JP2017060093A - Color gamut converter, color gamut conversion method and color gamut conversion program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color gamut converter, a color gamut conversion method and a color gamut conversion program that are capable of solving a problem that it has been difficult to accurately display color information in a display system having a different color gamut.SOLUTION: A color space converter 12 calculates luminosity and chromaticity on a pixel basis for a wide color gamut image. A hue/saturation calculator 14 calculates saturation and hue from the chromaticity on a pixel basis for the wide color gamut image. A narrow color gamut color system luminosity, saturation and hue calculator 10 calculates luminosity, saturation and hue of a point on the outer periphery of a narrow color gamut to generate the saturation of the narrow color gamut as a function of luminosity and hue. A saturation comparator 16 refers to the function to acquire the saturation in the narrow color gamut corresponding to the luminosity and hue of pixels of the wide color gamut image, and determines a saturation ratio by dividing the saturation of the pixel of the wide color gamut image by the corresponding saturation in the narrow color gamut. A saturation enlargement magnification determining unit 18 determines a saturation enlargement magnification on the basis of the saturation ratio. A chromaticity divider 20 divides the chromaticity of the pixel of the wide color gamut image by the saturation enlargement magnification. A color space inverse transformer 22 generates an output image of the narrow color gamut from the chromaticity divided by the luminosity and saturation enlargement magnification of the input image of the wide color gamut.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a color gamut conversion technique for converting a color gamut of a color space of an image.

  A conventional general video system is an international standard BT. 709 (sRGB (standard RGB)) standard color display. On the other hand, the color expression range (hereinafter referred to as “color gamut”) tends to expand in order to improve the performance of recent devices. For example, a liquid crystal display device using a liquid crystal panel using LEDs with high emission color purity as a backlight, a projector using a laser light source, and the like have a considerably wide color gamut.

  On the other hand, in response to this situation, a color space such as AdobeRGB (trademark) corresponding to a wide color gamut is proposed and used. In addition, BT. In 2020, a color system having a larger color gamut is set.

  As a method for converting color data between systems having different color gamuts, Patent Literature 1 and Patent Literature 2 describe a method of displaying a signal acquired in a wide color gamut in a narrow color gamut. Further, as a method for expanding the color gamut, there is a method described in Patent Document 3 by the present inventor.

JP 2000-165692 A JP 2002-359748 A JP 2014-93617 A

  If an image produced with a wide color gamut is displayed as it is on a display system with a narrow color gamut, the saturation of the primary colors used as the standard for the color system is higher than those with a narrow color gamut, so the displayed image is relatively chroma. It looks like a dull hue with a low degree. On the other hand, in a method for adapting an image produced in a wide color gamut to a display system in a narrow color gamut, as in the methods described in Patent Document 1 and Patent Document 2, much of the color information is rejected. . Although the method described in Patent Document 3 performs conversion from a narrow color gamut to a wide color gamut, since the original video does not have information on the wide color gamut, the overall saturation is improved. Although it is possible, the color information of the actual scene cannot be reproduced correctly.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a color gamut conversion technology that ensures compatibility so that color information of video can be accurately displayed even in display systems having different color gamuts. There is.

  In order to solve the above-described problem, a color gamut conversion device according to an aspect of the present invention includes a color gamut that converts an input video for a display system of a first color gamut into an output video for a display system of a second color gamut. A color space conversion unit that calculates brightness and chromaticity in pixel units for an input video image in a first color gamut; and a saturation from the chromaticity in pixel units for the input video image in the first color gamut. And the input video hue / saturation calculation unit for calculating the hue, the brightness, saturation, and hue of the point on the outer periphery of the second gamut, and the saturation of the second gamut to the brightness and hue. A second color gamut color system lightness / saturation / hue calculation unit that is generated as a function for the first color gamut and the second corresponding to the lightness and hue of an input video pixel in the first color gamut Obtaining the saturation in the second color gamut, and calculating the saturation of the input image pixel in the first color gamut in the second color gamut. A saturation comparison unit for obtaining a saturation ratio divided by the above, a saturation enlargement magnification determination unit for determining a saturation enlargement magnification based on the saturation ratio, and the color of the pixel of the input image in the first color gamut A chromaticity division unit that divides the degree by the saturation magnification, and a second gamut composed of the chromaticity divided by the brightness and the saturation magnification of the input video of the first gamut And an output unit for outputting the output video together with the saturation enlargement magnification.

  Another embodiment of the present invention is also a color gamut conversion device. This device is a color gamut conversion device that converts an input video for a display system of the second color gamut into an output video for a display system of the first color gamut, and the pixel for the input video of the second color gamut A color space conversion unit that calculates brightness and chromaticity in units, and obtains a saturation enlargement magnification for each pixel of the input video in the second color gamut, and obtains the chromaticity of the pixel of the input video in the second color gamut. A chromaticity multiplication unit that multiplies the saturation expansion magnification, and an output image of the first color gamut composed of the chromaticity multiplied by the lightness and the saturation expansion magnification of the input image of the second color gamut. And an output unit for outputting.

  Yet another embodiment of the present invention is a color gamut conversion method. This method is a color gamut conversion method for converting an input video for a display system of a first color gamut into an output video for a display system of a second color gamut, and the pixel for the input video of the first color gamut Calculating brightness and chromaticity in units; calculating saturation and hue from the chromaticity in pixel units for an input image in the first gamut; and calculating points on the outer periphery of the second gamut. Calculating brightness, saturation, and hue, and generating saturation of the second color gamut as a function with respect to brightness and hue; and referring to the function, an input video pixel of the first color gamut A saturation obtained by obtaining the saturation in the second color gamut corresponding to the lightness and hue of the image and dividing the saturation of the input video pixel of the first color gamut by the corresponding saturation in the second color gamut. Determining a saturation ratio; determining a saturation magnification based on the saturation ratio; and Dividing the chromaticity of the pixels of the input video in one color gamut by the saturation magnification, and the chromaticity divided by the lightness and the saturation magnification of the input video in the first color gamut. And outputting an output image of the second color gamut constituted by the saturation enlargement magnification.

  Yet another embodiment of the present invention is a color gamut conversion method. This method is a color gamut conversion method for converting an input video for a display system of the second color gamut into an output video for a display system of the first color gamut, and the pixel is input to the input video of the second color gamut. Calculating brightness and chromaticity in units, obtaining a saturation expansion factor for each pixel of the input video in the second color gamut, and calculating the saturation to the chromaticity of the pixels of the input video in the second color gamut Multiplying an enlargement magnification; and outputting an output image of a first color gamut composed of the chromaticity multiplied by the lightness and the saturation enlargement magnification of an input image of a second color gamut. Including.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to accurately display color information of a video even in a display system having a different color gamut.

It is a block diagram of the video coding apparatus which concerns on this Embodiment. It is a block diagram of the video decoding apparatus which concerns on this Embodiment. It is a flowchart which shows the procedure of the moving image encoding process by the video encoding apparatus of FIG. It is a flowchart which shows the procedure of the moving image decoding process by the video decoding apparatus of FIG. FIG. 2 is a configuration diagram of a narrow color gamut signal / saturation expansion magnification separation processing unit in FIG. 1. FIG. 3 is a configuration diagram of a wide color gamut recovery processing unit in FIG. 2. 6 is a flowchart showing a procedure of separation processing performed by a narrow color gamut signal / saturation expansion magnification separation processing unit of FIG. It is a flowchart which shows the procedure of the recovery process by the wide color gamut recovery process part of FIG.

  FIG. 1 is a configuration diagram of a video encoding apparatus 100 according to the present embodiment. FIG. 3 is a flowchart showing the procedure of the moving image encoding process by the video encoding device 100 of FIG. Hereinafter, the configuration and operation of the video encoding device 100 will be described with reference to these drawings.

  The narrow color gamut signal / saturation enlargement magnification separation processing unit 110 receives a wide color gamut RGB video signal and separates the input wide color gamut RGB image into a narrow color gamut RGB image and a saturation enlargement magnification α. Conversion processing is performed (S10). Details of this conversion processing will be described later.

  The narrow color gamut signal / saturation expansion magnification separation processing unit 110 supplies the converted narrow color gamut RGB signal to the RGB-YPbPr conversion unit 120 in order to encode the moving image encoding method such as MPEG. The magnification α is supplied to the saturation enlargement magnification encoding unit 140.

  The RGB-YPbPr conversion unit 120 converts RGB of the input image into Y color difference (S12). This conversion is based on a general color space conversion matrix and includes thinning out of color difference signals. The RGB-YPbPr conversion unit 120 supplies the converted YPbPr signal to the video signal encoding unit 130.

  The video signal encoding unit 130 encodes the YPbPr signal as a moving image, and provides the encoded image data to the bitstream integration unit 150 (S14). In the MPEG system, discrete cosine transform (DCT) and motion prediction / compensation techniques are used.

  The saturation enlargement magnification encoding unit 140 performs moving image encoding on the saturation enlargement magnification α, and supplies the encoded alpha data to the bitstream integration unit 150 (S16). Here, encoding with an alpha channel used in the multi-level shape coding (gray scale shape coding) discussed in MPEG4 is assumed, and the saturation enlargement factor α is stored in the alpha channel to encode a moving image.

  The bit stream integration unit 150 integrates the encoded narrow color gamut image data and the encoded saturation enlargement ratio, and outputs the result as a bit stream (S18). In the case of an encoding method having an alpha channel as described above, this is integrated into a bit stream using the method.

  FIG. 2 is a configuration diagram of the video decoding apparatus 200 according to the present embodiment. FIG. 4 is a flowchart showing the procedure of the moving picture decoding process performed by the video decoding apparatus 200 shown in FIG. Hereinafter, the configuration and operation of the video decoding apparatus 200 will be described with reference to the functional configuration diagram of FIG. 2 and the flowchart of FIG. 4.

  The bit stream separation unit 210 receives the bit stream encoded by the video encoding device 100, and separates the input bit stream into narrow color gamut RGB signal data and saturation enlargement factor α data (S20). ). The bit stream separation unit 210 supplies the data of the narrow color gamut RGB signal to the video signal decoding unit 220 and supplies the data of the saturation enlargement factor α to the saturation enlargement factor decoding unit 230.

  The video signal decoding unit 220 decodes the data of the narrow color gamut RGB signal, and supplies the decoded data of the narrow color gamut RGB signal to the YPbPr-RGB conversion unit 240 and the high frequency component evaluation unit 250 (S22). . The saturation expansion factor decoding unit 230 decodes the data of the saturation expansion factor α, and supplies the decoded data of the saturation expansion factor α to the high frequency component evaluation unit 250 (S26).

  The YPbPr-RGB conversion unit 240 converts the data of the decoded narrow color gamut RGB signal (YPbPr signal) from YPbPr to RGB, and restores the narrow color gamut RGB signal (S24). This conversion is based on a general color space conversion matrix, and includes interpolation of color difference signals. The YPbPr-RGB converter 240 outputs the restored narrow color gamut RGB signal as it is, and supplies the restored narrow color gamut RGB signal to the wide color gamut recovery processing unit 260.

  The high frequency component evaluation unit 250 receives the data (YPbPr signal) regarding the decoded narrow color gamut RGB signal and the data of the decoded saturation enlargement factor α, and the data (YPbPr signal) regarding the narrow color gamut RGB signal. The presence or absence of a high-frequency component is determined for the luminance Y of () (S28). This determination is performed by comparing the sum of absolute values of the difference between the luminance Y of the target pixel and the luminance of the adjacent eight pixels with a threshold value. For example, when expressing a color with 8 bits, if the sum of the absolute values of the differences is about 30 or more, it is determined that there is a high frequency component. If the luminance Y has a high frequency component (Y in S28), the saturation magnification α = 1 is set so that the color gamut expansion processing is not performed (S30). When there is no high frequency component in the luminance Y (N in S28), the data of the saturation enlargement factor α decoded for performing the color gamut expansion processing is used (S32). In this case, the alpha channel pixel value is set to α = (A + 100) / 140 when A = α * 140−100, as will be described later.

  The wide color gamut recovery processing unit 260 receives the narrow color gamut RGB signal restored from the YPbPr-RGB conversion unit 240, and the saturation expansion magnification α set according to the presence or absence of the high frequency component from the high frequency component evaluation unit 250. And a process of restoring the wide color gamut RGB signal by converting the narrow color gamut RGB signal into a wide color gamut based on the saturation magnification α (S34). Details of the wide color gamut recovery processing will be described later.

  Here, the reason why the color gamut expansion processing is not performed when the image has a high frequency component will be described. The data stored in the alpha channel is often less correlated with surrounding pixels and frames, especially at contours, compared to general video signals, and at the same rate as general video signals. When encoding is performed, there is a high probability that block noise, mosquito noise, aliasing, and the like will occur. In this way, if color gamut expansion processing is performed on a signal whose quality has deteriorated due to high-frequency components, there is a high possibility that errors will be noticeable. I tried to do it.

  FIG. 5 is a configuration diagram of the narrow color gamut signal / saturation expansion magnification separation processing unit 110 of FIG. FIG. 7 is a flowchart showing the procedure of the separation process performed by the narrow color gamut signal / saturation expansion magnification separation processing unit 110 shown in FIG. The configuration and operation of the narrow color gamut signal / saturation expansion magnification separation processing unit 110 will be described below with reference to these drawings.

  The narrow color gamut color system lightness / saturation / hue calculation unit 10 calculates the lightness / saturation / hue of the outer periphery of the narrow color gamut for the lightness L * from 0 to 100 in advance, A process of generating saturation as a function of lightness and hue is performed (S40). This function can be configured as a look-up table (LUT) in which the saturation at the outer periphery of the narrow color gamut is associated with the lightness and hue. Specifically, it is calculated as follows.

Narrow color gamut side, that is, BT. 709 CIE xy chromaticity diagram R point (0.640, 0.330), G point (0.300, 0.600), B point (0.150, 0.060) color gamut triangle First, an equation of a straight line is obtained for each side, and further, for example, about 1000 divisions are performed, and chromaticity a * and b * are derived for the xy coordinates of each point to obtain a hue h. Y is derived by the following equations (14) and (17), and the others are calculated by the following equations (1), (2), (3), (5) to (8).
z = 1-xy (1)
X = x * y / Y (2)
Z = z * y / Y (3)
L * = 116f (Y / Yn) -16 (4)
a * = 500 [f (X / Xn) -f (Y / Yn)] (5)
b * = 200 [f (Y / Yn) -f (Z / Zn)] (6)
f (t) = t ^ (1/3) (when t> (6/29) ^ 3 = 0.008856) (7)
f (t) = [(29/3) ^ 3t + 16] / 116 (other cases) (8)
However, under a D65 light source, Xn = 95.045, Yn = 100, Zn = 108.892

About the data of about 1000 points obtained above,
h ′ = atan (b * / a *) (9)
The phase, that is, the hue h ′ is calculated by the above, and the frequency converted from this is set as the hue h, and the lightness L * and chromaticity a * and b * when the hue h is closest to an integer are incorporated into the array. A look-up table of lightness L *, lightness a * and b * with lightness of 0 to 100 and hue of 0 ° to 360 ° is obtained by making a round on all sides. Here, atan means an inverse tangent.

  The color space conversion unit 12 receives an input of a wide color gamut RGB video (S42). For example, BT. A wide color gamut RGB image corresponding to the 2020 color gamut is input. The color space conversion unit 12 converts the input RGB color space image into an L * a * b * color space image, and calculates the brightness and chromaticity of each pixel. The color space conversion unit 12 includes an RGB-linear RGB conversion unit, a linear RGB-CIE XYZ conversion unit, and a CIE XYZ-L * a * b * conversion unit, from RGB to linear RGB, from linear RGB to CIE XYZ, The color space of the wide color gamut RGB image is converted from CIE XYZ to L * a * b *. Hereinafter, it is assumed that processing is performed in pixel units by raster scanning.

  The RGB-linear RGB conversion unit converts the color space from RGB to linear RGB for the input image by general normalization and inverse gamma conversion (S44).

The linear RGB-CIE XYZ conversion unit is, for example, a BT. In the case of 2020, the following expression is converted (S46).
X = 100 * (0.6370 * R + 0.1446 * G + 0.1689 * B) (10)
Y = 100 * (0.2627 * R + 0.6780 * G + 0.0593 * B) (11)
Z = 100 * (0.0000 * R + 0.0281 * G + 1.0610 * B) (12)

  The CIE XYZ-L * a * b * conversion unit calculates lightness L *, chromaticity a *, and b * using the above-described equations (4) to (8) (S48).

The hue / saturation calculation unit 14 calculates the hue h and the saturation C * converted in frequency from the chromaticity a * and b * finally derived by the color space conversion unit 12 (S50). The hue h is calculated by the above formula (9) and converted into a frequency. Saturation C * is calculated by the length of a vector having chromaticity a * and b * as components as shown in the following equation.
C * = sqrt (a * ^ 2 + b * ^ 2) (13)

  The saturation comparison unit 16 uses the pixel and brightness of the video signal on the LUT generated by the narrow color gamut color system lightness / saturation / hue calculation unit 10 for the saturation of the pixel of the video signal obtained above. The saturation having the same hue is acquired (S52), and the saturation Ca of the pixel of the video signal is compared with the saturation Cb on the LUT (S54).

When the saturation Ca of the video signal is larger than the saturation Cb of the LUT as described below, the saturation enlargement magnification determination unit 18 sets the saturation enlargement factor α to the ratio of the saturation Ca of the video signal to the saturation Cb of the LUT. (S56), otherwise α = 1 (S58).
if (Ca> Cb) α = Ca / Cb;
else α = 1.0;

  The saturation enlargement magnification determination unit 18 outputs the saturation enlargement magnification α determined in this way and supplies the saturation enlargement magnification α to the chromaticity division unit 20.

  The significance of the saturation enlargement magnification determining unit 18 determining the saturation enlargement magnification α in this way will be described. When Ca> Cb, the color gamut of the input video signal exceeds the narrow color gamut, so the color gamut reduction processing is performed as described later. Otherwise, the input video signal is a signal within the narrow color gamut. Since it is a level, it is used as it is without reducing the color gamut. Narrow color gamut color system is BT. 709, the wide color gamut color system is BT. In the case of 2020, the upper limit is generally about 2.4, and the lower limit is 1.0 with no expansion, so the value of A = α * 140-100 is set to 8 bits in a 32-bit bitmap. Store in the alpha channel.

  The chromaticity division unit 20 reduces the color gamut of the input video by dividing the chromaticity a * and b * by the saturation enlargement magnification α (S60).

  The color space inverse conversion unit 22 performs a conversion opposite to the color space conversion performed by the color space conversion unit 12 on the video that has been subjected to the color gamut reduction processing by the chromaticity division unit 20 according to the saturation enlargement magnification α. To generate and output a narrow color gamut RGB image. The color space inverse conversion unit 22 inversely converts an image in the L * a * b * color space into an image in the original RGB color space. The color space conversion unit 12 includes an L * a * b * -CIE XYZ conversion unit, a CIE XYZ-linear RGB conversion unit, and a linear RGB-RGB conversion unit, and from L * a * b * to CIE XYZ, CIE XYZ The color space of the video that has undergone the color gamut reduction processing is converted from linear RGB to linear RGB and from linear RGB to RGB.

The L * a * b * -CIE XYZ conversion unit converts the color space from L * a * b * to CIE XYZ conversion according to the equations (14) to (19) (S62).
Y = fy ^ 3 * Yn (fy> 6/29), Y = (3/29) ^ 3 (116fy-16) Yn (fy <6/29) (14)
X = fx ^ 3 * Xn (fx> 6/29), X = (3/29) ^ 3 (116fx-16) Xn (fx <6/29) (15)
Z = fz ^ 3 * Zn (fz> 6/29), Z = (3/29) ^ 3 (116fz-16) Zn (fz <6/29) (16)
fy = (L * + 16) / 116 (17)
fx = fy + (a * / 500) (18)
fz = fy− (b * / 200) (19)
However, under a D65 light source, Xn = 95.045, Yn = 100, Zn = 108.892

The CIE XYZ-linear RGB conversion unit is, for example, a BT. When outputting as a signal 709, the color space is converted from CIE XYZ to linear RGB by the following equation (S64).
R = 0.01 * (3.2410 * X-1.5374 * Y-0.4986 * Z) (20)
G = 0.01 * (− 0.9692 * X + 1.8760 * Y + 0.0416 * Z) (21)
B = 0.01 * (0.0556 * X−0.2040 * Y + 1.0570 * Z) (22)

  The linear RGB-RGB conversion unit converts the color space from linear RGB to RGB by general gamma conversion and constant multiplication (for example, 255 times for 8 bits) (S66).

  The narrow color gamut signal / saturation expansion magnification separation processing unit 110 outputs a signal in which the color space is inversely converted by the color space inverse conversion unit 22 as a narrow color gamut RGB image, and the saturation expansion used for the reduction process. The magnification α is output (S68).

  FIG. 6 is a block diagram of the wide color gamut recovery processing unit 260 of FIG. FIG. 8 is a flowchart showing the procedure of the recovery process by the wide color gamut recovery processing unit 260 of FIG. Hereinafter, the configuration and operation of the wide color gamut recovery processing unit 260 will be described with reference to these drawings.

  The color space conversion unit 30 receives an input of a narrow color gamut RGB video (S70). Since the signal generated by the video encoding apparatus 100 is input, the BT. An image corresponding to the 709 color gamut is input. The color space conversion unit 30 includes an RGB-linear RGB conversion unit, a linear RGB-CIE XYZ conversion unit, and a CIE XYZ-L * a * b * conversion unit, from RGB to linear RGB, from linear RGB to CIE XYZ, The color space of the narrow color gamut RGB image is converted from CIE XYZ to L * a * b *. Hereinafter, it is assumed that processing is performed in pixel units by raster scanning.

  The chromaticity multiplication unit 32 receives an input of the saturation enlargement magnification α (S72). In accordance with the specification of the encoding method by the video encoding apparatus 100, alpha channel data A of a 32-bit bitmap is input here, and the result obtained by (A + 100) / 140 is defined as a saturation enlargement factor α.

  The RGB-linear RGB conversion unit converts the color space from RGB to linear RGB for the input image by general normalization and inverse gamma conversion (S74).

The linear RGB-CIE XYZ conversion unit is, for example, a BT. In the case of 709, the following expression is converted (S76).
X = 100 * (0.4124 * R + 0.3576 * G + 0.1805 * B) (23)
Y = 100 * (0.2126 * R + 0.7152 * G + 0.0722 * B) (24)
Z = 100 * (0.0193 * R + 0.1192 * G + 0.9505 * B) (25)

  The CIE XYZ-L * a * b * conversion unit calculates lightness L *, chromaticity a *, and b * using the above-described equations (4) to (8) (S78).

  The chromaticity multiplication unit 32 multiplies the color gamut of the input video by multiplying the chromaticity a * and b * finally derived by the color space conversion unit 30 by the saturation expansion magnification α (S80). .

  The color space inverse conversion unit 34 performs a conversion opposite to the color space conversion performed by the color space conversion unit 30 on the image that has been subjected to the color gamut expansion processing by the color space conversion unit 30 in accordance with the saturation expansion magnification α. To generate and output a wide color gamut RGB image. The color space inverse conversion unit 34 includes an L * a * b * -CIE XYZ conversion unit, a CIE XYZ-linear RGB conversion unit, and a linear RGB-RGB conversion unit. From the L * a * b * to the CIE XYZ, the CIE The color space of an image that has undergone color gamut expansion processing is converted from XYZ to linear RGB and from linear RGB to RGB.

  The L * a * b * -CIE XYZ conversion unit converts the color space from L * a * b * to CIE XYZ conversion according to the equations (14) to (19) (S82).

The CIE XYZ-linear RGB conversion unit is, for example, a BT. When outputting as a 2020 signal, the color space is converted from CIE XYZ to linear RGB by the following equation (S84).
R = 0.01 * (1.7167 * X-0.3557 * Y-0.2534 * Z) (26)
G = 0.01 * (− 0.6667 * X + 1.6165 * Y + 0.0158 * Z) (27)
B = 0.01 * (0.0176 * X-0.0428 * Y + 0.9421 * Z) (28)

  The linear RGB-RGB conversion unit converts the color space from linear RGB to RGB by general gamma conversion and constant multiplication (for example, 255 times for 8 bits) (S86).

  The wide color gamut recovery processing unit 260 outputs the signal whose color space is inversely converted by the color space inverse conversion unit 34 as a wide color gamut RGB image (S88).

  As described above, according to the present embodiment, by converting a wide color gamut video signal into a signal format of a narrow color gamut video and a saturation magnification factor, By outputting a narrow color gamut image including color information, compatibility with a narrow color gamut display system can be realized. In addition, if a video file of this signal format is used, in a wide color gamut display system, it is possible to return to a wide color gamut image by multiplying the chromaticity of the narrow color gamut image by the saturation enlargement magnification. Can be reproduced.

  Further, in the decoding process, a wide color gamut video signal can be reproduced while avoiding an encoding error by controlling the saturation enlargement magnification by which the chromaticity is multiplied according to the high frequency of the video signal.

  The present invention has been described based on the embodiments. The embodiments are exemplifications, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. .

  In the above description, the saturation enlargement factor α is stored in the alpha channel. However, the saturation enlargement factor α may be stored in the lower bits of the video signal. For example, a frame image according to 48-bit Tiff (each color of RGB is 16 bits) is continued to make BT. When transmitting a 2020 standard moving image, the RGB image information has an upper limit of 12 bits for each color according to the standard, so there is a total of 12 bits for each lower 4 bits of each color. If 8 bits are used for storing the saturation enlargement magnification α, it is possible to transmit the video with the saturation enlargement magnification α stored in the lower bits in a high-definition multi-bit moving image. Alternatively, as another method, the saturation enlargement factor α may be stored in a file separate from the video and provided as auxiliary information.

  In the above description, the case of converting from the wide color gamut to the narrow color gamut has been described. However, the color gamut conversion is not necessarily limited to the conversion from the wide color gamut area to the narrow color gamut. The present embodiment can be applied to arbitrary color gamut conversion as long as the color gamut reduction / enlargement processing is required when converting from the first color gamut to the second color gamut.

  It should be noted that the functional configuration of each device described in the embodiments can be realized by cooperation of hardware resources and software resources, or only by hardware resources. Processors, ROM, RAM, and other LSIs can be used as hardware resources. Programs such as operating systems and applications can be used as software resources.

  10 Narrow Color Gamut Color System Lightness / Saturation / Hue Calculation Unit, 12 Color Space Conversion Unit, 14 Hue / Saturation Calculation Unit, 16 Saturation Comparison Unit, 18 Saturation Expansion Ratio Determination Unit, 20 Chromaticity Division Unit, 22 color space inverse transform unit, 30 color space transform unit, 32 chromaticity multiplication unit, 34 color space inverse transform unit, 100 video encoding device, 110 narrow color gamut signal / saturation expansion magnification separation processing unit, 120 RGB-YPbPr Conversion unit, 130 video signal encoding unit, 140 saturation expansion rate encoding unit, 150 bitstream integration unit, 200 video decoding device, 210 bitstream separation unit, 220 video signal decoding unit, 230 saturation expansion rate decoding Conversion unit, 240 YPbPr-RGB conversion unit, 250 high-frequency component evaluation unit, 260 wide color gamut recovery processing unit.

Claims (7)

A color gamut conversion device that converts an input video for a display system of a first color gamut into an output video for a display system of a second color gamut,
A color space conversion unit that calculates brightness and chromaticity in pixel units for an input video in the first color gamut;
An input video hue / saturation calculation unit for calculating saturation and hue from the chromaticity for each input pixel of the first color gamut;
Calculating the brightness, saturation, and hue of a point on the outer periphery of the second gamut, and generating the saturation of the second gamut as a function of the brightness and hue; Saturation / hue calculation section,
With reference to the function, the saturation of the second color gamut corresponding to the brightness and hue of the input video pixel of the first color gamut is obtained, and the input video pixel of the first color gamut is obtained. A saturation comparison unit for obtaining a saturation ratio obtained by dividing the saturation by the corresponding saturation in the second color gamut;
A saturation magnification determination unit that determines a saturation magnification based on the saturation ratio;
A chromaticity division unit that divides the chromaticity of a pixel of the input video in the first color gamut by the saturation magnification;
An output unit that outputs an output image of the second color gamut composed of the chromaticity divided by the lightness and the saturation expansion magnification of the input image of the first color gamut together with the saturation expansion magnification; A color gamut conversion device comprising:   The saturation enlargement ratio determination unit sets the saturation enlargement ratio as the saturation ratio when the saturation ratio is greater than 1, and sets the saturation enlargement ratio as 1 in other cases. The color gamut conversion device according to claim 1. A color gamut conversion device that converts an input video for a display system of a second color gamut into an output video for a display system of a first color gamut,
A color space conversion unit that calculates brightness and chromaticity in units of pixels for the input image in the second color gamut;
A chromaticity multiplication unit that obtains a saturation enlargement magnification for each pixel of the input video in the second color gamut and multiplies the chromaticity of the pixel of the input video in the second color gamut by the saturation enlargement magnification;
An output unit that outputs an output image of the first color gamut composed of the chromaticity multiplied by the lightness and the saturation magnification of the input image of the second color gamut. Area converter. A color gamut conversion method for converting an input video for a display system of a first color gamut into an output video for a display system of a second color gamut,
Calculating brightness and chromaticity in pixel units for an input video in the first color gamut;
Calculating saturation and hue from the chromaticity for each input pixel of the first color gamut;
Calculating brightness, saturation, and hue of a point on the outer periphery of the second gamut, and generating saturation of the second gamut as a function of brightness and hue;
With reference to the function, the saturation of the second color gamut corresponding to the brightness and hue of the input video pixel of the first color gamut is obtained, and the input video pixel of the first color gamut is obtained. Obtaining a saturation ratio by dividing the saturation by the corresponding saturation in the second color gamut;
Determining a saturation magnification based on the saturation ratio;
Dividing the chromaticity of pixels of the input video in the first color gamut by the saturation magnification factor;
Outputting the output image of the second color gamut composed of the chromaticity divided by the lightness and the saturation enlargement magnification of the input image of the first color gamut together with the saturation enlargement magnification. A color gamut conversion method characterized by that. A color gamut conversion program for converting an input video for a display system of a first color gamut into an output video for a display system of a second color gamut,
Calculating brightness and chromaticity in pixel units for an input video in the first color gamut;
Calculating saturation and hue from the chromaticity for each input pixel of the first color gamut;
Calculating brightness, saturation, and hue of a point on the outer periphery of the second gamut, and generating saturation of the second gamut as a function of brightness and hue;
With reference to the function, the saturation of the second color gamut corresponding to the brightness and hue of the input video pixel of the first color gamut is obtained, and the input video pixel of the first color gamut is obtained. Obtaining a saturation ratio by dividing the saturation by the corresponding saturation in the second color gamut;
Determining a saturation magnification based on the saturation ratio;
Dividing the chromaticity of pixels of the input video in the first color gamut by the saturation magnification factor;
Outputting the output image of the second color gamut composed of the chromaticity divided by the lightness and the saturation magnification of the input image of the first color gamut together with the saturation magnification. A color gamut conversion program that is executed by a computer. A color gamut conversion method for converting an input video for a display system of a second color gamut into an output video for a display system of a first color gamut,
Calculating brightness and chromaticity in pixel units for the input video in the second color gamut;
Obtaining a saturation enlargement factor for each pixel of the input image in the second color gamut, and multiplying the saturation enlargement factor by the chromaticity of the pixel of the input image in the second color gamut;
And a step of outputting an output image of the first color gamut composed of the chromaticity multiplied by the lightness and the saturation magnification of the input image of the second color gamut. Conversion method. A color gamut conversion program for converting an input video for a display system of a second color gamut into an output video for a display system of a first color gamut,
Calculating brightness and chromaticity in pixel units for the input video in the second color gamut;
Obtaining a saturation enlargement factor for each pixel of the input image in the second color gamut, and multiplying the saturation enlargement factor by the chromaticity of the pixel of the input image in the second color gamut;
Outputting a first color gamut output video composed of the chromaticity multiplied by the brightness and the saturation magnification of the input video of the second color gamut. Color gamut conversion program.

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