JP7145719B2 - Video signal converter and program - Google Patents

Description

The present invention performs gradation conversion between HLG (Hybrid Log Gamma) video and SDR (Standard Dynamic Range) video of HDR (High Dynamic Range) video. The present invention relates to a video signal conversion device and program.

Conventionally, the white level in SDR of high definition broadcasting is about 100% of the video signal. When this video signal is displayed on an SDR display with a peak luminance of 100 cd/m ² , it is displayed with a luminance of approximately 100 cd/m ² .

On the other hand, in HLG, a report has been formulated that defines the reference white level as 75% of the video signal (see, for example, Non-Patent Documents 1, 2, and 3).

Broadcasters are beginning to consider integrated production in which HLG video and SDR video with different dynamic ranges are produced at the same time. In the integrated production of HDR video and SDR video, a conversion method is known that generates SDR video by performing certain gain processing on a linear signal of scene light acquired by an HDR-compatible camera (for example, See Patent Document 1).

Also known is a conversion method in which only HDR video is produced and the HDR video is collectively converted to SDR video in the final stage of the production system.

In the former conversion method, conversion is performed in a camera system, and there is a problem that the finally obtained HDR video and SDR video differ in color reproducibility. This is due to the difference in EOTF (Electro Optical Transfer Function) when converting video signals into display light.

On the other hand, in the latter conversion method, when a telop is synthesized with an HDR video, it is necessary to convert the HDR video into the SDR video in consideration of the reference white level so that the white level of the telop does not change.

In a general video signal conversion device, gain processing is performed so that the HLG display luminance of 200 cd/m ² corresponds to the SDR display luminance of 88 cd/m ² to 100 cd/m ² . It realizes conversion from video to SDR video. This corresponds to gain processing for making the reference white level of 75% of the HLG video signal correspond to the white level of approximately 95% of the SDR video signal.

On the other hand, there is also known a technique for maintaining high-saturation gradation when performing color correction processing and dynamic range compression processing on a video signal (see, for example, Patent Document 2). In this method, the video signal is multiplied by a predetermined matrix to perform the first color correction process, and the video signal after color correction is subjected to dynamic range compression such as knee process and clip process. Then, the second color correction process is performed by multiplying the video signal after the dynamic range compression process by a predetermined matrix. Patent Document 2 is a published patent publication published after the filing date of the earlier application of the present application and before the filing date of the present application.

JP 2016-197854 A JP 2018-142947 A

Report ITU-R BT.2408-0, “Operational practices in HDR television production” Recommendation ITU-R BT.2100-0, “Image parameter values for high dynamic range television for use in production and international program exchange” Recommendation ITU-R BT.1886, “Reference electro-optical transfer function for flat panel displays used in HDTV studio production”

However, the conversion method that considers the reference white level by the general video signal conversion device described above does not consider the signal level of the skin of a person, which is one of the important impression factors in constructing a video. Therefore, there is a problem that the signal level of the skin of the person is lower than the skin level of the SDR image, and the image looks dark.

In addition, about 80% or more of the HLG video signal is clipped at 109%, which is the upper limit of the SDR video signal, and there is also a problem that highlights are overexposed (see the characteristics of the prior art shown in FIG. 4 described later). reference).

For this reason, in addition to considering the reference white level as in the past, it has been desired to consider the skin level of the person and perform conversion to suppress the crushed white of highlights.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above problems. To provide a video signal conversion device and a program capable of suppressing overexposure of highlights without changing the white level of the image.

In order to solve the above-mentioned problem, the video signal conversion device of claim 1 is a video signal conversion device that converts HLG (Hybrid Log Gamma) video to SDR (Standard Dynamic Range) video, an HLG video/optical conversion unit that converts the video signal of the HLG image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the HLG image, and the HLG video/optical conversion unit a gain processing unit for performing gain processing on the converted first display optical signal to obtain a skin level characteristic of the SDR image corresponding to the skin level of the HLG image to obtain a second display optical signal; a tristimulus value and chromaticity conversion unit that converts the second display light signal obtained by the gain processing unit into tristimulus values and chromaticity coordinates; A luminance value of the stimulus values is defined as a first luminance, and with respect to the first luminance, characteristics of the white level of the SDR image corresponding to the reference white level of the HLG image are obtained, and a value of the video signal of the SDR image is obtained. a compression processing unit for performing compression processing to obtain a characteristic that increases to the upper limit value of the video signal of the SDR image corresponding to the upper limit value of the video signal of the HLG image, and obtaining a second luminance; and the tristimulus value and an SDR luminance/light conversion unit that converts the second luminance obtained by the compression processing unit into a third display optical signal of the SDR video using the chromaticity coordinates converted by the chromaticity conversion unit; an SDR light/video conversion unit for converting the third display light signal converted by the SDR luminance/light conversion unit into a video signal of the SDR image by an inverse function of the EOTF of the SDR image. characterized by

The video signal conversion device of claim 2 is the video signal conversion device of claim 1, wherein the gain processing unit multiplies the first display light signal by a predetermined gain value to obtain the gain processing to determine the second display light signal, wherein the predetermined gain value is based on a skin level value of the HLG image and a skin level value of the SDR image corresponding to the skin level of the HLG image; , is preset by the user.

Further, the video signal conversion device of claim 3 is the video signal conversion device of claim 1 or 2, wherein the compression processing unit corresponds to the reference white level of the HLG video for the first luminance. A reference white level compression processing unit that performs compression processing to obtain the characteristics of the white level of the SDR image and obtains a third luminance; and a highlight color reproduction compression processing unit that performs compression processing to obtain a characteristic that a video signal value of an image increases to the upper limit value, and obtains the second luminance.

A video signal conversion device according to claim 4 is a video signal conversion device for converting an HLG (Hybrid Log Gamma) image into an SDR (Standard Dynamic Range) image, wherein the video signal of the HLG image is is converted into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the HLG video, and the first display converted by the HLG video/optical converter. a tristimulus value and chromaticity conversion unit for converting a display light signal into tristimulus values and chromaticity coordinates; and performing a first calculation for obtaining a skin level characteristic of the SDR image corresponding to the skin level of the HLG image with respect to the first luminance using a predetermined fitting function; a processing unit that performs a second calculation to obtain a characteristic that the value of the signal increases to the upper limit value of the video signal of the SDR image corresponding to the upper limit value of the video signal of the HLG image, and obtains a second luminance; SDR luminance/light conversion for converting the second luminance obtained by the processing unit into a second display light signal of the SDR image using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. and an SDR light/video conversion unit for converting the second display light signal converted by the SDR luminance/light conversion unit into a video signal of the SDR image by an inverse function of the EOTF of the SDR image. It is characterized by having

A video signal conversion device according to claim 5 is a video signal conversion device for converting HLG (Hybrid Log Gamma) video into SDR (Standard Dynamic Range) video, wherein the video signal of the HLG video is is converted into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the HLG video, and the first display converted by the HLG video/optical converter. a crosstalk matrix processing unit for performing crosstalk matrix processing for reducing variations in luminance for each RGB color component in the display light signal and obtaining a second display light signal; 2. a tristimulus value and chromaticity conversion unit for converting the display light signal into tristimulus values and chromaticity coordinates; 1 luminance, and performs a first calculation for obtaining the skin level characteristics of the SDR image corresponding to the skin level of the HLG image using a predetermined fitting function for the first luminance; a processing unit that performs a second calculation for obtaining a characteristic that the value of the video signal increases to the upper limit value of the video signal of the SDR image corresponding to the upper limit value of the video signal of the HLG image, and obtains a second luminance; , an SDR luminance/light converting the second luminance obtained by the processing unit into a third display light signal of the SDR image using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit; and an inverse process to the crosstalk matrix process for undoing luminance variations for each RGB color component in the third display light signal converted by the SDR luminance/light converter. an inverse crosstalk matrix processing unit for performing crosstalk matrix processing to obtain a fourth display optical signal; and an SDR light/video converter for converting the SDR image into a video signal.

Further, the video signal conversion device of claim 6 is the video signal conversion device of claim 5, wherein instead of the tristimulus value and chromaticity conversion unit, an HLG light/tristimulus value conversion unit, a chroma processing unit and an HLG chromaticity conversion unit, wherein the HLG light/tristimulus value conversion unit converts the second display light signal obtained by the crosstalk matrix processing unit into tristimulus values, and the chroma processing unit converts the The tristimulus value space of the tristimulus values converted by the HLG light/tristimulus value conversion unit is converted into the CIELAB space, and the hue angle in the CIELAB space is adjusted so that the color above the reference white level approaches an achromatic color or white. is held, chroma correction processing is performed to reduce chroma in the CIELAB space, tristimulus values after chroma correction processing are obtained, and the HLG chromaticity conversion unit converts the tristimulus values obtained by the chroma processing unit to , converting into chromaticity coordinates, the processing unit performs the first calculation and the second calculation with the luminance value of the tristimulus values obtained by the chroma processing unit as the first luminance, The second luminance is obtained, and the SDR luminance/light conversion unit converts the second luminance obtained by the processing unit to the SDR image using the chromaticity coordinates converted by the HLG chromaticity conversion unit. characterized in that it is converted into the third display light signal.

Further, the video signal conversion device of claim 7 is the video signal conversion device of claim 6, wherein the chroma processing unit is the tristimulus value converted by the HLG light/tristimulus value conversion unit. a color space conversion unit that converts the stimulus value space into the CIELAB space and obtains brightness and color coordinates; and based on the color coordinates obtained by the color space conversion unit, converts the chroma and the hue angle before chroma correction processing a chroma correcting unit that reduces the chroma before chroma correction processing and obtains the color coordinates after chroma correction processing while maintaining the hue angle so that colors above the reference white level become achromatic or approach white; and converting the CIELAB space based on the lightness obtained by the color space conversion unit and the color coordinates after chroma correction obtained by the chroma correction unit into the tristimulus value space, and converting the tristimulus after chroma correction. and a color space inverse transform unit for obtaining a value.

Further, the video signal conversion apparatus according to claim 8 is the video signal conversion apparatus according to any one of claims 4 to 7, wherein the first calculation by the predetermined fitting function in the processing unit is performed by the A gain processing operation for multiplying the first luminance by a predetermined gain value, wherein the predetermined gain value is the skin level value of the HLG image and the skin level of the SDR image corresponding to the skin level of the HLG image. It is characterized by being preset by the user based on the value.

Further, the video signal conversion device according to claim 9 is the video signal conversion device according to any one of claims 4 to 8, wherein the second calculation by the predetermined fitting function in the processing unit is performed by the It is characterized in that it is an operation of logarithmization processing for logarithmizing the first luminance.

A video signal conversion device according to claim 10 is a video signal conversion device for converting SDR (Standard Dynamic Range) video into HLG (Hybrid Log Gamma) video, wherein the video signal of the SDR video is is converted into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the SDR image, and the first display converted by the SDR video/optical conversion unit. a tristimulus value and chromaticity conversion unit for converting a display light signal into tristimulus values and chromaticity coordinates; obtaining a characteristic that the value of the video signal of the HLG image increases to the upper limit value of the video signal of the HLG image corresponding to the upper limit value of the video signal of the SDR image with respect to the first luminance, and Extended processing is performed to obtain characteristics in which the reference white level of the HLG image and the white level of the SDR image correspond to each other, and the extension processing unit that obtains the second luminance and the tristimulus value and chromaticity conversion unit convert the Using the chromaticity coordinates, the HLG luminance/light conversion unit converts the second luminance obtained by the expansion processing unit into a second display light signal of the HLG image, and the HLG luminance/light conversion unit converts the second luminance. a reverse gain processing unit for obtaining a third display optical signal by performing reverse gain processing for obtaining characteristics corresponding to the skin level of the HLG image and the skin level of the SDR image on the second display optical signal thus obtained. and an HLG light/video conversion unit for converting the third display optical signal obtained by the inverse gain processing unit into a video signal of the HLG image by an inverse function of the EOTF of the HLG image. Characterized by

A video signal conversion device according to claim 11 is a video signal conversion device for converting an SDR (Standard Dynamic Range) video into an HLG (Hybrid Log Gamma) video, wherein the video signal of the SDR video is is converted into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the SDR image, and the first display converted by the SDR video/optical conversion unit. a tristimulus value and chromaticity conversion unit for converting a display light signal into tristimulus values and chromaticity coordinates; With respect to the first luminance, the value of the video signal of the HLG image is increased by a predetermined inverse fitting function to the upper limit of the video signal of the HLG image corresponding to the upper limit of the video signal of the SDR image. A first calculation is performed to obtain a characteristic that the reference white level of the HLG image and the white level of the SDR image correspond to each other. A processing unit that performs a second calculation for obtaining a characteristic corresponding to the skin level of the SDR image and obtains a second luminance, and a processing unit that uses the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. an HLG luminance/light conversion unit for converting the second luminance obtained by the processing unit into a second display light signal of the HLG image; and the second display light converted by the HLG luminance/light conversion unit. an HLG light/video converter for converting a signal into a video signal of the HLG image by an inverse function of the EOTF of the HLG image.

A video signal conversion device according to claim 12 is a video signal conversion device for converting SDR (Standard Dynamic Range) video into HLG (Hybrid Log Gamma) video, wherein the video signal of the SDR video is is converted into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the SDR image, and the first display converted by the SDR video/optical conversion unit. a crosstalk matrix processing unit for performing crosstalk matrix processing for reducing variations in luminance for each RGB color component in the display light signal and obtaining a second display light signal; 2. a tristimulus value and chromaticity conversion unit for converting the display light signal into tristimulus values and chromaticity coordinates; With 1 luminance, the value of the video signal of the HLG image is adjusted to the upper limit of the video signal of the HLG image corresponding to the upper limit of the video signal of the SDR image by a predetermined inverse fitting function with respect to the first luminance. performing a first computation for obtaining an increasing characteristic, performing a computation for obtaining a characteristic in which the reference white level of the HLG image and the white level of the SDR image correspond, and further performing a skin level of the HLG image. and the skin level of the SDR image to perform a second calculation for obtaining the corresponding characteristics, a processing unit for obtaining a second luminance, and the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit an HLG luminance/light conversion unit that converts the second luminance obtained by the processing unit into a third display optical signal of the HLG image, and the third display converted by the HLG luminance/light conversion unit. Inverse crosstalk matrix processing, which is the inverse of the crosstalk matrix processing, is performed to restore luminance variations for each RGB color component in the optical signal, thereby obtaining a fourth display optical signal. and an HLG light/video conversion unit for converting the fourth display optical signal obtained by the inverse crosstalk matrix processing unit into a video signal of the HLG image by an inverse function of the EOTF of the HLG image. characterized by

In addition, the video signal conversion device of claim 13 is the video signal conversion device of claim 12, wherein instead of the HLG luminance/light conversion unit, an HLG tristimulus value conversion unit, a chroma processing unit, and an HLG tristimulus value conversion unit are used. and a light conversion unit, wherein the HLG tristimulus value conversion unit converts the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit and the second luminance obtained by the processing unit into the second luminance and the chroma processing unit converts the space of the tristimulus values converted by the HLG tristimulus value conversion unit into the CIELAB space, and colors above the reference white level are achromatic colors or white while maintaining the hue angle in the CIELAB space so as to approach the HLG tristimulus value/light conversion unit. converts the tristimulus values obtained by the chroma processing unit after chroma correction processing into fifth display light signals, and the inverse crosstalk matrix processing unit converts the tristimulus values by the HLG tristimulus value/light conversion unit. Further, the inverse crosstalk matrix processing is performed to restore luminance variations for each RGB color component in the fifth display light signal, and the fourth display light signal is obtained.

Further, a program according to claim 14 causes a computer to function as the video signal conversion device according to any one of claims 1 to 9.

A program according to claim 15 causes a computer to function as the video signal conversion device according to any one of claims 10 to 13.

As described above, according to the present invention, when converting between HLG video and SDR video, the signal level of the human skin does not decrease and the white level of the telop does not change. Furthermore, crushed highlights can be suppressed.

1 is a block diagram showing a configuration example of a video signal conversion device of Example 1; FIG. 5 is a flow chart showing an example of processing of the video signal conversion device according to the first embodiment; 4 is a block diagram showing a configuration example of a compression processing unit; FIG. FIG. 3 is a diagram for explaining the correspondence between the skin level of an HLG video signal and the skin level of an SDR video signal, and the characteristics obtained by gain processing considering the skin level; FIG. 10 is a diagram for explaining characteristics obtained by compression processing considering a reference white level; FIG. 10 is a diagram for explaining characteristics obtained by compression processing that takes color reproduction of highlights into consideration; FIG. 4 is a diagram showing the characteristic of luminance, which is a linear signal of display light; FIG. 11 is a block diagram showing a configuration example of a video signal conversion device of Example 2; 10 is a flow chart showing a processing example of the video signal conversion device of Example 2. FIG. FIG. 4 is a diagram for explaining characteristics of display brightness obtained by processing applying a fitting function; FIG. 10 is a diagram illustrating the correspondence relationship between the HLG display luminance and the SDR display luminance when the knee point is changed in the pattern <1>; FIG. 10 is a diagram illustrating the correspondence relationship between the HLG display luminance and the SDR display luminance when the knee point is changed in pattern <2>; FIG. 4 is a diagram for explaining characteristics of a video signal obtained by processing applying a fitting function; 2 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device of Embodiment 1; FIG. FIG. 11 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device of the second embodiment; FIG. 11 is a block diagram showing a configuration example of a video signal conversion device of Example 3; 11 is a flow chart showing an example of processing of the video signal conversion device of Example 3. FIG. FIG. 11 is a block diagram showing a configuration example of a video signal conversion device of Example 4; 14 is a flow chart showing a processing example of the video signal conversion device of Example 4. FIG. 3 is a block diagram showing a configuration example of a chroma processing unit; FIG. 8 is a flowchart illustrating an example of processing by a chroma processing unit; FIG. 11 is a bird's-eye view for explaining chroma correction processing; FIG. 10 is a diagram illustrating chroma correction processing when the parameter σ is small; FIG. 10 is a diagram illustrating chroma correction processing when the parameter σ is large; FIG. 10 is a diagram showing display luminance characteristics when a fitting function set by _a predetermined gain value k1 or the like is applied; FIG. 26 is a diagram showing video signal characteristics corresponding to the display luminance characteristics shown in FIG. 25; FIG. 10 is a diagram showing characteristics of display luminance when predetermined parameters ε, σ, etc. are set; FIG. 28 is a diagram showing video signal characteristics corresponding to the display luminance characteristics shown in FIG. 27; FIG. 11 is a diagram for explaining a processing example of the video signal conversion device of Example 4 in L ^* a ^* b ^* space; FIG. 30 is a schematic diagram showing the L ^* a ^* b ^* space of FIG. 29 on the L ^* a ^* plane; FIG. 30 is a schematic diagram showing the L ^* a ^* b ^* space of FIG. 29 on the a ^* b ^* plane; FIG. 11 is a diagram for explaining a processing example of the video signal conversion device of Example 4 in L ^* a ^* b ^* space; FIG. 11 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device of Example 3; FIG. 11 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device of Embodiment 4;

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated in detail using drawing. A first embodiment (Example 1) of the present invention described below performs gain processing, reference white level, and color reproduction of highlights in consideration of a person's skin level when converting an HLG video into an SDR video. It is characterized by performing a compression process that considers the As a result, the signal level of the person's skin does not become low, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed.

A second embodiment (embodiment 2) of the present invention provides a fitting function that is calculated in consideration of a person's skin level, reference white level, and color reproduction of highlights when converting an HLG image into an SDR image. is characterized by using As a result, in addition to the same effect as in the first embodiment, the problem of signal discontinuity in the first embodiment can be solved, continuous characteristics can be obtained, and banding in the highlight region can be improved. can.

In addition, the third embodiment (Example 3) of the present invention uses the same fitting function as in Example 2 when converting an HLG image into an SDR image, and adjusts luminance variations for each RGB color component. It is characterized by performing crosstalk matrix processing for mitigation. Thus, in addition to the effect of the second embodiment, it is possible to suppress hue change due to hard clipping of a specific color component in highlights, and to sufficiently realize color reproduction of highlights.

The fourth embodiment (Example 4) of the present invention uses the same fitting function as in Example 2 and performs the same crosstalk matrix processing as in Example 3 when converting HLG video into SDR video. and further performs chroma correction processing for bringing colors above the reference white level closer to an achromatic color or white. Thus, in addition to the effects of the third embodiment, it is possible to realize color reproduction of achromatic or near-white highlights. That is, in the fourth embodiment, color reproduction of highlights can be realized more effectively than in the third embodiment.

[Embodiment 1: Video signal converter]
First, the configuration and processing of the video signal conversion device of the first embodiment will be described. As described above, when converting an HLG image into an SDR image, the first embodiment performs gain processing in consideration of the human skin level and compression processing in consideration of the reference white level and color reproduction of highlights. As a result, the signal level of the person's skin does not decrease, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed.

FIG. 1 is a block diagram showing a configuration example of the video signal conversion device of the first embodiment, and FIG. 2 is a flow chart showing a processing example of the video signal conversion device of the first embodiment. This video signal conversion device 1 includes an HLG video/light conversion section 10, a gain processing section 11, a tristimulus value and chromaticity conversion section 12, a compression processing section 13, an SDR luminance/light conversion section 14, and an SDR light/video conversion section. 15.

The HLG video/optical converter 10 receives an HLG video signal E _h ', which is a video signal of an HLG image (step S201). Then, the HLG video/optical converter 10 converts the HLG video signal E _h ' into the HLG display optical signal Fd, which is a linear signal of display light, by the EOTF of the HLG video (step S202). The HLG video/optical converter 10 outputs the HLG display optical signal Fd to the gain processor 11 .

The gain processing unit 11 receives the HLG display light signal Fd from the HLG video/light conversion unit 10 and also receives _a preset gain value k1. Then, based on the gain value k1, the gain processing unit 11 obtains the display optical signal _Fdg by performing gain processing on the display optical signal Fd in consideration of the skin level (step S203). Then, the gain processing unit 11 outputs the display light signal Fdg to the tristimulus value and chromaticity conversion unit 12 .

The tristimulus value and chromaticity conversion unit 12 receives the display light signal Fdg from the gain processing unit 11 and converts the display light signal Fdg into tristimulus values XYZ and chromaticity coordinates x, y as color information (step S204). The tristimulus value and chromaticity conversion unit 12 outputs the luminance Y of the tristimulus values XYZ to the compression processing unit 13 and outputs the chromaticity coordinates x, y to the SDR luminance/light conversion unit 14 .

The compression processing unit 13 receives the luminance Y from the tristimulus values and the chromaticity conversion unit 12, and performs compression processing on the luminance Y in consideration of the reference white level to obtain the luminance Y _comp,1st (step S205). . Then, the compression processing unit 13 obtains the luminance Y _comp,2nd by performing compression processing on the luminance Y _comp,1st in consideration of the color reproduction of the highlight (step S206). The compression processor 13 outputs the luminance Y _comp,2nd to the SDR luminance/light converter 14 .

The SDR luminance/light conversion unit 14 receives the luminance Y _comp,2nd from the compression processing unit 13 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 12 . Then, the SDR luminance/light converter 14 obtains tristimulus values X _comp and Z _comp from the luminance Y _comp,2nd using the chromaticity coordinates x and y (step S207).

The SDR luminance/light converter 14 obtains the SDR display light signal Fds from the luminance Y _comp,2nd and the tristimulus values X _comp , Z _comp (step S208). The SDR luminance/light converter 14 then outputs the SDR display light signal Fds to the SDR light/video converter 15 .

The SDR light/video converter 15 receives the SDR display light signal Fds from the SDR luminance/light converter 14 . Then, the SDR light/video conversion unit 15 converts the display light signal Fds into the SDR video signal E _s ', which is the video signal of the SDR image, by the inverse function of the EOTF of the SDR image (step S209). The SDR light/video converter 15 outputs the SDR video signal E _s ' (step S210).

In Example 1, the signal level of the human skin does not decrease, the white level of the telop does not change, and the overexposure of highlights is suppressed in the SDR video signal E _s with respect to the HLG video signal E _h '. ' is processed to generate . In the first embodiment, the gain processing unit 11 performs gain processing on the display light signal Fd, taking into account the skin level, and the compression processing unit 13 performs compression processing on the luminance Y, taking into consideration the reference white level. It is characterized by performing compression processing in consideration of color reproduction.

(HLG video/optical converter 10)
Next, the HLG video/optical converter 10 shown in FIG. 1 will be described in detail. As described above, the HLG video/optical converter 10 converts the HLG video signal E _h ' into the display optical signal Fd, which is a linear signal of display light, by the EOTF of the HLG video. That is, the HLG video/optical converter 10 converts the RGB signal, which is the HLG video signal E _h ', into the display optical signal Fd, which is a linear signal of display light, by the EOTF of the HLG video.

リニア信号Ｅに変換するのは、後段のディスプレイにおいて光信号として出力するためである。ここで、ａ＝０．１７８８３２７７，ｂ＝１－４ａ＝０．２８４６６８９２，ｃ＝０．５－ａ・ｌｎ（４ａ）＝０．５５９９１０７３である。なお、ｌｎ（ｘ）はｘの自然対数を示す。 The HLG video/optical conversion unit 10 receives an HLG video signal E _h ', and converts the HLG video signal E _h ' into a scene using an inverse function of the optical-electrical transfer function (OETF) of the HLG image. Convert to an optical linear signal E={Rs, Gs, Bs}. A linear signal E of scene light is calculated by the following equation.

The reason for converting into the linear signal E is to output it as an optical signal in the subsequent display. Here, a=0.17883277, b=1-4a=0.28466892, and c=0.5-a.ln(4a)=0.55991073. Note that ln(x) indicates the natural logarithm of x.

The HLG video/optical converter 10 then converts the linear signal E into a display optical signal Fd={Rd, Gd, Bd} according to the HLG video Opto Optical Transfer Function (OOTF). The HLG video/light converter 10 then outputs the display optical signal Fd to the gain processor 11 .

ここで、ｃ₁＝０．２６２７，ｃ₂＝０．６７８０，ｃ₃＝０．０５９３，α＝１０００，β＝０，γ＝１．２とする。このα，βは、ディスプレイのピーク輝度Ｌ_W及び黒の輝度Ｌ_Bとして、α＝Ｌ_W－Ｌ_B、β＝Ｌ_Bでそれぞれ求められる。γは、ディスプレイのピーク輝度Ｌ_Wに応じたシステムガンマである。 The display light signal Fd is calculated by the following formula.

Here, c ₁ =0.2627, c ₂ =0.6780, c ₃ =0.0593, α=1000, β=0, γ=1.2. These α and β are obtained by α=L _W −L _B and β=L _B as peak luminance L _W and black luminance L _B of the display, respectively. γ is the system gamma according to the peak luminance L _W of the display.

Incidentally, the system gamma γ is calculated by the following formula.

(Gain processing unit 11)
Next, the gain processing section 11 shown in FIG. 1 will be described in detail. As described above, the gain processing unit 11 obtains the display light signal Fdg by performing gain processing on the display light signal Fd in consideration of the skin level based _on the preset gain value k1.

When performing gain processing considering the skin level, the correspondence relationship between the skin level of the HLG image and the skin level of the SDR image is important. FIG. 4 is a diagram for explaining the correspondence between the skin level of the HLG video signal and the skin level of the SDR video signal, and the characteristics obtained by the gain processing considering the skin level.

In this figure, the result of analyzing the correspondence of the skin level of the same person in the HLG video and SDR video of the same content individually produced is represented as a plot (see circles). This HLG video program is content produced based on the reference white level of 75% of the HLG video signal.

The horizontal axis indicates the level of the HLG video signal, and the vertical axis indicates the level of the SDR video signal. The solid line indicates the characteristics of the prior art, and the dashed line indicates the characteristics of an example in which the skin level is taken into consideration, that is, the characteristics when the gain processing unit 11 performs gain processing in consideration of the skin level.

The characteristics of the prior art indicated by the solid line show the characteristics when gain processing is performed to make the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of about 88 cd/m ² (see point a in FIG. 7, which will be described later). ). As described above, this corresponds to the characteristics when performing gain processing for matching the reference white level of 75% of the HLG video signal to the white level of about 95% of the SDR video signal (see point e).

The characteristics of an example in consideration of the skin level indicated by the dashed line are the HLG video signal and the SDR when the display light signal Fdg obtained by the gain processing unit 11 is converted into the SDR video signal by the inverse function of the EOTF of the SDR video. It shows the correspondence between video signals.

Analysis of skin levels by the inventors shows that skin levels are related to about 45%-55% of HLG video signals corresponding to about 60%-85% of SDR video signals. That is, the skin level Vh _skin of the HLG video signal is about 50% of that of the HLG video signal (see point a), while the skin level Vs _skin of the SDR video signal is about 67% of that of the SDR video signal (see point a). b).

In the characteristics of the prior art indicated by the solid line, the skin level of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal of approximately 50% is approximately 55% (see point c). Therefore, it can be seen that the skin level of the SDR image in the prior art is lower than the skin level of the SDR image in the example in which the skin level is considered.

前述のとおり、Ｌ_Wは、ディスプレイのピーク輝度であり、ＥＯＴＦは、電気－光伝達関数である。 That is, in the first embodiment, the characteristics of the example in consideration of the skin level indicated by the solid line, that is, the characteristics of the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal (see point f) are obtained. It is necessary to perform gain processing so that Therefore, as Gain, which is the gain value k1 in gain processing, a value obtained by either _one of the following two equations is used.

As before, L _W is the peak luminance of the display and EOTF is the electro-optical transfer function.

The Gain in the above equation (4) is used when the HLG video/light converter 10 calculates the display light signal Fd based on the luminance value [cd/m ² ]. Also, the gain in the above equation (5) is used when the HLG video/light converter 10 calculates the display light signal Fd based on the normalized signal.

When the Gain of the formula (4) is used, the brightness value [cd/m ² ] is used as a reference, so it matches the values obtained by the formulas (2) and (3).

Further, when the gain of the above equation (5) is used, the normalized signal is used as a reference, so in the above equation (2) for calculating the display optical signal Fd by the HLG video/light converter 10, α=1 and do.

Here, as an example of gain processing considering the skin level, the skin level Vh _skin 50% of the HLG video signal is changed to the skin level Vs Correspond to _skin 67% (see point f). In this case, the Gains obtained from the formulas (4) and (5) are 7.5439 and 0.7544, respectively, assuming that the display peak luminance of the HLG video is 1000 cd/m ² .

That is, the gain processing unit 11 receives the display light signal Fd from the HLG video/light conversion unit 10, and multiplies the display light signal Fd by Gain, which is _a preset gain value k1, to obtain the display light Obtain the signal Fdg. This gain value k1 is _a value that can obtain the characteristics of the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal. Then, the gain processing unit 11 outputs the display light signal Fdg to the tristimulus value and chromaticity conversion unit 12 .

The display light signal Fdg is calculated by the following formula.

Note that Gain, which is the gain value k1, may be set in advance by the user through the calculation of equation ( ₄ ) or (5), or may be set in advance to an arbitrary value. good. In short, the gain value k1 may be freely changed by the user as _a setting item that allows image adjustment.

As a result, in the gain processing unit 11, the relationship between the HLG video signal and the SDR video signal is made to have the characteristic of the broken line shown in FIG. be able to. Therefore, the skin level can be improved as compared with the prior art, and the signal level of the person's skin in the SDR video will not be lower than in the HLG video.

(Tristimulus value and chromaticity converter 12)
Next, the tristimulus value and chromaticity conversion unit 12 shown in FIG. 1 will be described in detail. As described above, the tristimulus value and chromaticity conversion unit 12 converts the display light signal Fdg into tristimulus values XYZ and chromaticity coordinates x, y.

The tristimulus value and chromaticity conversion unit 12 receives the display light signal Fdg={Rdg, Gdg, Bdg} from the gain processing unit 11, and first converts the display light signal Fdg={Rdg, Gdg, Bdg} into tristimulus values. Convert to XYZ. The tristimulus values XYZ are calculated by the following formulas.

The tristimulus value and chromaticity conversion unit 12 then converts the tristimulus values XYZ into chromaticity coordinates x, y. The chromaticity coordinates x, y are calculated by the following formulas.

The tristimulus value and chromaticity conversion unit 12 outputs the luminance Y of the tristimulus values XYZ to the compression processing unit 13 and outputs the chromaticity coordinates x, y to the SDR luminance/light conversion unit 14 . The luminance Y is used for compression processing by the compression processing unit 13, and the chromaticity coordinates x, y are used for processing for restoring the luminance to a linear signal of display light by the SDR luminance/light conversion unit 14. FIG.

(Compression processing unit 13)
Next, the compression processing unit 13 shown in FIG. 1 will be described in detail. As described above, the compression processing unit 13 obtains the luminance Y _comp,1st by performing compression processing on the luminance Y with consideration given to the reference white level, and compresses the luminance Y _comp,1st in consideration of the color reproduction of the highlight. Luminance Y _comp,2nd is obtained by performing the processing.

FIG. 3 is a block diagram showing a configuration example of the compression processing unit 13 shown in FIG. The compression processing section 13 includes a reference white level compression processing section 16 and a highlight color reproduction compression processing section 17 .

In the characteristics of the example considering the skin level shown in FIG. 4, the white level corresponding to the reference white level of 75% of the HLG video signal is shifted in the SDR video signal compared to the prior art. Also, the SDR video signal is clipped at its upper limit of 109% in an area of about 70% or more of the HLG video signal (see area d in FIG. 4). Therefore, the reference white level compression processing unit 16 and the highlight color reproduction compression processing unit 17 of the compression processing unit 13 perform compression processing in consideration of the reference white level and the color reproduction of the highlights, and correct the characteristics so that this clip does not exist. do.

(Compression Processing Considering Reference White Level/Reference White Level Compression Processing Unit 16)
Next, the compression processing in consideration of the reference white level by the reference white level compression processing section 16 will be described in detail. This compression processing is processing to prevent the white level of the telop from changing.

In integrated production where HLG video and SDR video are produced at the same time, the reference white level is considered so that the white level of the telop synthesized with the HLG video does not change in the SDR video when the HLG video is converted to SDR video. There is a need to.

In Example 1, as in the prior art, the reference white level is adjusted by performing gain processing for matching the HLG display luminance of 200 cd/m ² to the SDR display luminance of about 88 cd/m ² to 100 cd/m ² . It realizes the conversion from the considered HLG video to the SDR video. This gain processing corresponds to gain processing for making the reference white level of 75% of the HLG video signal correspond to the white level of approximately 95% of the SDR video signal.

In order to achieve this, the reference white level compression processing unit 16 inputs the luminance Y from the tristimulus value and chromaticity conversion unit 12, and performs compression processing on the luminance Y in consideration of the reference white level according to the following equation. By doing so, the luminance Y _comp,1st is obtained. The reference white level compression processing unit 16 outputs the luminance Y _comp,1st to the highlight color reproduction compression processing unit 17 .

Here, Y represents the luminance that has been gain-processed by the gain processing unit 11 and converted by the tristimulus value and chromaticity conversion unit 12 . Kp is the knee point during compression processing, and W is the width from the change start point to the change end point for smoothing the signal change near the knee point. Y _95%SDR indicates the brightness of the display light corresponding to the white level of approximately 95% of the SDR video signal. Y _75%HLG indicates the brightness of the display light corresponding to the reference white level of 75% of the HLG video signal. Knee point Kp corresponds to point f in FIG. 7, which will be described later, which corresponds to point e in FIG. 5, to be described later.

Specifically, the reference white level compression processing unit 16 sets the same value as the luminance Y to the luminance Y _comp,1st in a region where the luminance Y is lower than a predetermined value based on the knee point (equation (7) ). In addition, the reference white level compression processing unit 16 smoothes the signal change of the luminance Y based on the luminance Y _95%SDR , Y _75%HLG and the width W in the area of the width W based on the knee point of the luminance Y. Then, the brightness Y _comp,1st is calculated (the middle expression of the above expression (7)).

The reference white level compression processing unit 16 calculates a luminance Y _comp,1st having a slope based on the luminances Y _95%SDR and Y _75%HLG in an area where the luminance Y is higher than a predetermined value based on the knee point. (the lower expression of the above expression (7)).

By this compression processing, the luminance Y _comp,1st in consideration of the reference white level can be obtained from the luminance Y gain-processed by the gain processing section 11 .

FIG. 5 is a diagram for explaining the characteristics obtained by the compression processing considering the reference white level. The horizontal axis indicates the level of the HLG video signal, and the vertical axis indicates the level of the SDR video signal. FIG. 5 shows characteristics of an example considering a reference white level in addition to the characteristics of the prior art (solid line) and the characteristics of an example considering a skin level (broken line) shown in FIG. The dashed-dotted line shows the characteristics of an example considering the reference white level.

Here, the characteristic in the example considering the reference white level is the characteristic obtained by performing the processing considering the skin level and then performing the processing considering the reference white level. The same applies to FIGS. 6, 7, 10 and 13, which will be described later.

The characteristics of the example in consideration of the reference white level indicated by the dashed-dotted line are the calculation of the compression processing of the above equation (9) representing the gain processing that makes the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of about 88 cd/m ² . 2 shows the correspondence between HLG and SDR video signals obtained by .

From FIG. 5, the characteristics of the example considering the reference white level indicated by the dashed-dotted line show that the skin level It can be seen that the characteristics match those obtained by the gain processing in consideration of . The characteristics of this area are obtained from the upper expression of the above equation (9) and correspond to area c in FIG. 7, which will be described later. Knee point Kp corresponds to point f in FIG. 7, which will be described later, which corresponds to point e in FIG.

In the area of W/2 around the knee point Kp (point f in FIG. 7 (corresponding to point e in FIG. 5), which will be described later), rounding is performed according to the middle expression of the above expression (9). done. As a result, steep characteristics can be relaxed and smoothed.

In addition, the characteristics of the example considering the reference white level are the area from about 80% to 109%, which is the upper limit of the SDR video signal corresponding to about 60% to about 85% of the HLG video signal (see area b). ), the white level of the SDR video signal is about 95% (see point d), which is lower than the characteristic obtained by the gain processing considering the skin level and corresponds to the reference white level of 75% of the HLG video signal. It can be seen that it contains

Further, the characteristic of the example considering the reference white level shows that the HLG video signal is clipped at 109%, which is the upper limit of the SDR video signal, in the region of about 85% or more (see region c). Therefore, in compression processing that takes into consideration the color reproduction of highlights, which will be described later, the characteristics are corrected so that this clip does not exist. The characteristics of the regions b and c are obtained by the lower expression of the above equation (9) and correspond to the region g in FIG. 7, which will be described later.

As a result, in the compression processing considering the reference white level of the reference white level compression processing unit 16, the relationship between the HLG video signal and the SDR video signal is different from the characteristics of the example considering the reference white level shown in FIG. Become.

In other words, the compression processing in consideration of the reference white level of the reference white level compression processing unit 16 reduces the white level of the SDR video signal to approximately 95%, which corresponds to the reference white level of 75% of the HLG video signal, in the area above the knee point Kp. Since the characteristics are included, the white level of the telop does not change. In this case, in the area lower than the knee point Kp, since the characteristics considering the skin level are maintained, the skin level of the HLG image can be made to correspond to the skin level of the SDR image.

(Compression processing considering color reproduction of highlights/highlight color reproduction compression processing unit 17)
Next, the compression processing in consideration of color reproduction of highlights by the highlight color reproduction compression processing unit 17 will be described in detail. This compression processing is processing for suppressing overexposure of highlights.

If a clip occurs in the highlights of the HLG video, it will be expressed as overexposure in the SDR video. When HDR video is converted to SDR video, overexposure may become conspicuous due to the difference in dynamic range.

In order to prevent this, the highlight color reproduction compression processing unit 17 receives the luminance Y comp,1st from the reference white level compression processing unit 16 and performs highlight color reproduction with respect to the luminance Y _{comp,1st according} to the following equation. Luminance Y _comp,2nd is obtained by performing compression processing taking into consideration. The highlight color reproduction compression processing unit 17 outputs the luminance Y _comp,2nd to the SDR luminance/light conversion unit 14 . This formula maps 100% of the HLG video signal to the upper limit of 109% of the SDR video signal.

Here, Y _comp,1st is the luminance obtained by compression processing considering the reference white level, and W is the width from the change start point to the change end point for smoothing the signal change near the knee point. Y _95%SDR indicates the brightness of the display light corresponding to the white level of approximately 95% of the SDR video signal. Y _109%SDR indicates the brightness of the display light corresponding to 109% of the SDR video signal. Y _100%HLG respectively indicate the brightness of the display light corresponding to 100% of the HLG video signal. The knee point is Y _{95% SDR} and corresponds to point a in FIG. 7 described later, which corresponds to point c in FIG. 6 described later.

Specifically, the highlight color reproduction compression processing unit 17 sets the same value as the luminance Y _comp,1st as the luminance Y _comp,2nd in a region where the luminance Y comp, _1st is lower than a predetermined value based on the knee point. (the upper equation of the above equation (10)). In addition, the highlight color reproduction compression processing unit 17, based on Y _95%SDR , Y _109%SDR , Y _100%HLG and the width W in a region where the luminance Y _comp,1st has a width W with reference to the knee point, , and brightness Y _comp,1st are subjected to rounding processing to smooth signal changes, and brightness Y _comp,2nd is calculated (the middle equation of the above equation (10)).

The highlight color reproduction compression processing unit 17 performs a luminance gradient based on Y _95%SDR , Y _109%SDR and Y _100%HLG in an area where Y _comp,1st is higher than a predetermined value based on the knee point. Y _comp,2nd is calculated (the lower expression of the above expression (10)).

By this compression processing, it is possible to obtain the luminance Y _comp,2nd considering the color reproduction of the highlight from the luminance Y _comp,1st obtained considering the reference white level.

FIG. 6 is a diagram for explaining characteristics obtained by compression processing that takes color reproduction of highlights into consideration. The horizontal axis indicates the level of the HLG video signal, and the vertical axis indicates the level of the SDR video signal. FIG. 6 shows the characteristics of the prior art shown in FIG. The characteristics of the example considering reproduction are given. A two-dot chain line shows the characteristics of an example considering the color reproduction of highlights.

Here, the characteristics of the example that takes into account the color reproduction of the highlights indicated by the two-dot chain line are the processing that takes into account the skin level and the processing that takes into account the reference white level. It is a characteristic obtained by performing processing. The same applies to FIGS. 7, 10 and 13, which will be described later.

The characteristics of an example that considers the color reproduction of highlights indicated by the chain double-dashed line are expressed by the above equation (10 ) shows the correspondence between the HLG video signal and the SDR video signal obtained by the operation of .

From FIG. 6, the characteristics of the example in consideration of the color reproduction of the highlight indicated by the two-dot chain line are the area (area a ) matches the characteristics obtained by the compression processing considering the reference white level. The characteristics of this area are obtained from the upper expression of the above equation (10) and correspond to the area b in FIG. 7, which will be described later. The knee point is Y _{95% SDR} and corresponds to point a in FIG. 7, which will be described later, which corresponds to point c in FIG.

In the area of W/2 around the knee point (point a in FIG. 7 (corresponding to point d in FIG. 5)), rounding is performed according to the middle expression of the above expression (10). will be As a result, steep characteristics can be relaxed and smoothed.

In addition, the characteristics of the example considering the color reproduction of the highlight are the white level of about 95% or more of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal (highlight area, see area b) , is not clipped at 109%, which is the upper limit of the SDR video signal. In this region, the white level of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal corresponds to about 95% of the white level of the SDR video signal (see point c). It can be seen that the characteristic increases up to the upper limit of 109% (see point d). The characteristics of the area b are obtained by the lower expression of the above equation (10) and correspond to the area d in FIG. 7, which will be described later.

As a result, in the compression processing that takes into consideration the color reproduction of the highlights in the highlight color reproduction compression processing unit 17, the relationship between the HLG video signal and the SDR video signal is the same as that shown in FIG. It becomes the characteristic of the example which did.

In other words, the compression processing that takes into consideration the color reproduction of the highlights in the highlight color reproduction compression processing unit 17 has characteristics that are not clipped at 109%, which is the upper limit value of the SDR video signal, in the region above the knee point. It is possible to suppress overexposure in highlights. In this case, in the area lower than the knee point, since the characteristic considering the reference white level is maintained, the white level of the telop does not change, and the skin level of the HLG image corresponds to the skin level of the SDR image. can be made

In this way, the highlight color reproduction compression processing unit 17 determines that the value of the SDR video signal corresponding to the HLG video signal corresponds to the reference white level of 75% of the HLG video signal for the luminance Y _comp,1st . Compression processing to obtain increasing characteristics for the highlight area (area b in FIG. 6) between the white level of about 95% (point c in FIG. 6) and the upper limit (point d in FIG. 6). to obtain the luminance Y _comp,2nd .

Therefore, the reference white level compression processing unit 16 and the highlight color reproduction compression processing unit 17 of the compression processing unit 13 determine that the value of the SDR video signal corresponding to the HLG video signal with respect to the luminance Y is as shown from point e in FIG. 6 through point c to point d in FIG. 6, the luminance Y _comp,2nd is obtained by performing compression processing to obtain an increasing characteristic.

Point e in FIG. 5 is greater than the skin level Vs _skin of the SDR video signal, which corresponds to the skin level Vh _skin of the HLG video signal, and is about the white level of the SDR video signal, which corresponds to the reference white level of 75% of the HLG video signal. A point with a given value of luminance Y less than 95%. Point c in FIG. 6 is the point at which the white level of the SDR video signal is approximately 95%, corresponding to the reference white level of 75% in the HLG video signal, and point d in FIG. 6 is the upper limit point.

(Luminance characteristics)
FIG. 4 described above shows the characteristics of the video signal in consideration of the skin level by the gain processing section 11, and FIGS. Each shows its characteristics. However, the gain processing unit 11 and the compression processing unit 13 do not process the video signal, but process the luminance, which is the linear signal of the display light.

Therefore, the characteristics of luminance, which is a linear signal of display light, corresponding to the characteristics of video signals considering the skin level, the characteristics of the video signal considering the reference white level, and the characteristics of the video signal considering the color reproduction of highlights explain.

FIG. 7 is a diagram showing characteristics of luminance, which is a linear signal of display light. The horizontal axis indicates HLG display luminance [cd/m ² ], and the vertical axis indicates SDR display luminance [cd/m ² ]. The upper limit of HLG display luminance is 1000 cd/m ² , which corresponds to the upper limit of 100% for HLG video signals. Also, the upper limit of SDR display luminance is 123 cd/m ² , which corresponds to the upper limit of 109% for SDR video signals.

A solid line indicates the characteristics of the prior art. That is, the characteristics of the prior art show the characteristics when gain processing is performed to make the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of about 88 cd/m ² .

The dashed line indicates the characteristics of an example in which the skin level is taken into account, that is, the characteristics when the gain processing unit 11 performs gain processing in consideration of the skin level. This characteristic indicates the correspondence relationship between the tristimulus values corresponding to the display light signal Fdg obtained by the gain processing unit 11 and the luminance Y obtained by the chromaticity conversion unit 12 .

The dashed-dotted line indicates the characteristics of an example in which the reference white level is taken into account, that is, the characteristics when the compression processing unit 13 performs compression processing in consideration of the reference white level. This characteristic indicates the luminance correspondence obtained by the compression processing operation of the above equation (9), which represents the conventional gain processing that makes the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of about 88 cd/m ² . ing.

The characteristics of the prior art shown by the solid line and the characteristics of the example considering the reference white level shown by the dashed-dotted line are for a point with an SDR display luminance of about 88 cd/m ² corresponding to an HLG display luminance of 200 cd/m ² (see a). It has characteristics including

A chain double-dashed line indicates the characteristics of an example in consideration of color reproduction of highlights, that is, the characteristics when compression processing is performed in consideration of color reproduction of highlights by the compression processing unit 13 . This characteristic is a compression process for making 100% of the HLG video signal correspond to the upper limit of 109% of the SDR video signal. The correspondence relationship of the luminance obtained by the calculation of the above equation (10) representing the compression processing for matching the luminance of the display light is shown.

It can be seen that the characteristics of the example taking into account the color reproduction of the highlights shown in the dash-dotted line include points (see point a) with an HLG display luminance of 200 cd/m ² and an SDR display luminance of about 88 cd/m ² . Further, the characteristics of the example considering the color reproduction of this highlight match the characteristics of the example considering the reference white level indicated by the dashed line in region b, and the characteristics of the example considering the skin level indicated by the dashed line in region c. is found to match

Furthermore, the characteristics of the example considering the color reproduction of the dashed- ^two dotted line highlight are that in the area d, the HLG display luminance 123 cd/m ² , which is the upper limit of SDR display luminance corresponding to 1000 cd/m ² , which is the upper limit of .

(SDR luminance/light converter 14)
Next, the SDR luminance/light converter 14 shown in FIG. 1 will be described in detail. The processing of the SDR luminance/light converter 14 is the reverse of that of the tristimulus and chromaticity converter 12 . The SDR luminance/light conversion unit 14 receives the luminance Y _comp,2nd from the compression processing unit 13 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 12 .

The SDR luminance/light converter 14 first obtains tristimulus values X _comp and Z _comp from the chromaticity coordinates x and y and the luminance Y _comp,2nd using the following equations.

ここで、Ｆｄｓ＜０となる信号があった場合は、Ｆｄｓ＝０とする。この３行３列の行列は、前記式（７）に示した３行３列の行列の逆行列である。 The SDR luminance/light converter 14 then obtains the SDR display light signal Fds={Rds, Gds, Bds} from the luminance Y _comp,2nd and the tristimulus values X _comp and Z _comp by the following equation. .

Here, if there is a signal that satisfies Fds<0, then Fds=0. This matrix of 3 rows and 3 columns is the inverse matrix of the matrix of 3 rows and 3 columns shown in Equation (7).

The SDR luminance/light converter 14 outputs the display light signal Fds={Rds, Gds, Bds} to the SDR light/video converter 15 .

(SDR light/video converter 15)
Next, the SDR light/video converter 15 shown in FIG. 1 will be described in detail. The SDR light/video conversion unit 15 receives the SDR display light signal Fds from the SDR luminance/light conversion unit 14, and converts the display light signal Fds into the SDR video signal by the inverse function of the EOTF of the SDR image in the following equation. Convert to E _s '.

As described above, according to the video signal conversion device 1 of the first embodiment, the HLG video/optical converter 10 converts the HLG video signal E _h ' into the display optical signal Fd using the EOTF of the HLG video.

The gain processing unit 11 performs gain processing on the display optical signal Fd taking into account the skin level, that is, gain processing for obtaining the characteristics of the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal. Thus, the display light signal Fdg is obtained.

As a result, the skin level can be improved as compared with the prior art, and the signal level of the human skin in the SDR video will not be lower than in the HLG video. However, the SDR video signal is clipped at the upper limit value in a predetermined area due to the gain processing considering the skin level. Therefore, compression processing is performed by the compression processing unit 13 .

The tristimulus value and chromaticity conversion unit 12 converts the display light signal Fdg into tristimulus values XYZ and chromaticity coordinates x, y.

The compression processing unit 13 performs compression processing in consideration of the reference white level for the luminance Y, that is, conventional gain processing that makes the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of 88 cd/m ² to 100 cd/m ² . Correspondingly, the luminance Y _comp,1st is determined by performing a compression process to obtain the characteristic of the white level of about 95% of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal.

As a result, the white level of the telop does not change as in the prior art. However, the SDR video signal is clipped at the upper limit value in a predetermined area due to compression processing that takes this reference white level into consideration. Therefore, compression processing is performed in consideration of color reproduction of highlights.

The compression processing unit 13 performs compression processing in consideration of color reproduction of highlights with respect to the luminance Y _comp,1st . From the white level of about 95% of the SDR video signal corresponding to the white level of 75% to the upper limit of 109% of the SDR video signal corresponding to 100% of the HLG video signal (HLG display luminance of 1000 cd/ ^m2 ) Luminance Y _comp,2nd is obtained by performing compression processing to obtain characteristics that increase up to a point of luminance 123 cd/m ² ).

As a result, the SDR video signal is not clipped at the upper limit value, so that crushed highlights can be suppressed.

The SDR luminance/light converter 14 obtains the SDR display light signal Fds from the luminance Y _comp,2nd using the chromaticity coordinates x, y. Then, the SDR optical/video converter 15 converts the display optical signal Fds into the SDR video signal E _s ' by the inverse function of the EOTF of the SDR video.

As described above, when converting an HLG image into an SDR image, gain processing considering the skin level of a person and compression processing considering the reference white level and color reproduction of highlights are performed. As a result, the signal level of the person's skin does not decrease, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed.

For example, in integrated production in which HLG video and SDR video are produced at the same time, the video signal conversion apparatus 1 of the first embodiment is used after HLG program production. As a result, it is possible to generate an SDR video that has a skin level as if the program was produced in HLG, that takes into consideration the reference white level, and that suppresses the blown-up highlights of highlights.

The _{SDR luminance} /light _conversion unit 14 of the video signal conversion device 1 shown in FIG. As shown in equation (12), the inverse matrix of the matrix for converting from wide color gamut RGB to tristimulus values is used. The matrix for converting from RGB of this wide color gamut to tristimulus values is the matrix of the above equation (7) used when the tristimulus value and chromaticity conversion unit 12 converts the display light signal Fdg into tristimulus values XYZ. .

この行列は、狭い色域のＲＧＢから三刺激値に変換するマトリクスの逆行列である。 On the other hand, the SDR luminance/light converter 14 may use the following formula when calculating the SDR display light signal Fds from the luminance Y _comp,2nd and the tristimulus values X _comp and Z _comp . .

This matrix is the inverse of the matrix that converts from narrow gamut RGB to tristimulus values.

As a result, the tristimulus value and chromaticity conversion unit 12 uses a matrix for converting wide color gamut RGB to tristimulus values, and the SDR luminance/light conversion unit 14 converts narrow color gamut RGB to tristimulus values. Wide to narrow gamut conversion can be done by using the inverse of the matrix to convert and converting from tristimulus values back to RGB.

[Embodiment 2: Video signal converter]
Next, the configuration and processing of the video signal conversion device of the second embodiment will be described. As described above, the second embodiment uses a fitting function that includes operations that take into consideration the human skin level, the reference white level, and the color reproduction of highlights when converting an HLG image into an SDR image.

As a result, the signal level of the person's skin does not decrease, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed. In addition, the problem of signal discontinuity caused by the first embodiment can be solved, continuous characteristics can be obtained, and banding in the highlight region can be improved.

FIG. 8 is a block diagram showing a configuration example of the video signal conversion device of the second embodiment, and FIG. 9 is a flow chart showing a processing example of the video signal conversion device of the second embodiment. The video signal conversion device 2 includes an HLG video/light conversion section 20, a tristimulus value and chromaticity conversion section 21, a compression processing section 22, an SDR luminance/light conversion section 23, and an SDR light/video conversion section 24. .

The HLG video/optical converter 20 receives an HLG video signal E _h ', which is a video signal of an HLG image (step S901). Then, the HLG video/optical converter 20 converts the HLG video signal E _h ' into the HLG display optical signal Fd, which is a linear signal of display light, by the EOTF of the HLG video (step S902). The HLG video/light converter 20 outputs the HLG display light signal Fd to the tristimulus value and chromaticity converter 21 .

The tristimulus value and chromaticity conversion unit 21 receives the display light signal Fd from the HLG video/light conversion unit 20, and converts the display light signal Fd into tristimulus values XYZ and chromaticity coordinates x, y which are color information. (step S903). Then, the tristimulus value and chromaticity conversion unit 21 outputs the luminance Y to the compression processing unit 22 and outputs the chromaticity coordinates x, y to the SDR luminance/light conversion unit 23 .

The compression processing unit 22 receives the luminance Y from the tristimulus value and chromaticity conversion unit 21, and applies a predetermined fitting function to the luminance Y based on the preset gain value k1 and the SDR knee _point Y _SDRkp . By performing the processing, the brightness Y _comp is obtained (step S904). The compression processor 22 then outputs the luminance Y _comp to the SDR luminance/light converter 23 . The predetermined fitting function is a function that includes operations that consider the human skin level, the reference white level, and the color reproduction of highlights. SDR knee point Y _SDRkp is the knee point of the SDR display luminance signal.

The SDR luminance/light conversion unit 23 receives the luminance Y _comp from the compression processing unit 22 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 21 . Then, the SDR luminance/light converter 23 obtains tristimulus values X _comp and Z _comp from the luminance Y _comp using the chromaticity coordinates x and y (step S905).

The SDR luminance/light converter 23 obtains the SDR display light signal Fds from the luminance Y _comp and the tristimulus values X _comp and Z _comp (step S906). The SDR luminance/light converter 23 then outputs the SDR display light signal Fds to the SDR light/video converter 24 .

The SDR light/video converter 24 receives the SDR display light signal Fds from the SDR luminance/light converter 23 . Then, the SDR light/video converter 24 converts the display light signal Fds into an SDR video signal E _s ', which is a video signal of the SDR image, by the inverse function of the EOTF of the SDR image (step S907). The SDR optical/video converter 24 outputs the SDR video signal E _s ' (step S908).

In the second embodiment, the SDR video signal E _s ' does not lower the signal level of the person's skin, does not change the white level of the telop, and suppresses overexposure of the highlights, with respect to the HLG video signal E _h '. is generated. Embodiment 2 is characterized in that the compression processing unit 22 performs processing on luminance Y using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights.

(HLG video/optical converter 20)
Next, the HLG video/optical converter 20 shown in FIG. 8 will be described in detail. As described above, the HLG video/optical converter 20 converts the HLG video signal E _h ' into the display optical signal Fd, which is a linear signal of display light, by the EOTF of the HLG video. That is, the HLG video/optical converter 20 converts the RGB signal, which is the HLG video signal E _h ', into the display optical signal Fd, which is a linear signal of display light, by the EOTF of the HLG video.

The HLG video/optical conversion unit 20 performs the same processing as the HLG video/optical conversion unit 10 shown in FIG. 1, so detailed description thereof will be omitted here.

(Tristimulus value and chromaticity converter 21)
Next, the tristimulus value and chromaticity converter 21 shown in FIG. 8 will be described in detail. As described above, the tristimulus value and chromaticity conversion unit 21 converts the display light signal Fd into tristimulus values XYZ and chromaticity coordinates x, y.

The tristimulus value and chromaticity conversion unit 21 receives the display light signal Fd={Rd, Gd, Bd} from the HLG video/light conversion unit 20, and first converts the display light signal Fd={Rd, Gd, Bd} into Convert to tristimulus values XYZ. The tristimulus values XYZ are calculated by the following formulas.

The tristimulus value and chromaticity conversion unit 21 then converts the tristimulus values XYZ into chromaticity coordinates x, y. The chromaticity coordinates x, y are calculated by the following formulas.

The tristimulus value and chromaticity conversion unit 21 outputs the luminance Y to the compression processing unit 22 and outputs the chromaticity coordinates x, y to the SDR luminance/light conversion unit 23 . The luminance Y is used for processing by the compression processor 22, and the chromaticity coordinates x, y are used for processing by the SDR luminance/light converter 23 to restore the luminance to a linear signal of display light.

(Compression processing unit 22)
Next, the compression processing unit 22 shown in FIG. 8 will be described in detail. As described above, the compression processing unit 22 considers the human skin level, the reference white level, and the color reproduction of the highlights for the luminance Y based on the preset gain value k1 and the SDR knee _point Y _SDRkp . Luminance Y _comp is obtained by performing processing using a fitting function.

FIG. 10 is a diagram for explaining characteristics of display luminance obtained by processing applying a fitting function. The horizontal axis indicates HLG display luminance [cd/m ² ], and the vertical axis indicates SDR display luminance [cd/m ² ]. FIG. 10 shows the characteristics of the prior art shown in FIG. 7 (solid line), the characteristics of the example considering the skin level (broken line), the characteristics of the example considering the reference white level (chain line), and the color reproduction of the highlights. In addition to the properties of the considered example (dashed-dotted line), the properties of the example with the fitting function applied are shown.

The dotted line indicates the characteristics of an example in which the fitting function is applied, that is, the compression processing unit 22 processes the luminance Y, which is input data, using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights. shows the characteristics when performing This corresponds to the luminance Y _comp which is the output data of the compression processing unit 22 . The characteristics of the prior art indicated by the solid line show the characteristics when only gain processing is performed on luminance Y, which is input data, with consideration given to the reference white level.

The characteristics of the example to which the fitting function shown by the dotted line is applied reflect the following processing (A), (B), and (C) for the characteristics of the prior art shown by the solid line.
(A) Gain processing considering the skin level, that is, processing for obtaining the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal.
(B) Compression processing (logarithmization processing) considering the reference white level, that is, the conventional gain that makes the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of 88 cd/m ² to 100 cd/m ² (see point a). A process to characterize the white level of the SDR video signal at approximately 95% (see point a in FIG. 13 below) corresponding to the reference white level of 75% for the HLG video signal, as corresponding to the process.
(C) Compression processing (logarithmization processing) considering the color reproduction of highlights, that is, 109%, which is the upper limit of the SDR video signal in the highlight area (see area b, see area b in FIG. 13 to be described later) 109% (SDR display luminance of 123 cd/m ² ), which is the upper limit of the SDR video signal corresponding to 100% of the HLG video signal (HLG display luminance of 1000 cd/m ² ) (see point c. , see point c in FIG. 13 to be described later).

The compression processing unit 22 performs gain processing and compression processing (logarithmization processing) on the luminance Y according to the following equation using a fitting function that _realizes the characteristics of the dotted line shown in FIG. Ask for

Here, Y is the tristimulus value and luminance calculated by the chromaticity conversion unit 21 . k1 is _a gain value considering the skin level. k ₂ is a correction value for matching the slopes of the tangents of the linear signal and the logarithmic nonlinear signal at the point of inflection Y=Y _HLGkp .

k ₃ is a linear signal of HLG 100% (HLG display luminance of 1000 cd/m ² corresponding to 100% of the HLG video signal) and a linear signal of SDR 109% (SDR display luminance of 123 cd/m ² corresponding to 109% of the SDR video signal). Correction value for linear signal, or linear signal of HLG75% (HLG display luminance corresponding to 75% of HLG video signal) linear signal of SDR100% (SDR display luminance corresponding to 100% of SDR video signal) It is a correction value determined by a constraint condition that corresponds to the signal. _k4 is a correction value for matching the contact values of the linear signal and the logarithmic nonlinear signal. Y _HLGkp is the knee point of the HLG display luminance signal corresponding to the SDR knee point Y _SDRkp , which is the knee point of the SDR display luminance signal.

Gain value k ₁ , SDR knee point Y _SDRkp , HLG knee point Y _HLGkp , SDR 109% video signal Vs ₁₀₉ (or SDR 100% video signal Vs ₁₀₀ ), HLG 100% video signal Vh ₁₀₀ (or HLG 75% video signal Vh ₇₅ ), the EOTF for SDR video and the EOTF for HLG video are preset by the user.

The correction value k ₂ is obtained by using the gain value k ₁ preset by the user, the HLG knee point Y _HLGkp , and the correction value k ₃ calculated by the compression processing unit 22, as shown in Equation (18) described later. It is calculated by the compression processing unit 22 .

The correction value k ₃ is the gain value k ₁ preset by the user, the SDR knee point Y _SDRkp , the HLG knee point Y _HLGkp , the SDR 109% video signal Vs ₁₀₉ (or the SDR 100% video signal Vs ₁₀₀ ), and the HLG 100% It is calculated by the compression processing unit 22 using the video signal Vh ₁₀₀ (or the HLG 75% video signal Vh ₇₅ ), the EOTF of the SDR image, and the EOTF of the HLG image. Details will be described later. The correction value k ₄ is calculated by the compression processing unit 22 using the SDR knee point Y _SDRkp and the correction values k ₂ and k ₃ calculated by the compression processing unit 22 as shown in Equation (18) described later. . Details will be described later.

Specifically, the compression processing unit 22 performs gain processing for multiplying the luminance Y by a preset gain value k ₁ in a region where the luminance Y is lower than the HLG knee point Y _HLGkp , and linearizes the luminance. Y _comp is calculated (the upper equation of the above equation (17)).

The knee points of the SDR knee point Y _SDRkp and the HLG knee point Y _HLGkp are arbitrarily set by the user. This knee point corresponds to point d in FIG. 10, which corresponds to point d in FIG. 13, which will be described later.

The upper expression of the above equation (17) is represented by the solid line in FIG. 10 in the region where the luminance Y is lower than the HLG knee point Y _HLGkp (in the region from the origin to the knee point of point d shown in FIG. 10). It shows the gain processing that raises the characteristics of the conventional technology to the characteristics of a straight line from the origin to the point d indicated by the dotted line. This gives the linearized luminance _Ycomp .

The compression processing unit 22 applies correction values k ₂ , k ₃ , and k ₄ to the luminance Y in a region where the luminance Y is equal to or higher than the HLG knee point Y _HLGkp , and a luminance Y having a logarithmic characteristic based on the HLG knee point Y _HLGkp . _Comp is calculated (the lower expression of the above expression (17)).

The lower expression of the above equation (17) is represented by the dotted line in FIG. 10 in the area where the luminance Y is equal to or higher than the HLG knee point Y _HLGkp (in the area from the knee point d to the point c shown in FIG. 10). Like the characteristics, the knee point of point d, point a (SDR display luminance point of 88 cd/m ² to 100 cd/m ² corresponding to HLG display luminance of 200 cd/m ² , HLG video signal reference white level of 75%) The logarithmization process including the point c) and point c of the white level of the SDR video signal. This gives the logarithmized luminance _Ycomp .

By this gain processing and logarithmization processing, it is possible to obtain the luminance Y _comp in consideration of the human skin level, the reference white level, and the color reproduction of the highlights from the tristimulus values and the luminance Y calculated by the chromaticity conversion unit 21 . can.

(gain value _k1 )
_First , the gain value k1 of the above equation (17) representing the fitting function will be explained. The gain value k1 is _a value considering the skin level, and is set in advance by the user based on the correspondence relationship between the skin level of the HLG image and the skin level of the SDR image.

That is, as explained with reference to FIG. 4, the skin level Vh _skin of the HLG video signal is approximately 50% of that of the HLG video signal (see point a), whereas the skin level Vs _skin of the SDR video signal is approximately 50% of that of the SDR video signal. about 67% of the video signal (see point b).

Therefore, the gain value k1 can obtain the characteristics of the example considering the skin level shown by the dashed line in FIG. ₄ , that is, the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal. It needs to be set to achieve the properties.

Therefore, the value calculated by the user using the above equation (4) or the above equation ( ₅ ) is used as the gain value k1. As described above, the formula (4) is used when the HLG video/light converter 20 calculates the display light signal Fd based on the luminance value [cd/m ² ]. Also, the above equation (5) is used when the HLG video/light converter 20 calculates the display light signal Fd based on the normalized signal.

The gain values k ₁ obtained by the formulas (4) and (5) are 7.5439 and 0.7544, respectively, when the display peak luminance of the HLG image is 1000 cd/m ² .

_The gain value k1 may be set in advance by the user through the calculation of the above equation (4) or (5), or may be set in advance to an arbitrary value. In short, the gain value k1 may be freely changed by the user as _a setting item that allows image adjustment.

As _a result, by using the gain value k1, the relationship between the HLG video signal and the SDR video signal is made to have the characteristics of the dashed line shown in FIG. can correspond to Therefore, the skin level can be improved over the prior art, and the signal level of the person's skin in the SDR video signal will not be lower than in the HLG video signal.

(correction value _k3 )
Next, the correction value _k3 of the equation (17) representing the fitting function will be described. The correction value k ₃ is a value for making the HLG 100% linear signal correspond to the SDR 109% linear signal (or the HLG 75% linear signal to the SDR ₁₀₀ % linear signal). is calculated by the following process using Note that the correction value _k3 may be set in advance by the user instead of being calculated by the processing of the compression processing unit 22 .

The correction value _k3 is a value that defines constraints in the fitting function. As an example of the constraint condition, there are the following two patterns, one of which is selected by the user's setting.
<1> Pattern for matching HLG 100% to SDR 109% <2> Pattern for matching HLG 75% to SDR 100%

<1> is a pattern that makes the HLG display luminance of 1000 cd/m ² corresponding to 100% of the HLG video signal correspond to the SDR display luminance of 123 cd/m ² corresponding to 109% of the SDR video signal. <2> is a pattern in which the HLG display luminance corresponding to 75% of the HLG video signal corresponds to the SDR display luminance corresponding to 100% of the SDR video signal.

(Pattern of <1>)
First, as the pattern <1>, in the conversion based on the normalized signal, a constraint is given so that the HLG 100% linear signal corresponds to the SDR 109% linear signal.

When the correction value k ₃ of the logarithmic function part of the above equation (17) is changed, the compression processing unit 22 calculates the increase from the inflection point Y _SDRkp to the value of the linear signal of SDR 109% and the logarithmic function A value that coincides with the increment from the point of inflection to the value of the linear signal of HLG 100% is calculated, and this value is defined as _k3 .

つまり、補正値ｋ₃が算出されることで、必然的に補正値ｋ₂，ｋ₄も算出されることになる。 Here, in the above equation (17), the unknown correction values k ₂ and k ₄ can be calculated from the preset gain value k ₁ , the correction value k ₃ to be calculated, etc., as shown in the following equations. can. The SDR knee point Y _SDRkp and the HLG knee point Y _HLGkp are preset by the user.

That is, by calculating the correction value k ₃ , the correction values k ₂ and k ₄ are also calculated inevitably.

ここで、Ｖｓ₁₀₉はＳＤＲ１０９％のビデオ信号、Ｖｈ₁₀₀はＨＬＧ１００％のビデオ信号である。ＥＯＴＦ_SDR（）は、ＳＤＲ映像のＥＯＴＦであり、ＥＯＴＦ_HLG（）は、ＨＬＧ映像のＥＯＴＦである。 The formula for calculating the correction value _k3 is as follows.

Here, Vs ₁₀₉ is a video signal of SDR 109%, and Vh ₁₀₀ is a video signal of HLG 100%. EOTF _SDR ( ) is the EOTF for SDR video, and EOTF _HLG ( ) is the EOTF for HLG video.

The first and second terms on the right side of the above equation (19) correspond to the increase from Y _SDRkp , which is the inflection point, to the linear signal value of SDR 109%. The third term corresponds to the lower expression of the above expression (17), and corresponds to the increase from Y _HLGkp , which is the inflection point of the logarithmic function, to the value of the linear signal of HLG 100%.

For example, if the SDR knee point Y _SDRkp is 80% of the SDR video signal and the HLG video/optical converter 20 calculates the display optical signal Fd based on the normalized signal, then the HLG knee point Y _HLGkp =0.07759235. , gain value k ₁ =7.54391909, correction value k ₂ =0.17357417, correction value k ₃ =0.70346967 and correction value k ₄ =0.79634823.

Note that the SDR knee point Y _SDRkp may be a preset fixed value, or may be freely changed by the user as an image adjustable setting item. In addition, the compression processing unit 22 receives a gain value k ₁ and an SDR knee point Y _SDRkp preset by the user, and calculates the SDR knee point Y _SDRkp according to the preset correspondence relationship between the video signals of the HLG image and the SDR image. _HLG knee point _{Y HLGkp} corresponding to . ₄ may be calculated.

Also, in integrated production where HLG video and SDR video are produced at the same time, when the HLG video is converted to SDR video, the reference white level is set so that the white level of the telop synthesized with the HLG video does not change in the SDR video. should be considered.

In Example 2, the reference white level is taken into account by performing gain processing such that the HLG display luminance of 200 cd/m ² corresponds to the SDR display luminance of 88 cd/m ² to 100 cd/m ² as in the conventional technique. It realizes conversion from HLG video to SDR video.

FIG. 11 is a diagram illustrating the correspondence relationship between the HLG display luminance and the SDR display luminance when the knee point is changed in pattern <1>. The horizontal axis indicates HLG display luminance [cd/m ² ], and the vertical axis indicates SDR display luminance [cd/m ² ]. FIG. 11 shows the characteristics when the SDR knee point Y _SDRkp =80%, 85%, 90% and 95%.

From these characteristics, even if the SDR knee point Y _SDRkp is varied in the range of 80%, 85%, 90%, and 95%, the HLG display luminance of 200 cd/m ² corresponds to the SDR display luminance of about 90 cd/m ² to 105 cd. /m ² .

As described above, in the prior art, by performing gain processing such that the HLG display luminance of 200 cd/m ² corresponds to the SDR display luminance of 88 cd/m ² to 100 cd/m ² , the HLG image considering the reference white level is obtained. to SDR video conversion.

Also in the video signal conversion device 2 of the second embodiment, the conversion from the HLG video to the SDR video in consideration of the reference white level can be realized by the processing using the formula (17) according to the pattern of <1>. That is, as shown in FIG. 13, which will be described later, the processing using the above equation (17) results in a characteristic that includes a point at the white level of about 95% of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal. As a result, the white level of the telop does not change.

(Pattern of <2>)
Next, as a pattern <2>, a case where a constraint is given so that a linear signal of HLG 75% corresponds to a linear signal of SDR 100% in the conversion based on the normalized signal will be described.

As in the pattern <1>, the compression processing unit 22 calculates the increment from the inflection point Y _SDRkp to the linear signal value of SDR 100% and the logarithmic function from the inflection point to the linear signal value of HLG 75%. Calculate a value that coincides with the increment of , and set that value to _k3 .

ここで、Ｖｓ₁₀₀はＳＤＲ１００％のビデオ信号、Ｖｈ₇₅は、ＨＬＧ７５％のビデオ信号である。 The formula for calculating the correction value _k3 is as follows.

Here, Vs ₁₀₀ is a video signal of SDR 100%, and Vh ₇₅ is a video signal of HLG 75%.

The first and second terms on the right side of the above equation (20) correspond to the increment from the inflection point Y _SDRkp to the linear signal value of SDR 100%. The third term corresponds to the lower expression of the above expression (17), and corresponds to the increase from Y _HLGkp , which is the inflection point of the logarithmic function, to the value of the linear signal of HLG 75%.

For example, if the SDR knee point Y _SDRkp is 80% of the SDR video signal and the HLG video/optical converter 20 calculates the display optical signal Fd based on the normalized signal, then the HLG knee point Y _HLGkp =0.07759235. , gain value k ₁ =7.54391909, correction value k ₂ =0.28126377, correction value k ₃ =0.51949509 and correction value k ₄ =0.79149370.

Incidentally, the SDR knee point Y _SDRkp may be set to a fixed value set in advance as in the pattern <1>, or may be freely changed by the user as a setting item for image adjustment. good too. In addition, the compression processing unit 22 inputs the gain value k1 and the SDR knee point Y _SDRkp preset by the user in the same manner as in the pattern < ₁ >, and converts the preset video signals of the HLG image and the SDR image. According to the correspondence relationship, the HLG knee point Y _HLGkp corresponding to the SDR knee point Y _SDRkp is calculated, and as described above, the correction value _k3 that becomes a value that matches the signal increment from the point of inflection to the point of the constraint condition is determined. may be calculated to calculate the correction values k ₂ and k ₄ .

FIG. 12 is a diagram illustrating the correspondence relationship between the HLG display luminance and the SDR display luminance when the knee point is changed in pattern <2>. The horizontal axis indicates HLG display luminance [cd/m ² ], and the vertical axis indicates SDR display luminance [cd/m ² ]. FIG. 12 shows the characteristics when the SDR knee point Y _SDRkp =80%, 85%, 90% and 95%.

From these characteristics, an HLG display luminance of 200 cd/ ^m2 corresponds to an SDR display luminance of approximately 100 cd/ ^m2 even though the SDR knee point Y _SDRkp is varied between 80%, 85%, 90%, and 95%. I know you are.

In the case of pattern <1> shown in FIG. 11, the HLG display luminance of 200 cd/m ² corresponds to the SDR display luminance of approximately 90 cd/m ² to 105 cd/m ² by setting the knee point, and the reference white level is Varies within this range.

On the other hand, in the case of pattern < ² > shown in ^FIG . 12, the gradation expression of the highlights changes depending on the setting of the knee point. Therefore, the reference white level is always constant.

As described above, in the video signal conversion device 2 of the second embodiment, the conversion from the HLG video to the SDR video in consideration of the reference white level can be realized by the processing using the formula (17) according to the pattern of <2>. can be done. That is, as shown in FIG. 13, which will be described later, the processing using the above equation (17) results in a characteristic that includes a point at the white level of about 95% of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal. As a result, the white level of the telop does not change.

₍ correction values k2, _k4 )
Next, the correction values k ₂ and k ₄ of the equation (17) representing the fitting function will be explained. _The correction value k2 is a value for matching the tangent slopes of the linear signal and the logarithmic nonlinear signal, and the correction value _k4 is a value for matching the contact values of the linear signal and the logarithmic nonlinear signal. be.

The compression processing unit 22 uses a preset gain value k ₁ to calculate a correction value k ₃ that matches the increase in the signal from the inflection point to the constraint condition point. Correction values k ₂ and k ₄ are calculated from gain value k ₁ , correction value k ₃ and the like by equation (18).

(SDR luminance/light converter 23)
Next, the SDR luminance/light converter 23 shown in FIG. 8 will be described in detail. The processing of the SDR luminance/light converter 23 is the reverse of that of the tristimulus value and chromaticity converter 21 . The SDR luminance/light conversion unit 23 receives the luminance Y _comp from the compression processing unit 22 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 21 .

The SDR luminance/light converter 23 first obtains tristimulus values X _comp and Z _comp from the chromaticity coordinates x and y and the luminance Y _comp using the following equations.

ここで、Ｆｄｓ＜０となる信号があった場合は、Ｆｄｓ＝０とする。 The SDR luminance/light converter 23 then obtains the SDR display light signal Fds={Rds, Gds, Bds} from the luminance Y _comp and the tristimulus values X _comp and Z _comp according to the following equation.

Here, if there is a signal that satisfies Fds<0, then Fds=0.

The SDR luminance/light converter 23 outputs the display light signal Fds={Rds, Gds, Bds} to the SDR light/video converter 24 .

(SDR light/video converter 24)
Next, the SDR light/video converter 24 shown in FIG. 8 will be described in detail. The SDR light/video conversion unit 24 receives the SDR display light signal Fds from the SDR luminance/light conversion unit 23, and converts the display light signal Fds into the SDR video signal by the inverse function of the EOTF of the SDR image in the following equation. Convert to E _s '.

(video signal)
Next, characteristics of a video signal obtained by processing applying a fitting function will be described. FIG. 10 described above shows the characteristics of the display brightness obtained by the process applying the fitting function. The video signal characteristics correspond to this display luminance characteristic.

FIG. 13 is a diagram for explaining characteristics of a video signal obtained by processing applying a fitting function. The horizontal axis indicates the level of the HLG video signal, and the vertical axis indicates the level of the SDR video signal. FIG. 13 shows the characteristics of the conventional technology (solid line) shown in FIG. In addition to the properties of the considered example (dashed-dotted line), the properties of the example with the fitting function applied are shown.

The dotted line indicates the characteristics of an example in which the fitting function is applied, that is, the characteristics in the case of performing processing using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights by the compression processing unit 22 .

The characteristic of the example to which the fitting function shown by the dotted line is applied is the gain processing considering the skin level of (A) and the reference white level of (B) for the characteristic of the prior art shown by the solid line. The compression processing and the compression processing in consideration of the color reproduction of the highlight in (C) are reflected.

In the characteristics of an example that considers the color reproduction of highlights shown by the two-dot chain line, the white level of the SDR video signal corresponds to the reference white level of 75% of the HLG video signal, which corresponds to the white level of about 95%. and signal continuity is lost.

On the other hand, in the characteristics of the example to which the fitting function shown by the dotted line is applied, before and after the white level of about 95% of the SDR video signal (see point a) corresponding to the reference white level of 75% of the HLG video signal, , signal continuity is maintained, and banding and the like in highlight regions are also improved.

In this way, the compression processing unit 22 performs a gain processing operation on the luminance Y to obtain the characteristics of the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal using the fitting function. 13, the value of the SDR video signal corresponding to the HLG video signal increases in the region from point d in FIG. 13 through point a in FIG. 13 to point c in FIG. The brightness Y _comp is obtained by performing the calculation.

Point d in FIG. 13 indicates that the value of the skin level Vs skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal is greater than the value of the skin level Vs _skin of the SDR video signal and the white level of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal. A point with a predetermined value of luminance Y less than the value of about 95% of the level. Point a in FIG. 13 is the value point of about 95% white level of the SDR video signal corresponding to the reference white level 75% of the HLG video signal, and point c in FIG. 13 is the point of the upper limit value.

In this case, the compression processing unit 22 obtains the characteristic of the white level of about 95% of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal, and The value of the SDR video signal corresponding to the signal changes from the white level of about 95% of the SDR video signal corresponding to the reference white level of 75% of the HLG video signal (point a in FIG. 13) to the upper limit value (point c in FIG. 13). ), an operation for obtaining increasing characteristics is performed for the highlighted area (area b in FIG. 13).

As described above, according to the video signal conversion device 2 of the second embodiment, the HLG video/optical converter 20 converts the HLG video signal E _h ′ into the display optical signal Fd using the EOTF of the HLG video. Then, the tristimulus value and chromaticity conversion unit 21 converts the display light signal Fd into tristimulus values XYZ and chromaticity coordinates x, y.

The compression processing unit 22 performs processing using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights for the luminance Y based on the gain value k1 and the SDR knee _point Y _SDRkp set in advance. to obtain the luminance Y _comp .

The SDR luminance/light converter 23 obtains the tristimulus values X _comp and Z _comp from the luminance Y _comp using the chromaticity coordinates x and y, and calculates the SDR from the luminance Y _comp and the tristimulus values X _comp and Z _comp . Determine the display light signal Fds. Then, the SDR optical/video converter 24 converts the display optical signal Fds into the SDR video signal E _s ' by the inverse function of the EOTF of the SDR video.

In this manner, when converting an HLG image into an SDR image, processing is performed using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights.

The fitting function includes a gain process that considers the human skin level, that is, an operation to obtain the characteristics of the skin level Vs _skin of the SDR video signal corresponding to the skin level Vh _skin of the HLG video signal.

As a result, the skin level can be improved as compared with the prior art, and the signal level of the human skin in the SDR video will not be lower than in the HLG video.

In addition, the fitting function includes compression processing that considers the reference white level, that is, compression processing that corresponds to conventional gain processing that makes the HLG display luminance of 200 cd/m ² correspond to the SDR display luminance of 88 cd/m ² to 100 cd/m ² . , to characterize the white level of the SDR video signal at approximately 95%, corresponding to the reference white level of 75% for the HLG video signal. As a result, the white level of the telop does not change as in the prior art.

Furthermore, the fitting function includes compression processing that considers the color reproduction of highlights, that is, 100% of the HLG video signal (HLG display luminance of 1000 cd 109% (SDR display luminance 123 cd/m ² ), which is the upper limit of the SDR video signal corresponding to 109% (SDR display luminance 123 cd/m ² ).

As a result, the SDR video signal is not clipped at the upper limit value, so that it is possible to suppress overexposure in highlights.

Therefore, in Example 2, the signal level of the person's skin does not decrease, the white level of the telop does not change, and furthermore the whitening of highlights can be suppressed. In addition, as compared with the first embodiment described above, signal continuity is maintained, and banding of images with smooth gradation is improved in highlight regions.

For example, in integrated production in which HLG video and SDR video are produced at the same time, the video signal converter 2 of the second embodiment is used after HLG program production. As a result, it is possible to generate an SDR video that has a skin level as if the program was produced in HLG, that takes into consideration the reference white level, and that suppresses the blown-up highlights of highlights.

The _{SDR luminance} /light _conversion unit 23 of the video signal conversion device 2 shown in FIG. 8 uses the above equation ( 22), the inverse matrix of the matrix for conversion from wide color gamut RGB to tristimulus values is used. The matrix for conversion from wide color gamut RGB to tristimulus values is the matrix of the above equation (15) used when the tristimulus value and chromaticity converter 21 converts the display light signal Fd into tristimulus values XYZ.

この行列は、狭い色域のＲＧＢから三刺激値に変換するマトリクスの逆行列である。 On the other hand, the SDR luminance/light conversion unit 23 may use the following formula when calculating the SDR display light signal Fds from the luminance Y _comp and the tristimulus values X _comp and Z _comp .

This matrix is the inverse of the matrix that converts from narrow gamut RGB to tristimulus values.

As a result, the tristimulus value and chromaticity conversion unit 21 uses a matrix for converting wide color gamut RGB to tristimulus values, and the SDR luminance/light conversion unit 23 converts narrow color gamut RGB to tristimulus values. Wide to narrow gamut conversion can be done by using the inverse of the matrix to convert and converting from tristimulus values back to RGB.

[Embodiment 1: Video signal conversion device that performs inverse conversion]
Next, a device for performing inverse conversion of the video signal conversion device 1 of the first embodiment will be described. When converting an SDR video into an HLG video, this device performs expansion processing in consideration of color reproduction of highlights and a reference white level, and inverse gain processing in consideration of a person's skin level. As a result, the signal level of the person's skin can be maintained, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed.

FIG. 14 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device 1 of Example 1 shown in FIG. This video signal conversion device 3 includes an SDR video/light converter 30, a tristimulus value and chromaticity converter 31, an extension processor 32, an HLG luminance/light converter 33, an inverse gain processor 34, and an HLG light/video converter. A portion 35 is provided.

The SDR video/optical converter 30 receives the SDR video signal E _s ', and converts the SDR video signal E _s ' into an SDR display optical signal Fds, which is a linear signal of display light, according to the EOTF of the SDR image. Then, the SDR video/optical converter 30 outputs the SDR display optical signal Fds to the tristimulus value and chromaticity converter 31 . The SDR video/optical conversion section 30 corresponds to the SDR optical/video conversion section 15 shown in FIG. 1 and performs the opposite processing.

The tristimulus value and chromaticity conversion unit 31 receives the display light signal Fds from the SDR video/light conversion unit 30, and converts the display light signal Fds into tristimulus values XYZ and chromaticity coordinates x, y which are color information. do. The tristimulus value and chromaticity conversion unit 31 outputs the luminance Y of the tristimulus values XYZ to the extension processing unit 32 and outputs the chromaticity coordinates x, y to the HLG luminance/light conversion unit 33 . The tristimulus value and chromaticity conversion unit 31 corresponds to the SDR luminance/light conversion unit 14 shown in FIG. 1 and performs the opposite processing.

The expansion processing unit 32 receives the luminance Y from the tristimulus values and the chromaticity conversion unit 31, and performs expansion processing on the luminance Y taking into account the color reproduction of the highlight, thereby obtaining the luminance Y _exp,1st . Then, the expansion processing unit 32 obtains the luminance Y _exp,2nd by performing expansion processing on the luminance Y _exp,1st in consideration of the reference white level. The extension processing unit 32 outputs the luminance Y _exp,2nd to the HLG luminance/light conversion unit 33 . The expansion processing unit 32 corresponds to the compression processing unit 13 shown in FIG. 1 and performs the opposite processing.

Specifically, the extension processing unit 32 first performs the inverse processing of the highlight color reproduction compression processing unit 17 shown in FIG. (10) is performed by the formula for the inverse calculation of (10), and the luminance Y _exp,1st is obtained.

Next, the expansion processing unit 32 performs the _inverse processing of the reference white level compression processing unit 16 shown in FIG. ) is performed to obtain the luminance Y _exp,2nd .

In other words, the extension processing unit 32 determines that the value of the HLG video signal corresponding to the SDR video signal with respect to the luminance Y in the extension processing considering the color reproduction of the highlight and the reference white level is about 95 of the white level of the SDR video signal. % from a predetermined value smaller than the value of the reference white level 75% of the HLG video signal to the upper limit value through the value of the reference white level 75%. Processing is performed to obtain characteristics in which the white level and the white level of the SDR image correspond.

The HLG luminance/light conversion unit 33 receives the luminance Y _exp,2nd from the expansion processing unit 32 and the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 31 . Then, the HLG luminance/light converter 33 obtains tristimulus values X _exp and Z _exp from the luminance Y _exp,2nd using the chromaticity coordinates x and y.

The HLG luminance/light converter 33 obtains the HLG display light signal Fdg from the luminance Y _exp,2nd and the tristimulus values X _exp , Z _exp . The HLG luminance/light converter 33 outputs the HLG display light signal Fdg to the inverse gain processor 34 . The HLG luminance/light conversion unit 33 corresponds to the tristimulus value and chromaticity conversion unit 12 shown in FIG. 1 and performs the opposite processing.

The inverse gain processing unit 34 receives the HLG display light signal Fdg from the HLG luminance/light conversion unit 33 and also receives _a preset gain value k1. Then, the reverse gain processing unit 34 multiplies the display light signal _Fdg by the reciprocal of the gain value k1 to perform reverse gain processing in consideration of the skin level to obtain the display light signal Fd. Here, the inverse gain processing considering the skin level is processing for obtaining characteristics corresponding to the skin level of the HLG video signal and the skin level of the SDR video signal. The inverse gain processor 34 outputs the display optical signal Fd to the HLG light/video converter 35 . The inverse gain processing unit 34 corresponds to the gain processing unit 11 shown in FIG. 1 and performs the opposite processing.

The HLG light/video conversion unit 35 receives the display light signal Fd from the inverse gain processing unit 34 and converts the display light signal Fd into the HLG video signal E _h ' by the inverse function of the EOTF of the HLG video. The HLG light/video converter 35 then outputs an HLG video signal E _h '. The HLG light/video conversion section 35 corresponds to the HLG video/light conversion section 10 shown in FIG. 1, and performs the opposite processing.

As a result, the signal level of the person's skin can be maintained, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed.

[Embodiment 2: Video signal conversion device that performs inverse conversion]
Next, a device for performing inverse conversion of the video signal conversion device 2 of the second embodiment will be described. This apparatus uses a fitting function that includes calculations that take into consideration the color reproduction of highlights, the reference white level, and the human skin level when converting an SDR image into an HLG image.

As a result, the signal level of the person's skin can be maintained, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed. Also, the problem of signal discontinuity caused by the video signal conversion device 3 can be solved, continuous characteristics can be obtained, and banding in highlight areas can be improved.

FIG. 15 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device 2 of the second embodiment. The video signal conversion device 4 includes an SDR video/light conversion section 40, a tristimulus value and chromaticity conversion section 41, an extension processing section 42, an HLG luminance/light conversion section 43, and an HLG light/video conversion section 44. .

The SDR video/optical converter 40 receives the SDR video signal E _s ', performs the same processing as the SDR video/optical converter 30 shown in FIG. Output to the degree conversion unit 41 . The SDR video/optical conversion section 40 corresponds to the SDR optical/video conversion section 24 shown in FIG. 8 and performs the opposite processing.

The tristimulus value and chromaticity conversion unit 41 receives the display light signal Fds from the SDR video/light conversion unit 40 and performs the same processing as the tristimulus value and chromaticity conversion unit 31 shown in FIG. Then, the tristimulus value and chromaticity conversion unit 41 outputs the luminance Y to the extension processing unit 42 and outputs the chromaticity coordinates x, y to the HLG luminance/light conversion unit 43 . The tristimulus value and chromaticity conversion unit 41 corresponds to the SDR luminance/light conversion unit 23 shown in FIG. 8 and performs the opposite processing.

The expansion processing unit 42 inputs the luminance Y from the tristimulus value and chromaticity conversion unit 41, and applies a predetermined inverse fitting function to the luminance Y based on the preset gain value k1 and the SDR knee _point Y _SDRkp . The luminance Y _exp is obtained by performing the processing by . The extension processing unit 42 then outputs the luminance Y _exp to the HLG luminance/light conversion unit 43 . The predetermined inverse fitting function is a function that considers the color reproduction of highlights, the reference white level, and the human skin level. The expansion processing unit 42 corresponds to the compression processing unit 22 shown in FIG. 8 and performs the reverse processing.

Specifically, the expansion processing unit 42 performs expansion processing (indexing processing) and inverse gain processing on the luminance Y according to the following equation using an inverse fitting function that realizes the characteristics of the dotted line shown in FIG. to find the luminance Y _exp .

The inverse fitting function that realizes the dotted line characteristic shown in FIG. 10 is a function for obtaining the HLG display luminance on the horizontal axis with respect to the SDR display luminance on the vertical axis. The expression (25) is an expression for performing an inverse operation to the expression (17) used by the compression processing unit 22 shown in FIG.

The expansion processing unit 42 performs an inverse gain process of multiplying the luminance Y by the reciprocal of _a gain value k1 set in advance in a region where the luminance Y is lower than the SDR knee point Y _SDRkp , and linearizes the luminance Y _exp is calculated (the upper equation of the above equation (25)).

The upper expression of the above equation (25) is represented by the solid line in FIG. 10 in the region where the luminance Y is lower than the SDR knee point Y _SDRkp (in the region from the origin to the knee point of point d shown in FIG. 10). The characteristic of the prior art is represented by the characteristic of a straight line from the origin to the point d indicated by the dotted line, and the inverse gain processing is shown for decreasing the luminance of the SDR display on the vertical axis. This gives the linearized luminance Y _exp .

The expansion processing unit 42 applies the correction values k ₂ , k ₃ , k ₄ and the HLG knee point Y _HLGkp to the luminance Y in a region where the luminance Y is equal to or higher than the SDR knee point Y _SDRkp . Calculate _exp (the lower expression of the above expression (25)).

The lower expression of the above equation (25) is represented by the dotted line in FIG. 10 in the area where the luminance Y is equal to or higher than the SDR knee point Y _SDRkp (in the area from the knee point d to the point c shown in FIG. 10). Like the characteristic, it shows the indexing process including the d point knee point, a point and c point. This gives the indexed luminance Y _exp .

By the exponentialization process and the inverse gain process, the brightness Y _exp considering the color reproduction of the highlight, the reference white level and the human skin level is obtained from the tristimulus values and the brightness Y calculated by the chromaticity conversion unit 41. be able to.

That is, the extension processing unit 42 performs the extension processing (exponentialization processing) and the inverse gain processing using the inverse fitting function so that the value of the HLG video signal corresponding to the SDR video signal is the white value of the SDR video signal with respect to the luminance Y. An indexing process for obtaining increasing characteristics for a region from a predetermined value smaller than the reference white level 75% of the HLG video signal corresponding to a level of about 95% to the upper limit value through the reference white level 75% value. and a calculation for obtaining characteristics corresponding to the reference white level of the HLG video and the white level of the SDR video, and further, the skin level Vh _skin of the HLG video signal and the skin level Vs _skin of the SDR video signal are calculated. performs inverse gain processing to obtain characteristics corresponding to .

The HLG luminance/light conversion unit 43 receives the luminance Y _exp from the expansion processing unit 42 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 41 . Then, the HLG luminance/light converter 43 obtains tristimulus values X _exp and Z _exp from the luminance Y _exp using the chromaticity coordinates x and y.

The HLG luminance/light converter 43 obtains the HLG display light signal Fd from the luminance Y _exp and the tristimulus values X _exp and Z _exp . The HLG luminance/light converter 43 outputs the HLG display light signal Fd to the HLG light/video converter 44 . The HLG luminance/light conversion unit 43 corresponds to the tristimulus value and chromaticity conversion unit 21 shown in FIG. 8, and performs reverse processing.

The HLG light/video converter 44 receives the display light signal Fd from the HLG luminance/light converter 43, performs the same processing as the _HLG light/video converter 35 shown in FIG. to output The HLG light/video conversion section 44 corresponds to the HLG video/light conversion section 20 shown in FIG. 8 and performs the opposite processing.

As a result, the signal level of the person's skin can be maintained, the white level of the telop does not change, and furthermore, the overexposure of highlights can be suppressed. Also, the HLG video signal E _h ' has a continuous characteristic, and the banding in the highlight region can be improved compared to the video signal conversion device 3 .

[Embodiment 3: Video signal converter]
Next, the configuration and processing of the video signal conversion device according to the third embodiment will be described. As described above, the third embodiment uses a fitting function similar to that of the second embodiment when converting an HLG image into an SDR image, and performs crosstalk matrix processing for reducing variations in luminance for each RGB color component. I do. Thus, in addition to the effect of the second embodiment, it is possible to suppress hue change due to hard clipping of a specific color component in highlights, and to sufficiently realize color reproduction of highlights.

FIG. 16 is a block diagram showing a configuration example of the video signal conversion device of Example 3, and FIG. 17 is a flow chart showing a processing example of the video signal conversion device of Example 3. As shown in FIG. This video signal conversion device 5 includes an HLG video/light conversion section 50, a crosstalk matrix processing section 51, a tristimulus value and chromaticity conversion section 52, a compression processing section 53, an SDR luminance/light conversion section 54, an inverse crosstalk matrix A processing unit 55 and an SDR light/video conversion unit 56 are provided.

Comparing the video signal conversion device 2 of the second embodiment shown in FIG. They are common in that tristimulus value and chromaticity conversion units 21 and 52, compression processing units 22 and 53, SDR luminance/light conversion units 23 and 54, and SDR light/video conversion units 24 and 56 are provided. On the other hand, the video signal conversion device 5 includes a crosstalk matrix processing unit 51 and an inverse crosstalk matrix processing unit 55, and is different from the video signal conversion device 2 which does not include these components.

The HLG video/optical converters 20 and 50 perform similar processing. Tristimulus value and chromaticity converters 21, 52, compression processors 22, 53, SDR luminance/light converters 23, 54, and SDR light/video converters 24, 56 also perform similar processing.

The HLG video/optical converter 50 receives an HLG video signal E _h ', which is a video signal of an HLG image (step S1701). 1 and the HLG video/optical conversion unit 20 shown in FIG. 8, the HLG video/optical conversion unit 50 converts the HLG video signal E from the EOTF of the HLG video. _h ' is converted into an HLG display light signal Fd, which is a linear signal of display light (step S1702). The HLG video/light converter 50 outputs the HLG display optical signal Fd to the crosstalk matrix processor 51 .

The crosstalk matrix processor 51 receives the display optical signal Fd from the HLG video/optical converter 50 . Then, the crosstalk matrix processing unit 51 performs crosstalk matrix processing for reducing variations in luminance for each RGB color component in the display light signal Fd based on a preset parameter ε. _xHLG is obtained (step S1703). The crosstalk matrix processor 51 outputs the display light signals RGB _xHLG to the tristimulus value and chromaticity converter 52 .

The tristimulus value and chromaticity conversion unit 52 receives the display light signal RGB _xHLG from the crosstalk matrix processing unit 51 . 1 and the tristimulus value and chromaticity converter 21 shown in FIG. 8, the tristimulus value and chromaticity converter 52 converts the display light signals RGB _xHLG is converted into tristimulus values X _HLG Y _HLG Z _HLG and chromaticity coordinates x, y as color information (step S1704). Then, the tristimulus value and chromaticity conversion unit 52 outputs the luminance Y _HLG to the compression processing unit 53 and outputs the chromaticity coordinates x, y to the SDR luminance/light conversion unit 54 .

In this case, the tristimulus value and chromaticity conversion unit 52 converts the display light signal RGB _xHLG ={R _xHLG , G _xHLG , B _xHLG } into the tristimulus values X _HLG Y _HLG Z _HLG using the formula (7) ) is used. Specifically, an equation obtained by replacing X, Y, Z, Rdg, Gdg, and Bdg in Equation (7) with X _HLG , Y _HLG , Z _HLG , R _xHLG , G _xHLG , and B _xHLG is used. Also, the tristimulus value and chromaticity conversion unit 52 uses the above equation (8) when converting the tristimulus values X _HLG Y _HLG Z _HLG to the chromaticity coordinates x, y. Specifically, an equation obtained by replacing X, Y, and Z in equation (8) with X _HLG , Y _HLG , and Z _HLG is used.

The compression processing unit 53 inputs the luminance Y _HLG from the tristimulus value and chromaticity conversion unit 52 . Then, similarly to the compression processing unit 22 shown in FIG. 8, the compression processing unit 53 performs compression processing on the luminance Y _HLG using a predetermined fitting function, based on _a preset gain value k1, etc. Y _SDR is obtained (step S1705). The compression processor 53 then outputs the luminance Y _SDR to the SDR luminance/light converter 54 . The predetermined fitting function is a function that includes operations that consider the human skin level, the reference white level, and the color reproduction of highlights.

The SDR luminance/light conversion unit 54 receives the luminance Y _SDR from the compression processing unit 53 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 52 . 1 and the SDR luminance/light conversion unit 23 shown in FIG. 8, the SDR luminance/light conversion unit 54 converts the luminance using the chromaticity coordinates x and y. Tristimulus values X _SDR and Z _SDR are obtained from Y _SDR (step S1706).

In this case, the SDR luminance/light conversion unit 54 uses the above equation (21) when obtaining the tristimulus values X _SDR and Z _SDR from the luminance Y _SDR using the chromaticity coordinates x and y. Specifically, equations obtained by replacing X _comp , Z _comp and Y _comp in equation (21) with X _SDR , Z _SDR and Y _SDR are used.

The SDR luminance/light converter 54 converts the luminance Y _SDR and tristimulus values X _SDR , Z The _SDR display optical signal RGB _xSDR ={R _xSDR , G _xSDR , B _xSDR } is obtained from the SDR (step S1707). The SDR luminance/light converter 54 then outputs the SDR display optical signal RGB _xSDR to the inverse crosstalk matrix processor 55 .

In this case, the SDR luminance/light converter 54 obtains the SDR display light signal RGB _xSDR ={R _xSDR , G _xSDR , B _xSDR } from the luminance Y _SDR and the tristimulus values X _SDR and Z _SDR . Equation (22) is used. Specifically, a formula obtained by replacing Rds, Gds, Bds, X _comp , Y _comp and Z _comp in the above formula (22) with R _xSDR , G _xSDR , B _xSDR , X _SDR , Y _SDR and Z _SDR is used. .

The inverse crosstalk matrix processor 55 inputs the SDR display optical signal RGB _xSDR from the SDR luminance/light converter 54 . Then, the inverse crosstalk matrix processing unit 55 performs processing that is the reverse of the crosstalk matrix processing for reducing luminance variations for each RGB color component by the crosstalk matrix processing unit 51, based on a preset parameter ε. I do. In other words, the inverse crosstalk matrix processing unit 55 performs inverse crosstalk matrix processing for restoring luminance variations for each RGB color component, and obtains the SDR display light signal Fds (step S1708). The parameter ε is the same as the parameter ε used in the crosstalk matrix processing section 51 . The inverse crosstalk matrix processor 55 outputs the SDR display optical signal Fds to the SDR light/video converter 56 .

The SDR light/video converter 56 receives the SDR display light signal Fds from the inverse crosstalk matrix processor 55 . 1 and the SDR light/video conversion unit 24 shown in FIG. 8, the SDR light/video conversion unit 56 uses the inverse function of the EOTF of the SDR image to convert the display The optical signal Fds is converted into an SDR video signal E _s ', which is a video signal of an SDR image (step S1709). The SDR optical/video converter 56 outputs the SDR video signal E _s ' (step S1710).

(Crosstalk matrix processing unit 51)
Next, the crosstalk matrix processing section 51 shown in FIG. 16 will be described in detail. As described above, the crosstalk matrix processing unit 51 performs crosstalk matrix processing for reducing variations in luminance for each RGB color component in the display light signal Fd, and obtains the display light signal _RGBxHLG .

The crosstalk matrix processed display light signal _RGBxHLG ={ _RxHLG , _GxHLG , _BxHLG } can be obtained by using the display light signal Fd={Rd, Gd, Bd} and a preset parameter ε as follows: Calculated by That is, the display light signal _RGBxHLG ={ _RxHLG , _GxHLG , _BxHLG } is obtained by multiplying the crosstalk matrix xM by the display light signal Fd={Rd, Gd, Bd}.

Here, the crosstalk matrix xM is represented by the following matrix, and ε is a preset user parameter whose value can be arbitrarily adjusted within the range of 0≦ε≦0.33.

The closer the parameter ε is to 0, the lower the degree of reduction in luminance variation for each _RGB color component. close to the display light signal Fd. When the parameter ε=0, no crosstalk matrix processing is performed, and the display optical signal RGB _xHLG output by the crosstalk matrix processing section 51 is the same as the display optical signal Fd input by the crosstalk matrix processing section 51 . On the other hand, the closer the parameter ε is to 0.33, the higher the extent to which the variation in luminance for each RGB color component is reduced.

In this way, the display light signal _RGBxHLG ={ _RxHLG , _GxHLG , _BxHLG } in which the variation in the color components of the display light signal Fd={Rd, Gd, Bd} is reduced is obtained by the crosstalk matrix processing. .

Note that the crosstalk matrix processing does not change the lightness L ^* in the CIELAB space (L ^* a ^* b ^* space) described later, but reduces the chroma C ^* _ab so that it approaches the L ^* axis, which is the achromatic color axis. Color coordinates a ^* and b ^* change. In other words, crosstalk matrix processing reduces variations in color components in the _RGB space, and in the L ^* a ^{* b *} space, the color coordinates a ^{* and} b ^* changes. Details will be described later with reference to FIGS. 29 to 32. FIG.

(Inverse crosstalk matrix processing unit 55)
Next, the inverse crosstalk matrix processing section 55 shown in FIG. 16 will be described in detail. As described above, the inverse crosstalk matrix processing unit 55 performs the inverse crosstalk matrix processing for reducing the luminance variation for each RGB color component by the crosstalk matrix processing unit 51 on the SDR display light signal RGB _xSDR . to obtain the SDR display optical signal Fds. In other words, the inverse crosstalk matrix processing unit 55 performs inverse crosstalk matrix processing for restoring variations in brightness for each RGB color component.

ここで、Ｆｄｓ＜０となる信号は、Ｆｄｓ＝０とする。 The inverse crosstalk matrix processed display light signal Fds={Rds, Gds, Bds} is obtained by using the display light signal _RGBxSDR ={ _RxSDR , _GxSDR , _BxSDR } and a preset parameter ε as follows: Calculated by the formula. That is, the display light signal Fds={Rds, Gds, Bds} is obtained by multiplying the inverse matrix xM ^-1 of the crosstalk matrix xM by the display light signal _RGBxSDR ={ _RxSDR , _GxSDR , _BxSDR }. be done.

Here, a signal that satisfies Fds<0 is assumed to be Fds=0.

The closer the parameter ε is to 0, the lower the degree to which the variation in luminance for each RGB color component is restored. It becomes close to the input display light signal RGB _xSDR . When the parameter ε=0, inverse crosstalk matrix processing is not performed, and the display optical signal Fds output by the inverse crosstalk matrix processing unit 55 is the same as the display optical signal RGB _xSDR input by the inverse crosstalk matrix processing unit 55. Become. On the other hand, the closer the parameter ε is to 0.33, the higher the extent to which the variation in luminance for each RGB color component is restored.

Thus, the inverse crosstalk matrix processing restores the variation reduced by the crosstalk matrix processing, and obtains the SDR display light signal Fds={Rds, Gds, Bds} in which the crosstalk matrix processing is canceled. be able to.

Before and after the inverse crosstalk matrix processing, the color coordinates a ^* and b ^* change, although the lightness L ^* in the L ^* a ^* b ^* space, which will be described later, does not change.

(Compression processing unit 53)
Next, the compression processing unit 53 shown in FIG. 16 will be described in detail. As described above, the compression processing unit 53 performs processing similar to that of the compression processing unit 22 shown in FIG. That is, the compression processing unit 53 applies a fitting function, which is a logarithmic function that considers the human skin level, the reference white level, and the color reproduction of highlights, to the luminance Y _HLG based on a preset gain value k ₁ and the like. Compression processing is performed, and luminance Y _SDR is obtained.

The compression processing unit 53 obtains the luminance Y _SDR by performing gain processing and compression processing (logarithmization processing) on the luminance Y _HLG according to the following equation using a fitting function. This formula corresponds to the above formula (17).

Here, the parameters k ₁ , k ₂ , k ₃ , k ₄ , Y _HLGkp are parameters having the same meaning as explained in the above equation (17). As described above, k1 is _a gain value that considers the skin level, that is, a parameter that is calculated based on the HLG and SDR skin levels. As described above, k ₂ is a correction value for matching the slopes of the tangent lines of the linear signal and the logarithmic nonlinear signal at the inflection point Y=Y _HLGkp , that is, the continuity condition of the first derivative value at the knee point. is a parameter.

_k3 is a correction value determined by the constraint condition that a linear signal of HLG 100% corresponds to a linear signal of SDR 109%, or a linear signal of HLG 75% corresponds to SDR 100% in the explanation of the above equation (17). did. Here, _k3 is a correction value obtained from the constraint condition of the reference white level. That is, k ₃ is a correction value obtained from the constraint that the reference white level Y _HLG75% of HLG75% corresponds to the white level Y _SDRwp of SDR.

k4 is a correction value for matching the contact values of the linear signal and the logarithmic non _- linear signal, that is, the correction value calculated from the continuous condition of the knee point values. Y _HLGkp is the knee point of the HLG display luminance signal corresponding to the SDR knee point Y _SDRkp , which is the knee point of the SDR display luminance signal, as described above. These five parameters are unknowns, but it is possible to reduce these unknowns to one of the correction values _k3 .

Here, the gain value k ₁ and the SDR knee point Y _SDRkp are set in advance by the user, and the correction values k ₂ , k ₃ , k ₄ and the HLG knee point Y _HLGkp are calculated by the compression processing unit 53 using formulas described later. shall be The gain value k ₁ , the correction values k ₂ , k ₃ , k ₄ and the HLG knee point Y _HLGkp may be preset by the user.

(gain value _k1 )
As described in the second embodiment, the gain value k1 is _a parameter preset by the user based on the correspondence between the HLG skin level and the SDR skin level.

As shown in FIG. 4, the skin level Vh _skin of the HLG video signal is approximately 50% of that of the HLG video signal, while the skin level Vs _skin of the SDR video signal is approximately 67% of that of the SDR video signal. According to the characteristics of the prior art, the skin level of the SDR video signal is about 55%, which corresponds to the skin level Vh _skin of the HLG video signal of about 50%. Therefore, the skin level of the SDR image in the prior art is lower than the skin level of the SDR image in the example considering the skin level.

In other words, in order to consider the skin level, it is necessary to perform gain processing for matching the skin level. Therefore, as the gain value k1, the value of Gain shown in the above equation ( ₄ ) or the above equation (5) is used.

Here, the HLG knee point Y _HLGkp is determined from the SDR knee point Y _SDRkp and the gain value k ₁ when converting from HLG to SDR, as in the following equation.

The SDR knee point Y _SDRkp is a value obtained by converting the knee point in the SDR video signal into SDR display luminance. When this SDR knee point Y _SDRkp is set to a high value, a signal with HLG 75% or more is likely to be compressed to SDR 109%, which is the upper limit of the video signal of SDR knee point Y _SDRkp , and signal rounding processing is likely to occur. Become. Therefore, the SDR knee point Y _SDRkp is preferably higher than the skin level Vs _skin of the SDR video signal shown in FIG. 4 as a reference. Therefore, the range of values that the SDR knee point Y _SDRkp can take may be set as a parameter arbitrarily set by the user, from SDR 80% or more to 95%.

₍ correction value k2)
Next, the correction value _k2 will be explained. As described above, the correction value k2 is a parameter calculated from the continuity condition of the _first derivative value at the knee point. Processing different from the correction value k2 calculation processing described in the _second embodiment will be described below. This process is also applied to the second embodiment, and the process of the second embodiment is also applied to the fourth embodiment.

At the knee point, the first derivative values of SDR and HLG match, so the following equation is derived from the upper and lower equations of Equation (29).

この補正値ｋ₂は、補正値ｋ₃が決定されると、前記式（３２）にて一意的に決定される。 The following equation is derived by arranging equation (31) using the unknown correction value k ₃ , the known gain value k ₁ , and the HLG knee point Y _HLGkp calculated by equation (30).

This correction value k2 is uniquely determined by the above equation ₍ 32) when the correction value _k3 is determined.

₍ correction value k4)
Next, the correction value _k4 will be explained. As described above, the correction value _k4 is a parameter calculated from the continuous condition of the knee point values. Processing different from the correction value k4 calculation processing described in the _second embodiment will be described below. This process is also applied to the second embodiment, and the process of the second embodiment is also applied to the fourth embodiment.

補正値ｋ₂は、前述のとおり、補正値ｋ₃が決定されると一意的に決定されるため、補正値ｋ₄も、補正値ｋ₃が決定されると、前記式（３３）にて一意的に決定される。つまり、補正値ｋ₂，ｋ₄は、補正値ｋ₃が決定されることで、一意的に決定される。 In the tone mapping curve, which is the characteristic of the lower expression of the above expression (29), the gain value k ₁ and the SDR knee point Y _SDRkp set by the user, and the HLG knee point Y _HLGkp calculated by the above expression (30) are The following formula is derived by rearranging by using

Since the correction value k2 is uniquely determined when the correction value _k3 is determined as described above _, the correction value _k4 is also determined by the above equation ₍ 33) when the correction value k3 is determined. Uniquely determined. That is, the correction values k ₂ and k ₄ are uniquely determined by determining the correction value k ₃ .

(correction value _k3 )
Next, the correction value _k3 will be explained. As described above, the correction value _k3 is a parameter obtained from the constraint condition of the reference white level, that is, the parameter obtained from the constraint condition that the reference white level Y _HLG75% of HLG75% corresponds to the white level Y _SDRwp of SDR. is. This process is also applied to the second embodiment, and the process of the second embodiment is also applied to the fourth embodiment.

前記式（３４）において、左辺がＳＤＲのリニア信号の変化量を示し、右辺が前記式（２９）の下段の式にて得られる変化量を示す。 The correction value k ₃ is the knee point HLG knee point Y _HLGkp and SDR knee point Y _SDRkp (Y _HLGkp , Y _SDRkp ), and the reference white level point HLG75% reference white level Y _HLG75% and SDR white point Y HLG75%. Between levels Y _SDRwp (Y _HLG75% , Y _SDRwp ), the amount of change in the linear signal of the SDR and the amount of change obtained by the lower expression of the above equation (29) are calculated by the following equation.

In the above equation (34), the left side indicates the amount of change in the SDR linear signal, and the right side indicates the amount of change obtained by the lower expression of the above equation (29).

In this way, the compression processing unit 53 uses the gain value k ₁ and the SDR knee point Y _SDRkp preset by the user to obtain the correction values k ₂ , k ₃ , Calculate _{k4 and HLG knee point Y HLGkp .} From this, the compression processing unit 53 can set the fitting function of the above equation (29), and using the fitting function, performs gain processing and compression processing (logarithmization processing) on the luminance Y _HLG , Determine the luminance Y _SDR .

For example, the SDR knee point Y _SDRkp =80%, the skin level Vh _skin =50% of the HLG video signal corresponds to the skin level Vs _skin =67% of the SDR video signal, and the constraint condition for the reference white level is HLG 75%. Assume a case where an SDR of 96% is supported. In this case, the five parameters are HLG knee point Y _HLGkp =77.59235745, gain value k1 _{= 0.75439191} , correction value k2 =17.1208962, correction value _k3 = _0.70751034 , correction value k4 =79.58220851.

FIG. 25 is _a diagram showing the characteristics of the display luminance when the fitting function set by the gain value k1 and the like in the above example is applied, and corresponds to the example of applying the dotted line fitting function shown in FIG. . The horizontal axis indicates the HLG display luminance [cd/m ² ], that is, the HLG luminance Y _HLG that is the input data of the compression processing unit 53, and the vertical axis indicates the SDR display luminance [cd/m ² ], that is, the compression processing unit 53 shows the luminance Y _SDR of the SDR which is the output data of 53. FIG.

The characteristics shown in FIG. 25 are obtained when the compression processing unit 53 performs processing on luminance Y _HLG , which is input data, using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights. 2 shows the relationship between luminance Y _HLG and luminance Y _SDR .

FIG. 26 is a diagram showing video signal characteristics corresponding to the display luminance characteristics shown in FIG. 25, and corresponds to an example in which the dotted line fitting function shown in FIG. 13 is applied. The horizontal axis indicates the level [%] of the HLG video signal, and the vertical axis indicates the level [%] of the SDR video signal.

The characteristics shown in FIG. 26 are the _{HLG video signal corresponding to the luminance Y HLG and} the _SDR It shows the relationship between video signals.

As described above, according to the video signal conversion device 5 of the third embodiment, the HLG video/optical converter 50 converts the HLG video signal E _h ' into the display optical signal Fd using the EOTF of the HLG video. Then, the crosstalk matrix processing unit 51 performs crosstalk matrix processing for reducing variations in luminance for each RGB color component in the display light signal Fd, and obtains the display light signal _RGBxHLG .

A tristimulus value and chromaticity conversion unit 52 converts the display light signals RGB _xHLG into tristimulus values XYZ and chromaticity coordinates x, y. The compression processing unit 53 performs processing on the luminance Y _HLG using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights based on a preset gain value k ₁ or the like. Determine the luminance Y _SDR .

The SDR luminance/light converter 54 obtains tristimulus values X _{SDR and Z SDR from the luminance Y SDR using the chromaticity coordinates x and y, and converts the luminance Y SDR and the tristimulus values X SDR and Z SDR to SDR} . Determine the display light signal RGB _xSDR .

The inverse crosstalk matrix processing unit 55 performs the reverse processing of the crosstalk matrix processing for reducing the luminance variation for each RGB color component by the crosstalk matrix processing unit 51, that is, reduces the luminance variation for each RGB color component. Inverse crosstalk matrix processing for restoration is performed to obtain the SDR display light signal Fds. Then, the SDR optical/video converter 56 converts the display optical signal Fds into the SDR video signal E _s ' by the inverse function of the EOTF of the SDR video.

As a result, compression processing is performed using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights. Without this, it is possible to suppress overexposure in highlights.

Furthermore, since crosstalk matrix processing is performed, compression processing is performed in a state in which variations in luminance for each RGB color component are reduced, and the degree of hard clipping of specific color components (especially blue components) in highlights is reduced. can be suppressed.

Therefore, in addition to the effects of the second embodiment, it is possible to suppress hue change due to hard clipping of a specific color component in highlights, and to sufficiently realize color reproduction of highlights. In this case, in the crosstalk matrix processing unit 51 and the inverse crosstalk matrix processing unit 55, the degree of reduction in luminance variation for each color component is changed according to the value of the parameter ε. It is possible to adjust accordingly.

16, the _{SDR luminance} /light converter 54 of the video signal conversion device 5 shown in _{FIG .} Formulas in which Rds, Gds, Bds, X _comp , Y _comp and Z _comp in (22) are replaced with R _xSDR , G _xSDR , B _xSDR , X _SDR , Y _SDR and Z _SDR are used. In other words, an inverse matrix of a matrix for conversion from wide color gamut RGB to tristimulus values is used.

On the other hand, the SDR luminance/light converter 54 may use an inverse matrix for converting from narrow color gamut RGB to tristimulus values. In this case, the SDR luminance/light converter 54 obtains the SDR display light signal RGB _xSDR ={R _xSDR , G _xSDR , B _xSDR } from the luminance Y _SDR and the tristimulus values X _SDR and Z _SDR . Equation (24) is used. Specifically, a formula obtained by replacing Rds, Gds, Bds, X _comp , Y _comp and Z _comp in the above formula (24) with R _xSDR , G _xSDR , B _xSDR , X _SDR , Y _SDR and Z _SDR is used. .

As a result, the tristimulus value and chromaticity conversion unit 52 uses a matrix for converting wide color gamut RGB to tristimulus values, and the SDR luminance/light conversion unit 54 converts narrow color gamut RGB to tristimulus values. Wide to narrow gamut conversion can be done by using the inverse of the matrix to convert and converting from tristimulus values back to RGB.

[Embodiment 4: Video signal converter]
Next, the configuration and processing of the video signal conversion device of the fourth embodiment will be described. As described above, in converting an HLG image into an SDR image, the fourth embodiment uses the same fitting function as in the second embodiment, performs the same crosstalk matrix processing as in the third embodiment, and sets the reference white level Chroma correction processing is performed to make the above colors closer to achromatic colors or white. Thus, in addition to the effects of the third embodiment, it is possible to realize color reproduction of achromatic or near-white highlights. That is, in the fourth embodiment, color reproduction of highlights can be realized more effectively than in the third embodiment.

Conventionally, in the color reproduction of highlights, there are cases where the designer intentionally sets the colors to be achromatic or white. Therefore, in the fourth embodiment, in order to reflect the creator's intention in the same manner as in the conventional art, color reproduction of achromatic or near-white highlights is realized.

FIG. 18 is a block diagram showing a configuration example of a video signal conversion device according to the fourth embodiment, and FIG. 19 is a flowchart showing a processing example of the video signal conversion device according to the fourth embodiment. This video signal conversion device 6 includes an HLG video/light conversion section 60, a crosstalk matrix processing section 61, an HLG light/tristimulus value conversion section 62, a chroma processing section 63, an HLG chromaticity conversion section 64, a compression processing section 65, An SDR luminance/light conversion section 66 , an inverse crosstalk matrix processing section 67 and an SDR light/video conversion section 68 are provided.

Comparing the video signal conversion device 5 of the third embodiment shown in FIG. Crosstalk matrix processing units 51 and 61, compression processing units 53 and 65, SDR luminance/light conversion units 54 and 66, inverse crosstalk matrix processing units 55 and 67, and SDR light/video conversion units 56 and 68. common in On the other hand, the video signal conversion device 6 includes an HLG light/tristimulus value conversion unit 62 and an HLG chromaticity conversion unit 64 instead of the tristimulus value and chromaticity conversion unit 52 of the video signal conversion device 5, and further performs chroma processing. It differs from the video signal conversion device 5 in that it includes a unit 63 .

HLG video/light converters 50, 60, crosstalk matrix processors 51, 61, compression processors 53, 65, SDR luminance/light converters 54, 66, inverse crosstalk matrix processors 55, 67, and SDR light/video The converters 56 and 68 perform similar processing.

The HLG video/optical converter 60 receives an HLG video signal E _h ', which is a video signal of an HLG image (step S1901). 16, the HLG video/light conversion unit 60 converts the HLG video signal E _h ' into an HLG display signal, which is a linear signal of display light, according to the EOTF of the HLG video. It is converted into an optical signal Fd (step S1902). The HLG video/light converter 60 outputs the HLG display optical signal Fd to the crosstalk matrix processor 61 .

The crosstalk matrix processor 61 receives the display optical signal Fd from the HLG video/optical converter 60 . 16, the crosstalk matrix processing unit 61 corrects variations in brightness for each RGB color component in the display light signal Fd based on a preset parameter ε. Crosstalk matrix processing for reducing crosstalk is performed to obtain display light signals RGB _xHLG (step S1903). The crosstalk matrix processor 61 outputs the display light signal RGB _xHLG to the HLG light/tristimulus value converter 62 .

The HLG light/tristimulus value converter 62 receives the display light signal RGB _xHLG from the crosstalk matrix processor 61 . Then, the HLG light/tristimulus value converter 62 converts the display light signal RGB _xHLG into the tristimulus values X _HLG Y _HLG Z _HLG in the same way as the tristimulus value and chromaticity converter 52 shown in FIG. (Step S1904). The HLG light/tristimulus value converter 62 outputs the tristimulus values X _HLG Y _HLG Z _HLG to the chroma processor 63 .

The chroma processor 63 receives the tristimulus values X _HLG Y _HLG Z _HLG from the HLG light/tristimulus value converter 62 . Then, the chroma processing unit 63 performs chroma correction processing to bring colors equal to or higher than the reference white level closer to an achromatic color or white based on a preset parameter σ, and tristimulus values X _HLG Y after chroma correction processing _HLG Z _HLG is obtained (step S1905). The chroma processing unit 63 then outputs the tristimulus values X _HLG Y _HLG Z _HLG after the chroma correction processing to the HLG chromaticity conversion unit 64 .

The HLG chromaticity conversion unit 64 receives the tristimulus values X _HLG Y _HLG Z _HLG after chroma correction processing from the chroma processing unit 63 . Then, the HLG chromaticity conversion unit 64 converts the tristimulus values X _HLG Y _HLG Z _HLG after chroma correction processing into chromaticity coordinates x, y as color information (step S1906). Then, the HLG chromaticity converter 64 outputs the luminance Y _HLG to the compression processor 65 and outputs the chromaticity coordinates x, y to the SDR luminance/light converter 66 .

The compression processing unit 65 inputs the luminance Y _HLG from the HLG chromaticity conversion unit 64 . Then, similarly to the compression processing unit 53 shown in FIG. 16, the compression processing unit 65 performs compression processing on the luminance Y _HLG using a predetermined fitting function based on a preset gain value k ₁ and the like. Y _SDR is obtained (step S1907). The compression processor 65 then outputs the luminance Y _SDR to the SDR luminance/light converter 66 .

The SDR luminance/light converter 66 receives the luminance Y _SDR from the compression processor 65 and the chromaticity coordinates x, y from the HLG chromaticity converter 64 . 16, the SDR luminance/light converter 66 converts the tristimulus values X _SDR and Z _SDR from the luminance Y _SDR using the chromaticity coordinates x and y. (step S1908).

The _{SDR luminance} /light converter 66, like the _{SDR luminance} /light converter 54 shown in FIG _. , G _xSDR , B _xSDR } (step S1909). The SDR luminance/light converter 66 then outputs the SDR display optical signal RGB _xSDR to the inverse crosstalk matrix processor 67 .

The inverse crosstalk matrix processor 67 receives the SDR display optical signal RGB _xSDR from the SDR luminance/light converter 66 . Similar to the inverse crosstalk matrix processing unit 55 shown in FIG. 16, the inverse crosstalk matrix processing unit 67 performs the crosstalk processing for each RGB color component by the crosstalk matrix processing unit 61 based on a preset parameter ε. Inverse processing of the crosstalk matrix processing for reducing luminance variations is performed. That is, the inverse crosstalk matrix processing unit 67 performs inverse crosstalk matrix processing for restoring luminance variations for each RGB color component, and obtains the SDR display light signal Fds (step S1910). The parameter ε is the same as the parameter ε used in the crosstalk matrix processing section 61 . The inverse crosstalk matrix processor 67 outputs the SDR display optical signal Fds to the SDR light/video converter 68 .

The SDR light/video converter 68 receives the SDR display light signal Fds from the inverse crosstalk matrix processor 67 . 16, the SDR light/video conversion unit 68 converts the display light signal Fds into an SDR video signal, which is a video signal of the SDR image, by an inverse function of the EOTF of the SDR image. It is converted into a signal E _s ' (step S1911). The SDR light/video converter 68 outputs the SDR video signal E _s ' (step S1912).

(Chroma processor 63)
Next, the chroma processor 63 shown in FIG. 18 will be described in detail. As described above, the chroma processing unit 63 performs chroma correction processing to bring colors equal to or higher than the reference white level closer to an achromatic color or white based on the preset parameter σ. _{Find HLG} Y _HLG Z _HLG .

FIG. 20 is a block diagram showing a configuration example of the chroma processing section 63, and FIG. 21 is a flow chart showing a processing example of the chroma processing section 63. As shown in FIG. The chroma processing section 63 includes a color space conversion section 57 , a chroma correction section 58 and a color space inverse conversion section 59 .

The color space converter 57 inputs the tristimulus values X _HLG Y _HLG Z _HLG from the HLG light/tristimulus value converter 62 (step S2101). Then, the color space conversion unit 57 converts the space of the tristimulus values X _HLG Y _HLG Z _HLG (tristimulus value space) into the L ^* a ^* b ^* space, which is the CIELAB space, and converts the lightness L ^* and color coordinates a ^* and b ^* are obtained (step S2102).

Here, X _n , Y _n , Z _n are the tristimulus values on the perfect diffuse reflection surface. In the case of HLG, the brightness Y at 75% HLG corresponds to Y _n , so if the peak brightness is 1000 [cd/m ² ], then X _n =192.9312, Y _n =203, and Z _n =221.0467. . Also, the internal function f in the above equation (35) is obtained by the following equation. The parameter δ is a constant with δ=6/29.

The color space conversion section 57 outputs the lightness L ^* to the color space inverse conversion section 59 and outputs the color coordinates a ^* and b ^* to the chroma correction section 58 .

The chroma correction unit 58 inputs the color coordinates a ^* and b ^* from the color space conversion unit 57, performs chroma correction in the area above the reference white level based on the parameter σ, and converts the color coordinate a ^* after the chroma correction processing. _Cor and b ^* _cor are obtained (step S2103).

In the chroma correction process, in the L ^* a ^* b ^* space, the lightness corresponding to the HLG reference white level is set to L ^* _wp , and the chroma C ^* _ab at the lightness L ^* equal to or higher than the lightness L ^* _wp is corrected at the high lightness L ^*. This is a process of correcting so as to approach the achromatic color axis as it becomes larger.

Specifically, the chroma correction unit 58 calculates the chroma C ^* _ab and the hue angle _hab from the color coordinates a ^* and b ^* using the following equations.

Then, the chroma correction unit 58 multiplies the chroma C ^* _ab by a correction factor f _cor based on the parameter σ, and obtains the chroma C ^* _ab,cor in which chroma having a lightness equal to or higher than the reference white level is corrected. . In order to prevent hue change, the chroma correction unit 58 adjusts the color coordinates a ^* _cor , b ^* after the chroma correction processing based on the corrected chroma C ^* _ab,cor while maintaining the hue angle h _ab at the same value. Calculate _cor .

In this case, the chroma correction unit 58 obtains the correction factor f _cor using the following formula, and obtains the corrected chroma C ^* _ab,cor .

L ^* _wp is the brightness corresponding to the HLG reference white level, and L ^* _max is the brightness corresponding to the upper limit value of the HLG video signal. If the lightness L ^* _wp corresponding to the HLG reference white level is 100 and the HLG peak luminance is 1000 [cd/m ² ], the lightness L ^* _max corresponding to the upper limit of the HLG video signal is 181.37522735. becomes. A parameter σ is a user parameter that can be arbitrarily adjusted to a real number satisfying σ≧0. When σ≧1 and f _cor <0, f _cor =0.

The correction factor f _cor is calculated based on the parameter σ, the lightness L ^* _wp corresponding to the HLG reference white level, and the lightness L ^* _max corresponding to the upper limit of the HLG video signal, as shown in Equation (38) above. .

If the lightness L ^* is less than or equal to the lightness L ^* _wp corresponding to the HLG reference white level, the correction factor f _cor is 1 and the corrected chroma C ^* _ab,cor is equal to the uncorrected chroma C ^* _ab . On the other hand, when the lightness L ^* exceeds the lightness L ^* _wp corresponding to the HLG reference white level, the correction factor f _cor approaches 0 from 1 as the lightness L ^* increases, and the corrected chroma C ^* _{ab, cor} gradually becomes smaller than chroma C ^* _ab before correction.

The post-correction chroma C ^* _ab,cor is calculated based on the correction factor f _cor and the pre-correction chroma C ^* _ab , as in Equation (39) above. The chroma C ^* _{ab ,cor} is obtained by multiplying the correction factor f _cor based on the parameter σ by the chroma C ^* ab, because the corrected chroma C ^* _ab,cor is obtained from the uncorrected chroma C ^* _ab . is also small, and the color coordinates a ^* _cor and b ^* _cor after chroma correction processing are brought closer to the achromatic color axis or white.

ここで、前記式（４０）は、色相角ｈ_abを同じ値に保持することを示しており、これは、色相変化を防ぐため、すなわちＲＧＢの色成分のバランスを変化させないためである。 Further, the chroma correction unit 58 uses the following formula based on the hue angle hab calculated by the formula (37) and the chroma C ^* _{ab ,cor} after the chroma correction process calculated by the formula (39). Then, the color coordinates a ^* _cor and b ^* _cor after chroma correction processing are calculated.

Here, the above equation (40) indicates that the hue angle h _ab is kept at the same value, in order to prevent hue change, that is, to keep the balance of RGB color components unchanged.

The chroma correction section 58 outputs the color coordinates a ^* _cor and b ^* _cor after the chroma correction processing to the color space inverse conversion section 59 .

FIG. 22 is a bird's-eye view for explaining chroma correction processing. The horizontal axis indicates the color coordinate a ^* , and the vertical axis indicates the color coordinate b ^* . Let the position of the color coordinates a ^* and b ^* before chroma correction processing be a point α.

The chroma correction unit 58 calculates the chroma C ^* _{ab ,cor} from the ^chroma C ^* _ab based on the parameter σ ^. , the color coordinates a ^* _cor and b ^* _cor after chroma correction processing are calculated.

When the parameter σ=0, the color coordinates a ^* _cor , b ^* _cor after chroma correction processing are equal to the color coordinates a ^* , b ^* before chroma correction processing. That is, the positions of the color coordinates a ^* _cor and b ^* _cor after the chroma correction process are the same as the positions of the color coordinates a ^* and b ^* before the chroma correction process, and (a ^* ,b ^* )=( a ^* _cor , b ^* _cor ).

On the other hand, when the parameter σ>0, the color coordinates a ^* _cor , b ^* _cor after chroma correction processing have different values from the color coordinates a ^* , b ^* before chroma correction processing. When the parameter σ=1, the position of the color coordinates a ^* _cor and b ^* _cor after the chroma correction process is the point β.

In this way, since the hue angle h _ab is kept at the same value, the color coordinates a ^* _cor and b ^* _cor after the chroma correction process are obtained by a straight line between the points α and β according to the parameter σ. Take the value of any position on the line when drawn. The closer the parameter σ is to 0, the closer the color coordinates a ^* _cor and b ^* _cor after the chroma correction process are to the point α. On the other hand, the closer the parameter σ is to 1, the closer the color coordinates a ^* _cor and b ^* _cor after the chroma correction process are to the point β and to the L ^* axis, which is the achromatic color axis.

FIG. 23 is a diagram for explaining the chroma correction processing when the parameter σ is small, and FIG. 24 is a diagram for explaining the chroma correction processing when the parameter σ is large. The horizontal axis indicates chroma C _ab and the vertical axis indicates lightness L ^* .

When the parameter σ is small, the amount of decrease in chroma C _ab (the amount of decrease from chroma C ^* _ab before chroma correction processing to chroma C ^* _ab,cor after chroma correction processing) is smaller than when the parameter σ is large. Also, both when the parameter σ is small and when the parameter σ is large, when the value of chroma C ^* _ab before chroma correction processing is large (C _ab,2 ), when the value of chroma C ^* _ab before chroma correction processing is small Compared to (C _ab,1 ), the amount of decrease in chroma C _ab is large.

Here, the closer the parameter σ is to ⁰ , the less the color coordinates a ^* _cor and b ^* _{cor approach} the achromatic _axis ^. It becomes close to the color coordinates a ^* and b ^* input by the correction unit 58 . When the parameter σ=0, no chroma correction processing is performed, and the color coordinates a ^* _cor and b ^* _cor output by the chroma correction unit 58 are the same as the color coordinates a ^* and b ^* input by the chroma correction unit 58. . The larger the parameter σ, the more closely the color coordinates a ^* _cor and b ^* _cor approach the achromatic axis.

That is, the closer the parameter σ is to 0, the lower the extent to which colors above the reference white level approach _{achromatic colors} or _white . , the tristimulus values X _HLG Y _HLG Z _HLG input by the chroma processing unit 63 . When the parameter σ=0, no chroma correction processing is performed, and the tristimulus values X _HLG Y _HLG Z _HLG input and output by the chroma processor 63 are the same. On the other hand, the larger the parameter σ, the higher the degree to which colors above the reference white level approach achromatic colors or white. In addition, since the achromatic or nearly white signal is compressed by the compression processing unit 65, which will be described later, it is possible to realize the color reproduction of an achromatic or nearly white highlight instead of a colored white. .

20 and 21, the color space inverse conversion unit 59 receives the lightness L ^* from the color space conversion unit 57 and the color coordinates a ^* _cor , b ^* _cor after chroma correction processing from the chroma correction unit 58. Enter Then, the color space inverse conversion unit 59 converts the L ^* a ^* b ^* space, which is the CIELAB space, into a space of tristimulus values X _HLG Y _HLG Z _HLG (tristimulus value space), Stimulus values X _HLG Y _HLG Z _HLG are obtained (step S2104).

Here, X _n , Y _n , and Z _n are tristimulus values on the perfect diffuse reflection surface, as in Equation (35) above. In the case of HLG, the brightness Y at 75% HLG corresponds to Y _n , so if the peak brightness is 1000 [cd/m ² ], then X _n =192.9312, Y _n =203, and Z _n =221.0467. . The parameter .delta. is a constant of .delta.=6/29 as in the above equation (35).

Also, the internal functions f _x , f _y , and f _z in the above equation (41) are calculated by the following equations.

The color space inverse conversion unit 59 outputs the tristimulus values X _HLG Y _HLG Z _HLG after the chroma correction processing to the HLG chromaticity conversion unit 64 (step S2105).

In the video signal conversion device 6 shown in FIG. 18, for example, the parameter ε used for crosstalk matrix processing is 0.33, the parameter σ used for chroma correction processing is 1.0, the SDR knee point Y _SDRkp =80%, and the HLG video signal Suppose that the skin level Vh _skin =50% of the SDR video signal corresponds to the skin level Vs _skin =67% of the SDR video signal, and HLG 75% corresponds to SDR 96% as a constraint condition for the reference white level.

FIG. 27 is a diagram showing characteristics of display brightness when the parameters ε, σ, etc. are set in the above example, and corresponds to the example of FIG. 25 and the example of applying the dotted line fitting function shown in FIG. . The horizontal axis indicates HLG display luminance [cd/m ² ], and the vertical axis indicates SDR display luminance [cd/m ² ].

The characteristics shown in FIG. 27 correspond to the luminance Y _HLG corresponding to the HLG video signal E _h ', which is the input data of the video signal conversion device 6, and the SDR video signal E _s ', which is the output data of the video signal conversion device 6. Fig. 4 shows the relationship between luminance Y _SDR ;

FIG. 28 is a diagram showing video signal characteristics corresponding to the display luminance characteristics shown in FIG. 27, and corresponds to the example of FIG. 26 and the example to which the dotted line fitting function shown in FIG. 13 is applied. The horizontal axis indicates the level [%] of the HLG video signal, and the vertical axis indicates the level [%] of the SDR video signal.

The characteristics shown in FIG. 28 show the relationship between the HLG video signal E _h ', which is the input data of the video signal conversion device 6, and the SDR video signal E _s ', which is the output data of the video signal conversion device 6. .

Next, L^*a^*b^*Space is used for explanation. 29 and 32 show processing examples of the video signal conversion device 6.^*a^*b^*It is a figure explaining in space. 29 and 32, the horizontal axis is the color coordinate a^*, b^* and the vertical axis is the brightness L^*indicate.

FIG. 30 is a schematic diagram showing the L ^* a ^* b ^* space of FIG. 29 on the L ^* a ^* plane. In FIG. 30, the horizontal axis indicates color coordinates a ^* , and the vertical axis indicates L ^* .

29 and 30, (1) indicates a signal on the L ^* a ^* b ^* space corresponding to the input signal (HLG video signal E _h ') of the video signal converter 6 (thick dotted line). (2) indicates a signal on the L ^* a ^* b ^* space corresponding to the signal after crosstalk matrix processing (display light signal RGB _xHLG output by the crosstalk matrix processing unit 61) (thin dotted line). (3) indicates a signal in the L ^* a ^* b ^* space corresponding to the chroma-processed signal (the tristimulus values X _HLG Y _HLG Z _HLG output by the chroma processing unit 63) (thin solid line). (4) indicates a signal in the L ^* a ^* b ^* space corresponding to the signal after compression (luminance Y _SDR output from compression processing section 65) (thick solid line).

With reference to the input signal shown in (1) and the ^{crosstalk matrix} -processed signal shown in (2), the ^crosstalk The signal after talk matrix processing is reduced in the direction of the L ^* axis, which is the achromatic axis, compared to the input signal shown in (1) (see arrow α).

That is, from FIGS. 29 and 30, when viewed from the plane of the color coordinates a ^* and b ^* with the lightness L ^* fixed, the values of the color coordinates a ^* and b ^* in (2) are centered on the lightness L ^* axis. , it is smaller than the color coordinates a ^* and b ^* of (1) (the absolute value is smaller).

This is because the crosstalk matrix processing does not change the lightness L ^* in the L ^* a ^* b ^* space, but reduces the chroma C ^* _ab and ^{changes the color coordinates a* and} It shows that b ^* changes. In other words, the crosstalk matrix process acts to reduce color component variation in the RGB space, and reduces the chroma C ^* _ab in the L ^* a ^* b ^* space without changing the lightness L ^* . That is, the color coordinates a ^* and b ^* act to approach the L ^* axis, which is the achromatic color axis.

In addition, assuming that the signal after crosstalk matrix processing is compressed, the ^crosstalk matrix processing is performed with ^achromatic The color coordinates a ^* and b ^* are made small so as to approach the L ^* axis, which is the axis. In other words, the crosstalk matrix processing acts to suppress the spread of the color coordinates a ^* and b ^* that occurs when the signal after the crosstalk matrix processing is compressed.

Returning to FIGS. 29 and 30, with reference to the signal after crosstalk matrix processing shown in (2) and the signal after chroma processing shown in (3), color coordinates a ^* and b ^* with fixed lightness L ^* are obtained. From the aspect of (3), the signal after chroma processing shown in (3) has a lightness L ^* greater than or equal to the lightness L ^* _wp corresponding to the reference white level compared to the signal after crosstalk matrix processing shown in (2). , it shrinks in the direction of the L ^* axis, which is the achromatic axis (see arrow β).

FIG. 31 is a schematic diagram showing the L ^* a ^* b ^* space of FIG. 29 on the a ^* b ^* plane, and shows a region of lightness L ^* equal to or higher than lightness L ^* _wp corresponding to the reference white level. The horizontal axis indicates the color coordinate a ^* , and the vertical axis indicates the color coordinate b ^* . The signal after chroma processing shown in (3) is reduced in the L ^* axis direction, which is the origin of the a ^* b ^* plane, while maintaining a similar shape to the signal after crosstalk matrix processing shown in (2). (see arrow).

That is, the values of the color coordinates a* and b* in (3) are obtained by moving the color coordinates a ^* and b ^* in (2) around the L ^* axis in a region of lightness L ^* equal to or higher than the lightness L ^* _wp corresponding to the reference white level. ^* and b ^* (the absolute value is smaller). Small values of color coordinates a ^* and b ^* and being close to the L ^* axis mean that the hue is achromatic or close to white.

Returning to FIGS. 29 and 30, referring to the signal after chroma processing shown in (3) and the signal after compression processing shown in (4), lightness L ^* and color coordinates a ^* and b ^* in (4) are calculated. are compressed toward the origin of the axis of lightness L ^* with respect to lightness L ^* and color coordinates a ^* , b ^* in (3) (see arrow γ).

In this way, the signal after chroma processing shown in (3) is compressed in a state closer to achromatic color or white than the signal after crosstalk matrix processing shown in (2).

As a result, the spread of color coordinates a ^* and b ^* due to compression processing can be smaller for the signal after chroma processing shown in (3) than for the signal after crosstalk matrix processing shown in (2). ) is closer to the L ^* axis, which is the achromatic axis. That is, by compressing the signal after the chroma processing shown in (3) instead of the signal after the crosstalk matrix processing shown in (2), it is possible to realize the color reproduction of an achromatic color or a highlight close to white. .

In this case, if the chroma-processed signal shown in (3) is compressed, an achromatic or nearly white video signal can be obtained. On the other hand, if the signal after the crosstalk matrix processing shown in (2) is compressed, it may become a video signal that is close to white and includes a tint. In other words, compressing the signal after chroma processing shown in (3) is more likely to produce an achromatic or white video signal than compressing the signal after crosstalk matrix processing shown in (2). Color reproduction of reflected highlights can be achieved.

The degree of the achromatic or nearly white video signal obtained by compressing the signal after the chroma processing shown in (3), that is, the degree of leaving the white color including the tint, depends on the value of the parameter σ used by the chroma processing section 63. It is determined. As the parameter σ is closer to 0, the video signal after the compression process has a higher degree of remaining white color including color, and as the parameter σ is larger, the video signal becomes achromatic or closer to white.

In FIG. 32, (4) indicates a signal in L ^* a ^* b ^* space corresponding to the signal after compression processing (brightness Y _SDR output by compression processing section 65) (thick solid line), and FIG. It is the same as the signal after compression processing shown in (4). (5) indicates a signal in the L ^* a ^* b ^* space corresponding to the signal after the inverse crosstalk matrix processing (the display light signal Fds output by the inverse crosstalk matrix processing unit 67) (thin solid line). (6) indicates a signal on the L ^* a ^* b ^* space corresponding to the output signal (SDR video signal E _s ') of the video signal converter 6 (thick dotted line).

Referring to the signal after compression processing shown in (4) and the signal after inverse crosstalk matrix processing shown in (5), when viewed in terms of color coordinates a ^* and b ^* with fixed lightness L ^* , (5 ^{) are larger than the color coordinates a*, b* of ( 4} ) around the lightness L ^* axis (absolute values are larger).

This is the ^crosstalk matrix processing for obtaining the signal after the ^crosstalk matrix processing shown in (2) of FIG. Compatible with processing. In the inverse crosstalk matrix processing for obtaining the signal after the inverse crosstalk matrix processing shown in (5) of FIG. 32, the values of the color coordinates a ^* and b ^* are increased so as to restore the RGB variations. processing.

As described above, according to the video signal conversion device 6 of the fourth embodiment, the HLG video/optical converter 60 converts the HLG video signal E _h ' into the display optical signal Fd using the EOTF of the HLG video. Then, the crosstalk matrix processing unit 61 performs crosstalk matrix processing for reducing variations in brightness for each RGB color component in the display light signal Fd, and obtains the display light signal _RGBxHLG . The HLG light/tristimulus converter 62 converts the display light signal RGB _xHLG into tristimulus values X _HLG Y _HLG Z _HLG .

Based on a preset parameter σ, the chroma processing unit 63 performs chroma correction processing on the tristimulus values X _HLG Y _HLG Z _HLG to bring colors above the reference white level closer to an achromatic color or white. Calculate tristimulus values X _HLG Y _HLG Z _HLG after correction processing. The HLG chromaticity conversion unit 64 converts the tristimulus values X _HLG Y _HLG Z _HLG after chroma correction processing into chromaticity coordinates x, y.

The compression processing unit 65 performs processing on the luminance Y _HLG using a fitting function that considers the human skin level, the reference white level, and the color reproduction of highlights based on a preset gain value k ₁ or the like. Determine the luminance Y _SDR .

The SDR luminance/light converter 66 obtains tristimulus values X _{SDR and Z SDR from the luminance Y SDR using the chromaticity coordinates x and y, and converts the luminance Y SDR and the tristimulus values X SDR and Z SDR to SDR} . Determine the display light signal RGB _xSDR .

The inverse crosstalk matrix processing unit 67 performs the reverse processing of the crosstalk matrix processing for reducing the luminance variation for each RGB color component by the crosstalk matrix processing unit 61, that is, reduces the luminance variation for each RGB color component. Inverse crosstalk matrix processing for restoration is performed to obtain the SDR display light signal Fds. Then, the SDR optical/video converter 68 converts the display optical signal Fds into the SDR video signal E _s ' by the inverse function of the EOTF of the SDR video.

Thus, in addition to the effects of the third embodiment, it is possible to realize color reproduction of achromatic or near-white highlights.

That is, since the compression process is performed using the fitting function, the signal level of the person's skin does not decrease, the white level of the telop does not change, and whitening of highlights can be suppressed.

In addition, since crosstalk matrix processing is performed, compression processing is performed in a state in which variations in luminance for each RGB color component are reduced. can be suppressed, and the color reproduction of highlights can be sufficiently realized. In this case, it is possible to adjust the color reproduction of the highlights based on the parameter ε according to the production intention.

Furthermore, without changing the hue angle h _ab , chroma correction processing is performed to obtain a small value of chroma C ^* _ab,cor , and tristimulus values X _HLG Y _HLG Z _HLG after chroma correction are obtained. Compression processing is performed in a chromatic or near-white state. As a result, color reproduction of an achromatic or nearly white highlight can be realized while suppressing the degree of hard clipping of a specific color component in the highlight and suppressing hue change.

In this case, it is possible to adjust the color reproduction of the highlights based on the parameter σ according to the production intention. In other words, the creator can make adjustments according to the production intention, from colored color reproduction in the highlights to color reproduction that is close to white, and can realize color reproduction of the highlights that further reflects the production intention. can.

Therefore, in addition to the effects of the third embodiment, color reproduction of achromatic or near-white highlights can be realized. That is, in the fourth embodiment, color reproduction of highlights can be realized more effectively than in the third embodiment.

18, the SDR luminance/light conversion unit 66 of the video signal conversion device 6 shown in FIG. The SDR display light signal RGB _xSDR may be obtained from the luminance Y _SDR and the tristimulus values X _SDR and Z _SDR by using the inverse matrix of the matrix for conversion to tristimulus values.

As a result, the HLG light/tristimulus converter 62 uses a matrix for converting wide color gamut RGB to tristimulus values, and the SDR luminance/light converter 66 converts narrow color gamut RGB to tristimulus values. Wide to narrow gamut conversion can be done by using the inverse of the matrix to convert and converting from tristimulus values back to RGB.

[Embodiment 3: Video signal conversion device that performs inverse conversion]
Next, a device for performing inverse conversion of the video signal conversion device 5 of the third embodiment will be described. This apparatus uses a fitting function similar to that of the second embodiment when converting an SDR image into an HLG image, and performs crosstalk matrix processing for reducing variations among RGB color components. Thus, in addition to the effect of the second embodiment, it is possible to suppress hue change due to hard clipping of a specific color component in highlights, and to sufficiently realize color reproduction of highlights.

FIG. 33 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device 5 of the third embodiment. This video signal conversion device 7 includes an SDR video/light conversion section 70, a crosstalk matrix processing section 71, a tristimulus value and chromaticity conversion section 72, an expansion processing section 73, an HLG luminance/light conversion section 74, and an inverse crosstalk matrix. A processing section 75 and an HLG light/video conversion section 76 are provided.

The SDR video/optical converter 70 receives the SDR video signal E _s ' and performs the same processing as the SDR video/optical converter 30 shown in FIG. 14 and the SDR video/optical converter 40 shown in FIG. . The SDR video/optical converter 70 then outputs the SDR display optical signal Fds to the crosstalk matrix processor 71 . The SDR video/optical conversion section 70 corresponds to the SDR optical/video conversion section 56 shown in FIG. 16 and performs the opposite processing.

The crosstalk matrix processor 71 receives the display optical signal Fds from the SDR video/optical converter 70 . Then, the crosstalk matrix processing unit 71, like the crosstalk matrix processing unit 51 shown in FIG. Crosstalk matrix processing for mitigation is performed to obtain the display light signal RGB _{x SDR} . The crosstalk matrix processor 71 outputs the display optical signal RGB _xSDR to the tristimulus value and chromaticity converter 72 .

The tristimulus value and chromaticity conversion unit 72 receives the display light signal RGB _xSDR from the crosstalk matrix processing unit 71, and converts the tristimulus value and chromaticity conversion unit 31 shown in FIG. 14 and the tristimulus value shown in FIG. and the same processing as that of the chromaticity conversion unit 41 is performed. Then, the tristimulus value and chromaticity conversion unit 72 outputs the luminance Y _SDR to the extension processing unit 73 and outputs the chromaticity coordinates x, y to the HLG luminance/light conversion unit 74 . The tristimulus value and chromaticity conversion unit 72 corresponds to the SDR luminance/light conversion unit 54 shown in FIG. 16 and performs the opposite processing.

The expansion processing unit 73 receives the luminance Y _SDR from the tristimulus value and chromaticity conversion unit 72 and performs the same processing as the expansion processing unit 42 shown in FIG. That is, the expansion processing unit 73 performs expansion processing (exponentialization processing) and inverse gain processing using a predetermined inverse fitting function, and obtains the color reproduction of highlights, the reference white level, and the human skin level from the luminance Y _SDR . Calculate the luminance Y _HLG taken into account. The extension processing unit 73 then outputs the luminance Y _HLG to the HLG luminance/light conversion unit 74 .

The HLG luminance/light conversion unit 74 receives the luminance Y _HLG from the extension processing unit 73 and also receives the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 72 . Then, the HLG luminance/light converter 74 performs the same processing as the _HLG luminance/light converter 43 shown in FIG. The HLG luminance/light conversion unit 74 corresponds to the tristimulus value and chromaticity conversion unit 52 shown in FIG. 16 and performs the opposite processing.

The inverse crosstalk matrix processor 75 receives the display light signal RGB _xHLG from the HLG luminance/light converter 74 . Similar to the inverse crosstalk matrix processing unit 55 shown in FIG. 16, the inverse crosstalk matrix processing unit 75 uses the preset parameter .epsilon. Inverse processing of the crosstalk matrix processing for reducing luminance variations is performed. That is, the inverse crosstalk matrix processing unit 75 performs inverse crosstalk matrix processing for restoring luminance variations for each of the RGB color components, and obtains the HLG display light signal Fd. The inverse crosstalk matrix processor 75 outputs the display optical signal Fd to the HLG light/video converter 76 .

The HLG light/video conversion unit 76 receives the display light signal Fd from the inverse crosstalk matrix processing unit 75 and converts the HLG light/video conversion unit 35 shown in FIG. 14 and the HLG light/video conversion unit 44 shown in FIG. , and outputs the HLG video signal E _h '. The HLG light/video conversion section 76 corresponds to the HLG video/light conversion section 50 shown in FIG. 16 and performs the opposite processing.

As a result, the signal level of the person's skin is maintained, the white level of the telop does not change, and furthermore, the effect of the second embodiment is achieved, such as suppressing the overexposure of highlights. Furthermore, hue change due to hard clipping of a specific color component in highlights can be suppressed, and color reproduction of highlights can be sufficiently realized.

[Embodiment 4: Video signal conversion device that performs inverse conversion]
Next, a device for performing inverse conversion of the video signal conversion device 6 of the fourth embodiment will be described. This device is characterized by using the same fitting function as in Example 2, performing crosstalk matrix processing in the same manner as in Example 3, and performing chroma correction processing when converting SDR video into HLG video. and Thus, in addition to the effects of the third embodiment, it is possible to realize color reproduction of achromatic or near-white highlights. That is, in the fourth embodiment, color reproduction of highlights can be realized more effectively than in the third embodiment.

FIG. 34 is a block diagram showing a configuration example of a video signal conversion device that performs inverse conversion of the video signal conversion device 6 of the fourth embodiment. This video signal conversion device 8 includes an SDR video/light conversion section 80, a crosstalk matrix processing section 81, a tristimulus value and chromaticity conversion section 82, an expansion processing section 83, an HLG tristimulus value conversion section 84, and a chroma processing section 85. , an HLG tristimulus value/light converter 86 , an inverse crosstalk matrix processor 87 and an HLG light/video converter 88 .

Comparing the video signal conversion device 7 of the third embodiment shown in FIG. Equipped with crosstalk matrix processing units 71 and 81, tristimulus value and chromaticity conversion units 72 and 82, expansion processing units 73 and 83, inverse crosstalk matrix processing units 75 and 87, and HLG light/video conversion units 76 and 88. have in common. On the other hand, the video signal conversion device 8 includes an HLG tristimulus value conversion unit 84 and an HLG tristimulus value/light conversion unit 86 instead of the HLG luminance/light conversion unit 74 of the video signal conversion device 7, and a chroma processing unit. It is different from the video signal conversion device 7 in that it has 85 .

SDR video/light converters 70, 80, crosstalk matrix processors 71, 81, tristimulus value and chromaticity converters 72, 82, expansion processors 73, 83, inverse crosstalk matrix processors 75, 87, and HLG light The /video converters 76 and 88 perform similar processing. Descriptions of the SDR video/light converter 80, the crosstalk matrix processor 81, the tristimulus value and chromaticity converter 82, the expansion processor 83, the inverse crosstalk matrix processor 87, and the HLG light/video converter 88 are omitted. do.

The HLG tristimulus value conversion unit 84 receives the luminance Y _HLG from the extension processing unit 83 and inputs the chromaticity coordinates x, y from the tristimulus value and chromaticity conversion unit 82 . 33, the HLG tristimulus value converter 84 converts the tristimulus values X _HLG and Z _HLG from the luminance Y _HLG using the chromaticity coordinates x and y. and outputs the tristimulus values X _HLG Y _HLG Z _HLG to the chroma processor 85 .

The chroma processing unit 85 receives the tristimulus values X _HLG Y _HLG Z _HLG from the HLG tristimulus value conversion unit 84 and performs the same processing as the chroma processing unit 63 shown in FIG. That is, the chroma processing unit 85 performs chroma correction processing to bring colors above the reference white level closer to achromatic colors or white based on a preset parameter σ, and tristimulus values X _HLG Y after chroma correction processing. _HLG Z _HLG is obtained, and tristimulus values X _HLG Y _HLG Z _HLG after chroma correction processing are output to the HLG tristimulus value/light converter 86 .

The HLG tristimulus value/light conversion unit 86 receives tristimulus values X _HLG Y _HLG Z _HLG after chroma correction processing from the chroma processing unit 85 . Then, the HLG tristimulus value/light conversion unit 86 converts the tristimulus values X _HLG Y _HLG Z _HLG into HLG display light signals RGB _xHLG , similarly to the HLG luminance/light conversion unit 74 shown in FIG. The display light signal RGB _xHLG is output to the inverse crosstalk matrix processor 87 .

Thus, in addition to the effects of the third embodiment, it is possible to realize color reproduction of achromatic or near-white highlights. That is, in the fourth embodiment, color reproduction of highlights can be realized more effectively than in the third embodiment.

Although the present invention has been described above with reference to Examples 1 to 4, the present invention is not limited to Examples 1 to 4, and can be variously modified without departing from the technical idea thereof. For example, in the video signal converters 1 to 8, the chromaticity coordinates x, y were used to return the luminance to the optical signal. may be used.

Specifically, the tristimulus value and chromaticity conversion units 12, 21, etc. convert the tristimulus values XYZ or the chromaticity coordinates x, y into chromaticity coordinates u', v', and convert the chromaticity coordinates u', v ' is output to the SDR luminance/light converters 14, 23 and the like. In this case, the SDR luminance/light converters 14, 23, etc. obtain the tristimulus values X _comp , Z _comp from the luminances Y _comp,2nd , Y _comp using the chromaticity coordinates u′, v′.

Also, the tristimulus value and chromaticity conversion units 31, 41, etc. convert the tristimulus values XYZ or chromaticity coordinates x, y into chromaticity coordinates u', v', and convert the chromaticity coordinates u', v' into HLG It is output to the luminance/light converters 33, 43 and the like. In this case, the HLG luminance/light converters 33, 43 and the like obtain tristimulus values X _exp , Z _exp from the luminances Y _exp,2nd , Y _exp using the chromaticity coordinates u′, v′.

A normal computer can be used as the hardware configuration of the video signal converters 1 to 8 of the first to fourth embodiments. The video signal converters 1 to 8 are configured by a computer having a CPU, a volatile storage medium such as a RAM, a nonvolatile storage medium such as a ROM, an interface, and the like.

HLG video/light conversion unit 10, gain processing unit 11, tristimulus value and chromaticity conversion unit 12, compression processing unit 13, SDR luminance/light conversion unit 14, and SDR light/video conversion unit provided in video signal conversion device 1 Each of the 15 functions is realized by causing the CPU to execute a program describing these functions. In addition, each of the HLG video/light conversion unit 20, the tristimulus value and chromaticity conversion unit 21, the compression processing unit 22, the SDR luminance/light conversion unit 23, and the SDR light/video conversion unit 24 provided in the video signal conversion device 2 Functions are also implemented by causing the CPU to execute programs describing these functions.

An SDR video/light converter 30, a tristimulus value and chromaticity converter 31, an expansion processor 32, an HLG luminance/light converter 33, an inverse gain processor 34, and an HLG light/video converter provided in the video signal converter 3 Each function of the unit 35 is realized by causing the CPU to execute a program describing these functions. In addition, each of the SDR video/light converter 40, the tristimulus value and chromaticity converter 41, the extension processor 42, the HLG luminance/light converter 43, and the HLG light/video converter 44 provided in the video signal converter 4 Functions are also implemented by causing the CPU to execute programs describing these functions.

HLG video/light conversion unit 50, crosstalk matrix processing unit 51, tristimulus value and chromaticity conversion unit 52, compression processing unit 53, SDR luminance/light conversion unit 54, inverse crosstalk matrix provided in video signal conversion device 5 Each function of the processing unit 55 and the SDR light/video conversion unit 56 is realized by causing the CPU to execute a program describing these functions. In addition, an HLG video/light conversion unit 60, a crosstalk matrix processing unit 61, an HLG light/tristimulus value conversion unit 62, a chroma processing unit 63, an HLG chromaticity conversion unit 64, and a compression processing unit provided in the video signal conversion device 6 65, SDR luminance/light conversion unit 66, inverse crosstalk matrix processing unit 67, and SDR light/video conversion unit 68 are realized by causing the CPU to execute programs describing these functions.

An SDR video/light converter 70, a crosstalk matrix processor 71, a tristimulus value and chromaticity converter 72, an extension processor 73, an HLG luminance/light converter 74, and an inverse crosstalk matrix provided in the video signal converter 7 Each function of the processing unit 75 and the HLG light/video conversion unit 76 is realized by causing the CPU to execute a program describing these functions. In addition, an SDR video/light converter 80, a crosstalk matrix processor 81, a tristimulus value and chromaticity converter 82, an extension processor 83, an HLG tristimulus value converter 84, and a chroma process are provided in the video signal converter 8. Each function of the unit 85, the HLG tristimulus value/light conversion unit 86, the inverse crosstalk matrix processing unit 87, and the HLG light/video conversion unit 88 is realized by causing the CPU to execute a program describing these functions. be.

These programs are stored in the storage medium and are read and executed by the CPU. In addition, these programs can be stored and distributed in storage media such as magnetic disks (floppy (registered trademark) disks, hard disks, etc.), optical disks (CD-ROM, DVD, etc.), semiconductor memories, etc., and distributed via networks. You can also send and receive

INDUSTRIAL APPLICABILITY The video signal conversion device and program of the present invention are useful as a technology for converting the dynamic range, for example, in integrated production in which HLG video and SDR video are produced at the same time.

1, 2, 3, 4, 5, 6, 7, 8 video signal converters 10, 20, 50, 60 HLG video/optical converter 11 gain processors 12, 21, 31, 41, 52, 72, 82 Stimulus value and chromaticity converters 13, 22, 53, 65 Compression processors 14, 23, 54, 66 SDR luminance/light converters 15, 24, 56, 68 SDR light/video converter 16 Reference white level compression processor 17 highlight color reproduction compression processing units 30, 40, 70, 80 SDR video/light conversion units 32, 42, 73, 83 expansion processing units 33, 43, 74 HLG luminance/light conversion unit 34 inverse gain processing units 35, 44 , 76, 88 HLG light/video conversion units 51, 61, 71, 81 crosstalk matrix processing units 55, 67, 75, 87 inverse crosstalk matrix processing unit 57 color space conversion unit 58 chroma correction unit 59 color space inverse conversion unit 62 HLG light/tristimulus value conversion units 63, 85 chroma processing unit 64 HLG chromaticity conversion unit 84 HLG tristimulus value conversion unit 86 HLG tristimulus value/light conversion unit

Claims (15)

In a video signal converter that converts HLG (Hybrid Log Gamma) video to SDR (Standard Dynamic Range) video,
an HLG video/optical conversion unit that converts the video signal of the HLG image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the HLG image;
gain processing for obtaining skin level characteristics of the SDR image corresponding to the skin level of the HLG image on the first display light signal converted by the HLG video/light conversion unit; a gain processing unit for obtaining a signal;
a tristimulus value and chromaticity conversion unit that converts the second display light signal obtained by the gain processing unit into tristimulus values and chromaticity coordinates;
A luminance value of the tristimulus values and the tristimulus values converted by the chromaticity conversion unit is defined as a first luminance, and the white of the SDR image corresponding to the reference white level of the HLG image for the first luminance. Compression processing is performed to obtain level characteristics and characteristics in which the value of the video signal of the SDR image increases to the upper limit value of the video signal of the SDR image corresponding to the upper limit value of the video signal of the HLG image. , a compression processor that obtains the second luminance;
SDR luminance/light for converting the second luminance obtained by the compression processor into a third display light signal of the SDR image using the tristimulus values and the chromaticity coordinates converted by the chromaticity converter a conversion unit;
an SDR light/video converter for converting the third display optical signal converted by the SDR luminance/light converter into a video signal of the SDR image by an inverse function of the EOTF of the SDR image;
A video signal conversion device comprising: In the video signal conversion device according to claim 1,
The gain processing unit
performing the gain processing by multiplying the first display light signal by a predetermined gain value to obtain the second display light signal;
The predetermined gain value is
The video signal conversion device is preset by a user based on the skin level value of the HLG video and the skin level value of the SDR video corresponding to the skin level of the HLG video. The video signal conversion device according to claim 1 or 2,
The compression processing unit is
a reference white level compression processing unit that performs compression processing on the first luminance to obtain characteristics of the white level of the SDR image corresponding to the reference white level of the HLG image, and obtains a third luminance;
The third luminance obtained by the reference white level compression processing unit is subjected to compression processing for obtaining a characteristic that the value of the video signal of the SDR image increases up to the upper limit value, thereby obtaining the second luminance. a color reproduction compression processor;
A video signal conversion device comprising: In a video signal converter that converts HLG (Hybrid Log Gamma) video to SDR (Standard Dynamic Range) video,
an HLG video/optical conversion unit that converts the video signal of the HLG image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the HLG image;
a tristimulus value and chromaticity converter for converting the first display light signal converted by the HLG video/light converter into tristimulus values and chromaticity coordinates;
A luminance value of the tristimulus values and the tristimulus values converted by the chromaticity conversion unit is defined as a first luminance, and the first luminance corresponds to the skin level of the HLG image by a predetermined fitting function. performing a first calculation for obtaining a skin level characteristic of the SDR image, wherein the value of the video signal of the SDR image corresponds to the upper limit of the video signal of the SDR image; a processing unit that performs a second calculation to obtain a characteristic that increases to a value and obtains a second luminance;
SDR luminance/light conversion for converting the second luminance obtained by the processing unit into a second display light signal of the SDR image using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. Department and
an SDR light/video converter for converting the second display light signal converted by the SDR luminance/light converter into a video signal of the SDR image by an inverse function of the EOTF of the SDR image;
A video signal conversion device comprising: In a video signal converter that converts HLG (Hybrid Log Gamma) video to SDR (Standard Dynamic Range) video,
an HLG video/optical conversion unit that converts the video signal of the HLG image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the HLG image;
performing crosstalk matrix processing for reducing variations in luminance for each RGB color component in the first display light signal converted by the HLG video/light conversion unit, and crosstalk matrix processing for obtaining a second display light signal; Department and
a tristimulus value and chromaticity conversion unit that converts the second display light signal obtained by the crosstalk matrix processing unit into tristimulus values and chromaticity coordinates;
A luminance value of the tristimulus values and the tristimulus values converted by the chromaticity conversion unit is defined as a first luminance, and the first luminance corresponds to the skin level of the HLG image by a predetermined fitting function. performing a first calculation for obtaining a skin level characteristic of the SDR image, wherein the value of the video signal of the SDR image corresponds to the upper limit of the video signal of the SDR image; a processing unit that performs a second calculation to obtain a characteristic that increases to a value and obtains a second luminance;
SDR luminance/light conversion for converting the second luminance obtained by the processing unit into a third display light signal of the SDR image using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. Department and
Inverse crosstalk matrix processing, which is the inverse of the crosstalk matrix processing, for restoring variations in luminance for each RGB color component in the third display light signal converted by the SDR luminance/light converter. to obtain a fourth display light signal; and
an SDR light/video conversion unit for converting the fourth display optical signal obtained by the inverse crosstalk matrix processing unit into a video signal of the SDR image by an inverse function of the EOTF of the SDR image;
A video signal conversion device comprising: In the video signal conversion device according to claim 5,
Instead of the tristimulus value and chromaticity conversion unit, an HLG light/tristimulus value conversion unit, a chroma processing unit, and an HLG chromaticity conversion unit,
The HLG light/tristimulus value conversion unit
converting the second display light signals obtained by the crosstalk matrix processing unit into tristimulus values;
The chroma processing unit
The tristimulus value space of the tristimulus values converted by the HLG light/tristimulus value conversion unit is converted into the CIELAB space, and the hue in the CIELAB space is adjusted so that the color above the reference white level approaches an achromatic color or white. Perform chroma correction processing to reduce the chroma in the CIELAB space while maintaining the corners, obtain tristimulus values after the chroma correction processing,
The HLG chromaticity conversion unit
converting the tristimulus values obtained by the chroma processing unit into chromaticity coordinates;
The processing unit is
setting the luminance value of the tristimulus values obtained by the chroma processing unit as the first luminance, performing the first calculation and the second calculation to obtain the second luminance;
The SDR luminance/light conversion unit
The image characterized by converting the second luminance obtained by the processing unit into the third display optical signal of the SDR image using the chromaticity coordinates converted by the HLG chromaticity conversion unit. Signal converter. In the video signal conversion device according to claim 6,
The chroma processing unit
a color space conversion unit that converts the tristimulus value space of the tristimulus values converted by the HLG light/tristimulus value conversion unit into the CIELAB space and obtains lightness and color coordinates;
Based on the color coordinates obtained by the color space conversion unit, the chroma and the hue angle before chroma correction processing are obtained, and the hue angle is held so that colors above a reference white level approach an achromatic color or white. a chroma correction unit that reduces the chroma before the chroma correction process and obtains the color coordinates after the chroma correction process;
The CIELAB space based on the lightness obtained by the color space conversion unit and the color coordinates after chroma correction obtained by the chroma correction unit is converted into the tristimulus value space, and the tristimulus values after chroma correction are converted into the tristimulus value space. a desired color space inverse transformation unit;
A video signal conversion device comprising: In the video signal conversion device according to any one of claims 4 to 7,
The first calculation by the predetermined fitting function in the processing unit is a gain processing calculation of multiplying the first luminance by a predetermined gain value,
The predetermined gain value is
A video signal conversion device characterized in that the video signal conversion device is preset by a user based on the skin level value of the HLG video and the skin level value of the SDR video corresponding to the skin level of the HLG video. In the video signal conversion device according to any one of claims 4 to 8,
A video signal conversion apparatus, wherein the second calculation by the predetermined fitting function in the processing section is a calculation of logarithmization processing for logarithmizing the first luminance. In a video signal conversion device that converts SDR (Standard Dynamic Range) video to HLG (Hybrid Log Gamma) video,
an SDR video/optical converter that converts the video signal of the SDR image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the SDR image;
a tristimulus value and chromaticity converter for converting the first display light signal converted by the SDR video/light converter into tristimulus values and chromaticity coordinates;
A luminance value of the tristimulus values and the tristimulus values converted by the chromaticity conversion unit is defined as a first luminance, and the value of the video signal of the HLG image is the value of the video signal of the SDR image with respect to the first luminance. Extended processing for obtaining a characteristic that the video signal of the HLG image increases to the upper limit value corresponding to the upper limit value of the signal, and obtaining a characteristic that the reference white level of the HLG image and the white level of the SDR image correspond to each other. an expansion processing unit that performs and obtains the second luminance;
HLG luminance/light for converting the second luminance obtained by the extension processing unit into a second display light signal of the HLG video using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. a conversion unit;
performing inverse gain processing on the second display light signal converted by the HLG luminance/light conversion unit to obtain characteristics in which the skin level of the HLG image and the skin level of the SDR image correspond to each other; an inverse gain processor for obtaining a display light signal;
an HLG light/video conversion unit for converting the third display optical signal obtained by the inverse gain processing unit into a video signal of the HLG image by an inverse function of the EOTF of the HLG image;
A video signal conversion device comprising: In a video signal conversion device that converts SDR (Standard Dynamic Range) video to HLG (Hybrid Log Gamma) video,
an SDR video/optical converter that converts the video signal of the SDR image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the SDR image;
a tristimulus value and chromaticity converter for converting the first display light signal converted by the SDR video/light converter into tristimulus values and chromaticity coordinates;
The luminance value of the tristimulus values and the tristimulus values converted by the chromaticity conversion unit is defined as a first luminance, and the value of the video signal of the HLG image is obtained by a predetermined inverse fitting function with respect to the first luminance. increases to the upper limit value of the video signal of the HLG image corresponding to the upper limit value of the video signal of the SDR image. A second calculation is performed to obtain a characteristic corresponding to the white level of the HLG image and a characteristic corresponding to the skin level of the SDR image, and a second luminance a processing unit for obtaining
HLG luminance/light conversion for converting the second luminance obtained by the processing unit into a second display light signal of the HLG image using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. Department and
an HLG light/video conversion unit for converting the second display light signal converted by the HLG luminance/light conversion unit into a video signal of the HLG image by an inverse function of the EOTF of the HLG image;
A video signal conversion device comprising: In a video signal conversion device that converts SDR (Standard Dynamic Range) video to HLG (Hybrid Log Gamma) video,
an SDR video/optical converter that converts the video signal of the SDR image into a first display optical signal by the EOTF (Electro Optical Transfer Function) of the SDR image;
crosstalk matrix processing for reducing variations in brightness for each RGB color component in the first display light signal converted by the SDR video/light conversion unit, and crosstalk matrix processing for obtaining a second display light signal; Department and
a tristimulus value and chromaticity conversion unit that converts the second display light signal obtained by the crosstalk matrix processing unit into tristimulus values and chromaticity coordinates;
The luminance value of the tristimulus values and the tristimulus values converted by the chromaticity conversion unit is defined as a first luminance, and the value of the video signal of the HLG image is obtained by a predetermined inverse fitting function with respect to the first luminance. increases to the upper limit value of the video signal of the HLG image corresponding to the upper limit value of the video signal of the SDR image. A second calculation is performed to obtain a characteristic corresponding to the white level of the HLG image and a characteristic corresponding to the skin level of the SDR image, and a second luminance a processing unit for obtaining
HLG luminance/light conversion for converting the second luminance obtained by the processing unit into a third display light signal of the HLG image using the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit. Department and
Inverse crosstalk matrix processing, which is the reverse of the crosstalk matrix processing, for restoring luminance variations for each RGB color component in the third display light signal converted by the HLG luminance/light conversion unit. to obtain a fourth display light signal; and
an HLG light/video conversion unit for converting the fourth display optical signal obtained by the inverse crosstalk matrix processing unit into a video signal of the HLG image by an inverse function of the EOTF of the HLG image;
A video signal conversion device comprising: In the video signal conversion device according to claim 12,
An HLG tristimulus value conversion unit, a chroma processing unit, and an HLG tristimulus value/light conversion unit instead of the HLG luminance/light conversion unit,
The HLG tristimulus value conversion unit
converting the tristimulus values and the chromaticity coordinates converted by the chromaticity conversion unit and the second luminance obtained by the processing unit into tristimulus values including the second luminance;
The chroma processing unit
The space of the tristimulus values converted by the HLG tristimulus value conversion unit is converted into the CIELAB space, and the hue angle in the CIELAB space is maintained so that the color above the reference white level approaches an achromatic color or white. , performing chroma correction processing to reduce chroma in the CIELAB space, obtaining tristimulus values after chroma correction processing,
The HLG tristimulus value/light conversion unit
converting the tristimulus values after chroma correction processing obtained by the chroma processing unit into a fifth display light signal;
The inverse crosstalk matrix processing unit,
performing the inverse crosstalk matrix processing for restoring luminance variations for each RGB color component in the fifth display light signal converted by the HLG tristimulus value/light conversion unit, and performing the fourth display light signal; A video signal conversion device characterized by: A program for causing a computer to function as the video signal conversion device according to any one of claims 1 to 9. A program for causing a computer to function as the video signal conversion device according to any one of claims 10 to 13.

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