unit 111, and the linear RGB → RGB conversion unit 112 output the color gamut expansion color signal of the second color gamut in the present invention. An output conversion means for converting to a color video signal and outputting it is configured.

On the other hand, the input / output saturation ratio calculation unit B includes saturation / hue calculation units 106 and 107 and a saturation ratio calculation unit 108. The saturation / hue calculation unit 106 includes saturations for a plurality of lightnesses at a plurality of points on each side of a polygon indicating a color gamut that is a base of an input color video signal of the signal processing unit A in the CIE xy chromaticity diagram. And the hue is calculated and the input side saturation is constructed as a function of lightness and hue. In the CIE xy chromaticity diagram, the saturation / hue calculation unit 107 calculates the saturation for a plurality of lightnesses at a plurality of points on each side of a polygon indicating the color gamut that is the basis of the output color video signal of the signal processing unit A. The hue is calculated and the output saturation is constructed as a function of brightness and hue. The saturation ratio calculation unit 108 divides the output side saturation by the input side saturation to calculate a saturation ratio that is a function of lightness and hue, and the calculated saturation ratio is a ^* b ^* magnification determination unit 105. To supply.

  In the CIE xy chromaticity diagram, the saturation / hue calculation unit 106 calculates a plurality of division points on each side of the first polygon that forms the first color gamut that is the basis of the color video signal before color signal conversion. For each, the saturation and hue for a plurality of brightness values are calculated, and the input-side saturation / hue calculation means in the present invention is configured to construct the input-side saturation as a function of the brightness and hue. On the other hand, the saturation / hue calculation unit 107 includes a plurality of divisions on each side of the second polygon forming the second color gamut that is the basis of the color video signal before color signal conversion in the CIE xy chromaticity diagram. For each point, the saturation and hue for a plurality of brightness values are calculated, and the output-side saturation / hue calculation means according to the present invention is configured to configure the output-side saturation as a function of the brightness and hue. The saturation ratio calculation unit 108 constitutes saturation ratio calculation means in the present invention that calculates the saturation ratio by dividing the output-side saturation by the input-side saturation.

  Next, the operation of the color video signal processing apparatus 100 of the present embodiment will be described in more detail with reference to the flowchart of FIG. 2, the CIE xy chromaticity diagram of FIG. 3, and the magnification determination explanatory diagram of FIG.

  First, the operation of the input / output saturation ratio calculation unit B will be described. In the CIE xy chromaticity diagram, a color gamut (hereinafter referred to as “input-side color gamut”) that is the basis of the input RGB video signal of the signal processing unit A in the CIE xy chromaticity diagram is input to the saturation / hue calculation unit 106 (step S1). Generally, the color gamut is specified by inputting chromaticity coordinates (x, y) of three primary color points R, G, and B in the CIE xy chromaticity diagram. Here, as an example, in the CIE xy chromaticity diagram shown in FIG. 3, the input side color gamut is R1 (0.640, 0.330) indicating the R point in the sRGB color space under the D65 light source, and G1 (0.300, 0.600) indicating the G point. ), A triangle 20 indicated by a solid line with B1 (0.150, 0.060) indicating the B point as a vertex.

Next, the saturation / hue calculation unit 106 calculates the saturation at the outer periphery of the input side color gamut for lightness values of 0 to 100 (step S2). Specifically, the saturation / hue calculation unit 106 first obtains linear equations for each of the three sides of the triangle 20 in the sRGB color space under the D65 light source, and then divides each side, for example, by 1000. The L ^* a ^* b ^* color space, which is a substantially complete color space established by the CIE, is divided into three dimensions, and the sRGB color space of the above-mentioned CIE xy chromaticity diagram expressed in two dimensions is divided. This is for conversion to the L ^* a ^* b ^* color space. Then, z is derived for each dividing point by Equation (1).

z = 1-xy (1)
Here, x and y in the expression (1) are values of x and y coordinates in the xy chromaticity diagram of the dividing point, and z is a value of z coordinate in the three-dimensional color space of the XYZ color system.

Subsequently, the saturation / hue calculation unit 106 calculates the brightness L ^* as an integer unit of 0 to 100, and Y is calculated based on Expression (2), Expression (5), Expression (6), and Expression (7). . X and Z at this time are calculated by Expression (8) and Expression (9). Here, in the following, X, Y, and Z indicate the values of the X, Y, and Z coordinates of the CIE XYZ color system, and Xn, Yn, and Zn are the three white points in the CIE XYZ as a reference. Stimulus value. Further, L ^* indicates the lightness of the L ^* a ^* b ^* color system, and a ^* and b ^* indicate the chromaticity of the L ^* a ^* b ^* color system.

Y = fy ³ Yn (fy> 6/29), Y = (3/29) ³ (116fy-16) Yn (fy <6/29) (2)
X = fx ³ Xn (fx> 6/29), X = (3/29) ³ (116fx−16) Yx (fx <6/29) (3)
Z = fz ³ Zn (fz> 6/29), Z = (3/29) ³ (116fz−16) Zx (fz <6/29) (4)
fy = (L ^* + 16) / 116 (5)
fx = fy + (a ^* / 500) (6)
fz = fy− (b ^* / 200) (7)
X = xY / y (8)
Z = zY / y (9)
Subsequently, the saturation / hue calculation unit 106 converts the coordinate values of the CIE XYZ into the coordinate values of the L ^* a ^* b ^* color system according to the equations (10) to (14).

L ^* = 116 f (Y / Yn) −16 (10)
a ^* = 500 [f (X / Xn) −f (Y / Yn)] (11)
b ^* = 200 [f (Y / Yn) −f (Z / Zn)] (12)
here
f (t) = t ^1/3 (when t> (6/29) ³ = 0.008856) (13)
f (t) = [(29/3) ³ t + 16] / 116 (other cases) (14)
However, under the D65 light source, Xn = 95.045, Yn = 100, Zn = 108.892
Next, the saturation / hue calculation unit 106 configures the saturation as a function of the brightness / hue for the outer periphery of the input side color gamut (step S3). Specifically, the phase, that is, the hue h ′ (unit radians) is calculated by the following equation for the data of each division point on one side of the triangle 20 for which the lightness L ^* is obtained by equation (10) in step S2.

h '= atan (b ^* / a ^* ) (15)
However, in formula (15), “atan” represents an inverse tangent.

Subsequently, the saturation / hue calculation unit 106 obtains a hue h (unit °) by converting the hue h ′ calculated by the equation (15) into a degree, and the lightness L ^* when the hue h is closest to an integer ^. And chromaticity a ^* and b ^* are incorporated in the array (or table) of the storage unit. In the same manner, the saturation / hue calculation unit 106 performs the above processing for all the dividing points on the three sides of the triangle 20 with the lightness L ^* changed, so that the hue of 0 ° to 360 ° is obtained. A table of lightness L ^* and chromaticity a ^* , b ^* is obtained. As a result, the saturation is an array with variables of lightness L ^* and hue h.

As described above, in the present embodiment, the saturation / hue calculation unit 106 has the sRGB color under the D65 light source indicating the input side color gamut that is the basis of the input RGB video signal of the signal processing unit A in the CIE xy chromaticity diagram. At a plurality of division points on each side of the triangle 20 in the space, the saturation and hue for a plurality of brightness values are calculated, and the input side saturation is constructed as a function of the brightness L ^* and the hue h.

  Next, in the CIE xy chromaticity diagram, a color gamut (hereinafter referred to as “output side color gamut”) that is the basis of the output RGB video signal of the signal processing unit A in the CIE xy chromaticity diagram is input to the saturation / hue calculation unit 107 (step S3). S4). Here, as an example, the output side color gamut includes R2 (0.640, 0.340) indicating the R point in the Adobe RGB color space, G2 (0.210, 0.710), B indicating the G point in the CIE xy chromaticity diagram shown in FIG. It is assumed that it is a triangle 22 indicated by a one-dot chain line having a vertex at B2 (0.150, 0.060) indicating a point.

  Next, the saturation / hue calculation unit 107 calculates the saturation at the outer periphery of the output color gamut for the lightness of 0 to 100 (step S5). In step S5, the saturation / hue calculation unit 107 performs the same processing as in step S2 by the saturation / hue calculation unit 106. Subsequently, the saturation / hue calculation unit 107 configures the saturation as a function of the brightness / hue for the outer periphery of the output side color gamut (step S6). In step S <b> 6, the saturation / hue calculation unit 107 performs the same processing as in step S <b> 3 by the saturation hue calculation unit 106.

In this way, in the present embodiment, the saturation / hue calculation unit 107 in the Adobe RGB color space indicating the output side color gamut that is the basis of the output RGB video signal of the signal processing unit A in the CIE xy chromaticity diagram. At a plurality of division points on each side of the triangle 22, saturation and hue for a plurality of brightness values are calculated, and output-side saturation is constructed as a function of the brightness L ^* and the hue h.

  Next, the saturation ratio calculation unit 108 calculates the saturation ratio by dividing the saturation of the outer periphery of the output side gamut by the saturation of the outer periphery of the input side gamut for lightness and hue (step S7). That is, the saturation ratio calculation unit 108 divides the output-side saturation calculated by the saturation / hue calculation unit 107 by the input-side saturation calculated by the saturation / hue calculation unit 106 to obtain a saturation ratio. Is calculated as a function of brightness and hue.

  Next, the operation of the signal processing unit A will be described. An RGB video signal in a narrow color gamut (here, sRGB color gamut under the D65 light source) to be actually subjected to color signal conversion is input to the RGB → linear RGB conversion unit 101 via the RGB video input terminal (step S8). ). Then, the RGB → linear RGB conversion unit 101 performs general normalization and gamma correction on the input RGB video signal for each pixel for conversion into a linear RGB signal (step S9).

  Subsequently, the linear RGB → CIE XYZ conversion unit 102 converts the linear RGB signal supplied from the RGB → linear RGB conversion unit 101 into a color signal in the CIE XYZ color space (step S10). Here, the linear RGB → CIE XYZ conversion unit 102 converts the RGB video signal in the sRGB color space under the D65 light source into a color signal indicated by the X, Y, and Z coordinates of the CIE XYZ color space according to the following equation: To pixel unit.

X = 100 * (0.4124 * R + 0.3576 * G + 0.1805 * B) (16)
Y = 100 * (0.2126 * R + 0.7152 * G + 0.0722 * B) (17)
Z = 100 * (0.0193 * R + 0.1192 * G + 0.9505 * B) (18)
Subsequently, the CIE XYZ → L ^* a ^* b ^* conversion unit 103 converts the color signal in the CIE XYZ color space supplied from the linear RGB → CIE XYZ conversion unit 102 into a color signal in the L ^* a ^* b ^* color space. (Step S11). Specifically, the CIE XYZ → L ^* a ^* b ^* conversion unit 103 converts the color signal of the CIE XYZ color space to L ^* a ^* b ^* color using the conversion formulas of the formulas (10) to (14). Convert to spatial color signal.

Subsequently, the hue / saturation calculation unit 104 calculates the hue and saturation of the color signal in the L ^* a ^* b ^* color space converted by the CIE XYZ → L ^* a ^* b ^* conversion unit 103 (step) S12). The calculation of hue and saturation is performed on a pixel-by-pixel basis by calculation processing using a calculation method similar to that of the saturation / hue calculation unit 106. The saturation C ^* of the L ^* a ^* b ^* color system is expressed by the following equation.

C ^* = √ {(a ^* ) ² + (b ^* ) ² } (19)
Next, the a ^* b ^* magnification determination unit 105 determines the magnification from the brightness, the saturation, and the saturation ratio (step S13). In other words, the a ^* b ^* magnification determination unit 105 includes the L ^* a ^* b ^* color space lightness L ^* and saturation C ^* supplied from the hue / saturation calculation unit 104, and the saturation ratio calculation unit. Using the saturation ratio obtained by calculation according to 108, the magnification of chromaticity a ^* and b ^* is determined. This magnification determination will be further described with reference to FIG.

FIG. 4 is a graph for explaining the determination of magnification, in which the vertical axis is a multiplier and the horizontal axis is C ^* / Cin [L ^* , h], and shows examples of functions that are candidates for magnification. Here, “C *” indicates the above-described saturation, and “Cin [L ^* , h]” indicates the saturation of the input-side color gamut input to the saturation / hue calculation unit 106. “Cin [L ^* , h]” is accessed by the calculated lightness L ^* and hue h of the color signal in the L ^* a ^* b ^* color space. Further, “rate [L ^* , h]” in FIG. 4 indicates the saturation ratio calculated by the saturation ratio calculation unit 108.

In FIG. 4, I represents the characteristic when the multiplier is uniformly set to the saturation ratio rate [L ^* , h] regardless of the saturation of the input video. II is a multiplier that is smaller than the saturation ratio rate [L ^* , h] when the saturation of the input video is low, and the multiplier is large in proportion to the value of C ^* / Cin [L ^* , h]. The characteristic which becomes. III is an intermediate characteristic between characteristic I and characteristic II, and indicates a characteristic that varies depending on the coefficient k.

In the present embodiment, a ^* b ^* magnification determining section 105 determines the multiplier indicated by characteristic III as the magnification. That is, the a ^* b ^* magnification determination unit 105 sets the value obtained by multiplying the value obtained by subtracting 1 from the saturation ratio rate [L ^* , h] and the coefficient k as the minimum value, and sets the saturation ratio rate [L ^* , h]. In the range where is the maximum value, a value that becomes larger as the saturation C ^* is higher is determined as the magnification. However, the multiplier indicated by the characteristic II may be determined as the magnification.

Next, the a ^* b ^* enlargement unit 109 uses the magnification determined by the a ^* b ^* magnification determination unit 105 as the chromaticity a ^* and b ^* of the color signal in the input L ^* a ^* b ^* color space. An enlargement process for multiplying each coordinate value is performed (step S14). As a result, the color gamut of the input RGB video signal converted into the color signal in the L ^* a ^* b ^* color space is expanded.

Subsequently, the L ^* a ^* b ^* → CIE XYZ conversion unit 110 converts the color signal of the L ^* a ^* b ^* color space whose color gamut is expanded by the a ^* b ^* expansion unit 109 into the intermediate work color space. Conversion into a color signal of a certain CIE XYZ color space (step S15). Specifically, the L ^* a ^* b ^* → CIE XYZ conversion unit 110 performs arithmetic processing according to the above-described formulas (2) to (7) on the color signal in the L ^* a ^* b ^* color space to perform CIE XYZ. Convert to color signal of color space.

Subsequently, the CIE XYZ → linear RGB conversion unit 111 converts the color signal in the CIE XYZ color space into a linear RGB signal (step S16). Here, the CIE XYZ → linear RGB converter 111 converts the color signal indicated by the X, Y, and Z coordinates of the CIE XYZ color space supplied from the L ^* a ^* b ^* → CIE XYZ converter 110 into a pixel. The unit is converted into an RGB video signal represented by the R point coordinates, G point coordinates, and B point coordinates in the Adobe RGB color space by the following known formula.

R = 0.01 * (2.0416 * X-0.5650 * Y-0.3447 * Z) (20)
G = 0.01 * (-1.0199 * X + 1.9171 * Y + 0.0481 * Z) (21)
B = 0.01 * (0.0340 * X-0.1229 * Y + 1.014 * Z) (22)
Next, the linear RGB → RGB conversion unit 112 converts the linear RGB video signal into an RGB video signal (step S17). That is, the linear RGB → RGB conversion unit 112 performs general gamma conversion and constant multiplication (for example, an RGB video signal) on the linear RGB video signal in the Adobe RGB color space supplied from the CIE XYZ → linear RGB conversion unit 111. Is converted to an RGB video signal suitable for display on a monitor screen.

  Finally, the linear RGB → RGB conversion unit 112 outputs the converted RGB video signal to the outside (step S18). This output RGB video signal is an RGB video signal in the Adobe RGB color space in which the color gamut is expanded compared to the input RGB video signal in the sRGB color space under the D65 light source.

  As described above, according to the present embodiment, the input-side color gamut and the output-side color gamut are designated in advance as the coordinates of the CIE xy chromaticity diagram, so that the color based on the input / output saturation ratio can be obtained. It is possible to determine the magnification at which the area can be expanded. And, by analyzing the brightness and hue of the actual input color video signal and multiplying the chromaticity of the input color video signal by the magnification according to the brightness and hue, it is possible to perform color signal conversion using the color gamut effectively. .

  Note that the present invention is not limited to the above-described embodiment. For example, a method for controlling the magnification itself based on lightness and hue, or a function different from the magnification determination function illustrated in FIG. 4 may be used. Good. The output side color gamut may be a color gamut of a known color space in which the color gamut is larger than the input side color gamut. Furthermore, the above color gamut is not limited to a triangle, and may be another polygon such as a quadrangle.

  Furthermore, the present invention also includes a color video signal processing program that causes a computer to execute the processing of each step shown in the flowchart of FIG. This color video signal processing program can be recorded on a recording medium and written to a computer, or distributed via a communication network and downloaded to a computer.

100 color video signal processing apparatus 101 RGB → linear RGB conversion unit 102 linear RGB → CIE XYZ conversion unit 103 CIE XYZ → L ^* a ^* b ^* conversion unit 104 hue / saturation calculation unit 105 a ^* b ^* magnification determination unit 106 107 Saturation / Hue Calculation Unit 108 Saturation Ratio Calculation Unit 109 a ^* b ^* Enlargement Unit 110 L ^* a ^* b ^* → CIE XYZ Conversion Unit 111 CIE XYZ → Linear RGB Conversion Unit 112 Linear RGB → RGB Conversion Unit

Claims (4)

In the CIE xy chromaticity diagram, for each of a plurality of division points on each side of the first polygon forming the first color gamut that is the basis of the color video signal before the color signal conversion, the chromaticity for a plurality of brightness values is represented. Input-side saturation / hue calculation means for calculating the degree and hue and constituting the input-side saturation as a function of their brightness and hue;
In the CIE xy chromaticity diagram, a plurality of division points on each side of the second polygon forming the second color gamut that forms the basis of the color video signal after color signal conversion wider than the first color gamut. For each, output saturation and hue calculation means for calculating the saturation and hue for a plurality of brightness values, and constituting the output saturation as a function of their brightness and hue,
Saturation ratio calculation means for calculating a saturation ratio by dividing the output side saturation by the input side saturation;
Hue / saturation calculating means for calculating the hue and saturation of the input color video signal of the first color gamut in units of pixels;
The magnification determined based on the hue and saturation calculated by the hue / saturation calculating unit and the saturation ratio calculated by the saturation ratio calculating unit is set to a hue determined by the hue / saturation calculating unit. Gamut expansion means for multiplying the calculated chromaticity of the color video signal by the chromaticity and outputting the color gamut expansion color signal of the color video signal;
An output conversion means for converting the color gamut expansion color signal into an output color video signal of the second color gamut and outputting the output color video signal. The color gamut expansion means includes:
The saturation calculated by the hue / saturation calculation means is high within a range in which a value obtained by multiplying a value obtained by subtracting 1 from the saturation ratio is a minimum value and the saturation ratio is a maximum value. A value that is so large is determined as a magnification, and the determined magnification is multiplied by the chromaticity of the color video signal for which the hue and saturation are calculated by the hue / saturation calculation means to obtain the color gamut expansion signal. The color video signal processing apparatus according to claim 1. In the CIE xy chromaticity diagram, for each of a plurality of division points on each side of the first polygon forming the first color gamut that is the basis of the color video signal before the color signal conversion, the chromaticity for a plurality of brightness values is represented. An input-side saturation / hue calculation step that calculates the degree and hue and constitutes the input-side saturation as a function of their brightness and hue;
In the CIE xy chromaticity diagram, a plurality of division points on each side of the second polygon forming the second color gamut that forms the basis of the color video signal after color signal conversion wider than the first color gamut. For each, the saturation and hue calculation steps for calculating the saturation and hue for a plurality of lightness values and constituting the output saturation as a function of their lightness and hue;
A saturation ratio calculating step of calculating a saturation ratio by dividing the output saturation by the input saturation;
A hue / saturation calculation step of calculating the hue and saturation of the input color video signal of the first color gamut in units of pixels;
The magnification determined based on the hue and saturation calculated in the hue / saturation calculation step and the saturation ratio calculated in the saturation ratio calculation step is determined by the hue / saturation calculation step. A color gamut expansion step of multiplying the calculated chromaticity of the color video signal by the chromaticity and outputting a color signal of the color video signal to expand the color gamut;
An output conversion step of converting the color gamut expansion color signal into an output color video signal of the second color gamut and outputting the output color video signal. On the computer,
In the CIE xy chromaticity diagram, for each of a plurality of division points on each side of the first polygon forming the first color gamut that is the basis of the color video signal before the color signal conversion, the chromaticity for a plurality of brightness values is represented. An input side saturation / hue calculation function that calculates the degree and hue and constitutes the input side saturation as a function of their brightness and hue;
In the CIE xy chromaticity diagram, a plurality of division points on each side of the second polygon forming the second color gamut that forms the basis of the color video signal after color signal conversion wider than the first color gamut. For each, output saturation and hue calculation functions that calculate saturation and hue for multiple brightnesses and configure output saturation as a function of their brightness and hue;
A saturation ratio calculation function for calculating a saturation ratio by dividing the output saturation by the input saturation;
A hue / saturation calculation function for calculating the hue and saturation of the input color video signal of the first color gamut in units of pixels;
The magnification determined based on the hue and saturation calculated by the hue / saturation calculation function and the saturation ratio calculated by the saturation ratio calculation function is determined by the hue / saturation calculation function. A color gamut expansion function that multiplies the chromaticity of the calculated color video signal by the chromaticity of the color video signal and outputs a color signal that expands the color gamut of the color video signal;
An output conversion function for converting the color gamut expanded color signal into an output color video signal of the second color gamut and outputting the same.

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