JP4989401B2 - Video signal processing apparatus, method and program thereof - Google Patents

Description

  The present invention relates to a video signal processing apparatus that converts a color signal using a color appearance model such as CIECAM02, a method thereof, and a program thereof.

In recent years, with the rapid spread of the Internet environment, color reproducibility between different devices and video media is becoming important. When considering color reproducibility between different devices and media, even if spectral structures and colorimetric values are matched, the color appearances do not always match. Here, the color appearance is visual such as brightness, vividness, and hue, and is influenced by the visual environment such as background color and illumination. Various color appearance models have been proposed so far, and the CIECAM02 model has been proposed by the CIE (International Lighting Commission) as a comprehensive model (see Non-Patent Document 1). The CIECAM02 model predicts the appearance of color under various visual environments using four environmental parameters.
CIE, CIE 159-2004, A color appearance model for color management systems: CIECAM02

  In order to predict the appearance of colors under various viewing environments, the color conversion process in the CIECAM02 model is very complicated. When this CIECAM02 model is applied to a video signal, the calculation time is long, and the apparatus performs the process High performance is required.

  It is an object of the present invention to provide a video signal processing apparatus, a method thereof, and a program thereof that can solve the above-described problems and that can perform color conversion processing that is substantially the same as the CIECAM02 model with a simple configuration and a short calculation time. To do.

  In order to solve the above-described problem, a video signal processing apparatus according to claim 1 is a video signal processing apparatus that converts a visual RGB signal before color conversion expressed in an RGB color space into a color signal in accordance with human visual sensitivity. The above-mentioned visual RGB signal before color conversion is configured to include CIECAM02 approximate conversion means for converting the visual RGB signal before color conversion into the visual RGB signal after color conversion expressed in the RGB color space by the expression (1) as the CIECAM02 approximate expression.

In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion.

  According to this configuration, the CIECAM02 approximate conversion means performs color conversion processing on the visual RGB signal before color conversion into the visual RGB signal after color conversion using the CIECAM02 approximate expression. Here, since the color is defined by the three elements of brightness, hue, and saturation, dividing into luminance conversion, hue conversion, and saturation conversion makes it easier to intuitively understand the color conversion processing. For this reason, the video signal processing device converts the luminance RGB and the saturation conversion by converting the visual RGB signal before color conversion into a luminance signal and a color difference signal by the CIECAM02 approximate expression. Next, the video signal processing device converts the luminance signal by a coefficient P related to brightness before color conversion (luminance conversion) and converts the color difference signal by a coefficient Q related to saturation before color conversion by the CIECAM02 approximate expression. (Saturation conversion). Note that the video signal processing apparatus does not perform hue conversion. Further, since the CIECAM02 approximate expression is only an operation using a matrix, the amount of calculation is significantly smaller than the calculation expression of the CIECAM model, and a result almost equal to the color conversion process using the CIECAM02 model can be obtained.

  The video signal processing apparatus according to claim 2 is the video signal processing apparatus according to claim 1, wherein the CIECAM02 approximate conversion unit includes a coefficient P relating to brightness before color conversion and a coefficient Q relating to saturation before color conversion. Is calculated using Equation (2).

In Equation (2), P _i is the brightness before color conversion, P _i-max is the maximum brightness before color conversion, C _{1 to} C ₅ are coefficients determined by the viewing environment, and h is the color before color conversion. , C represents the saturation before color conversion.

According to this configuration, the video signal processing apparatus calculates the coefficient P relating to the brightness before color conversion and the coefficient Q relating to the saturation before color conversion, which are elements of the matrix of the CIECAM02 approximate expression, by the CIECAM02 approximate conversion unit. Can do. By using the coefficients C _{1 to} C ₅ determined by the viewing environment as in Expression (2), the video signal processing apparatus can perform appropriate color conversion processing.

  The video signal processing device according to claim 3 is the video signal processing device according to claim 1 or 2, wherein the inverse gamma correction means, the XYZ signal conversion means before color conversion, the RGB signal conversion means before color conversion, The apparatus further comprises post-conversion XYZ signal conversion means, post-color conversion RGB signal conversion means, and gamma correction means.

  According to such a configuration, the video signal processing apparatus performs reverse gamma correction on the input RGB signal before color conversion by the inverse gamma correction means, and outputs the RGB signal before color conversion after reverse gamma correction. This is because the gamma correction performed on the input video signal affects the color conversion processing of the CIECAM02 approximate conversion means. Further, the video signal processing apparatus converts the RGB signal before color conversion after inverse gamma correction into the XYZ signal before color conversion expressed in the XYZ color space by the XYZ signal conversion means before color conversion. Further, the video signal processing device converts the XYZ signal before color conversion into the visual RGB signal before color conversion by the RGB signal conversion means before color conversion and outputs it to the CIECAM02 approximate conversion means.

  The video signal processing apparatus converts the color RGB visual RGB signal into the color converted XYZ signal by the color converted XYZ signal conversion means. The video signal processing apparatus converts the color-converted XYZ signal into the color-converted RGB signal expressed in the RGB color space by the color-converted RGB signal conversion means. This RGB signal corresponds to a wide range of devices such as a display, a video and a camera. Further, the video signal processing apparatus outputs the RGB signal after color conversion after gamma correction by performing gamma correction on the RGB signal after color conversion by the gamma correction unit. As a result, it is possible to prevent gamma correction from being individually performed by a device that has received a color-converted video signal.

  In order to solve the above-described problem, a video signal processing method according to claim 4 is a video signal processing for converting a visual RGB signal before color conversion expressed in an RGB color space into a color signal according to human visual sensitivity. The apparatus is configured to include a CIECAM02 approximate conversion step of converting the visual RGB signal before color conversion into a visual RGB signal after color conversion expressed in the RGB color space by Expression (1) as a CIECAM02 approximate expression.

In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion.

  In order to solve the above-described problem, the video signal processing program according to claim 5 is configured to convert the visual RGB signal before color conversion expressed in the RGB color space into a color signal in accordance with human visual sensitivity. The computer is configured to function as CIECAM02 approximate conversion means for converting the visual RGB signal before color conversion into a visual RGB signal after color conversion expressed in the RGB color space according to Expression (1) as a CIECAM02 approximate expression.

In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion.

  The video signal processing apparatus, method and program thereof according to the present invention have the following excellent effects. According to the first, second, fourth, and fifth aspects of the invention, since the CIECAM02 approximation formula with a small amount of calculation is used, the color conversion processing can be performed with a simple configuration and the same configuration as the CIECAM02 model with a simple configuration. It becomes possible. According to the third aspect of the present invention, since RGB signals can be input and RGB signals are output, it can be applied to a wide range of devices such as displays, videos, cameras, etc., and versatility can be enhanced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In each embodiment, means having the same function and the same member are denoted by the same reference numerals, and description thereof is omitted.

[Configuration of video signal processing device]
The configuration of the video signal processing apparatus will be described with reference to FIG. FIG. 1 is a block diagram of a video signal processing apparatus according to this embodiment of the present invention. The video signal processing apparatus 1 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a HDD (Hard Disk Drive), and an input / output interface. Further, the video signal processing apparatus 1 has a video signal conversion means 10, a CIECAM02 approximate conversion means 20, a color-converted XYZ signal conversion means 30, and a color-converted RGB signal conversion means in order to realize various functions described later. 40, a gamma correction unit 50, an input / output unit 60, and a storage unit 70.

  The video signal conversion means 10 converts a video signal input from the outside into a visual RGB signal before color conversion expressed in an RGB color space. For example, the video signal conversion unit 10 includes an inverse gamma correction unit 11, a pre-color conversion XYZ signal conversion unit 12, and a pre-color conversion RGB signal conversion unit 13.

  The inverse gamma correction unit 11 performs inverse gamma correction on the input RGB signal before color conversion and outputs an RGB signal before color conversion after reverse gamma correction. In this case, the inverse gamma correction unit 11 performs inverse gamma correction on the RGB signal before color conversion to the RGB signal before color conversion after reverse gamma correction using Expression (3), and outputs the RGB signal to the XYZ signal conversion unit 12 before color conversion. .

In Equation (3), E _R , E _G , and E _B represent RGB signals before color conversion after inverse gamma correction, and E _R ′, E _G ′, and E _B ′ represent RGB signals before color conversion.

  The XYZ signal conversion means 12 before color conversion converts the RGB signal before color conversion after inverse gamma correction, which has been subjected to inverse gamma correction by the inverse gamma correction means 11, into an XYZ signal before color conversion expressed in the XYZ color space. (Matrix conversion). In this case, the XYZ signal conversion means 12 before color conversion converts the RGB signal before color conversion after inverse gamma correction into an XYZ signal before color conversion using the equation (4), and outputs it to the RGB signal conversion means 13 before color conversion. To do.

However, expressed in equation (4), X, Y, Z color before conversion XYZ _{signals, E R, E G, E} B is the color before conversion RGB signal after inverse gamma correction.

  The pre-color conversion RGB signal conversion means 13 converts the pre-color conversion XYZ signal converted by the pre-color conversion XYZ signal conversion means 12 into a pre-color conversion visual RGB signal and outputs it to the CIECAM02 approximate conversion means 20. (Matrix conversion). In this case, the RGB signal conversion means 13 before color conversion converts the XYZ signal before color conversion into a visual RGB signal before color conversion using Expression (5).

In Equation (5), R _i , G _i and B _i represent visual RGB signals before color conversion, and X, Y and Z represent XYZ signals before color conversion.

  The CIECAM02 approximate conversion means 20 converts the visual RGB signal before color conversion converted by the video signal conversion means 10 into a visual RGB signal after color conversion expressed in the RGB color space by Expression (1) as a CIECAM02 approximate expression. Then, it is output to the XYZ signal conversion means 30 after color conversion.

In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion.

  Prior to this calculation, the CIECAM02 approximate conversion means 20 may calculate the coefficient P related to brightness before color conversion and the coefficient Q related to saturation before color conversion using Expression (2). .

In Equation (2), P _i is the brightness before color conversion, P _i-max is the maximum brightness before color conversion, C _{1 to} C ₅ are coefficients determined by the viewing environment, and h is the color before color conversion. , C represents the saturation before color conversion.

Here, the coefficients C _{1 to} C ₅ determined by the visual environment may be determined as follows. The result of color conversion processing of a video signal using the CIECAM02 model is compared with the result of color conversion processing of the video signal by the video signal processing apparatus 1, and the result is determined by the viewing environment so that the color appearances of the two results are substantially equal. The values of the coefficients C _{1 to} C ₅ are changed. For example, when a video signal captured under a peak luminance of 3000 cd / m ² and room light conditions is viewed under a peak luminance of 100 cd / m ² and a dark room condition, the coefficient C ₁ determined by the viewing environment = 0.2, coefficient C ₂ = 0.6 determined by the visual environment, coefficient C ₃ = −0.1 determined by the visual environment, coefficient C ₄ = 0.02 determined by the visual environment, coefficient C ₅ = 0 determined by the visual environment .2. The coefficients C _{1 to} C ₅ determined by the visual environment are not limited to the above values.

  The post-color conversion XYZ signal conversion means 30 converts the post-color conversion visual RGB signal converted by the CIECAM02 approximate conversion means 20 into a post-color conversion XYZ signal expressed in the XYZ color space (matrix conversion). In this case, the color-converted XYZ signal conversion unit 30 converts the color-converted visual RGB signal into the color-converted XYZ signal using the equation (6), and outputs the converted color-converted visual RGB signal to the color-converted RGB signal conversion unit 40.

In Equation (6), X, Y, and Z represent XYZ signals after color conversion, and R _d , G _d , and B _d represent visual RGB signals after color conversion.

  The post-color conversion RGB signal conversion unit 40 converts the post-color conversion XYZ signal converted by the post-color conversion XYZ signal conversion unit 30 into a post-color conversion RGB signal expressed in the RGB color space (matrix conversion). ). In this case, the RGB signal conversion means 40 after color conversion converts the XYZ signal after color conversion into an RGB signal after color conversion using the equation (7), and outputs it to the gamma correction means 50.

In Equation (7), E _R , E _G , and E _B represent RGB signals after color conversion, and X, Y, and Z represent XYZ signals after color conversion.

  The gamma correction unit 50 performs gamma correction on the color-converted RGB signal converted by the color-converted RGB signal conversion unit 40 and outputs the color-converted RGB signal after gamma correction. In this case, the gamma correction means 50 gamma-corrects the color-converted RGB signal to the color-converted RGB signal after gamma correction using Expression (8). Note that the video signal processing apparatus 1 is not limited to outputting the RGB signal after color conversion after gamma correction, and may output a signal expressed in another color space.

In Equation (8), E _R ′, E _G ′, and E _B ′ represent RGB signals after color conversion after gamma correction, and E _R , E _G , and E _B represent RGB signals after color conversion.

  The input / output unit 60 includes a LAN port, a display terminal, and the like, and outputs a video signal from another computer or the like to the inverse gamma correction unit 11 and other RGB signals after color conversion after gamma correction from the gamma correction unit 50. Output to a computer or display. In FIG. 1, the input / output unit 60 is integrally displayed for convenience of explanation, but may be configured separately.

The storage means 70 stores coefficients C _{1 to} C ₅ determined by the visual environment and other data necessary for the operation of the video signal processing apparatus 1. Further, the video signal processing device 1 may include a keyboard and a mouse for operating the video signal processing device 1.

Note that the video signal processing apparatus 1 may not include the inverse gamma correction unit 11 when an RGB signal that has not been gamma corrected is input. If an XYZ signal is input, the video signal processing apparatus 1 may not include the inverse gamma correction unit 11 and the pre-color conversion XYZ signal conversion unit 12. When a visual RGB signal before color conversion (see Expression (4)) is input, the video signal processing apparatus 1 includes an inverse gamma correction unit 11, an XYZ signal conversion unit 12 before color conversion, and an RGB signal conversion unit before color conversion. 13 may not be provided. Furthermore, when a signal expressed in another color space such as an HSV signal, a YUV signal, or L ^* a ^* b ^* is input as a video signal, the video signal processing apparatus 1 is expressed in these other color spaces. Means for converting the signal into a visual RGB signal before color conversion may be provided.

  Further, when the RGB signal is output without performing the gamma correction, the video signal processing apparatus 1 may not include the gamma correction unit 50. Further, when outputting the XYZ signal, the video signal processing apparatus 1 may not include the post-color conversion RGB signal conversion unit 40 and the gamma correction unit 50. Further, when outputting the signal after the color conversion process as it is, the video signal processing apparatus 1 may not include the post-color conversion XYZ signal conversion unit 30, the post-color conversion RGB signal conversion unit 40, and the gamma correction unit 50. Further, when the signal subjected to the color conversion process is converted into a signal expressed in another color space and output, the video signal processing apparatus 1 displays the color RGB visual RGB signal expressed in these other color spaces. Means for converting into a signal may be provided.

[Operation of video signal processor]
The operation of the video signal processing apparatus will be described with reference to FIG. 2 (see FIG. 1 as appropriate). FIG. 2 is a flowchart showing the operation of the video signal processing apparatus of FIG. First, the video signal processing apparatus 1 performs inverse gamma correction on the RGB signal before color conversion by the inverse gamma correction unit 11 and outputs the RGB signal before color conversion after inverse gamma correction (step S1). Further, the video signal processing apparatus 1 converts the RGB signal before color conversion after inverse gamma correction into the XYZ signal before color conversion (matrix conversion) by the XYZ signal conversion means 12 before color conversion (step S2). Further, the video signal processing apparatus 1 converts (matrix conversion) the pre-color conversion XYZ signals into the pre-color conversion visual RGB signals by the pre-color conversion RGB signal conversion means 13 (step S3). Further, the video signal processing apparatus 1 converts the visual RGB signal before color conversion into the visual RGB signal after color conversion by the CIECAM02 approximate conversion means 20 (step S4).

The details of the CIECAM02 approximate conversion process (step S4) in FIG. 2 will be described below with reference to FIG. FIG. 3 is a flowchart showing details of the CIECAM02 approximate conversion process of FIG. First, the video signal processing apparatus 1 reads out the coefficients C _{1 to} C ₅ determined by the viewing environment from the storage unit 70. In the video signal processing apparatus 1, the CIECAM02 approximate conversion unit 20 calculates the brightness P _i before color conversion, the hue h before color conversion, and the saturation C before color conversion using Equation (2). (Step S41).

  Subsequent to step S41, in the video signal processing apparatus 1, the CIECAM02 approximate conversion unit 20 uses the equation (2) to calculate the coefficient P related to brightness before color conversion and the coefficient Q related to saturation before color conversion. (Step S42). Furthermore, in the video signal processing apparatus 1, the CIECAM02 approximate conversion unit 20 converts the visual RGB signal before color conversion converted in step S3 into the visual RGB signal after color conversion, using Expression (1) (step S43). . As described above, the video signal processing apparatus 1 performs the CIECAM02 approximate conversion process in three steps.

  Returning to FIG. 2, the operation of the video signal processing apparatus 1 will be described. Following step S4 in FIG. 2, the video signal processing apparatus 1 converts the color-converted visual RGB signal into a color-converted XYZ signal (matrix conversion) by the color-converted XYZ signal conversion means 30 (step S5). Further, the video signal processing apparatus 1 converts the color-converted XYZ signals into color-converted RGB signals (matrix conversion) by the color-converted RGB signal conversion means 40 (step S6). Further, the video signal processing apparatus 1 gamma-corrects the color-converted RGB signal by the gamma correction means 50 and outputs the color-converted RGB signal after gamma correction (step S7).

  In the present embodiment, the video signal processing apparatus 1 has been described as an independent apparatus. However, the video signal processing apparatus according to the present invention may be incorporated in a device such as a display, a video, or a camera. The video signal processing apparatus 1 can also operate a general computer by a program that functions as each of the above-described means. This program may be distributed via a communication line, or may be distributed by writing in a recording medium such as a CD-ROM or a flash memory.

[Comparative example]
With reference to FIG. 4, how simple the CIECAM02 approximate conversion process in the video signal processing apparatus 1 is compared with the color conversion process based on the CIECAM02 model will be described. FIG. 4 is a flowchart showing color conversion processing based on the CIECAM02 model. Hereinafter, an apparatus that performs color conversion processing using the CIECAM02 model is referred to as a color conversion apparatus. First, similarly to the video signal processing apparatus 1, the color conversion apparatus performs inverse gamma correction on the input RGB signal using Expression (3) (step S101). Similarly to the video signal processing device 1, the color conversion device converts the inverse-gamma RGB signal into an XYZ signal (matrix conversion) using Equation (4) (step S102). Further, the color conversion apparatus converts the XYZ signal into an RGB signal (matrix conversion) using Expression (5), similarly to the video signal processing apparatus 1 (step S103).

  Here, the color conversion apparatus performs color conversion processing using the CIECAM02 model in steps S104 to S117 described later. The color conversion apparatus calculates an adaptation coefficient D by the equation (101) (step S104).

However, in the formula (101), D is adaptation coefficient, F is the coefficient by forceps conditions, _{L A} represents a peak intensity.

  Subsequent to step S104, the color conversion apparatus calculates a weighted RGB signal after chromatic adaptation according to equation (102) (step S105).

In Equation (102), R _C , G _C and B _C are weighted RGB signals after chromatic adaptation, R, G and B are visual RGB signals, D is an adaptation coefficient, and R _W , G _W and B _W are RGB signal at the reference white, Y _W represents luminance of the reference white.

  Subsequent to step S105, the color conversion apparatus calculates a predetermined coefficient k and the like according to equation (103) (step S106).

However, represented in formula _{(103), k, F L} , n, N bb, N cb, z is predetermined coefficient, _{Y b} is the background luminance, _{Y W} is the luminance of the reference white, a _{L A} peak luminance.

  Subsequent to step S106, the color conversion apparatus converts the weighted RGB signal after chromatic adaptation into an RGB signal expressed in the HPE color space according to equation (104) (step S107).

In Equation (104), R ′, G ′, and B ′ represent RGB signals expressed in the HPE color space, and R _C , G _C , and B _C represent weighted RGB signals after chromatic adaptation.

  Subsequent to Step S107, the color conversion apparatus performs Post-adaptation-non-linear compression on the RGB signal expressed in the HPE color space by Expression (105) (Step S108).

However, in the formula _{(105), R a ',} G a', B a 'RGB signals compressed, R', G ', B ' is RGB signal represented by HPE color space, _{F L} is the predetermined Represents a coefficient.

  Subsequent to step S108, the color conversion apparatus calculates predetermined coefficients a, b, and the like according to equation (106) (step S109).

However, represented in formula _{(106), a, b,} e t, h, h r are predetermined coefficients, the _{R a ', G a',} B a 'RGB signals compressed.

  In step S110, the color conversion apparatus calculates an achromatic color response A according to equation (107). Further, the color conversion apparatus calculates the lightness J (brightness with respect to white) according to the equation (108).

In equation (107), A represents an achromatic response, R _a ′, G _a ′, and B _a ′ represent compressed RGB signals, and N _bb represents a predetermined coefficient.

However, in the formula (108), J is the lightness, A is achromatic response, achromatic response in _{A W} is the reference _{white, a, b, e t,} N c, N cb is predetermined coefficient, _{R a} ', G _a ′ and B _a ′ represent compressed RGB signals.

  In step S110, the color conversion apparatus calculates brightness Q (visual degree related to a large amount of light) by Expression (109). Further, the color conversion apparatus calculates the saturation M by the equation (110).

However, in the formula (109), Q is the brightness, C is chroma, A is achromatic response, A _W achromatic response in reference white, J represents lightness.

However, M is a visual saturation, C is a saturation, and _FL is a predetermined coefficient.

In step S110, the color conversion apparatus calculates a predetermined coefficient i and the like so as to satisfy the relationship of h _i <h <h _{i + 1 according to} Table 1 and Expression (111). Further, the color conversion apparatus calculates the hue H according to the equation (112) (step S110).

However, in formula (111), h and h ₁ represent predetermined coefficients.

However, in the formula (112), H is the _{hue, e, e t, h,} h i denotes a predetermined coefficient.

  In each of Steps S111 to S117, the color conversion apparatus performs inverse conversion processing of Expressions (101) to (112). Similarly to the video signal processing apparatus 1, the color conversion apparatus converts RGB signals into XYZ signals (matrix conversion) using Expression (6) (step S118). Similarly to the video signal processing apparatus 1, the color conversion apparatus converts the XYZ signal into an RGB signal (matrix conversion) using Expression (7) (step S119). Further, the color conversion device performs gamma correction on the RGB signals using the equation (8), similarly to the video signal processing device 1 (step S120).

  As described above, the color conversion apparatus realizes the color conversion processing in the CIECAM02 model by the calculation of Step S104 to Step S117 (14 steps in total). As shown in FIG. 4, the color conversion processing in the CIECAM02 model is very complicated, and a color conversion device that realizes this requires high performance and a long calculation time. On the other hand, as shown in FIG. 3, the video signal processing apparatus 1 in FIG. 1 enables color signal conversion in steps S41 to S43 (3 steps in total). As described above, the amount of calculation of the video signal processing device 1 is ¼ or less of the amount of calculation of the color conversion device, so that the calculation time can be shortened and the configuration can be simplified.

  In addition, with reference to FIG. 5, the result of the color conversion processing by the CIECAM02 model and the result of the color conversion processing by the video signal processing apparatus according to the present invention will be exemplified and described. FIG. 5A shows a video (original video) before color conversion processing, and FIG. 5B shows a video after the original video has been subjected to color conversion processing using the CIECAM02 model. ) Is an image after the original image is color-converted by the image signal processing apparatus according to the present invention. As shown in FIG. 5B and FIG. 5C, even if the same video is compared with the case where the color conversion processing is performed by the video signal processing device 1 and when the color conversion processing is performed by the color conversion device, The visual difference between the two images cannot be discriminated with the naked eye.

1 is a block diagram of a video signal processing apparatus according to an embodiment of the present invention. It is a flowchart which shows operation | movement of the video signal processing apparatus of FIG. It is a flowchart which shows the detail of the CIECAM02 approximate conversion process of FIG. It is a flowchart which shows the color conversion process by a CIECAM02 model. (A) is an image (original image) before color conversion processing, (b) is an image after color conversion processing is performed on the original image using the CIECAM02 model, and (c) is the original image. It is the image | video after performing the color conversion process with the video signal processing apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Video signal processing apparatus 10 Video signal conversion means 11 Reverse gamma correction means 12 XYZ signal conversion means before color conversion 13 RGB signal conversion means before color conversion 20 CIECAM02 approximate conversion means 30 XYZ signal conversion means after color conversion 40 RGB signal after color conversion Conversion means 50 Gamma correction means 60 Input / output interface 70 Storage means

Claims (5)

In a video signal processing apparatus for converting a visual RGB signal before color conversion expressed in an RGB color space into a color signal in accordance with human visual sensitivity,
CIECAM02 approximate conversion means for converting the visual RGB signal before color conversion into a visual RGB signal after color conversion expressed in the RGB color space according to the expression (1) as a CIECAM02 approximate expression;
A video signal processing apparatus comprising:
In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion. 2. The CIECAM02 approximate conversion unit calculates a coefficient P related to brightness before the color conversion and a coefficient Q related to saturation before the color conversion using Expression (2). Video signal processing device.
In Equation (2), P _i is the brightness before color conversion, P _i-max is the maximum brightness before color conversion, C _{1 to} C ₅ are coefficients determined by the viewing environment, and h is the color before color conversion. , C represents the saturation before color conversion. A reverse gamma correction means for performing reverse gamma correction on an externally input RGB signal before color conversion and outputting an RGB signal before color conversion after reverse gamma correction;
XYZ signal conversion means before color conversion for converting the RGB signal before color conversion after the inverse gamma correction subjected to the inverse gamma correction by the inverse gamma correction means into an XYZ signal before color conversion expressed in an XYZ color space;
Pre-color conversion RGB signal conversion means for converting the pre-color conversion XYZ signal converted by the pre-color conversion XYZ signal conversion means into the pre-color conversion visual RGB signal and outputting it to the CIECAM02 approximate conversion means;
A post-color-conversion XYZ signal conversion unit that converts the post-color-conversion visual RGB signal converted by the CIECAM02 approximation conversion unit into a post-color conversion XYZ signal expressed in an XYZ color space;
A post-color-converted RGB signal converting means for converting the post-color-converted XYZ signal converted by the post-color-converted XYZ signal converting means into a post-color-converted RGB signal expressed in an RGB color space;
Gamma correction means for gamma-correcting the color-converted RGB signal converted by the color-converted RGB signal conversion means to output a color-converted RGB signal after gamma correction;
The video signal processing apparatus according to claim 1, further comprising: In a video signal processing apparatus for converting a visual RGB signal before color conversion expressed in an RGB color space into a color signal in accordance with human visual sensitivity,
A CIECAM02 approximate conversion step of converting the visual RGB signal before color conversion into a visual RGB signal after color conversion expressed in the RGB color space according to Equation (1) as a CIECAM02 approximate equation;
A video signal processing method comprising:
In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion. In order to convert the visual RGB signal before color conversion expressed in the RGB color space into a color signal in accordance with human visual sensitivity,
CIECAM02 approximate conversion means for converting the visual RGB signal before color conversion into a visual RGB signal after color conversion expressed in the RGB color space according to the expression (1) as a CIECAM02 approximate expression;
A video signal processing program characterized by functioning as
In Equation (1), R _i , G _i , B _i are the visual RGB signals before color conversion, R _d , G _d , B _d are the visual RGB signals after color conversion, and P is the brightness before color conversion. , Q represents a coefficient related to saturation before color conversion.