JP6980858B2 - Display method and display device - Google Patents

Description

The present disclosure relates to a display method and a display device.

Conventionally, an image signal processing device for improving a displayable luminance level has been disclosed (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-167418

However, in the above patent document, further improvement was required.

The display method according to one aspect of the present invention is to display an image of video data in which the brightness of the image is defined by the first EOTF (Electoro-Optical Transfer Function) showing the correspondence between the brightness of HDR (High Dynamic Range) and the code value. A display method for displaying on a display device, wherein the video data includes peak luminance information which is metadata indicating the peak luminance of the video, and in the display method, the video data is acquired and a part of the first EOTF. When the portion of the luminance range having the peak luminance indicated by the peak luminance information included in the acquired video data as the maximum luminance is defined as the second EOTF, it is a part of the second EOTF and the predetermined luminance is set. While maintaining the relative relationship of the luminance of the 5th EOTF with respect to the 5th EOTF which is a part of the luminance range to be the maximum luminance, the dynamic range of the luminance of the 5th EOTF is converted into the 6th EOTF which is reduced, and the luminance of the image is obtained. Of these, the second conversion is performed to convert the brightness of the dynamic range of the fifth EOTF to the brightness of the corresponding dynamic range of the sixth EOTF, and the image is displayed on the display device using the result of the second conversion. do.

The display method according to one aspect of the present invention is to display an image of video data in which the brightness of the image is defined by the first EOTF (Electoro-Optical Transfer Function) showing the correspondence between the brightness of HDR (High Dynamic Range) and the code value. A display method for displaying on a display device, wherein the video data includes peak luminance information indicating the peak luminance of the video, and in the display method, the video data is acquired and is a part of the first EOTF. While maintaining the relative relationship of the luminance of the second EOTF with respect to the second EOTF which is a part of the luminance range having the peak luminance as the maximum luminance indicated by the peak luminance information included in the acquired video data, the first The first conversion is performed to convert the brightness of the image to the brightness corresponding to the dynamic range of the third EOTF in which the dynamic range of the brightness of the second EOTF is reduced according to the maximum brightness of the 2EOTF according to the displayable brightness of the display device. , The image is displayed on the display device using the result of the first conversion.

It should be noted that these general comprehensive or specific embodiments may be realized in a recording medium such as an apparatus, a system, an integrated circuit, a computer program or a computer-readable CD-ROM, and the apparatus, a system, an integrated circuit, a computer may be realized. It may be realized by any combination of programs or recording media.

According to the above aspect, further improvement can be realized.

It is a figure for demonstrating the evolution of video technology. It is a figure for demonstrating the difference between an SDR signal and an HDR signal. It is explanatory drawing of the process of determining the code value of the luminance signal stored in the content, and the process of restoring the luminance from the code value at the time of reproduction. It is a figure for demonstrating an example of the display processing at the time of displaying an SDR signal by SDRTV. It is a figure for demonstrating an example of the display processing at the time of displaying an HDR signal by HDRTV. It is a figure which shows the scale of the luminance at the time of image taking. It is a figure which shows the example of the luminance of a photographed image. It is a figure for demonstrating the relationship between the flow of making a master for home entertainment corresponding to SDR, a distribution medium, and a display device. It is a figure which shows an example of the luminance as a result of mastering the original image shown in FIG. 7 into an SDR image. It is a figure which shows an example of the relationship between the original signal value and SDR signal value for converting (mastering) the original signal value into SDR signal value. It is a figure which shows an example of the luminance as a result of mastering the original image shown in FIG. 7 into an HDR image. It is a figure which shows an example of the relationship between the original signal value and HDR signal value for converting (mastering) the original signal value into HDR signal value. This is an example of the result of acquiring the HDR image obtained by the mastering of FIG. 10A and converting the luminance for a display device having a second maximum luminance of 500 nit. It is a figure which shows an example of the relationship between the HDR signal value and the TV signal value for luminance conversion of an HDR signal value into a TV signal value. It is a figure which shows the functional block of the display device which concerns on Embodiment 1. FIG. It is a figure for demonstrating the specific example of the conversion process (first conversion) in the conversion part of a display device. It is a figure for demonstrating another specific example of the conversion process in a conversion part. It is a figure for demonstrating an example of the display processing at the time of displaying an SDR signal by SDRTV according to the brightness in a viewing environment. It is a figure which shows the functional block of the display device which concerns on Embodiment 2. FIG.

(Knowledge that became the basis of the present invention)
The present inventor has found that the following problems arise with respect to the image signal processing apparatus described in the "Background Art" column.

In the image signal processing apparatus disclosed in Patent Document 1, the linear brightness is calculated for each pixel based on the linear RGB value calculated from the pixels constituting the subject, and the linear brightness is calculated for each pixel based on the linear RGB value and the linear brightness. The corrected linear brightness and the corrected linear RGB value of the composite pixel obtained by synthesizing a plurality of pixels including the pixel are calculated, and the corrected linear brightness and the corrected linear RGB value are gamma-corrected to calculate the display brightness and the display RGB value. .. As described above, in the image signal processing apparatus, the number of gradations that can be displayed is increased by correcting the linear luminance based on the corrected linear RGB value.

By the way, in recent years, with the evolution of video technology, HDR video, which is a video whose brightness is defined by HDR (High Dynamic Range), which is a dynamic range wider than the dynamic range in which the brightness of a conventional video is defined, is used in TVs and the like. A technique for displaying on a display device is known. Here, the transition of video technology will be described with reference to FIG.

FIG. 1 is a diagram for explaining the evolution of video technology.

Until now, the focus has been on expanding the number of display pixels to improve the image quality of images, from the standard 720 x 480 pixel image of Standard Definition (SD) to the 1920 x 1080 pixel of High Definition (HD), so-called 2K. Video is widespread.

In recent years, the introduction of so-called 4K video of Ultra High Definition (UHD) 3840 x 1920 pixels or 4K 4096 x 1920 pixels has been started with the aim of further improving the image quality.

In addition to increasing the resolution of images by introducing 4K, it is being considered to improve the image quality by expanding the dynamic range, expanding the color gamut, adding or improving the frame rate, and the like.

Regarding the expansion of the dynamic range, improvements in the performance of digital cameras and CMOS (Complementary metal-axis-semicon doctor) image sensors have made it possible to take images with a wide dynamic range of 14 Stops or more, which indicates exposure. Therefore, it is possible to shoot light brighter than 100% reflected light (bright light such as specular reflected light) while maintaining the gradation in the dark part. HDR is attracting attention as a signal standard that enables transmission of higher-luminance signals in order to utilize the performance improvement of the camera or image sensor to improve the expressive power.

The TV signal so far is called SDR (Standard Dynamic Range), and the peak brightness (maximum brightness) is 100 nits, whereas HDR (particularly, ST 2084 (PQ curve) which is EOTF standardized by SMPTE). In the case of HDR) encoded by), it has become possible to express peak luminance up to 10,000 nits or more.

As a specific application destination of HDR, it is assumed that it will be used for broadcasting, package media (Blu-ray (registered trademark) Disc, etc.), Internet distribution, etc., as well as HD and UHD.

Next, SDR and HDR will be described with reference to FIG.

FIG. 2 is a diagram for explaining the difference between the SDR signal and the HDR signal. The SDR signal is a video signal indicating an SDR image corresponding to SDR, and the HDR signal is a video signal indicating an HDR image corresponding to HDR.

The original signal obtained by taking a picture with a digital camera having a wide dynamic range (14 Stop, etc.) contains a wide range of luminance information of 0 to 10000 nits.

The SDR signal is an image satisfying a broadcasting standard such as bt709, and is an image signal obtained by performing color correction (grading) processing from the original signal so as to be an SDR image having a peak luminance of 100 nits. That is, the SDR signal is a video signal defined by a dynamic range in which the brightness of the video is 0 to 100 nits.

On the other hand, the HDR signal removes the restriction that the peak luminance is 100 nits like the SDR signal, and the maximum luminance of the dynamic range of the luminance is up to 10000 nits so as to meet the constraint of ST2084 (hereinafter referred to as "PQ curve"). It is a video signal obtained by performing color correction (grading) processing so as to obtain the HDR video of. That is, the HDR signal is a video signal defined by a dynamic range in which the brightness of the video is 0 to 10000 nits. The maximum brightness of the dynamic range of the brightness of the HDR signal is not limited to 10,000 nits, and may be, for example, 800 to 4,000 nits.

As described above, the dynamic range of the HDR brightness is a dynamic range in which the peak brightness is larger than the dynamic range of the SDR brightness. The minimum brightness of the dynamic range of the luminance of HDR is the same as the minimum brightness of the dynamic range of the luminance of SDR, and is 0 nit.

FIG. 3 is an explanatory diagram of a method of determining a code value of a luminance signal stored in the content and a process of restoring the luminance from the code value at the time of reproduction.

The video signal in this example is an HDR signal corresponding to HDR. The image after grading is quantized by the inverse EOTF of HDR, and the code value corresponding to the brightness of the image is determined. Image coding or the like is performed based on this code value, and a video stream is generated. At the time of reproduction, the decoding result of the stream is converted into a linear signal by dequantization based on HDR EOTF, and the brightness of each pixel is restored. Hereinafter, the quantization using the inverse EOTF of HDR is referred to as "EOTF conversion of the inverse HDR". Inverse quantization using HDR EOTF is called "HDR EOTF conversion". Similarly, the quantization using the inverse EOTF of SDR is called "EOTF conversion of inverse SDR". Inverse quantization using SDR EOTF is called "SDR EOTF conversion".

When the display control for displaying the HDR signal as described above on an HDR compatible display device (for example, HDRTV) is performed, the peak brightness that can be displayed by HDRTV (hereinafter referred to as "display peak brightness" is referred to rather than the peak brightness of the HDR signal). ) Is often small. Therefore, in order to match the peak brightness of the HDR signal with the display peak brightness of the HDRTV, it is necessary to reduce the dynamic range of the brightness of the HDR signal to the dynamic range of the brightness supported by the HDRTV.

However, in the brightness correction (conversion) of the image signal processing device and the like disclosed in Patent Document 1, the brightness is corrected to a dynamic range of brightness narrower than the dynamic range of HDR brightness in which the brightness of the image is defined. No consideration was given to the method of converting the brightness at the time of (conversion).

Therefore, there are the following problems.

When displaying an HDR signal with HDRTV due to the difference between SDR EOTF (gamma curve: relative brightness standard) and HDR EOTF (ST2084: PQ curve: absolute brightness standard), an SDR compatible display device (for example, SDRTV) Unlike the case of displaying the SDR signal in, there are the following problems.

The human eye recognizes the brightness of an image, not the absolute brightness, but the relative brightness. The SDR image is a relative brightness-based image in which the brightness of the original signal is quantized by the SDR EOTF (gamma curve) and graded into an SDR image having a peak brightness of 100 nits.

FIG. 4 is a diagram for explaining an example of display processing when the SDR signal is displayed by SDRTV. FIG. 4A is a diagram showing an SDR EOTF in which the brightness of the video of the SDR content is defined. FIG. 4B is a diagram showing EOTF of SDR converted according to the display peak luminance of SDRTV.

As shown in FIG. 4, when the display peak luminance of SDRTV is different from 100 nits (250 nits larger than 100 nits in this example), the relative contrast relationship is maintained according to the display performance of the luminance of the SDRTV. , Adjusted and displayed. Specifically, by multiplying the variable indicating the brightness of the SDR EOTF by 2.5 according to the display peak brightness of the SDRTV, the SDR EOTF is adjusted in a form that maintains the relative contrast relationship, and the SDRTV is adjusted. An EOTF that matches the display performance of the luminance of the above is generated, and the SDR image is displayed on the SDRTV using the EOTF. As a result, even if the luminance display performance of the SDRTV is different from the dynamic range of the luminance of the SDR content, the display is realized in a form close to the intention of the content creator.

As described above, when the SDR image represented by the SDR signal is displayed by SDRTV, the SDRTV displays the SDR image indicated by the SDR signal on the basis of relative luminance. On the other hand, when displaying the HDR image indicated by the HDR signal in HDRTV, the HDRTV is because the PQ curve was devised in consideration of human visual characteristics (all luminance ranges recognizable by humans). In addition, it is required to faithfully display the HDR image based on the absolute luminance standard of the PQ curve.

International standardization bodies for digital AV technology such as Blu-ray (registered trademark) Disc Association and UHD Alliance have graded HDR-compatible content up to a predetermined brightness (for example, 1000 nit) smaller than 10000 nit for the time being. Also allow it to exist).

FIG. 5 is a diagram for explaining an example of display processing when displaying an HDR signal in HDRTV. FIG. 5A is a diagram showing HDR EOTF in which the brightness of the video of the HDR content is defined. FIG. 5B is a diagram showing a tone mapping process (luminance conversion process) for converting the brightness of HDR content according to the display peak brightness of HDRTV.

As shown in FIG. 5, when displaying an HDR image defined by a dynamic range having a predetermined brightness as a peak brightness on an HDRTV having a display peak brightness of less than a predetermined brightness (for example, 500 nit), the HDR signal of the HDR image is displayed. It is required that the HDRTV express the predetermined luminance, which is the peak luminance of the HDR image, by performing the predetermined tone mapping process. That is, it is required to perform tone mapping processing to match a predetermined brightness with the display peak brightness of HDRTV so that the peak brightness of the HDR image can be expressed by HDRTV.

In this case, if only the luminance component is used, as shown in FIG. 5B, if tone mapping processing including knee curve processing using a knee curve showing the relationship between the input luminance and the output luminance is performed, the luminance of the image is increased. It can be converted according to the display peak luminance of HDRTV. However, when the same knee curve processing is applied independently to each RGB color of the video signal, the color may change.

In the predetermined tone mapping process, it is necessary to independently perform the same process for each color of RGB so that the color does not change. At this time, when the color of one pixel to be the target of the predetermined tone mapping process is composed of the luminance of each color of RGB arranged over the points to be knee-curved, the RGB balance after the predetermined tone mapping process is balanced. It collapses and the color changes before and after the tone mapping process. That is, it is the luminance in the luminance range that is not knee-curved in the first color of RGB (for example, R), and the luminance in the luminance range that is knee-curved in the second color (for example, B) that is different from the first color of RGB. In this case, the luminance does not change with the luminance within the non-knee-curved luminance range, and the luminance changes slightly with the luminance within the knee-curved luminance range. For this reason, the relative relationship between the brightness of RGB is broken before and after the predetermined tone mapping process, and the color changes. Further, even if each color of RGB has a luminance within the knee-curved luminance range, the rate of change in which the luminance is reduced depends on the magnitude of the luminance in the knee-curved luminance range, so that the RGB luminance is used. The relative relationship of is broken. Therefore, in order to reduce the change in color before and after the predetermined tone mapping process, a complicated process such as a three-dimensional color conversion process is required.

In particular, in the case of an OLED with extremely high contrast, if the HDR signal based on absolute luminance is processed with a knee curve, the color will change even if the OLED has high color reproducibility, which is sufficient. There is a problem that the display performance of the OLED cannot be brought out.

Based on the above studies, the present inventor has examined the following improvement measures in order to solve the above problems.

The display method according to one aspect of the present invention is to display an image of video data in which the brightness of the image is defined by the first EOTF (Electoro-Optical Transfer Function) showing the correspondence between the brightness of HDR (High Dynamic Range) and the code value. A display method for displaying on a display device, wherein the video data includes peak luminance information which is metadata indicating the peak luminance of the video, and in the display method, the video data is acquired and a part of the first EOTF. When the portion of the luminance range having the peak luminance indicated by the peak luminance information included in the acquired video data as the maximum luminance is defined as the second EOTF, it is a part of the second EOTF and the predetermined luminance is set. While maintaining the relative relationship of the luminance of the 5th EOTF with respect to the 5th EOTF which is a part of the luminance range to be the maximum luminance, the dynamic range of the luminance of the 5th EOTF is converted into the 6th EOTF which is reduced, and the luminance of the image is obtained. Of these, the second conversion is performed to convert the brightness of the dynamic range of the fifth EOTF to the brightness of the corresponding dynamic range of the sixth EOTF, and the image is displayed on the display device using the result of the second conversion. do.

The display method according to one aspect of the present invention is to display an image of video data in which the brightness of the image is defined by the first EOTF (Electoro-Optical Transfer Function) showing the correspondence between the brightness of HDR (High Dynamic Range) and the code value. A display method for displaying on a display device, wherein the video data includes peak luminance information indicating the peak luminance of the video, and in the display method, the video data is acquired and is a part of the first EOTF. While maintaining the relative relationship of the luminance of the second EOTF with respect to the second EOTF which is a part of the luminance range having the peak luminance as the maximum luminance indicated by the peak luminance information included in the acquired video data, the first The first conversion is performed to convert the brightness of the image to the brightness corresponding to the dynamic range of the third EOTF in which the dynamic range of the brightness of the second EOTF is reduced according to the maximum brightness of the 2EOTF according to the displayable brightness of the display device. , The image is displayed on the display device using the result of the first conversion.

According to this, it is possible to convert the dynamic range of the brightness of the image corresponding to HDR according to the displayable brightness of the display device without performing the brightness conversion processing such as the knee curve processing. Therefore, it is possible to easily perform the luminance conversion of the video of the video data according to the luminance of the display device, and it is possible to suppress the color change before and after the conversion.

Further, the third EOTF maintained the relative relationship of the luminance of the second EOTF by multiplying the value obtained by dividing the displayable luminance by the peak luminance by a variable representing the luminance in the second EOTF. The EOTF may be an EOTF in which the dynamic range of the brightness of the second EOTF is reduced according to the maximum brightness of the second EOTF according to the displayable brightness.

Therefore, it is possible to easily perform the luminance conversion of the video of the video data according to the luminance of the display device, and it is possible to suppress the color change before and after the conversion.

Further, a first determination is made as to whether or not the peak luminance indicated by the peak luminance information exceeds a predetermined luminance stored in advance by the display device, and as a result of the first determination, the peak luminance is said. When the predetermined brightness is exceeded, (i) the code of the fourth EOTF in which the display device stores in advance the brightness in the brightness range from the predetermined brightness of the second EOTF to the peak brightness of the brightness of the video. (Ii) The maximum brightness of the fifth EOTF is set to the fifth EOTF, which is a part of the second EOTF and is a part of the brightness range having the predetermined brightness as the maximum brightness, while maintaining the relative relationship of the brightness of the fifth EOTF. The dynamic range of the brightness of the 5th EOTF is reduced to the 6th EOTF according to the 1st brightness, and the brightness of the dynamic range of the 5th EOTF among the brightness of the video is the brightness of the corresponding dynamic range of the 6th EOTF. The fourth conversion including the fourth conversion may be performed, and the result of the second conversion may be used to display the image on the display device.

According to this, when the peak luminance exceeds the predetermined luminance as a result of the first determination, the second conversion is performed instead of the first conversion. In this way, when the peak luminance exceeds the predetermined luminance, the luminance conversion process (first conversion) is not performed while maintaining the luminance relative relationship, so that the luminance relative relationship before and after the luminance conversion process. Even if it is maintained, it is possible to prevent the appearance from being significantly different due to being too dark in the low luminance range.

Further, in the third conversion, the brightness in the brightness range of the second EOTF from the predetermined brightness to the peak brightness of the brightness of the video is determined by the set of the first brightness and the upper limit value of the narrow range and the said. It may be converted so as to satisfy a linear relationship between the second luminance and the set of the upper limit values of the full range.

Further, when the peak brightness is equal to or less than the predetermined brightness as a result of the first determination, the conversion to reduce the dynamic range of the brightness of the second EOTF in accordance with the first brightness as the displayable brightness is performed. It may be performed as the first conversion.

According to this, when the peak luminance is equal to or less than the predetermined value as a result of the first determination, the first conversion is performed instead of the second conversion, so that there is little possibility that the appearance will be significantly different before and after the conversion process. In some cases, a simpler conversion process can be performed. Therefore, the processing load can be reduced.

Further, the full range may be a range of integer values having a code value of 0 to 1023, and the narrow range may be a range of integer values having a code value of 64 to 940.

Further, the video data further includes the maximum frame average luminance information indicating the maximum frame average luminance which is the maximum value of the average luminance of each of the plurality of frames constituting the video, and the maximum frame average luminance information indicated by the maximum frame average luminance information. A second determination is made to determine whether or not the frame average brightness is ½ or less of the peak brightness, and as a result of the second determination, the maximum frame average brightness is ½ or less of the peak brightness. The second conversion may be performed using a value that is twice the maximum frame average brightness as the predetermined brightness.

In this way, by performing the second determination, it is possible to determine whether or not the proportion of pixels having a peak brightness or a brightness close to the peak brightness is large or small in the video of the video data, and when it is determined that the ratio is small, the maximum Since the second conversion is performed using a value twice the frame average brightness, the brightness of the image can be converted and displayed so as to maintain the gradation of the halftone and the dark part. Therefore, it is possible to reduce as much as possible that the gradation property in the luminance range in which the ratio of the luminance contained in the image is large in the luminance of the image is impaired.

Further, the video data further includes section peak luminance information indicating the section peak luminance which is the peak luminance of the section video for each of the plurality of section videos constituting the video, and is further acquired by the display method. Using the peak brightness information and the section peak brightness information included in the video data, it is determined whether or not the brightness change between two consecutive section images in the plurality of section images is rapid. When three determinations are made and the brightness change is abrupt as a result of the third determination, the dynamic range of the brightness of at least one of the two section images is converted so that the brightness change falls within a predetermined range. Then, as a result of the third determination, when the brightness change is not abrupt, the dynamic range in which the section peak luminance indicated by the section peak luminance information corresponding to the section video is the maximum luminance for each of the two section images. The first conversion may be performed with the EOTF in the second EOTF as the second EOTF.

In this way, since the processing is switched according to whether a sudden change in brightness occurs between continuous section images, it is possible to suppress sudden darkening or brightening of the image, and a sense of unity of the entire image. Can be suppressed from damaging.

Further, the ambient light in the space where the display device is installed is acquired, a fourth determination is made to determine whether or not the acquired ambient light is bright, and as a result of the fourth determination, the ambient light is released. When it is bright, the conversion using the 7th EOTF as the 3rd EOTF in which the dynamic range of the luminance of the 2nd EOTF is reduced according to the display peak luminance of the display device as the displayable luminance is performed as the 1st conversion. As a result of the fourth determination, when the ambient light is dark, the dynamic range of the brightness of the second EOTF is reduced according to the brightness reduced by a predetermined ratio from the display peak brightness as the displayable brightness. The conversion using the 8th EOTF may be performed as the first conversion.

As a result, even when a video image that is supposed to be displayed in absolute brightness is displayed on the display device, it is possible to easily realize the display according to the brightness of the viewing environment.

Further, the displayable luminance may be the display peak luminance of the display device.

Therefore, the brightness of the image can be converted and displayed according to the display peak brightness of the display device.

It should be noted that these general comprehensive or specific embodiments may be realized in a recording medium such as an apparatus, a system, an integrated circuit, a computer program or a computer-readable CD-ROM, and the apparatus, a system, an integrated circuit, a computer may be realized. It may be realized by any combination of programs or recording media.

Hereinafter, the display method and the display device according to one aspect of the present invention will be specifically described with reference to the accompanying drawings.

In addition, all of the embodiments described below show a specific example of the present invention. The numerical values, shapes, materials, arrangement positions and connection forms of components, steps, order of steps, etc. shown in the following embodiments are examples, and are not intended to limit the present invention. Further, among the components in the following embodiments, the components not described in the independent claim indicating the highest level concept are described as arbitrary components.

In the present disclosure, HDR (High Dynamic Range), which is a high-brightness signal with a high dynamic range encoded by SMPTE (Society of Motion Picture & Television Engineers) ST2084 standard EOTF (hereinafter referred to as “PQ curve”), is used. , On a display device (eg, TV, projector, tablet, smartphone, etc.) that has a dynamic range display capability that is different from the peak brightness (maximum brightness or maximum brightness) in the dynamic range of the brightness supported by the HDR signal. The present invention relates to an HDR signal format, a display method of the HDR signal, and a display device for realizing display.

(Embodiment 1)
Hereinafter, the first embodiment will be described with reference to FIGS. 6 to 14.

First, the flow of processing from taking an image to displaying the image on the display unit will be described in order with reference to FIGS. 6 to 11B.

[1-1. Concept of brightness scale when taking images]
FIG. 6 is a diagram showing a scale of luminance at the time of image capture.

As shown in FIG. 6, when an image is taken with a camera, the picture is taken with 18% gray, which is a gray having a reflectance of 18%, as a reference point for brightness. That is, 18% gray is a reference reflectance that serves as a reference for brightness. The Stop number is defined to increase by 1 each time the luminance is doubled, with the luminance at 18% gray as the reference point.

When an image is actually taken by the camera, the brightness obtained from the image sensor of the camera (for example, CMOS, CCD, etc.) changes according to the exposure due to the aperture, shutter speed, sensitivity setting, and the like. That is, the brightness obtained from the image sensor has a different value depending on the exposure even if a subject having the same brightness is photographed. Therefore, the value of the Stop number itself is not an absolute value but a relative value. That is, the stop number cannot represent the brightness.

For example, when shooting the night scene of (1) in FIG. 6, in order to prevent blackout, the dark part is darkened by slowing the shutter speed, opening the aperture, and so on. Set the exposure for the camera so that the bright areas are discarded while leaving the gradation of.

Further, when shooting the daytime indoor scene of FIG. 6 (2), the exposure is set for the camera so that the balance between the dark part and the bright part is good. Further, in the case of shooting the daytime outdoor scene of FIG. 6 (3), the exposure is set to the camera with the exposure reduced in order to prevent the whitening of the bright portion.

In order to convert the relative luminance thus obtained into absolute luminance, it is necessary to calculate the relative relationship with 18% gray.

[1-2. Brightness when taking an image]
FIG. 7 is a diagram showing an example of the brightness of the captured image.

As shown in FIG. 7, the captured image (hereinafter referred to as “original image”) 10A) has a luminance (hereinafter, 0 Stop) corresponding to 18% gray (0 Stop), which is a reference reflectance that serves as a reference for brightness (hereinafter, referred to as “original image”). A pixel having "reference brightness" or "18% Gray value") is shown. B) of the original image 10 shows a pixel having a luminance corresponding to 90% reflectance (90% gray) (2.3 Stops). C) of the original image 10 shows a pixel having a luminance corresponding to 2.3% gray (-3 Stops) of almost black. D) of the original image 10 shows the pixels obtained by photographing the sun, and a very bright luminance is obtained, and has a luminance corresponding to 1150% gray (6 Stops). E) of the original image 10 shows a pixel obtained by photographing a position where specular reflection is occurring, and has a luminance corresponding to 290% gray (4 Stops).

[1-3. Relationship between master generation, distribution method, and display device]
FIG. 8 is a diagram for explaining the relationship between a flow for producing a master for home entertainment corresponding to SDR, a distribution medium, and a display device.

The original image 10 as described with reference to FIG. 7 is an image having a maximum luminance of 1300 nits. That is, when a master image (SDR image) corresponding to an SDR having a maximum brightness of 100 nits is produced using the original image 10, the SDR cannot express a pixel having a brightness of 100 nits or more, so that the brightness of the original image is determined. It is not possible to produce a master image compatible with SDR by using it as it is without conversion. That is, if an attempt is made to produce a master image corresponding to SDR using the original image 10, it is necessary to convert the brightness of the original image to the brightness of the dynamic range corresponding to SDR.

[1-4. Mastering from original image to SDR image]
Next, the SDR grading process (mastering process) from the original image 10 to the SDR image will be described.

First, in order to adapt the video (image) of the content with high brightness component of 100 nits or more taken by the camera to the broadcasting standard such as Bt709, the brightness is kept linearly up to around 80 nits by normal grading processing. Then, the upper part is subjected to knee curve processing so that the maximum brightness is within 100 nits. Specifically, the knee curve process is a process of linearly displaying the luminance of a certain value or less and attenuating the luminance of the certain value or more according to the display peak luminance of the display device to be displayed.

FIG. 9A is a diagram showing an example of the brightness as a result of mastering the original image shown in FIG. 7 into an SDR image. FIG. 9B is a diagram showing an example of the relationship between the original signal value and the SDR signal value for converting (mastering) the original signal value into the SDR signal value. The original signal value is the luminance in the dynamic range of 0 to 1300 nits of the original image 10 (hereinafter referred to as “the luminance of the original image”), and the SDR signal value is the luminance in the luminance range of the SDR (hereinafter referred to as “SDR”). Brightness ".).

As shown in FIG. 9B, in the mastering from the original image 10 to the SDR image 11 in this example, the pixel corresponding to the reference reflectance of 18% gray (0 Stop) has a reference brightness as a reference for brightness. It is a pixel. Therefore, in mastering to an SDR image, even after the original image 10 is converted to the SDR image 11, the luminance (18 nit) of the original image corresponding to 18% gray in the original image 10 is not changed, and the SDR is not changed. Determined as the brightness of.

Here, as shown in FIG. 9B, in the mastering from the original image 10 to the SDR image 11, in the luminance range (0 to 90 nit) equal to or less than the luminance (90 nit) of the original image corresponding to 90% gray of the original image 10. , The brightness of the original image is not changed and is determined as the brightness of the SDR. Further, as shown in FIG. 9B, the luminance of the original image in the luminance range (90 to 1300 [nit]) of the original image 10 larger than the luminance (90 nit) of the original image corresponding to 90% gray of the original image 10 is set to 90. Allocate to the luminance of SDR in the luminance range of ~ 100 nit by linear conversion.

For example, in mastering to the SDR image 11 for pixels corresponding to 90% gray (2.3 Stops) such as B) of the SDR image 11, even after the original image 10 is converted to the SDR image 11. , The brightness (90 nits) of the original image corresponding to 90% gray in the original image 10 is not changed, and is determined as the brightness of the SDR.

Further, in the mastering to the SDR image for the pixels corresponding to 2.3% gray (-3 Stops) such as C) of the SDR image 11, the original image 10 is converted into the SDR image 11 in the same manner as described above. Even after the conversion, the brightness of the SDR is determined without changing the brightness (2 nits) of the original image corresponding to 2.3% gray in the original image 10.

For example, in mastering to an SDR image for pixels corresponding to 1150% gray (6 Stops) such as D) of the SDR image 11, the luminance (1150 nit) of the original image corresponding to 1150% gray in the original image 10 is set. Convert to 100 nits, which is the maximum brightness of SDR.

Further, in mastering to an SDR image for pixels corresponding to 290% gray (4 steps) such as E) of the SDR image 11, the brightness of the original image corresponding to 290% gray in the original image 10 is 95. Convert to nit.

[1-5. First mastering from original image to HDR image]
FIG. 10A is a diagram showing an example of the brightness as a result of mastering the original image shown in FIG. 7 into an HDR image. FIG. 10B is a diagram showing an example of the relationship between the original signal value and the HDR signal value for converting (mastering) the original signal value into the HDR signal value. The HDR signal value is the luminance in the HDR luminance range (hereinafter, referred to as “HDR luminance”). In the mastering from the original image to the HDR image in this example, since the brightness up to 2000 nit is allowed to be assigned as the brightness of the HDR, the brightness of the original image can be maintained as it is even in the HDR image.

For example, a pixel corresponding to 18% gray (0 Stop), which is a reference reflectance, such as A) of the HDR image 12 is a pixel having a reference luminance that serves as a reference for brightness, and therefore is mastered to an HDR image. Then, even after the original image 10 is converted into the HDR image 12, the brightness of the original image (18 nits) corresponding to the 18% gray in the original image 10 is determined without changing the brightness of the HDR.

Similarly, for example, a pixel corresponding to 90% gray (2.3 Stops) such as B) of HDR image 12 and 2.3% gray (-3 Stops) such as C) of HDR image 12. ), A pixel corresponding to 1150% gray (6 Stops) such as D) of the HDR image 12, and a 290% gray (4 Stops) such as E) of the HDR image 12. In mastering to an HDR image, each of the pixels is determined as the HDR brightness without changing the brightness of the original image.

[1-6. Specific example of luminance conversion]
FIG. 11A is an example of the result of acquiring the HDR image obtained by the mastering of FIG. 10A and converting the luminance for a display device having a second maximum luminance of 500 nits. FIG. 11B is a diagram showing an example of the relationship between the HDR signal value and the TV signal value for converting the HDR signal value into the TV signal value.

In this example, the second maximum luminance that HDRTV can display is limited to 500 nits. Therefore, it is necessary to convert the HDR luminance indicated by the HDR signal into the display luminance in the luminance range of the display.

The HDR signal is acquired, and the luminance (reference luminance) corresponding to 18% gray (0 Stop), which is the reference of the brightness, is extracted from the acquired HDR signal. The HDR signal indicating the brightness of the HDR image 13 holds 36 nits as the reference brightness, and it can be seen that the producer intentionally changed the reference brightness. Therefore, for the luminance indicated by the HDR signal, which is equal to or less than the luminance corresponding to 90% gray (180 nit), the luminance value indicated by the HDR signal is maintained as it is, and the luminance corresponding to 90% gray (180 nit). For the luminance exceeding the HDR signal, the first maximum luminance (HPL: 1300 nit) indicated by the HDR signal is linearly converted so as to be the second maximum luminance (DPL: 500 nit) that can be displayed by HDRTV. I do.

That is, in the luminance conversion (S304) in this example, when the reference luminance is a third reference value (36 nits) different from the first reference value (18 nits), it is greater than 36 nits and equal to or less than the fourth reference value (90 nits). For the HDR signal indicating the luminance, the luminance of the HDR indicated by the HDR signal is determined as the display luminance. Further, in the luminance conversion (S304), for the HDR signal showing the luminance exceeding 90 nits, the first maximum luminance (HPL) is set with respect to the luminance of HDR from 90 nits to the second maximum luminance (DPL) that can be displayed in HDRTV. The HDR luminance is converted to the display luminance by performing a linear transformation corresponding to the second maximum luminance (DPL).

By performing the brightness conversion in this way, the pixel A) corresponding to 18% gray of the HDR image 13, the pixel B) corresponding to 90% gray of the HDR image 13, and the 2.3% gray of the HDR image 13 are obtained. The corresponding pixel C) is determined as the display brightness without changing the brightness of the HDR image 13 as it is. Then, for the pixel D) corresponding to 1150% gray of the HDR image 13, 446 nit obtained by performing the above linear conversion is determined as the display luminance, and for the pixel E) corresponding to 290% gray of the HDR image 13. Determines 313 nits obtained by performing the above linear conversion as the display luminance.

[1-7. Display device and display method]
Next, a display device that performs the display method of the first embodiment will be described with reference to FIGS. 12 and 13.

FIG. 12 is a diagram showing a functional block of the display device according to the first embodiment. FIG. 13 is a diagram for explaining a specific example of the conversion process (first conversion) in the conversion unit of the display device.

As shown in FIG. 12, the display device 100 includes a conversion unit 101 and a display unit 102. The display device 100 is an HDR display device capable of displaying an HDR image, and is, for example, an HDRTV or HDR compatible display.

The conversion unit 101 acquires video data including an HDR signal and static metadata (peak brightness information for each title (The Maximum Content Light Level (MaxCLL)). The conversion unit 101 responds to the acquired static metadata. The HDR effect is controlled, and a process of converting the PQ curve into a gamma curve in the luminance range supported by the display unit 102 is performed. Specifically, the conversion unit 101 performs a process of converting the MaxCLL value as shown in FIG. From a part of the PQ curve without changing the relative relationship of the brightness of the PQ curve (second EOTF) in the brightness range of 0 to 800 nit so as to match (for example, 800 nit) with the display peak brightness (for example, 750 nit) of HDRTV. It is converted into a gamma curve (third EOTF) according to the display peak luminance of HDRTV. The conversion unit 101 is realized by, for example, a processor, a memory for storing a program, or the like.

In other words, the conversion unit 101 displays the maximum luminance of the second EOTF on the display unit 102 of the display device 100 while maintaining the relative relationship of the luminance of the second EOTF with respect to the second EOTF which is a part of the PQ curve as the first EOTF. The first conversion is performed to convert the luminance of the image to the luminance corresponding to the dynamic range of the third EOTF in which the dynamic range of the luminance of the second EOTF is reduced according to the displayable luminance (for example, the display peak luminance). The displayable luminance of the display unit 102 in this case is specifically the display peak luminance of the display unit 102. In this way, the conversion unit 101 does not perform tone mapping processing using the knee curve, which requires a complicated circuit, when displaying the video data of the HDR content whose brightness is defined by the PQ curve on the HDRTV. It is possible to suppress the change of the color of each pixel before and after the first conversion in the conversion unit 101.

Here, the first EOTF shows the correspondence between the luminance and the code value of HDR. The second EOTF is an EOTF of the first EOTF cut out in a luminance range in which 0 nit is the minimum luminance and the peak luminance indicated by the peak luminance information included in the acquired video data is the maximum luminance.

The third EOTF is obtained by, for example, multiplying the value obtained by dividing the displayable luminance by the peak luminance indicated by the peak luminance information by a variable representing the luminance in the second EOTF which is a part of the PQ curve. This is an EOTF in which the dynamic range of the brightness of the second EOTF is reduced according to the displayable brightness of the maximum brightness of the second EOTF while maintaining the relative relationship of the brightness of the second EOTF. That is, the relative relationship of the luminance of the second EOTF is the ratio between the plurality of luminancees associated with the plurality of different code values for the set of the plurality of luminancees and the code values associated with the second EOTF. Therefore, conversion while maintaining the relative relationship of the brightness of the second EOTF is when there is a first pre-conversion brightness on the second EOTF and a second pre-conversion brightness on the second EOTF different from the first pre-conversion brightness. Therefore, when the conversion of the first pre-conversion luminance is referred to as the first post-conversion luminance and the post-conversion of the second pre-conversion luminance is the second post-conversion luminance, the first pre-conversion luminance and the second pre-conversion luminance are the first. So that the 1 ratio and the 2nd ratio of the 1st conversion brightness and the 2nd conversion brightness are substantially equal (the error between the 1st ratio and the 2nd ratio after conversion is within a predetermined threshold value). To) is to convert.

The display unit 102 displays an image using the result of the first conversion in the conversion unit 101. The display unit 102 is realized by, for example, an LCD panel, a backlight, a drive circuit of the LCD panel, a control circuit of the backlight, and the like.

The third EOTF is generated by performing the first conversion while maintaining the relative relationship of the luminance of the second EOTF which is a part of the PQ curve. Therefore, the display unit 102 can display the video of the input video data while maintaining the contrast relationship at the time of content production. At this time, the display unit 102 does not maintain the absolute brightness of each pixel, but displays an image having a brightness different from the absolute brightness at the time of content production and maintaining the contrast ratio between the pixels.

Next, another specific example of the conversion process of the conversion unit 101 of the display device 100 will be described. FIG. 14 is a diagram for explaining another specific example of the conversion process in the conversion unit.

As shown in FIG. 14, when the MaxCLL of the video data of the HDR content exceeds a predetermined luminance (for example, 1000 nits), if the luminance is converted while maintaining the relative relationship up to the MaxCLL, the reduction ratio with respect to the overall luminance of the image becomes smaller. Therefore, the luminance in the low luminance range before the conversion (for example, the luminance of 100 nit or less) becomes very small after the conversion. Therefore, even if the MaxCLL value exceeds a predetermined brightness, if the luminance conversion process is performed while maintaining the luminance relative relationship uniformly, even if the luminance relative relationship is maintained before and after the conversion process. In the low-luminance range, the appearance may be significantly different due to being too dark. Therefore, among the luminance of the image, the first conversion for maintaining the relative relationship is performed in the luminance range of the predetermined luminance or less, and the region of the predetermined luminance or more is the Sparkle region and the second as the same processing as the Super White of SDR. Perform the conversion.

Specifically, when the MaxCLL of the video data exceeds 1000 nits, the conversion unit 101 sets the MaxCLL to 1023, which is the upper limit code value (CV) of the full range (see below), and the luminance of the video is increased. , The third conversion that linearly expresses the luminance in the luminance range from 1000 nits to MaxCLL, and the value corresponding to 1000 nits is set to 940, which is the upper limit code value (CV) of the narrow range (see below), and the luminance of the image is set to 940. , The luminance in the luminance range from 0 nit to 1000 nit is subjected to the fourth transformation of reducing the dynamic range of the luminance while maintaining the relative relationship of the luminance in the same manner as the first transformation described with reference to FIG. The image is displayed using the result of the second conversion including the third conversion and the fourth conversion. On the other hand, when the MaxCLL of the video data is 1000 nits or less, the conversion unit 101 performs the first conversion of setting the MaxCLL to 940, which is the upper limit code value (CV) of the narrow range.

In short, the conversion unit 101 makes a first determination as to whether or not the peak luminance indicated by the peak luminance information exceeds a predetermined luminance (for example, 1000 nits) stored in advance by the display device 100, and the result of the first determination is Accordingly, one of the first conversion and the second conversion is selectively performed. Specifically, when the peak luminance exceeds a predetermined luminance as a result of the first determination, a second conversion different from the first conversion is performed. The second conversion is a conversion including a third conversion for converting the luminance in the luminance range from the predetermined luminance to the peak luminance and a fourth transformation for converting the luminance in the luminance range from 0 nit to the predetermined luminance.

In the third conversion, the brightness of the image in the brightness range from the predetermined brightness of the second EOTF to the peak brightness indicated by the peak brightness information is the full range of the code value from the first brightness corresponding to the upper limit of the narrow range of the code value of 940. It is converted into the luminance in the luminance range up to the second luminance corresponding to 1023 which is the upper limit value of. Further, in the third conversion, the brightness in the brightness range from the predetermined brightness to the peak brightness of the second EOTF among the brightness of the image is set to the set of the upper limit values of the first brightness and the narrow range, and the upper limit values of the second brightness and the full range. Transform to satisfy a linear relationship with the set of.

Here, the full range is a range in which the code value of the fourth EOTF stored in advance by the display device 100 is specified, and when the code value is specified by 10 bits, for example, the setting is from 0 to 1023. It is a range of numerical values. That is, the full range is a range in which the minimum value to the maximum value are used among the integer values that can express the luminance code value by the bit length. Further, the narrow range is a range narrower than the full range, and when the code value is defined by 10 bits, it is, for example, a range of integer values from 64 to 940. That is, the narrow range is a range in which an integer value in a range narrower than the full range is used among the integer values that can express the luminance code value by the bit length.

In the fourth conversion, the maximum brightness of the fifth EOTF is set to the fifth EOTF, which is a part of the second EOTF and is a part of the brightness range in which the predetermined brightness is the maximum brightness, while maintaining the relative relationship of the brightness of the fifth EOTF. The dynamic range of the brightness of the 5th EOTF is reduced to the 6th EOTF according to the 1st brightness, and the brightness of the dynamic range of the 5th EOTF of the video is converted to the brightness of the corresponding dynamic range of the 6th EOTF.

On the other hand, when the peak brightness is equal to or less than the predetermined brightness as a result of the first determination, the conversion unit 101 performs conversion to reduce the dynamic range of the brightness of the second EOTF according to the first brightness as the displayable brightness. This is performed as the first conversion.

In this case, the display unit 102 displays the video using the result of the first conversion or the result of the second conversion.

[1-8. Effect, etc.]
According to the display method according to the present embodiment, the dynamic range of the luminance of the image corresponding to HDR can be converted according to the display peak luminance of the display device without performing the luminance conversion processing such as the knee curve processing. can. Therefore, it is possible to easily perform the luminance conversion of the video of the video data corresponding to HDR according to the display peak luminance, and it is possible to suppress the color change before and after the conversion.

Further, according to the display method according to the present embodiment, when the peak luminance exceeds the predetermined luminance as a result of the first determination, the second conversion is performed instead of the first conversion. In this way, when the peak luminance exceeds the predetermined luminance, the luminance conversion process (first conversion) is not performed while maintaining the luminance relative relationship, so that the luminance relative relationship before and after the luminance conversion process. Even if it is maintained, it is possible to prevent the appearance from being significantly different due to being too dark in the low luminance range.

Further, according to the display method according to the present embodiment, when the peak luminance is equal to or less than a predetermined value as a result of the first determination, the first conversion is performed instead of the second conversion, so that the appearance is good before and after the conversion process. If it is unlikely that there will be a large difference, a simpler conversion process can be performed. Therefore, the processing load can be reduced.

[1-9. Modification 1]
In the above embodiment, for example, 1000 nits is adopted as the predetermined luminance as the determination criterion of the first determination, but the following values may be adopted.

For example, the predetermined brightness is determined according to the value of the maximum frame average brightness information (MaxFALL: The Maximum Frame-Average Light Level) indicating the maximum frame average brightness which is the maximum value of the average brightness of each of the plurality of frames constituting the video. You may. The maximum frame average luminance information is information included in the static metadata included in the video data.

As a specific process, the conversion unit 101 makes a second determination to determine whether or not the maximum frame average luminance indicated by the maximum frame average luminance information is ½ or less of the peak luminance. Then, when the maximum frame average brightness is ½ or less of the peak brightness as a result of the second determination, the conversion unit 101 performs the second conversion using a value twice the maximum frame average brightness as the predetermined brightness.

In this way, by performing the second determination, it is possible to determine whether or not the proportion of pixels having a peak brightness or a brightness close to the peak brightness is large or small in the video of the video data, and when it is determined that the ratio is small, the maximum Since the second conversion is performed using a value twice the frame average brightness, the brightness of the image can be converted and displayed so as to maintain the gradation of the halftone and the dark part. Therefore, it is possible to reduce as much as possible that the gradation property in the luminance range in which the ratio of the luminance contained in the image is large in the luminance of the image is impaired.

[1-10. Modification 2]
In the above embodiment, the conversion unit 101 performs the first conversion or the second conversion for each content by using the peak luminance information included in the static metadata, but the present invention is not limited to this. For example, when the content contains dynamic metadata, the dynamic metadata corresponding to the section video for each of the plurality of section videos (cuts, a series of sequences) constituting the video of the video data of the content. May be used in place of MaxCLL, which is static metadata, to perform the first conversion or the second conversion. The dynamic metadata is section peak luminance information (The Maximum Sequence Light Level: MaxSLL) indicating the peak luminance (section peak luminance) of the section video for each of the plurality of section videos. As a result, HDR content can be displayed more efficiently using the peak luminance of HDRTV.

When the section peak brightness corresponding to each section image is lower than the display peak brightness of HDRTV, the brightness of the section image is displayed as it is without performing the conversion process of maintaining the relative relationship and extending in the bright direction. You may.

In addition, when the section peak brightness corresponding to each section image is significantly lower than the peak brightness (eg 1/2 or less) or when the section peak brightness of continuous section images is significantly different from each other (difference of 50% or more). If the above processing is performed as it is, the low-luminance range (dark part) may suddenly become bright and the entire image may not be unified. Therefore, instead of using the section peak luminance as it is, the section peak luminance (MaxSLL) is corrected by, for example, (MaxCLL + MaxSLL) / 2, (MaxSLL (x) + MaxSLL (X + 1)) / 2. Then, by performing the above processing using the corrected numerical value, a sudden change in luminance may be suppressed.

That is, the conversion unit 101 uses the peak luminance information and the interval peak luminance information included in the acquired video data to determine whether or not the luminance change between two consecutive interval images in the plurality of interval images is rapid. Judgment The third judgment is performed. Then, when the brightness change is abrupt as a result of the third determination, the conversion unit 101 converts the dynamic range of the brightness of at least one of the two section images so that the brightness change falls within a predetermined range. Further, when the brightness change is not abrupt as a result of the third determination, the conversion unit 101 has a dynamic range in which the section peak luminance indicated by the section peak luminance information corresponding to the section video is the maximum luminance for each of the two section images. The first conversion is performed with the EOTF in the second EOTF as the second EOTF. In this way, since the processing is switched according to whether a sudden change in brightness occurs between continuous section images, it is possible to suppress sudden darkening or brightening of the image, and a sense of unity of the entire image. Can be suppressed from damaging.

(Embodiment 2)
Next, the second embodiment will be described with reference to FIGS. 15 and 16.

[2-1. Second issue]
The display method of reducing the dynamic range of the brightness of the video in the HDR content and displaying it on the HDRTV is different from the case of changing the dynamic range of the brightness of the video in the SDR content and displaying it on the SDRTV, and has the following problems. There is also.

FIG. 15 is a diagram for explaining an example of display processing in the case where the SDR signal is displayed by SDRTV according to the brightness in the viewing environment.

As described in FIG. 4, in SDRTV, the SDR signal of the SDR content is inversely quantized using the SDR EOTF (gamma curve) to maintain the relative brightness (contrast ratio) instead of the absolute brightness. It is displayed. By the way, as shown in FIG. 15, an SDRTV is provided with a dimming element, and the emission intensity of the backlight of the display unit is dynamically changed according to the brightness of the viewing environment acquired by the dimming element. There is a method of displaying the SDR content while maintaining the contrast ratio between the dark part and the bright part according to the brightness of the viewing environment.

In the example of FIG. 15, when displaying the SDR content corresponding to the SDR EOTF shown in FIG. 15 (a) on the SDRTV, the display control is changed depending on whether the viewing environment is a dark room or a bright room. is doing. The SDRTV has the ability to display a luminance (for example, 250 nits) in which the display peak luminance exceeds 100 nits, which is the peak luminance of the dynamic range of the EOTF (gamma curve) luminance of the SDR. In such SDRTV, if it is determined that the viewing environment is a dark room, the peak brightness to be displayed is suppressed to 100 nits and displayed as shown in (b-1) of FIG. 15 (b). On the other hand, if it is determined that the viewing environment is a bright room, the peak luminance to be displayed as shown in (b-2) of FIG. 15 (b) is extended to a maximum of 250 nits and displayed. In this way, in SDRTV, the brightness of the SDR signal image of the SDR content is managed by the relative brightness, so the peak brightness of the image displayed on the SDRTV while maintaining the relative brightness is changed according to the brightness of the viewing environment. Can be easily done.

Not only for SDRTV that displays the SDR signal while maintaining the relative brightness of the image, but also for HDRTV that displays the HDR signal image obtained by quantizing the absolute brightness of the captured image with the PQ curve. However, it is required to perform display control that changes the dynamic range of the brightness of the image according to the brightness of the viewing environment (dark room, dark room, slightly bright room, etc.) instead of displaying with absolute brightness. In other words, for HDRTV, as with SDRTV, even if the brightness of the viewing environment changes, by performing display control that maintains an appropriate contrast ratio and displays it, the same HDR effect can be given to the viewer as much as possible. It is required to provide.

However, since the HDR video of HDR content is created by the content creator on the premise that it is displayed in absolute brightness, the HDR signal is a conversion method that converts the brightness of the video while maintaining the relative brightness to the brightness of the video. Even if it is applied as it is to the image of, it is difficult to display the image of appropriate brightness on the display unit.

Further, in the case of HDR video of HDR content, the peak brightness is often up to about 800 to 4000 nits, which exceeds the peak brightness of normal HDRTV. Therefore, even when the viewing environment is dark, it is necessary to maximize the emission intensity of the backlight in order to display the peak brightness of the HDR image. Is difficult.

Further, since the dynamic range of the brightness of the HDR EOTF (PQ curve) is 0 to 10,000 nit and the dynamic range of the brightness of the SDR EOTF (gamma curve) is 0 to 100 nit, the HDR EOTF is used. However, the dynamic range of brightness is 100 times larger than that of SDR's EOTF. In addition, the content itself can be displayed on the display device by fully using 0 to 100 nits in the case of SDR video, but in the case of HDR video, it is displayed on the display device using a dynamic range of brightness of 0 to 10,000 nits. This is rare, and there is a high possibility that an image having a peak brightness of about 800 to 4000 nits will be displayed on the display device. That is, as in the case of displaying the SDR video on the SDRTV, it is not possible to simply control the backlight so that the peak brightness of the dynamic range of the HDR EOTF brightness is matched with the HDRTV display peak brightness.

[2-2. Display device and display method]
Next, a display device that performs the display method of the second embodiment will be described with reference to FIG.

FIG. 16 is a diagram showing a functional block of the display device according to the second embodiment.

As shown in FIG. 16, the display device 100a includes a conversion unit 101a, a display unit 102, and a viewing environment optical input unit 103. Since the display unit 102 has the same configuration as the display unit 102 of the display device 100 of the first embodiment, detailed description thereof will be omitted.

The viewing environment light input unit 103 detects the intensity of the ambient light (that is, the brightness of the viewing environment) in the space where the display device 100a is installed, and sends the detection result to the conversion unit 101a. The viewing environment optical input unit 103 is realized by, for example, an illuminance sensor.

The conversion unit 101a makes a fourth determination to determine whether or not the ambient light is bright according to the intensity of the ambient light detected by the viewing ambient light input unit 103. Then, when the ambient light is bright as a result of the fourth determination, the conversion unit 101a performs the conversion using the seventh EOTF as the third EOTF as the first conversion. The seventh EOTF is an EOTF in which the dynamic range of the luminance of the second EOTF is reduced according to the displayable luminance with the display peak luminance of the display device as the displayable luminance. Further, when the ambient light is dark as a result of the fourth determination, the conversion unit 101a performs the conversion using the eighth EOTF as the third EOTF as the first conversion. The eighth EOTF is an EOTF in which the dynamic range of the brightness of the second EOTF is reduced in accordance with the brightness reduced by a predetermined ratio from the display peak brightness of the display device.

Specifically, when the detected ambient light intensity is equal to or less than a predetermined threshold value and it is determined that the viewing environment is dark, the maximum emission intensity of the backlight is not maximized and the emission intensity of the backlight of the display unit 102 is not maximized. Therefore, for example, the emission intensity is reduced by 20%. Further, when it is determined that the intensity of the detected ambient light exceeds a predetermined threshold value and the viewing environment is bright, the emission intensity of the backlight is maximized. If it is determined that the viewing environment is dark, the first conversion is performed according to the brightness 20% lower than the display peak brightness, and if it is determined that the viewing environment is bright, the first conversion is performed according to the display peak brightness. Perform the conversion.

This makes it possible to easily realize a display according to the brightness of the viewing environment even when the HDR image, which is supposed to be displayed in absolute brightness, is displayed on the HDRTV.

(Other embodiments)
In each of the above embodiments, each component may be configured by dedicated hardware or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or a processor reading and executing a software program recorded on a recording medium such as a hard disk or a semiconductor memory. Here, the software that realizes the display method of each of the above embodiments is the following program.

That is, this program displays on a computer an image of video data in which the brightness of the image is defined by the first EOTF (Electoro-Optical Transfer Foundation), which indicates the correspondence between the brightness of HDR (High Dynamic Range) and the code value. The video data includes peak luminance information indicating the peak luminance of the video, and in the display method, the video data is acquired and is a part of the first EOTF. The second EOTF, while maintaining the relative relationship of the luminance of the second EOTF with respect to the second EOTF which is a part of the luminance range having the peak luminance as the maximum luminance indicated by the peak luminance information included in the video data. The first conversion is performed to convert the brightness of the image to the brightness corresponding to the dynamic range of the third EOTF in which the dynamic range of the brightness of the second EOTF is reduced according to the displayable brightness of the display device, and the first conversion is performed. (1) Using the result of the conversion, the display method of displaying the image on the display device is executed.

Although the display method and the display device according to one or more aspects of the present invention have been described above based on the embodiment, the present invention is not limited to this embodiment. As long as it does not deviate from the gist of the present invention, one or more of the present embodiments may be modified by those skilled in the art, or may be constructed by combining components in different embodiments. It may be included within the scope of the embodiment.

The present disclosure is useful as a display method, a display device, etc., which can easily perform luminance conversion of an HDR-compatible video data image according to the display peak luminance and can suppress a color change before and after the conversion. be.

100, 100a Display device 101, 101a Conversion unit 102 Display unit 103 Viewing environment optical input unit

Claims (2)

It is a display method for displaying the image of video data whose brightness is defined by the first EOTF (Electro-Optical Transfer Function), which shows the correspondence between the brightness of HDR (High Dynamic Range) and the code value.
The video data includes peak luminance information which is metadata indicating the peak luminance of the video.
In the above display method,
Acquire the video data and
When the portion of the brightness range in which the peak brightness indicated by the peak brightness information included in the acquired video data is the maximum brightness, which is a part of the first EOTF, is defined as the second EOTF.
A third conversion that converts the brightness of the image in the brightness range from the predetermined brightness to the peak brightness into a brightness range in which the display peak brightness of the display device is the maximum brightness.
A portion of the first 2EOTF, the predetermined luminance with respect to the 5EOTF a part of the luminance range of the maximum brightness, the first 5EOTF while maintaining the relative relationship of the luminance of the dynamic range of brightness of the first 5EOTF The second conversion including the fourth conversion of converting the brightness of the video into the reduced sixth EOTF and converting the brightness of the dynamic range of the fifth EOTF to the brightness of the corresponding dynamic range of the sixth EOTF. Do,
A display method for displaying the image on the display device using the result of the second conversion. It is a display device that displays the image of video data in which the brightness of the image is defined by the first EOTF (Electro-Optical Transfer Function), which shows the correspondence between the brightness of HDR (High Dynamic Range) and the code value.
The video data includes peak luminance information which is metadata indicating the peak luminance of the video.
The display device is
When the video data is acquired and the portion of the brightness range having the peak brightness indicated by the peak brightness information included in the acquired video data as the second EOTF is defined as a part of the first EOTF.
A third conversion that converts the brightness of the image in the brightness range from the predetermined brightness to the peak brightness into a brightness range in which the display peak brightness of the display device is the maximum brightness.
A portion of the first 2EOTF, the predetermined luminance with respect to the 5EOTF a part of the luminance range of the maximum brightness, the first 5EOTF while maintaining the relative relationship of the luminance of the dynamic range of brightness of the first 5EOTF The second conversion including the fourth conversion of converting the brightness of the video into the reduced sixth EOTF and converting the brightness of the dynamic range of the fifth EOTF to the brightness of the corresponding dynamic range of the sixth EOTF. The conversion part to be performed and
A display device including a display unit for displaying the image using the result of the second conversion in the conversion unit.

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