JP6868797B2 - Conversion method and conversion device - Google Patents

Description

The present disclosure relates to a conversion method relating to the brightness of an image.

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

The conversion method according to one aspect of the present disclosure is a conversion method for converting the brightness of an image to be displayed on a display device. The first luminance signal indicating the code value obtained by quantization is acquired, and the code value indicated by the acquired first luminance signal is determined based on the luminance range of the display device. It is converted into a second luminance value corresponding to the second luminance range, which is a maximum value smaller than the maximum value of the range and larger than 100 nits.

The display device according to one aspect of the present disclosure generates a video linear signal by converting a video signal having a luminance range of HDR (High Dynamic Range) using EOTF (Electro-Optical Transfer Function) for HDR. The maximum luminance of the first EOTF conversion unit and the first graphics signal having a luminance range of 100 nits is defined as a value determined at a predetermined ratio with respect to the maximum luminance that can be displayed by the display unit. By converting the first luminance conversion unit for converting into a second luminance signal having a luminance range and the second luminance signal by using the EOTF (Electro-Optical Transfer Function) for HDR. A second EOTF conversion unit that generates a graphics linear signal, a compositing unit that synthesizes the video linear signal and the graphics linear signal to generate a composite signal, and a display unit that displays the brightness range of the composite signal. A second luminance conversion unit that converts into a luminance range having a maximum luminance that can be displayed and having a maximum luminance larger than 100 nits, and the display unit that displays the combined signal after conversion by the second luminance conversion unit. And have.

The conversion method according to one aspect of the present disclosure is a conversion method for converting the brightness of an image to be displayed on a display device, and the brightness of the image is composed of a luminance value in the first luminance range, and the luminance value of the image is The first luminance signal indicating the code value obtained by quantization is acquired, and the code value indicated by the acquired first luminance signal is determined based on the luminance range of the display device. It is converted to a second luminance value corresponding to the second luminance range, which is a maximum value smaller than the maximum value of the range and larger than 100 nits, and in the conversion to the second luminance value, the luminance in the first luminance range is obtained. EOTF (Electro-Optical) in which a value is associated with a plurality of first code values.
Using the Transfer Function), the first luminance value associated with the first luminance signal in the EOTF is determined for the first luminance signal indicated by the acquired first luminance signal, and the determined first luminance value is determined. Regarding the value, the second luminance value corresponding to the second luminance range, which is previously related to the first luminance value, is determined, and the first luminance value corresponding to the first luminance range is referred to as the second luminance. The first luminance conversion for converting to the second luminance value corresponding to the range is performed, and the maximum value of the second luminance range is the maximum luminance value of the display device. In the first luminance conversion, the first luminance conversion is performed. When the brightness value is the first maximum brightness value which is the maximum value among the brightness values for a plurality of images constituting the video, the second maximum brightness value which is the maximum brightness of the display device is set to the second maximum brightness value. When the first brightness value is determined as the brightness value and is equal to or less than the average brightness value which is the average of the brightness values for a plurality of images constituting the video, the first brightness value is not converted and the first brightness value is not converted. Is determined as the second luminance value, and when the first luminance value is equal to or greater than the first maximum luminance value, the second maximum luminance value is determined as the second luminance value.

FIG. 1 is a diagram for explaining the evolution of video technology. FIG. 2 is a diagram for explaining the relationship between video production, a distribution method, and a display device when introducing a new video expression into the content. FIG. 3 is a diagram for explaining the relationship between the master, the distribution method, and the display device at the time of introducing HDR. FIG. 4A is a diagram for explaining the SDR display process in the SDRTV. FIG. 4B is a diagram for explaining SDR display processing in SDRTV having a peak brightness of 300 nits. FIG. 5 is a diagram for explaining the conversion from HDR to SDR. FIG. 6A is a diagram for explaining Case 1 in which only the HDR signal corresponding to HDR is stored in the HDR disk. FIG. 6B is a diagram for explaining the case 2 in which the HDR signal corresponding to HDR and the SDR signal corresponding to SDR are stored in the HDR disk. FIG. 7 is a diagram for explaining a conversion process from HDR to pseudo HDR. FIG. 8A is a diagram showing an example of EOTF (Electro-Optical Transfer Function) corresponding to each of HDR and SDR. FIG. 8B is a diagram showing an example of reverse EOTF corresponding to HDR and SDR, respectively. FIG. 9 is an explanatory diagram of a method of determining the code value of the luminance signal stored in the content and a process of restoring the luminance value from the code value at the time of reproduction. FIG. 10A is a diagram showing an example of display processing in which an HDR signal is converted and HDR display is performed in HDRTV. FIG. 10B is a diagram showing an example of a display process for performing HDR display using an HDR compatible playback device and SDRTV. FIG. 10C is a diagram showing an example of a display process for displaying HDR between an HDR compatible playback device and SDRTV connected to each other via a standard interface. FIG. 11 is a block diagram showing a configuration of a conversion device and a display device according to an embodiment. FIG. 12 is a flowchart showing a conversion method and a display method performed by the conversion device and the display device of the embodiment. FIG. 13A is a diagram for explaining the first luminance conversion. FIG. 13B is a diagram for explaining another example of the first luminance conversion. FIG. 14 is a diagram for explaining the second luminance conversion. FIG. 15 is a flowchart showing detailed processing of the display setting. FIG. 16 is a diagram for explaining the third luminance conversion. FIG. 17 is a diagram for explaining a conversion process from HDR to pseudo HDR. FIG. 18 is a diagram for explaining a reproduction operation of the dual disc. FIG. 19 is a flowchart showing a reproduction operation of the dual disc.

(Knowledge on which this disclosure was based)
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 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, respectively. .. 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.

However, in the luminance correction (conversion) of the image signal processing device and the like disclosed in Patent Document 1, when the luminance is corrected (converted) from the first luminance range to the second luminance range in which the luminance range is reduced. No consideration was given to the brightness conversion method.

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

The display device according to one aspect of the present disclosure generates a video linear signal by converting a video signal having a luminance range of HDR (High Dynamic Range) using EOTF (Electro-Optical Transfer Function) for HDR. The maximum luminance of the first EOTF conversion unit and the first graphics signal having a luminance range of 100 nits is defined as a value determined at a predetermined ratio with respect to the maximum luminance that can be displayed by the display unit. By converting the first luminance conversion unit for converting into a second luminance signal having a luminance range and the second luminance signal by using the EOTF (Electro-Optical Transfer Function) for HDR. A second EOTF conversion unit that generates a graphics linear signal, a compositing unit that synthesizes the video linear signal and the graphics linear signal to generate a composite signal, and a display unit that displays the brightness range of the composite signal. A second luminance conversion unit that converts into a luminance range having a maximum luminance that can be displayed and having a maximum luminance larger than 100 nits, and the display unit that displays the combined signal after conversion by the second luminance conversion unit. And have.

Further, for example, the graphics signal may be a signal for displaying subtitles or menus.

The display method according to one aspect of the present disclosure is a conversion method for converting the brightness of an image to be displayed on a display device. The first luminance signal indicating the code value obtained by quantization is acquired, and the code value indicated by the acquired first luminance signal is determined based on the luminance range of the display device. It is converted into a second luminance value corresponding to the second luminance range, which is a maximum value smaller than the maximum value of the range and larger than 100 nits.

According to this, the luminance can be appropriately converted from the first luminance range to the second luminance range in which the luminance range is reduced.

Further, for example, in the conversion to the second luminance value, the above-mentioned acquired using EOTF (Electro-Optical Transfer Function) in which the luminance value in the first luminance range and a plurality of first code values are related to each other. For the first code value indicated by the first luminance signal, the first luminance value associated with the first luminance signal in the EOTF is determined, and for the determined first luminance value, the first luminance value is set in advance. The associated second luminance value corresponding to the second luminance range is determined, and the first luminance value corresponding to the first luminance range is converted to the second luminance value corresponding to the second luminance range. The first luminance conversion to be converted may be performed.

Further, for example, the maximum value of the second luminance range is the maximum luminance value of the display device, and in the first luminance conversion, the first luminance value is a luminance value for a plurality of images constituting the image. In the case of the first maximum luminance value, which is the maximum value among the above, the second maximum luminance value, which is the maximum luminance value of the display device, may be determined as the second luminance value.

Further, for example, in the first luminance conversion, when the first luminance value is equal to or less than the average luminance value which is the average of the luminance values for a plurality of images constituting the video, the first luminance value is not converted. The first luminance value is determined as the second luminance value, and when the first luminance value is equal to or greater than the first maximum luminance value, the second maximum luminance value is determined as the second luminance value. May be good.

Further, for example, in the first luminance conversion, when the first luminance value is between the average luminance value and the first maximum luminance value, the natural logarithm is used to correspond to the first luminance value. The second luminance value may be determined.

Further, for example, the luminance information including at least one of the first maximum luminance value and the average luminance value which is the average of the luminance values for the plurality of images constituting the video may be acquired as the meta information of the video. ..

Further, for example, the luminance information includes at least one of the first maximum luminance value and the average luminance value which is the average of the luminance values for a plurality of images constituting the video by acquiring the first luminance signal from the recording medium. May be obtained via the network.

Further, for example, the first maximum value which is the luminance information corresponding to each of the plurality of scenes of the video and is the maximum value among the luminance values for the plurality of images constituting the scene for each scene. Luminance information including at least one of the luminance value and the average luminance value which is the average of the luminance values for the plurality of images constituting the scene is acquired, and in the first luminance conversion, the said The second luminance value may be determined according to the luminance information corresponding to the scene.

Further, for example, with respect to the determined second luminance value, a third luminance value corresponding to a third luminance range having a maximum value of 100 nits, which is previously related to the second luminance value, is determined, and the first luminance value is determined. The second luminance value corresponding to the two luminance ranges is converted into the third luminance value corresponding to the third luminance range, and the determined third luminance value is the third luminance. Using the inverse EOTF that associates the brightness value in the range with a plurality of third code values, the third brightness value is quantized, the third code value obtained by the quantization is determined, and the third brightness is determined. The third luminance value corresponding to the range may be converted into a third luminance signal indicating the third code value, and the third luminance signal may be output to the display device.

Further, for example, in the second luminance conversion, the determined second luminance value is converted to the second luminance value by using the luminance-related information corresponding to the display characteristic information which is the information indicating the display characteristic of the display device. The associated luminance value may be determined as the third luminance value, and the luminance conversion process may be switched according to the display characteristic information.

Further, for example, the display characteristic information is the display mode of the display device, and in the second luminance conversion, when the display mode is the normal mode, the third luminance value is directly proportional to the second luminance value. When the display mode is a dynamic mode in which the brightness is converted to a direct proportional value and the high-luminance pixel is brighter and the low-luminance pixel is darker than the normal mode, the third luminance value of the low-luminance pixel is. The third luminance value of the high-luminance pixel may be converted to a value lower than the direct-proportional value directly proportional to the second luminance value to a value higher than the direct-proportional value directly proportional to the second luminance value.

Further, for example, in the first luminance conversion, the second maximum luminance value may be determined by using the display characteristic information which is the information indicating the display characteristic of the display device.

Further, for example, the display characteristic information may be further acquired from the display device.

Further, for example, the acquisition of the display characteristic information may be performed immediately before the conversion to the second luminance value.

Further, for example, the acquisition of the display characteristic information may be performed at the timing when the display device is first connected.

It should be noted that these generally comprehensive or specific embodiments may be realized in a recording medium such as a device, system, integrated circuit, computer program or computer readable CD-ROM, system, method, integrated circuit, computer. 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 disclosure will be specifically described with reference to the accompanying drawings.

It should be noted that all of the embodiments described below show a specific example of the present disclosure. 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 disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components.

(Embodiment)
In the present disclosure, a TV or projector corresponding to an HDR (High Dynamic Range) signal, which is a high-luminance signal having a high luminance range, and an SDR (Standard Dynamic Range) signal, which is a normal luminance signal in the luminance range having a maximum luminance value of 100 nits. , An image conversion / playback method for displaying on a display device such as a tablet or a smartphone, and the device.

[1-1. background]
First, 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 increasing the number of display pixels in order to improve the image quality of images, from the standard 720 x 480 pixel images of Standard Definition (SD) to 1920 x 1080 pixels 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 × 1920 pixels or 4K 4096 × 1920 pixels has been started with the aim of further improving the image quality.

Then, it is being studied to improve the image quality by introducing 4K to increase the resolution of the image, expanding the dynamic range, expanding the color gamut, adding or improving the frame rate, and the like.

Among them, regarding the dynamic range, the maximum brightness is used to express bright light such as specular reflected light, which cannot be expressed by the current TV signal, with a brightness closer to reality while maintaining the dark area gradation in the conventional image. HDR (High Dynamic Range) is attracting attention as a method corresponding to a brightness range in which the value is expanded. Specifically, the conventional method of the brightness range supported by the TV signal is called SDR (Standard Dynamic Range), and the maximum brightness value is 100 nits, whereas the maximum brightness value is 1000 nits or more in HDR. It is expected that the brightness value will be increased. HDR is being standardized in SMPTE (Society of Motion Picture & Television Engineers) and ITU-R (International Telecommunication Union Radiocommunication Sector).

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

In the following, in an image corresponding to HDR, the luminance of the image is composed of the luminance value in the luminance range of HDR, and the luminance signal obtained by quantizing the luminance value of the image is referred to as an HDR signal. .. In an image corresponding to SDR, the luminance of the image is composed of the luminance value in the luminance range of SDR, and the luminance signal obtained by quantizing the luminance value of the image is called an SDR signal.

[1-2. Relationship between master generation, distribution method, and display device]
FIG. 2 is a diagram for explaining the relationship between video production, a distribution method, and a display device when introducing a new video expression into the content.

When introducing a new video expression (increase in the number of pixels, etc.) to improve the image quality of the video, it is necessary to (1) change the master for Home Entertainment on the video production side, as shown in FIG. .. Accordingly, it is necessary to update (2) distribution methods such as broadcasting, communication, and package media, and (3) display devices such as TVs and projectors that display the images.

[1-3. Relationship between master, distribution method, and display device when HDR is introduced]
In order for users to enjoy content that supports new video expressions (for example, high-brightness video content (HDR content)) at home, it is necessary to newly introduce both an HDR-compatible distribution method and an HDR-compatible display device. .. That is, in order to enjoy the content corresponding to the new video expression at home, the user needs to prepare a distribution method and a display device corresponding to the new video expression. This should be avoided even when new video expressions are introduced, such as when SD video is replaced with HD video, HD video is replaced with 3D video, and HD video is replaced with UHD (4K) video. I couldn't.

For this reason, it is expensive, it is not easy to replace in terms of size, weight, etc., it is necessary to replace the TV, and the change to a new video expression depends on the spread of display devices with new functions (for example, TV). Will be done. Initially, neither the media side nor the content side could make a large investment, so the spread of new video expressions often slowed down.

Therefore, as shown in FIG. 3, for HDR as well, in order to make full use of the original video expression of HDR, a TV compatible with HDR-compatible video display (hereinafter referred to as “HDR display”) (hereinafter referred to as “HDR display”). It is expected that replacement with "HDRTV") will be required.

[1-4. SDRTV]
An input signal having a brightness value of up to 100 nits is usually input to a TV (hereinafter referred to as "SDRTV") that supports only SDR-compatible video display (hereinafter referred to as "SDR display"). Therefore, the SDRTV is sufficient to express the luminance value of the input signal if its display capability is 100 nits. However, SDRTV actually has a function of reproducing an image with an optimum brightness value according to the viewing environment (dark room: cinema mode, bright room: dynamic mode, etc.), and has the ability to express an image of 200 nits or more. Many have. That is, such an SDRTV can display an image up to the maximum brightness (for example, 300 nits) of the display capability by selecting a display mode according to the viewing environment.

However, in the SDR type input signal input to the SDRTV, the upper limit of the brightness of the input signal is set to 100 nits, so as long as the SDR type input interface is used as before, a high-brightness image exceeding 100 nits of the SDRTV. It is difficult to use the reproduction capability for reproduction of HDR signals (see FIGS. 4A and 4B).

[1-5. HDR → SDR conversion]
High-brightness video content (hereinafter, "HDR content") distributed by HDR-compatible broadcasting, video distribution via a communication network, or distribution method such as HDR-compatible package media (for example, HDR-compatible Blu-ray Disc). The “HDR video”) is expected to be output by SDRTV via an HDR-compatible playback device (for example, a communication STB (Set Top Box), a Blu-ray device, or an IPTV playback device). When playing HDR content with SDRTV, "HDR → SDR conversion" is realized to convert the HDR signal corresponding to HDR to the SDR signal in the SDR brightness range with the maximum value of 100 nits so that the image can be displayed correctly with SDRTV. To do. As a result, the SDRTV can display the SDR video obtained by converting from the HDR video using the converted SDR signal (see FIG. 5).

However, even in this case, the user has purchased HDR-compatible content (for example, Blu-ray disc, HDR IPTV content) and HDR-compatible playback device (for example, Blu-ray device, HDR-compatible IPTV playback device). Nevertheless, with SDRTV, you can enjoy the video only with the SDR video expression (SDR expression). In other words, even if HDR content and a playback device compatible with HDR are prepared, if there is no display device compatible with HDR (for example, HDRTV) and only SDRTV, the image is displayed in HDR video expression (HDR expression). I can't watch it.

Therefore, if the user cannot prepare the HDRTV, the value of the HDR (that is, the superiority over the SDR due to the high image quality of the HDR) cannot be understood even if the HDR content or the transmission medium (playback device) is purchased. As described above, since the user does not know the value of HDR without HDRTV, it can be said that the spread of HDR contents and HDR-compatible distribution methods depends on the spread speed of HDRTV.

[1-6. Two methods to realize HDR → SDR conversion]
When sending an HDR signal to a TV using a Blu-ray disc (BD), two cases can be assumed as shown in FIGS. 6A and 6B below. FIG. 6A is a diagram for explaining Case 1 in which only the HDR signal corresponding to HDR is stored in the BD corresponding to HDR. FIG. 6B is a diagram for explaining the case 2 in which the HDR signal corresponding to HDR and the SDR signal corresponding to SDR are stored in the BD corresponding to HDR.

As shown in FIG. 6A, in case 1, when the HDRTV displays an image obtained by reproducing a BD on a Blu-ray device, the SDR is reproduced even when the HDR compatible BD (hereinafter referred to as “HDRBD”) is reproduced. Even when the corresponding BD (hereinafter referred to as "SDRBD") is reproduced, the Blu-ray device outputs the luminance signal stored in the BD to the HDRTV as it is without converting it. Since the HDRTV can display and process both the HDR signal and the SDR signal, it performs display processing according to the input luminance signal and displays the HDR image or the SDR image.

On the other hand, in case 1, when the SDRTV displays the image obtained by reproducing the BD on the Blu-ray device, when the HDRBD is reproduced, the Blu-ray device performs a conversion process of converting the HDR signal to the SDR signal. Then, the SDR signal obtained by the conversion process is output to SDRTV. Further, when the SDRBD is reproduced, the Blu-ray device outputs the SDR signal stored in the BD to the SDRTV as it is without converting it. As a result, the SDRTV displays the SDR image.

Further, as shown in FIG. 6B, in the case 2, when the HDRTV displays the image of the BD reproduced by the Blu-ray device, it is the same as the case 1.

On the other hand, in case 2, when the SDRTV displays the image obtained by reproducing the BD on the Blu-ray device, the Blu-ray device is stored in the BD regardless of whether the HDRBD is reproduced or the SDRBD is reproduced. The SDR signal is output to SDRTV as it is without conversion.

Even if you buy both HDRBD and HDR compatible Blu-ray devices in both Case 1 and Case 2, you can only enjoy SDR video without HDRTV. Therefore, HDRTV is required for users to view HDR video, and it is expected that it will take time for HDR-compatible Blu-ray devices or HDRBD to become widespread.

[1-7. HDR → Pseudo HDR conversion]
From the above, it can be said that in order to promote the spread of HDR, it is important to be able to promote the commercialization of HDR contents and distribution methods without waiting for the spread of HDRTV. For this purpose, if the existing SDRTV can make the HDR signal viewable not as an SDR image but as an HDR image or a pseudo HDR image closer to the HDR image than the SDR image, the user can view the HDRTV. Even if you don't buy it, you can watch higher quality video that is close to HDR video, which is clearly different from SDR video. That is, if the user can watch the pseudo HDR video with SDRTV, he / she can watch the video with higher image quality than the SDR video simply by preparing the HDR content and the HDR distribution device without preparing the HDRTV. .. In short, enabling pseudo-HDR video to be viewed on SDRTV can be a motivation for users to purchase HDR content and HDR distribution equipment (see FIG. 7).

In order to realize that the pseudo HDR image is displayed on the SDRTV, the HDR signal is displayed so that the image of the HDR content can be correctly displayed on the SDRTV when the HDR content is played back in the configuration in which the SDRTV is connected to the HDR distribution method. Instead of converting to an SDR video signal, the input of a video signal having a maximum value of 100 nits of SDRTV is used to generate a pseudo HDR signal for displaying a video having the maximum brightness of the display capability of SDRTV, for example, 200 nits or more. Therefore, it is necessary to realize "HDR → pseudo HDR conversion processing" that enables the generated pseudo HDR signal to be sent to SDRTV.

[1-8. About EOTF]
Here, EOTF will be described with reference to FIGS. 8A and 8B.

FIG. 8A is a diagram showing an example of EOTF (Electro-Optical Transfer Function) corresponding to each of HDR and SDR.

The EOTF is generally called a gamma curve, shows the correspondence between the code value and the luminance value, and converts the code value into the luminance value. That is, the EOTF is the relational information indicating the correspondence between the plurality of code values and the luminance values.

Further, FIG. 8B is a diagram showing an example of reverse EOTF corresponding to each of HDR and SDR.

The inverse EOTF indicates the correspondence between the luminance value and the code value, and contrary to the EOTF, the luminance value is quantized and converted into a code value. That is, the inverse EOTF is the relational information indicating the correspondence between the luminance value and the plurality of code values. For example, when the brightness value of the image corresponding to HDR is expressed by the code value of the gradation of 10 bits, the brightness value in the brightness range of HDR up to 10,000 nits is quantized and 1024 pieces from 0 to 1023. Maps to an integer value of. That is, by quantization based on the inverse EOTF, the luminance value in the luminance range up to 10,000 nits (the luminance value of the image corresponding to HDR) is converted into the HDR signal which is a 10-bit code value. In the EOTF corresponding to HDR (hereinafter referred to as "EOTF of HDR") or the reverse EOTF corresponding to HDR (hereinafter referred to as "reverse EOTF of HDR"), the EOTF corresponding to SDR (hereinafter referred to as "EOTF of SDR") It is possible to express a higher luminance value than the inverse EOTF corresponding to SDR (hereinafter, referred to as “inverse EOTF of SDR”). For example, in FIGS. 8A and 8B, the maximum luminance is obtained. The value (peak brightness) is 10,000 nits. That is, the luminance range of HDR includes the entire luminance range of SDR, and the peak luminance of HDR is larger than the peak luminance of SDR. The luminance range of HDR is a luminance range in which the maximum value is expanded from 100 nits, which is the maximum value of the luminance range of SDR, to 10,000 nits.

For example, HDR EOTF and HDR reverse EOTF include SMPTE 2084 standardized by the Society of Motion Picture and Television Engineers (SMPTE).

[1-9. How to use EOTF]
FIG. 9 is an explanatory diagram of a method of determining the code value of the luminance signal stored in the content and a process of restoring the luminance value from the code value at the time of reproduction.

The luminance signal indicating the luminance 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 value 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 dequantizing based on the EOTF of HDR, and the brightness value for each pixel is restored. Hereinafter, the quantization using the inverse EOTF of HDR is referred to as "EOTF conversion of 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".

[1-10. Necessity of pseudo HDR]
Next, the necessity of pseudo HDR will be described with reference to FIGS. 10A to 10C.

FIG. 10A is a diagram showing an example of display processing in which an HDR signal is converted and HDR display is performed in HDRTV.

As shown in FIG. 10A, when displaying an HDR image, even if the display device is an HDRTV, the maximum value of the HDR brightness range (peak brightness (HPL (HDR Peak Luminance): Example 1500 nit)) is displayed as it is. May not be possible. In this case, in order to match the linear signal after dequantization using HDR EOTF to the maximum value (peak brightness (DPL (Display Peak Iminance): Example 750 nit)) of the brightness range of the display device. Perform brightness conversion. Then, by inputting the video signal obtained by performing the luminance conversion to the display device, it is possible to display the HDR video that matches the luminance range of the maximum value which is the limit of the display device.

FIG. 10B is a diagram showing an example of a display process for performing HDR display using an HDR compatible playback device and SDRTV.

As shown in FIG. 10B, when displaying an HDR image, if the display device is SDRTV, the maximum value (peak brightness (DPL: 300 nit)) of the luminance range of SDRTV to be displayed exceeds 100 nit. , The maximum value of the "HDR EOTF conversion" and the luminance range of the SDRTV performed in the HDRTV in the "HDR → pseudo HDR conversion process" in the HDR compatible playback device (Blu-ray device) of FIG. 10B. If the signal obtained by performing "luminance conversion" using DPL (example: 300 nits) and performing "luminance conversion" can be directly input to the "display device" of SDRTV, the same effect as HDRTV can be obtained even if SDRTV is used. Can be realized.

However, SDRTV cannot be realized because there is no means for directly inputting such a signal from the outside.

FIG. 10C is a diagram showing an example of display processing for performing HDR display by using an HDR compatible playback device and SDRTV connected to each other via a standard interface.

As shown in FIG. 10C, it is usually necessary to input a signal to the SDRTV so that the effect of FIG. 10B can be obtained by using an input interface (HDMI (registered trademark, the same applies hereinafter) or the like) provided in the SDRTV. In SDRTV, the signal input via the input interface passes through "EOTF conversion of SDR", "luminance conversion for each mode", and "display device" in order, and the image is adjusted to the maximum brightness range of the display device. Is displayed. Therefore, in an HDR-compatible Blu-ray device, a signal (pseudo HDR signal) that can cancel "SDR EOTF conversion" and "mode-by-mode brightness conversion" that passes immediately after the input interface in SDRTV is transmitted. Generate. That is, in an HDR-compatible Blu-ray device, immediately after "HDR EOTF conversion" and "brightness conversion" using SDRTV peak brightness (DPL), "reverse brightness conversion for each mode" and "reverse SDR" By performing "EOTF conversion", the same effect as when the signal immediately after "luminance conversion" is input to the "display device" (broken arrow in FIG. 10C) is realized in a pseudo manner.

[1-11. Converter and display device]
FIG. 11 is a block diagram showing a configuration of a conversion device and a display device according to an embodiment. FIG. 12 is a flowchart showing a conversion method and a display method performed by the conversion device and the display device of the embodiment.

As shown in FIG. 11, the conversion device 100 includes an HDR EOTF conversion unit 101, a brightness conversion unit 102, an inverse brightness conversion unit 103, and an inverse SDR EOTF conversion unit 104. The display device 200 includes a display setting unit 201, an SDR EOTF conversion unit 202, a brightness conversion unit 203, and a display unit 204.

A detailed description of each component of the conversion device 100 and the display device 200 will be given in the description of the conversion method and the display method.

Hereinafter, the luminance range (0 to HPL [nit]) of HDR is referred to as a “first luminance range”. The brightness range (0 to DPL [nit]) of the display is referred to as a "second brightness range". The luminance range (0 to 100 [nit]) of the SDR is referred to as a “third luminance range”.

[1-12. Conversion method and display method]
The conversion method performed by the conversion device 100 will be described with reference to FIG. The conversion method includes steps S101 to S104 described below.

First, the HDR EOTF conversion unit 101 of the conversion device 100 acquires the HDR video in which the inverse HDR EOTF conversion has been performed. The HDR EOTF conversion unit 101 of the conversion device 100 performs HDR EOTF conversion on the HDR signal of the acquired HDR video (S101). As a result, the EOTF conversion unit 101 of the HDR converts the acquired HDR signal into a linear signal indicating the luminance value. The HDR EOTF is, for example, SMPTE 2084.

Next, the luminance conversion unit 102 of the conversion device 100 performs the first luminance conversion that converts the linear signal converted by the EOTF luminance range 101 of the HDR using the display characteristic information and the content luminance information (S102). .. In the first luminance conversion, the luminance value corresponding to the HDR luminance range which is the first luminance range (hereinafter referred to as “HDR luminance value”) is the luminance value corresponding to the display luminance range which is the second luminance range. (Hereinafter referred to as "display brightness value"). Details will be described later.

From the above, the EOTF conversion unit 101 of the HDR functions as an acquisition unit that acquires the HDR signal as the first luminance signal indicating the code value obtained by quantizing the luminance value of the video. Further, the HDR EOTF conversion unit 101 and the brightness conversion unit 102 determine the code value indicated by the HDR signal acquired by the acquisition unit based on the brightness range of the display (display device 200), which is the maximum of the luminance range of HDR. It functions as a conversion unit that converts into a display luminance value corresponding to the luminance range of the display, which is the maximum value (DPL) smaller than the value (HPL) and larger than 100 nits.

More specifically, the HDR EOTF conversion unit 101 uses the acquired HDR signal and the HDR EOTF in step S101 to determine the HDR code value as the first code value indicated by the acquired HDR signal. The HDR luminance value associated with the HDR code value in the HDR EOTF is determined. The HDR signal is obtained by quantizing the luminance value of a video (content) using the inverse EOTF of HDR in which the luminance value in the luminance range of HDR and the code values of a plurality of HDRs are related to each other. The code value of HDR is shown.

Further, in step S102, the luminance conversion unit 102 determines the display luminance value corresponding to the luminance range of the display, which is previously related to the luminance value of the HDR, with respect to the luminance value of HDR determined in step S101, and HDR. The first luminance conversion is performed to convert the luminance value of HDR corresponding to the luminance range of the above into the display luminance value corresponding to the luminance range of the display.

Further, before step S102, the conversion device 100 includes content luminance information including at least one of the maximum luminance value (CPL: Content Peak lumen) and the average luminance value (CAL: Content Average luminance) of the video (content). Is acquired as information about the HDR signal. The CPL (first maximum brightness value) is, for example, the maximum value among the brightness values for a plurality of images constituting the HDR video. Further, CAL is, for example, an average luminance value which is an average of luminance values for a plurality of images constituting an HDR video.

Further, the conversion device 100 acquires the display characteristic information of the display device 200 from the display device 200 before the step S102. The display characteristic information is the maximum value (DPL) of the brightness that can be displayed by the display device 200, the display mode of the display device 200 (see below), the input / output characteristics (EOTF supported by the display device), and the like. Information indicating display characteristics.

Further, the conversion device 100 may transmit recommended display setting information (see below, hereinafter also referred to as “setting information”) to the display device 200.

Next, the reverse brightness conversion unit 103 of the conversion device 100 performs reverse brightness conversion according to the display mode of the display device 200. As a result, the inverse luminance conversion unit 103 performs the second luminance conversion that converts the luminance value corresponding to the luminance range of the display which is the second luminance range into the luminance value corresponding to the luminance range of SDR which is the third luminance range. Do (S103). Details will be described later. That is, the inverse luminance conversion unit 103 uses the display luminance value obtained in step S102 as a third luminance value corresponding to the luminance range of the SDR having a maximum value of 100 nits, which is previously related to the display luminance value. Luminance value corresponding to SDR (hereinafter referred to as "luminance value of SDR") The luminance value of SDR is determined, and the display luminance value corresponding to the luminance range of the display is changed to the luminance value of SDR corresponding to the luminance range of SDR. Perform the second luminance conversion to be converted.

Then, the EOTF conversion unit 104 of the inverse SDR of the conversion device 100 generates a pseudo HDR image by performing the EOTF conversion of the inverse SDR (S104). That is, the EOTF conversion unit 104 of the inverse SDR is the inverse EOTF (Electro-Optical) of the SDR (Standard Dynamic Range), which is the third relational information in which the luminance value in the luminance range of the HDR is associated with the plurality of third code values. Using the Transfer Function), the determined SDR luminance value is quantized, the third code value obtained by the quantization is determined, and the SDR luminance value corresponding to the SDR luminance range is indicated by the third code value. A pseudo HDR signal is generated by converting to an SDR signal as a third luminance signal. The third code value is a code value corresponding to SDR, and is hereinafter referred to as "SDR code value". That is, the SDR signal is the SDR obtained by quantizing the luminance value of the image using the inverse EOTF of the SDR in which the luminance value in the luminance range of the SDR and the code values of the plurality of SDRs are related. It is represented by a code value. Then, the conversion device 100 outputs the pseudo HDR signal (SDR signal) generated in step S104 to the display device 200.

The conversion device 100 generates the brightness value of SDR corresponding to the pseudo HDR by performing the first brightness conversion and the second brightness conversion on the brightness value of HDR obtained by dequantizing the HDR signal. Then, by quantizing the luminance value of the SDR using the EOTF of the SDR, an SDR signal corresponding to the pseudo HDR is generated. The luminance value of SDR is a numerical value within the luminance range of 0 to 100 nits corresponding to SDR, but since the conversion is performed based on the luminance range of the display, the EOTF and SDR of HDR are compared with the luminance value of HDR. It is a numerical value different from the luminance value in the luminance range of 0 to 100 nit corresponding to SDR obtained by performing the luminance conversion using EOTF.

Next, the display method performed by the display device 200 will be described with reference to FIG. The display method includes steps S105 to S108 described below.

First, the display setting unit 201 of the display device 200 sets the display setting of the display device 200 by using the setting information acquired from the conversion device 100 (S105). Here, the display device 200 is an SDRTV. The setting information is information indicating the recommended display settings for the display device, and is information indicating how to EOTF the pseudo HDR image and what setting should be displayed to display a beautiful image (that is,). Information for switching the display setting of the display device 200 to the optimum display setting). The setting information includes, for example, the gamma curve characteristic at the time of output in the display device, the display mode such as the living mode (normal mode) and the dynamic mode, and the numerical value of the backlight (brightness). Further, a message prompting the user to manually change the display setting of the display device 200 may be displayed on the display device 200 (hereinafter, also referred to as “SDR display”). Details will be described later.

Prior to step S105, the display device 200 acquires an SDR signal (pseudo HDR signal) and setting information indicating display settings recommended for the display device 200 when displaying an image.

Further, the display device 200 may acquire the SDR signal (pseudo HDR signal) before step S106 or after step S105.

Next, the EOTF conversion unit 202 of the SDR of the display device 200 performs EOTF conversion of the SDR on the acquired pseudo HDR signal (S106). That is, the SDR EOTF conversion unit 202 reverse-quantizes the SDR signal (pseudo-HDR signal) using the SDR EOTF. As a result, the EOTF conversion unit 202 of the SDR converts the SDR code value indicated by the SDR signal into the SDR luminance value.

Then, the luminance conversion unit 203 of the display device 200 performs the luminance conversion according to the display mode set in the display device 200. As a result, the luminance conversion unit 203 converts the luminance value of the SDR corresponding to the luminance range of the SDR (0 to 100 [nit]) into the display luminance value corresponding to the luminance range of the display (0 to DPL [nit]). The third luminance conversion is performed (S107). Details will be described later.

From the above, the display device 200 uses the setting information acquired in step S105 to obtain the third code value indicated by the acquired SDR signal (pseudo HDR signal) in steps S106 and S107, and displays the brightness range of the display (pseudo-HDR signal). It is converted into a display luminance value corresponding to 0 to DPL [nit]).

More specifically, in the conversion from the SDR signal (pseudo-HDR signal) to the display luminance value, in step S106, the EOTF in which the luminance value in the luminance range of the SDR and the plurality of third code values are related is used. For the SDR code value indicated by the acquired SDR signal, the luminance value of the SDR associated with the SDR code value by the SDR EOTF is determined.

Then, in the conversion to the display luminance value, in step S107, the display luminance value corresponding to the luminance range of the display, which is previously related to the determined luminance value of the SDR, is determined, and the SDR corresponding to the luminance range of the SDR A third luminance conversion is performed to convert the luminance value into a display luminance value corresponding to the luminance range of the display.

Finally, the display unit 204 of the display device 200 displays the pseudo HDR image on the display device 200 based on the converted display luminance value (S108).

[1-13. 1st brightness conversion]
Next, the details of the first luminance conversion (HPL → DPL) in step S102 will be described with reference to FIG. 13A. FIG. 13A is a diagram for explaining an example of the first luminance conversion.

The luminance conversion unit 102 of the conversion device 100 performs the first luminance conversion that converts the linear signal (HDR luminance value) obtained in step S101 by using the display characteristic information and the content luminance information of the HDR image. .. The first luminance conversion converts the HDR luminance value (input luminance value) into a display luminance value (output luminance value) that does not exceed the display peak luminance (DPL). The DPL is determined using the maximum brightness and display mode of the SDR display, which are display characteristic information. The display mode is, for example, mode information such as a theater mode for displaying darkly on an SDR display and a dynamic mode for displaying brightly. When the display mode is, for example, a mode in which the maximum brightness of the SDR display is 1,500 nits and the display mode is 50% of the maximum brightness, the DPL is 750 nits. Here, the DPL (second maximum brightness value) is the maximum value of the brightness that can be displayed in the display mode currently set by the SDR display. That is, in the first luminance conversion, the DPL as the second maximum luminance value is determined by using the display characteristic information which is the information indicating the display characteristic of the SDR display.

Further, in the first luminance conversion, CAL and CPL of the content luminance information are used, the luminance values below the CAL are made the same before and after the conversion, and the luminance values are changed only for the luminance values near the CPL and above. To do. That is, as shown in FIG. 13A, in the first luminance conversion, when the luminance value of the HDR is CAL or less, the luminance value of the HDR is not converted, and the luminance value of the HDR is determined as the display luminance value. When the luminance value of the HDR is CPL or more, the DPL as the second maximum luminance value is determined as the display luminance value.

Further, in the first luminance conversion, the peak luminance (CPL) of the HDR image in the luminance information is used, and when the luminance value of HDR is CPL, the DPL is determined as the display luminance value.

In the first luminance conversion, as shown in FIG. 13B, the linear signal (HDR luminance value) obtained in step S101 may be converted so as to clip to a value not exceeding the DPL. By performing such luminance conversion, the processing in the conversion device 100 can be simplified, and the device can be reduced in size, reduced in power consumption, and speeded up in processing. Note that FIG. 13B is a diagram for explaining another example of the first luminance conversion.

[1-14. Second brightness conversion]
Next, the details of the second luminance conversion (DPL → 100 [nit]) in step S103 will be described with reference to FIG. FIG. 14 is a diagram for explaining the second luminance conversion.

The reverse luminance conversion unit 103 of the conversion device 100 performs reverse luminance conversion according to the display mode with respect to the display luminance value in the luminance range (0 to DPL [nit]) of the display converted in the first luminance conversion in step S102. Give. In the reverse luminance conversion, when the luminance conversion process (step S107) according to the display mode by the SDR display is performed, the display luminance value of the display luminance range (0 to DPL [nit]) after the step S102 process is acquired. It is a process to enable it. That is, the second luminance conversion is the inverse luminance conversion of the third luminance conversion.

By the above processing, the second luminance conversion sets the display luminance value (input luminance value) of the display luminance range which is the second luminance range to the SDR luminance value (output luminance value) of the SDR luminance range which is the third luminance range. Value).

In the second luminance conversion, the conversion formula is switched depending on the display mode of the SDR display. For example, when the display mode of the SDR display is the normal mode, the brightness is converted into a direct proportional value that is directly proportional to the display brightness value. Further, in the second luminance conversion, when the display mode of the SDR display is the dynamic mode in which the high-luminance pixels are brighter and the low-luminance pixels are darker than in the normal mode, the low-luminance pixels are used by using the inverse function. The brightness value of the SDR is converted to a value higher than the direct proportional value directly proportional to the display luminance value, and the luminance value of the SDR of the high-luminance pixel is converted to a value lower than the direct proportional value directly proportional to the display luminance value. That is, in the second luminance conversion, the display luminance value determined in step S102 is related to the display luminance value by using the luminance-related information corresponding to the display characteristic information which is the information indicating the display characteristic of the SDR display. The brightness value is determined as the brightness value of the SDR, and the brightness conversion process is switched according to the display characteristic information. Here, the luminance-related information according to the display characteristic information includes the display luminance value (input luminance value) defined for each display parameter (display mode) of the SDR display and the SDR, as shown in FIG. 14, for example. This is information related to the luminance value (output luminance value).

[1-15. Display settings]
Next, the details of the display setting in step S105 will be described with reference to FIG. FIG. 15 is a flowchart showing detailed processing of the display setting.

In step S105, the display setting unit 201 of the SDR display performs the following steps S201 to S208.

First, the display setting unit 201 uses the setting information to determine whether or not the EOTF (EOTF for SDR display) set in the SDR display is consistent with the EOTF assumed at the time of generating the pseudo HDR video (SDR signal). Judgment (S201).

When the display setting unit 201 determines that the EOTF set in the SDR display is different from the EOTF (EOTF matching the pseudo HDR image) indicated by the setting information (Yes in S201), the display setting unit 201 uses the EOTF for the SDR display as a system. It is determined on the side whether switching is possible (S202).

When the display setting unit 201 determines that the switching is possible, the display setting unit 201 switches the SDR display EOTF to an appropriate EOTF using the setting information (S203).

From steps S201 to S203, in the display setting setting (S105), the EOTF set in the SDR display is set to the recommended EOTF according to the acquired setting information. Further, as a result, in step S106 performed after step S105, the brightness value of SDR can be determined using the recommended EOTF.

When it is determined that the switching is not possible on the system side (No in S202), a message prompting the user to manually change the EOTF is displayed on the screen (S204). For example, the message "Please set the display gamma to 2.4" is displayed on the screen. That is, when the display setting unit 201 cannot switch the EOTF set in the SDR display in the display setting setting (S105), the display setting unit 201 switches the EOTF set in the SDR display (EOTF for SDR display) to the recommended EOTF. A message prompting the user to do so is displayed on the SDR display.

Next, the SDR display displays a pseudo HDR image (SDR signal), and before the display, it is determined whether or not the display parameters of the SDR display match the setting information by using the setting information (S205).

When the display setting unit 201 determines that the display parameters set in the SDR display are different from the setting information (Yes in S205), the display setting unit 201 determines whether the display parameters of the SDR display can be switched (S206). ..

When the display setting unit 201 determines that the display parameters of the SDR display can be switched (Yes in S206), the display setting unit 201 switches the display parameters of the SDR display according to the setting information (S207).

From step S204 to step S207, in the display setting setting (S105), the display parameter set in the SDR display is set to the recommended display parameter according to the acquired setting information.

When it is determined that the switching is not possible on the system side (No in S206), a message prompting the user to manually change the display parameters set in the SDR display is displayed on the screen (S208). For example, display the message "Set the display mode to dynamic mode and maximize the backlight" on the screen. That is, in the setting (S105), when the display parameter set in the SDR display cannot be switched, a message for prompting the user to switch the display parameter set in the SDR display to the recommended display parameter is sent to the SDR display. Display on.

[1-16. Third brightness conversion]
Next, the details of the third luminance conversion (100 → DPL [nit]) in step S107 will be described with reference to FIG. FIG. 16 is a diagram for explaining the third luminance conversion.

The luminance conversion unit 203 of the display device 200 converts the luminance value of the SDR in the luminance range (0 to 100 [nit]) of the SDR into (0 to DPL [nit]) according to the display mode set in step S105. .. This process is performed so as to be an inverse function of the inverse luminance conversion for each mode of S103.

In the third luminance conversion, the conversion formula is switched depending on the display mode of the SDR display. For example, when the display mode of the SDR display is the normal mode (that is, when the set display parameter is a parameter corresponding to the normal mode), the display luminance value is converted into a direct proportional value which is directly proportional to the luminance value of the SDR. .. Further, in the third luminance conversion, when the display mode of the SDR display is the dynamic mode in which the high-luminance pixels are brighter and the low-luminance pixels are darker than in the normal mode, the display brightness value of the low-luminance pixels is the SDR. The display luminance value of the high-luminance pixel is converted to a value lower than the direct-proportional value that is directly proportional to the luminance value, and is converted to a value higher than the direct-proportional value that is directly proportional to the luminance value of SDR. That is, in the third luminance conversion, the luminance value of the SDR determined in step S106 is previously associated with the luminance value of the SDR by using the luminance-related information corresponding to the display parameter indicating the display setting of the SDR display. The value is determined as the display luminance value, and the luminance conversion process is switched according to the display parameters. Here, the luminance-related information according to the display parameters is the luminance value (input luminance value) of the SDR and the display luminance defined for each display parameter (display mode) of the SDR display, as shown in FIG. 16, for example. This is information related to the value (output luminance value).

[1-17. Effect, etc.]
A normal SDRTV has an input signal of 100 nits, but has the ability to express an image of 200 nits or more according to the viewing environment (dark room: cinema mode, bright room: dynamic mode, etc.). However, since the upper limit of the brightness of the input signal to the SDRTV was set to 100 nits, that ability could not be used directly.

When displaying HDR video in SDRTV, the peak brightness of SDRTV to be displayed exceeds 100 nits (usually 200 nits or more), and the HDR video is not converted into SDR video of 100 nits or less, but the brightness exceeds 100 nits. "HDR → pseudo HDR conversion processing" is performed so as to maintain the gradation of the range to some extent. Therefore, it can be displayed on the SDRTV as a pseudo HDR image close to the original HDR.

When this "HDR → pseudo HDR conversion processing" technology is applied to Blu-ray, as shown in FIG. 17, only the HDR signal is stored in the HDR disc, and when SDRTV is connected to the Blu-ray device, Blu The -ray device performs "HDR → pseudo HDR conversion processing", converts the HDR signal into a pseudo HDR signal, and sends it to SDRTV. As a result, the SDRTV can display an image having a pseudo HDR effect by converting the received pseudo HDR signal into a luminance value. In this way, even if there is no HDR compatible TV, if an HDR compatible BD and an HDR compatible Blu-ray device are prepared, even with SDRTV, it is possible to display a pseudo HDR image with higher image quality than the SDR image. it can.

Therefore, it was thought that an HDR-compatible TV was necessary to view the HDR image, but a pseudo HDR image in which the HDR-like effect can be realized can be viewed with the existing SDRTV. As a result, the spread of HDR-compatible Blu-ray can be expected.

The HDR signal sent by broadcasting, package media such as Blu-ray, and Internet distribution such as OTT is converted into a pseudo HDR signal by performing HDR-pseudo HDR conversion processing. This makes it possible to display the HDR signal as a pseudo HDR image on the existing SDRTV.

(Other embodiments)
As described above, embodiments have been described as an example of the techniques disclosed in this application. However, the technique in the present disclosure is not limited to this, and can be applied to embodiments in which changes, replacements, additions, omissions, etc. are made as appropriate. It is also possible to combine the components described in the above embodiment to form a new embodiment.

Therefore, in the following, other embodiments will be illustrated.

The HDR video is, for example, a Blu-ray disc, a DVD, a video distribution site on the Internet, a broadcast, or a video in an HDD.

The conversion device 100 (HDR → pseudo HDR conversion processing unit) may exist inside a disc player, a disc recorder, a set-top box, a television, a personal computer, or a smartphone. The conversion device 100 may exist inside the server device in the Internet.

The display device 200 (SDR display unit) is, for example, a television, a personal computer, or a smartphone.

The display characteristic information acquired by the conversion device 100 may be acquired from the display device 200 via an HDMI cable or a LAN cable using HDMI or another communication putrocol. As the display characteristic information acquired by the conversion device 100, the display characteristic information included in the model information of the display device 200 or the like may be acquired via the Internet. Further, the user may manually operate the display characteristic information and set the display characteristic information in the conversion device 100. Further, the display characteristic information of the conversion device 100 may be acquired immediately before the pseudo HDR image generation (steps S101 to S104), or at the time of initial setting of the device or at the time of connecting the display. For example, the display characteristic information may be acquired immediately before the conversion to the display luminance value, or may be performed at the timing when the conversion device 100 is first connected to the display device 200 with the HDMI cable.

Further, the CPL and CAL of the HDR video may be one for each content, or may exist for each scene. That is, in the conversion method, the first maximum luminance value which is the luminance information corresponding to each of the plurality of scenes of the video and is the maximum value among the luminance values for the plurality of images constituting the scene for each scene. And the luminance information (CPL, CAL) including at least one of the average luminance value which is the average of the luminance values for the plurality of images constituting the scene is acquired, and in the first luminance conversion, for each of the plurality of scenes, The display luminance value may be determined according to the luminance information corresponding to the scene.

Further, the CPL and CAL may be bundled in the same medium (Blu-ray disc, DVD, etc.) as the HDR video, or acquired from a place different from the HDR video, such as the conversion device 100 acquiring from the Internet. You may. That is, the luminance information including at least one of CPL and CAL may be acquired as the meta information of the video, or may be acquired via the network.

Further, in the first luminance conversion (HPL → DPL) of the converter 100, the fixed values may be used without using the CPL, CAL, and the display peak luminance (DPL). Further, the fixed value may be changed from the outside. Further, CPL, CAL, and DPL may be switched by several types. For example, DPL may be set to only three types of 200 nit, 400 nit, and 800 nit, and the value closest to the display characteristic information is used. You may try to do so.

Further, the EOTF of HDR does not have to be SMPTE 2084, and another type of EOTF of HDR may be used. Further, the maximum luminance (HPL) of the HDR image does not have to be 10,000 nits, and may be, for example, 4,000 nits or 1,000 nits.

The bit width of the code value may be, for example, 16, 14, 12, 10, or 8 bits.

Further, although the EOTF conversion of the inverse SDR is determined from the display characteristic information, a fixed conversion function (which can be changed from the outside) may be used. The EOTF conversion of the inverse SDR is performed by, for example, Rec. ITU-R BT. The functions specified in 1886 may be used. Further, the types of EOTF conversion of the inverse SDR may be narrowed down to several types, and the one closest to the input / output characteristics of the display device 200 may be selected and used.

Further, the display mode may be a fixed mode and may not be included in the display characteristic information.

Further, the conversion device 100 does not have to transmit the setting information, and the display device 200 may have a fixed display setting or may not change the display setting. In this case, the display setting unit 201 becomes unnecessary. Further, the setting information may be flag information as to whether or not the image is a pseudo HDR image. For example, in the case of a pseudo HDR image, the setting may be changed to the brightest display. That is, in the display setting setting (S105), when the acquired setting information indicates that it is a signal indicating a pseudo HDR image converted by using DPL, the brightness setting of the display device 200 is set to be displayed brightest. You may switch to.

Further, the first luminance conversion (HPL → DPL) of the conversion device 100 is performed by, for example, the following formula.

Here, L indicates a luminance value normalized to 0 to 1, and S1, S2, a, b, and M are values set based on CAL, CPL, and DPL. ln is the natural logarithm. V is the converted luminance value normalized to 0 to 1. As in the example of FIG. 13A, when CAL is 300 nits, CPL is 2,000 nits, DPL is 750 nits, CAL + 50 nits are not converted, and conversion is performed for 350 nits or more, the respective values are, for example, as follows. It becomes a value like.

S1 = 350/10000
S2 = 2000/10000
M = 750/10000
a = 0.023
b = S1-a * ln (S1) = 0.112105

That is, in the first luminance conversion, when the luminance value of the SDR is between the average luminance value (CAL) and the first maximum luminance value (CPL), the natural logarithm is used to correspond to the luminance value of the HDR. Determine the display brightness value.

By converting the HDR video using information such as the content peak brightness and content average brightness of the HDR video, the conversion formula can be changed according to the content, and it is possible to convert so as to maintain the gradation of HDR as much as possible. It becomes. In addition, adverse effects such as being too dark and being too bright can be suppressed. Specifically, the gradation is maintained as much as possible by mapping the content peak brightness of the HDR video to the display peak brightness. In addition, the overall brightness is kept unchanged by not changing the pixel values below the average brightness.

Further, by converting the HDR image using the peak brightness value and the display mode of the SDR display, the conversion formula can be changed according to the display environment of the SDR display, and there is a feeling of HDR according to the performance of the SDR display. An image (pseudo HDR image) can be displayed with the same gradation and brightness as the original HDR image. Specifically, the display peak brightness is determined by the maximum brightness and display mode of the SDR display, and the HDR image is converted so as not to exceed the peak brightness value. The gradation is displayed with almost no reduction, and the brightness value that cannot be displayed is lowered to the brightness that can be displayed.

As described above, it is possible to reduce the brightness information that cannot be displayed, and to display the image in a form close to the original HDR image without degrading the tone of the displayable brightness. For example, for a display having a peak brightness of 1,000 nits, the overall brightness is maintained by converting to a pseudo HDR image having a peak brightness of 1,000 nits, and the brightness value changes depending on the display mode of the display. Therefore, the brightness conversion formula is changed according to the display mode of the display. If a brightness larger than the peak brightness of the display is allowed in the pseudo HDR image, the large brightness may be replaced with the peak brightness on the display side and displayed, in which case the overall brightness is darker than the original HDR image. Become. On the contrary, when the brightness smaller than the peak brightness of the display is converted as the maximum brightness, the small brightness is replaced with the peak brightness on the display side, and the image becomes brighter as a whole than the original HDR image. Moreover, since it is smaller than the peak brightness on the display side, the performance related to the tone of the display is not used to the maximum.

Further, on the display side, by switching the display setting using the setting information, it is possible to better display the pseudo HDR image. For example, when the brightness is set to be dark, high-luminance display cannot be performed, so that the HDR feeling is impaired. In that case, the display settings are changed or a message prompting the user to change the display is displayed to maximize the performance of the display so that a high-gradation image can be displayed.

In content such as Blu-ray, the video signal and the graphics signal such as subtitles and menus are multiplexed as independent data. At the time of reproduction, each is decoded individually, and the decoding result is synthesized and displayed. Specifically, subtitles and menu planes are superimposed on the video plane.

Here, even if the video signal is HDR, the graphics signal such as subtitles and menus may be SDR. In the HPL → DPL conversion of a video signal, the following two types of conversions (a) and (b) are possible.

(A) When performing HPL → DPL conversion after synthesizing graphics 1. Converts graphics EOTF from SDR EOTF to HDR EOTF.
2. The graphics after EOTF conversion are combined with the video.
3. 3. HPL → DPL conversion is performed on the synthesis result.

(B) When performing HPL → DPL conversion before synthesizing graphics 1. Converts graphics EOTF from SDR EOTF to HDR EOTF.
2. HPL → DPL conversion is performed on the video.
3. 3. The graphics after EOTF conversion and the video after DPL conversion are combined.

In the case of (b), the order of 1 and 2 may be exchanged.

In both the methods (a) and (b), the peak brightness of the graphics is 100 nits, but for example, when the DPL is a high brightness such as 1000 nits, the brightness of the graphics remains 100 nits. , The brightness of the graphics may decrease for the video after HPL → DPL conversion. In particular, adverse effects such as darkening of subtitles superimposed on the video are expected. Therefore, for graphics, the brightness may be converted according to the value of DPL. For example, the brightness of the subtitle may be set in advance as a percentage of the DPL value, and may be converted based on the set value. Graphics other than subtitles such as menus can be processed in the same way.

In the above, the reproduction operation of the HDR disc in which only the HDR signal is stored has been described.

Next, the multiplexed data stored in the dual disk in which both the HDR signal and the SDR signal are stored, which is shown in Case 2 of FIG. 6B, will be described with reference to FIG. FIG. 18 is a diagram for explaining the multiplexed data stored in the dual disk.

In the dual disk, as shown in FIG. 18, the HDR signal and the SDR signal are stored as different multiplexed streams. For example, in an optical disk such as Blu-ray, data of a plurality of media such as video, audio, subtitles, and graphics are stored as one multiplexing stream by an MPEG-2 TS-based multiplexing method called M2TS. These multiplexed streams are referenced from playback control metadata such as playlists, and are played back by the player analyzing the metadata during playback, or individual languages stored in the multiplexed streams. Select the data of. In this example, a case is shown in which playlists for HDR and SDR are stored separately, and each playlist refers to an HDR signal or an SDR signal. Further, identification information or the like indicating that both the HDR signal and the SDR signal are stored may be separately shown.

It is possible to multiplex both the HDR signal and the SDR signal in the same multiplexing stream, but multiplex so as to satisfy a buffer model such as T-STD (System Target Data Coder) specified in MPEG-2 TS. In particular, it is difficult to multiplex two videos having a high bit rate within a predetermined data read rate range. For this reason, it is desirable to separate the multiplexed streams.

Data such as audio, subtitles, and graphics need to be stored for each multiplexing stream, and the amount of data increases as compared with the case of multiplexing into one stream. However, the increase in the amount of data can reduce the amount of video data by using a video coding method having a high compression rate. For example, by changing the MPEG-4 AVC used in the conventional Blu-ray to HEVC (High Efficiency Video Coding), it is expected that the compression rate will be improved by 1.6 to 2 times. In addition, 4K is stored in the dual disk, such as a combination of 2K HDR and SDR, a combination of 4K SDR and 2K HDR, two 2K, or a combination of 2K and 4K. By prohibiting the storage of two optical discs, only combinations that fit in the capacity of the optical disc may be allowed.

FIG. 19 is a flowchart showing a reproduction operation of the dual disc.

First, the playback device determines whether or not the optical disc to be played back is a dual disc (S301). Then, when it is determined that the dual disk is used (Yes in S301), it is determined whether the output destination TV is HDRTV or SDRTV (S302). If it is determined to be HDRTV (Yes in S302), the process proceeds to step S303, and if it is determined to be SDRTV (No in S302), the process proceeds to step S304. In step S303, the HDR video signal is acquired from the multiplexed stream including the HDR signal in the dual disk, decoded, and output to the HDRTV. In step S304, the SDR video signal is acquired from the multiplexed stream including the SDR signal in the dual disk, decoded, and output to SDRTV. If it is determined in step S301 that the reproduction target is not a dual disc (No in S301), the reproduction possibility is determined by a predetermined method, and the reproduction method is determined based on the determination result (S305).

In the conversion method of the present disclosure, when the HDR video is displayed in SDRTV, the HDR video is converted into an SDR video of 100 nit or less by utilizing the fact that the peak brightness of the displayed SDRTV exceeds 100 nit (usually 200 nit or more). Instead, it realizes "HDR → pseudo HDR conversion processing" that can be converted so as to maintain the gradation of a region exceeding 100 nits to some extent, converted into a pseudo HDR image close to the original HDR, and displayed on the SDRTV.

Further, in the conversion method, the conversion method of "HDR → pseudo HDR conversion processing" may be switched depending on the display characteristics (maximum brightness, input / output characteristics, and display mode) of SDRTV.

Display characteristic information can be acquired by (1) automatically acquiring it through HDMI or a network, (2) generating it by having the user enter information such as the manufacturer name and product number, and (3) the manufacturer name and product number, etc. It is conceivable to acquire from the cloud etc. using the information of.

The timing of acquiring the display characteristic information of the conversion device 100 is as follows: (1) acquisition immediately before pseudo-HDR conversion, and (2) when the display device 200 (SDRTV or the like) is connected for the first time (when the connection is established). ) Can be obtained.

Further, in the conversion method, the conversion method may be switched according to the luminance information (CAL, CPL) of the HDR video.

For example, as a method of acquiring the luminance information of the HDR image of the conversion device 100, (1) it is acquired as meta information attached to the HDR image, and (2) it is acquired by having the user input the title information of the content. And (3) It is conceivable to acquire from the cloud or the like by using the input information that the user has influential.

Further, as details of the conversion method, (1) conversion is performed so as not to exceed DPL, (2) conversion is performed so that CPL becomes DPL, and (3) brightness below CAL and its periphery is not changed. 4) Convert using the natural logarithm, and (5) Clip with DPL.

Further, in the conversion method, in order to enhance the effect of the pseudo HDR, it is possible to transmit the display settings such as the display mode and display parameters of the SDRTV to the display device 200 to switch the display settings. For example, the user is prompted to set the display settings. The message may be displayed on the screen.

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.

Although the display method and the display device according to one or more aspects of the present disclosure have been described above based on the embodiment, the present disclosure is not limited to this embodiment. As long as it does not deviate from the gist of the present disclosure, 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 conversion method, a conversion device, and the like capable of appropriately converting the luminance from the first luminance range to the second luminance range in which the luminance range is reduced.

100 Conversion device 101 Conversion unit 102 Luminance conversion unit 103 Inverse brightness conversion unit 104 Inverse SDR EOTF conversion unit 200 Display device 201 Display setting unit 202 SDR EOTF conversion unit 203 Luminance conversion unit 204 Display unit

Claims (2)

It is a conversion method that converts the brightness of the image displayed on the display device.
The brightness of the image consists of the brightness values in the first brightness range.
The first luminance signal indicating the code value obtained by quantizing the luminance value of the image is acquired, and the first luminance signal is acquired.
The second luminance, which is a maximum value smaller than the maximum value of the first luminance range and larger than 100 nits, which determines the code value indicated by the acquired first luminance signal based on the luminance range of the display device. Convert to the second brightness value corresponding to the range,
In the conversion to the second luminance value,
The first code value indicated by the first luminance signal acquired by using EOTF (Electro-Optical Transfer Function) in which the luminance value in the first luminance range is associated with a plurality of first luminance signals is said to be the same. The first luminance value associated with the first code value in the EOTF is determined, and the first luminance value is determined.
With respect to the determined first luminance value, a second luminance value corresponding to the second luminance range, which is previously related to the first luminance value, is determined, and the first luminance value corresponding to the first luminance range is determined. Is converted to the second luminance value corresponding to the second luminance range, and the first luminance conversion is performed.
The maximum value of the second luminance range is the maximum luminance value of the display device.
In the first luminance conversion,
When the first luminance value is the first maximum luminance value which is the maximum value among the luminance values for a plurality of images constituting the video, the second maximum luminance value which is the maximum luminance value of the display device is set. Determined as the second luminance value,
For each region where the first luminance value is low luminance, medium luminance, and high luminance, different conversion formulas for converting the first luminance value into the second luminance value are set, and the first luminance value is set. Converted to the second luminance value,
A conversion method in which the conversion formula shows a straight line in the low-luminance and high-luminance regions, and the conversion formula shows a curve in the medium-luminance region. A conversion device that converts the brightness of the image displayed on the display device.
The brightness of the image consists of the brightness values in the first brightness range.
An acquisition unit that acquires a first luminance signal indicating a code value obtained by quantizing the luminance value of the video, and an acquisition unit.
The second luminance, which is a maximum value smaller than the maximum value of the first luminance range and larger than 100 nits, which determines the code value indicated by the acquired first luminance signal based on the luminance range of the display device. It is equipped with a conversion unit that converts to the second luminance value corresponding to the range.
In the conversion to the second luminance value,
The first code value indicated by the first luminance signal acquired by using EOTF (Electro-Optical Transfer Function) in which the luminance value in the first luminance range is associated with a plurality of first luminance signals is said to be the same. The first luminance value associated with the first code value in the EOTF is determined, and the first luminance value is determined.
With respect to the determined first luminance value, a second luminance value corresponding to the second luminance range, which is previously related to the first luminance value, is determined, and the first luminance value corresponding to the first luminance range is determined. Is converted to the second luminance value corresponding to the second luminance range, and the first luminance conversion is performed.
The maximum value of the second luminance range is the maximum luminance value of the display device.
In the first luminance conversion,
When the first luminance value is the first maximum luminance value which is the maximum value among the luminance values for a plurality of images constituting the video, the second maximum luminance value which is the maximum luminance value of the display device is set. Determined as the second luminance value,
For each region where the first luminance value is low luminance, medium luminance, and high luminance, different conversion formulas for converting the first luminance value into the second luminance value are set, and the first luminance value is set. Converted to the second luminance value,
A conversion device in which the conversion formula shows a straight line in the low-luminance and high-luminance regions, and the conversion formula shows a curve in the medium-luminance region.

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