JP2020048220A - Conversion method and conversion device - Google Patents

Abstract

To provide a conversion method capable of realizing further improvements.SOLUTION: The conversion method is a conversion method for converting the brightness of an image to be displayed on a display device, in which the brightness of the image consists of brightness values in a first brightness range, The conversion method includes the steps of: acquiring a first brightness signal indicating a code value obtained by quantizing the luminance value of the video; and converting the code value indicated by the acquired first brightness signal which is determined on the basis of the brightness range of the display device into the second brightness value corresponding to the second brightness range that is less than the maximum value of the first brightness range and greater than 100 nits.SELECTED DRAWING: Figure 11

Description

  The present disclosure relates to a conversion method related to luminance of an image.

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

JP 2008-167418 A

  The conversion method according to an aspect of the present disclosure is a conversion method for converting the luminance of an image displayed on a display device, wherein the luminance of the image includes a luminance value in a first luminance range, and the luminance value of the image is Obtaining a first luminance signal indicating a code value obtained by being quantized, and determining a code value indicated by the obtained first luminance signal based on a luminance range of the display device; Conversion 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 nit.

  The display device according to an aspect of the present disclosure generates a video linear signal by converting a video signal having a luminance range of HDR (High Dynamic Range) by using an EOTF (Electro-Optical Transfer Function) for HDR. A first EOTF conversion unit and a first graphics signal having a maximum luminance of 100 nit in a luminance range, a value determined at a predetermined ratio with respect to the maximum luminance that can be displayed by the display unit is defined as the maximum luminance A first luminance conversion unit for converting into a second graphics signal having a luminance range, and converting the second graphics signal using an EOTF (Electro-Optical Transfer Function) for HDR. Graphics linear signal A second EOTF converting unit, a synthesizing unit for synthesizing the video linear signal and the graphics linear signal to generate a synthesized signal, and a maximum luminance range of the synthesized signal that can be displayed by the display unit. A second luminance conversion unit that converts the luminance into a luminance range having a maximum luminance larger than 100 nit; and the display unit that displays the synthesized signal after the conversion by the second luminance conversion unit.

The conversion method according to an aspect of the present disclosure is a conversion method for converting the luminance of an image displayed on a display device, wherein the luminance of the image includes a luminance value in a first luminance range, and the luminance value of the image is Obtaining a first luminance signal indicating a code value obtained by being quantized, and determining a code value indicated by the obtained first luminance signal based on a luminance range of the display device; The second luminance value is converted to a second luminance value corresponding to a second luminance range that is a maximum value smaller than the maximum value of the range and larger than 100 nits. In the conversion to the second luminance value, the luminance in the first luminance range is converted. EOTF (Electro-Optical) that associates a value with a plurality of first code values.
Using a Transfer Function, a first luminance value associated with the first code value in the EOTF is determined for the first code value indicated by the acquired first luminance signal, and the determined first luminance value is determined. Determining a second brightness value corresponding to the second brightness range, which is pre-related to the first brightness value, and assigning the first brightness value corresponding to the first brightness range to the second brightness value. Performing a first luminance conversion for converting to the second luminance value corresponding to the range, wherein a maximum value of the second luminance range is a maximum value of the luminance of the display device; When the luminance value is a 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 value of the luminance of the display device is set to the second maximum luminance value. Determined as luminance value, If the first luminance value is equal to or less than an average luminance value that is an average of luminance values for a plurality of images forming the video, the first luminance value is not converted, and the first luminance value is replaced with the second luminance value. 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 the video technology. FIG. 2 is a diagram for explaining the relationship between a video production, a distribution method, and a display device when a new video expression is introduced into content. FIG. 3 is a diagram for explaining the relationship between the master, the distribution method, and the display device when HDR is introduced. FIG. 4A is a diagram for describing the SDR display processing in the SDRTV. FIG. 4B is a diagram for describing the SDR display processing in the SDRTV having a peak luminance 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 an HDR signal corresponding to HDR is stored in an HDR disc. FIG. 6B is a diagram for explaining Case 2 in which an HDR disc stores an HDR signal corresponding to HDR and an SDR signal corresponding to SDR. FIG. 7 is a diagram for explaining the conversion processing from HDR to pseudo HDR. FIG. 8A is a diagram illustrating an example of an EOTF (Electro-Optical Transfer Function) corresponding to each of HDR and SDR. FIG. 8B is a diagram illustrating an example of inverse EOTF corresponding to each of HDR and SDR. FIG. 9 is an explanatory diagram of a method of determining a code value of a luminance signal stored in a content and a process of restoring a luminance value from the code value during reproduction. FIG. 10A is a diagram illustrating an example of a display process for converting an HDR signal and performing HDR display in the HDRTV. FIG. 10B is a diagram illustrating an example of a display process of performing HDR display using an HDR-compatible playback device and SDRTV. FIG. 10C is a diagram illustrating an example of a display process for performing HDR display of an HDR-compatible playback device and an SDRTV connected to each other via a standard interface. FIG. 11 is a block diagram illustrating a configuration of the conversion device and the display device according to the embodiment. FIG. 12 is a flowchart illustrating a conversion method and a display method performed by the conversion device and the display device according to the embodiment. FIG. 13A is a diagram for describing the first luminance conversion. FIG. 13B is a diagram for describing another example of the first luminance conversion. FIG. 14 is a diagram for describing the second luminance conversion. FIG. 15 is a flowchart showing the detailed processing of the display setting. FIG. 16 is a diagram for describing the third luminance conversion. FIG. 17 is a diagram for explaining the conversion processing from HDR to pseudo HDR. FIG. 18 is a diagram for explaining the reproducing operation of the dual disc. FIG. 19 is a flowchart showing a reproducing operation of the dual disk.

(Knowledge underlying the present disclosure)
The inventor has found that the following problems occur with respect to the image signal processing device described in the section of “Background Art”.

  The image signal processing device disclosed in Patent Document 1 calculates a linear luminance for each pixel based on a linear RGB value calculated from pixels constituting a subject, and calculates a linear luminance for each pixel based on the linear RGB value and the linear luminance. A corrected linear luminance and a corrected linear RGB value of a combined pixel obtained by combining a plurality of pixels including the pixel are calculated, and the corrected linear luminance and the corrected linear RGB value are gamma-corrected to calculate a display luminance and a display RGB value. . As described above, the image signal processing device attempts to increase the number of displayable gradations by correcting the linear luminance based on the corrected linear RGB values.

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

  Based on the above examinations, the present inventors examined the following improvement measures to solve the above-mentioned problems.

  The display device according to an aspect of the present disclosure generates a video linear signal by converting a video signal having a luminance range of HDR (High Dynamic Range) by using an EOTF (Electro-Optical Transfer Function) for HDR. A first EOTF conversion unit and a first graphics signal having a maximum luminance of 100 nit in a luminance range, a value determined at a predetermined ratio with respect to the maximum luminance that can be displayed by the display unit is defined as the maximum luminance A first luminance conversion unit for converting into a second graphics signal having a luminance range, and converting the second graphics signal using an EOTF (Electro-Optical Transfer Function) for HDR. Graphics linear signal A second EOTF converting unit, a synthesizing unit for synthesizing the video linear signal and the graphics linear signal to generate a synthesized signal, and a maximum luminance range of the synthesized signal that can be displayed by the display unit. A second luminance conversion unit that converts the luminance into a luminance range having a maximum luminance larger than 100 nit; and the display unit that displays the synthesized signal after the conversion by the second luminance conversion unit.

  Further, for example, the graphics signal may be a signal for displaying a subtitle or a menu.

  A display method according to an aspect of the present disclosure is a conversion method for converting luminance of a video displayed on a display device, wherein the luminance of the video includes a luminance value of a first luminance range, and the luminance value of the video is Obtaining a first luminance signal indicating a code value obtained by being quantized, and determining a code value indicated by the obtained first luminance signal based on a luminance range of the display device; Conversion 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 nit.

  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.

  Also, for example, in the conversion to the second luminance value, the EOTF (Electro-Optical Transfer Function) obtained by associating the luminance value in the first luminance range with a plurality of first code values is used. For the first code value indicated by the first luminance signal, a first luminance value associated with the first code value in the EOTF is determined, and the determined first luminance value is previously determined as the first luminance value. Determining a related second luminance value corresponding to the second luminance range, and converting the first luminance value corresponding to the first luminance range to the second luminance value corresponding to the second luminance range; A first luminance conversion for conversion may be performed.

  Further, for example, the maximum value of the second luminance range is a maximum value of the luminance 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 video. In the case of the first maximum luminance value that is the maximum value among the above, the second maximum luminance value that is the maximum value of the luminance of the display device may be determined as the second luminance value.

  Also, for example, in the first luminance conversion, when the first luminance value is equal to or less than an average luminance value that is an average of luminance values for a plurality of images forming 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. Is also good.

  Also, 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 first luminance value corresponds to the first luminance value using a natural logarithm. The second luminance value may be determined.

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

  Further, for example, the first luminance signal is further acquired from a recording medium, and luminance information including at least one of the first maximum luminance value and an average luminance value that is an average of luminance values for a plurality of images forming the video. May be obtained via a network.

  Further, for example, the first maximum value is luminance information corresponding to each of a plurality of scenes of the video, and is a maximum value among luminance values for a plurality of images constituting the scene for each scene. Luminance information including at least one of a luminance value and an average luminance value that is an average of the luminance values for a plurality of images forming the scene; and in the first luminance conversion, for each of the plurality of scenes, The second luminance value may be determined according to the luminance information corresponding to a 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 pre-related to the second luminance value, is determined, and the third luminance value is determined. Performing a second luminance conversion for converting the second luminance value corresponding to the two luminance ranges to the third luminance value corresponding to the third luminance range, and determining the determined third luminance value as the third luminance value The third luminance value is quantized using an inverse EOTF that associates the luminance value in the range with a plurality of third code values, a third code value obtained by quantization is determined, and the third luminance value 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 using luminance relation information corresponding to display characteristic information that is information indicating display characteristics of the display device. The associated luminance value may be determined as the third luminance value, and the luminance conversion processing may be switched according to the display characteristic information.

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

  Further, for example, the display characteristic information may be further obtained 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 a timing when the display device is first connected to the display device.

  Note that these general or specific aspects may be realized by a recording medium such as an apparatus, a system, an integrated circuit, a computer program or a computer-readable CD-ROM, and a system, a method, an integrated circuit, and a computer. It may be realized by an arbitrary combination of a program or a recording medium.

  Hereinafter, a display method and a display device according to an embodiment of the present disclosure will be specifically described with reference to the accompanying drawings.

  Each of the embodiments described below shows a specific example of the present disclosure. Numerical values, shapes, materials, arrangement positions and connection forms of components, steps, order of steps, and the like shown in the following embodiments are merely examples and do not limit the present disclosure. In addition, among the components in the following embodiments, components not described in the independent claims indicating the highest concept are described as arbitrary components.

(Embodiment)
The present disclosure relates to a TV and a projector corresponding to an HDR (High Dynamic Range) signal which is a high luminance signal having a high luminance range, and a TV and a projector corresponding to an SDR (Standard Dynamic Range) signal which is a normal luminance signal having a maximum luminance value of 100 nit. The present invention relates to an image conversion / reproduction method and apparatus for displaying on a display device such as a tablet, a smartphone, and the like.

[1-1. background]
First, the transition of the video technology will be described with reference to FIG. FIG. 1 is a diagram for explaining the evolution of the video technology.

  Up to now, emphasis has been placed on increasing the number of display pixels in order to improve the image quality of video, and from a 720 × 480 pixel video of Standard Definition (SD) to a 1920 × 1080 pixel of High Definition (HD), so-called 2K. Video is widespread.

  In recent years, the introduction of a so-called 4K video of 3840 × 1920 pixels of Ultra High Definition (UHD) or 4096 × 1920 pixels of 4K has been started in order to further improve the quality of video.

  In addition to increasing the resolution of an image by introducing 4K, it is being studied to increase the image quality of the image by expanding the dynamic range, expanding the color gamut, or adding or improving the frame rate.

  Among them, as for the dynamic range, the maximum luminance is used to express bright light such as specular reflection light, which cannot be expressed by the current TV signal, with more realistic brightness while maintaining the dark part gradation in the conventional video. HDR (High Dynamic Range) has been attracting attention as a method corresponding to a luminance range in which the value is enlarged. Specifically, the method of the luminance range to which the TV signal corresponds so far is called SDR (Standard Dynamic Range), and the maximum luminance value is 100 nit, whereas the maximum luminance value is 1000 nit or more in HDR. It is assumed that the brightness value is increased. HDR is being standardized in SMPTE (Society of Motion Picture & Television Engineers) and ITU-R (International Telecommunications Union Radiocommunications Sector).

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

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

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

  In order to introduce a new image expression (such as an increase in the number of pixels) for improving the image quality of an image, as shown in FIG. 2, it is necessary to change (1) the master for home entertainment on the image production side. . Accordingly, it is necessary to update (2) the distribution method of broadcasting, communication, package media, and the like, and (3) the display device such as a TV and a projector for displaying the video.

[1-3. Relationship between master, distribution method, and display device when HDR is introduced]
In order for a user to enjoy content (for example, high-brightness video content (HDR content)) corresponding to a new video expression 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. Could not.

  For this reason, it is expensive, it is not easy to replace even in terms of size and weight, it is necessary to replace the TV, and the change to a new video expression depends on the spread of display devices (for example, TVs) having new functions. Will do. At the outset, neither the media side nor the content side can make a large investment, so that the spread of new video expressions has often slowed down.

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

[1-4. SDRTV]
To a TV (hereinafter, referred to as “SDRTV”) corresponding to only display of an image corresponding to SDR (hereinafter, referred to as “SDR display”), an input signal having a luminance value of up to 100 nit is input. For this reason, the SDRTV is sufficient to express the luminance value of the input signal if the display capability is 100 nit. However, the SDRTV actually has a function of reproducing a video having an optimum luminance value according to a viewing environment (dark room: cinema mode, bright room: dynamic mode, etc.), and is capable of expressing a video of 200 nit or more. Many have. That is, such an SDRTV can display an image up to the maximum brightness (for example, 300 nit) of the display capability by selecting a display mode according to the viewing environment.

  However, in the SDR system input signal input to the SDRTV, since the luminance upper limit of the input signal is determined to be 100 nit, as long as the SDR system input interface is used as usual, the high brightness video exceeding 100 nits of the SDRTV is provided. It is difficult to use the playback capability for HDR signal playback (see FIGS. 4A and 4B).

[1-5. HDR → SDR conversion]
HDR compatible broadcasting, moving image distribution via a communication network, or high luminance video content (hereinafter referred to as “HDR content”) distributed by a distribution method such as an HDR compatible package medium (for example, an HDR compatible Blu-ray Disc) or the like. It is assumed that the “HDR video” is output by an 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 on SDRTV, "HDR-> SDR conversion" is performed to convert HDR signals corresponding to HDR into SDR signals in an SDR luminance range with a maximum value of 100 nits so that images can be displayed correctly on SDRTV. I do. Thereby, the SDRTV can display the SDR video obtained by being converted from the HDR video by using the converted SDR signal (see FIG. 5).

  However, even in this case, even if the user purchases an HDR-compatible content (eg, Blu-ray disc, HDR IPTV content) and an HDR-compatible playback device (eg, Blu-ray device, HDR-compatible IPTV playback device). Regardless, in SDRTV, video can be enjoyed only in SDR video expression (SDR expression). In other words, even if HDR content and a playback device that supports HDR are prepared, if there is no display device (for example, HDRTV) that supports HDR and only SDRTV, the video can be displayed in HDR video representation (HDR representation). Can't watch.

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

[1-6. Two methods for realizing 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 describing Case 1 in which only HDR signals corresponding to HDR are stored in an HDR-compatible BD. FIG. 6B is a diagram for describing Case 2 in which an HDR-compatible BD stores an HDR signal corresponding to HDR and an SDR signal corresponding to SDR.

  As shown in FIG. 6A, in case 1, when displaying an image obtained by playing back a BD on a Blu-ray device on the HDRTV, even when a HDR-compatible BD (hereinafter, referred to as “HDRBD”) is played, the SDR is used. Even when a corresponding BD (hereinafter, referred to as “SDRBD”) is reproduced, the Blu-ray device outputs the luminance signal stored in the BD to the HDRTV without conversion. The HDRTV can perform display processing on both the HDR signal and the SDR signal. Therefore, the HDRTV performs display processing according to the input luminance signal, and displays an HDR video or an SDR video.

  On the other hand, in case 1, when displaying an image in which a BD is reproduced on a Blu-ray device on the SDRTV, when the HDRBD is reproduced, the Blu-ray device performs a conversion process of converting an HDR signal into an SDR signal. Then, the SDR signal obtained by the conversion process is output to SDRTV. When the SDRBD is reproduced, the Blu-ray device outputs the SDR signal stored in the BD to the SDRTV without conversion. Thereby, the SDRTV displays the SDR video.

  In addition, as shown in FIG. 6B, in case 2, when displaying an image of a BD reproduced by a Blu-ray device on an HDRTV, the process is the same as in case 1.

  On the other hand, in case 2, when displaying an image in which a BD is reproduced on a Blu-ray device on the SDRTV, the Blu-ray device is stored in the BD regardless of whether the HDRBD is reproduced or the SDRBD is reproduced. The converted SDR signal is output to SDRTV without conversion.

  In both Case 1 and Case 2, if you buy a Blu-ray device that supports HDRBD and HDR, you can only enjoy SDR video without HDRTV. Therefore, in order for the user to view HDR video, HDRTV is required, and it is expected that it will take time to spread HDR-compatible Blu-ray devices or HDRBD.

[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 promote the commercialization of HDR contents and distribution methods without waiting for the spread of HDRTV. To this end, if the existing SDRTV can make the HDR signal viewable not as an SDR video but as an HDR video or a pseudo HDR video closer to the HDR video than the SDR video, the user can use the HDRTV. Even if you do not buy, you can watch a higher quality video that is clearly different from the SDR video and similar to the HDR video. In other words, if the user can view the pseudo HDR video on the SDRTV, the user can view the video with higher image quality than the SDR video only by preparing the HDR content and the HDR distribution device without preparing the HDRTV. . In short, making the pseudo HDR video viewable on the SDRTV can be a motivation for the user to purchase the HDR content and the HDR distribution device (see FIG. 7).

  In order to realize the display of the pseudo HDR video on the SDRTV, in the configuration in which the SDRTV is connected to the HDR distribution method, when the HDR content is reproduced, the HDR signal is displayed so that the HDR content video can be correctly displayed on the SDRTV. Instead of converting to an SDR video signal, a pseudo HDR signal for displaying a video having the maximum brightness of the display capability of the SDRTV, for example, 200 nit or more, is generated by using the input of a video signal having a maximum value of 100 nits of SDRTV. Then, 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, the EOTF will be described with reference to FIGS. 8A and 8B.

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

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

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

  The inverse EOTF indicates a correspondence between a luminance value and a code value, and is a method of quantizing a luminance value and converting it into a code value, contrary to the EOTF. That is, the inverse EOTF is relationship information indicating the correspondence between the luminance value and the plurality of code values. For example, when a luminance value of a video corresponding to HDR is represented by a code value of a 10-bit gradation, luminance values in a luminance range of HDR up to 10,000 nits are quantized to 1024 luminance values from 0 to 1023. Is mapped to an integer value. That is, by performing quantization based on the inverse EOTF, a luminance value (luminance value of a video corresponding to HDR) in a luminance range up to 10,000 nit is converted into an HDR signal which is a 10-bit code value. In the EOTF corresponding to HDR (hereinafter, referred to as “HDR EOTF”) or the inverse EOTF corresponding to HDR (hereinafter, referred to as “HDR inverse EOTF”), the EOTF corresponding to SDR (hereinafter, “SDR EOTF”) is used. ) Or an inverse EOTF corresponding to SDR (hereinafter referred to as “inverse EOTF of SDR”). For example, in FIG. 8A and FIG. The value (peak luminance) is 10,000 nit. That is, the HDR luminance range includes the entire SDR luminance range, and the HDR peak luminance is larger than the SDR peak luminance. The HDR luminance range is a luminance range obtained by expanding the maximum value from 100 nit, which is the maximum value of the SDR luminance range, to 10,000 nit.

  For example, the HDR EOTF and the HDR inverse EOTF are, for example, SMPTE 2084 standardized by the American 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 a code value of a luminance signal stored in a content and a process of restoring a luminance value from the code value during 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 a code value corresponding to the luminance value of the image is determined. Image encoding is performed based on the 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 inverse quantization based on the HDR EOTF, and the luminance value of 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 referred to as “HDR EOTF conversion”. Similarly, quantization using SDR inverse EOTF is referred to as “inverse SDR EOTF conversion”. Inverse quantization using SDR EOTF is referred to as “SDR EOTF conversion”.

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

  FIG. 10A is a diagram illustrating an example of a display process for converting an HDR signal and performing HDR display in the HDRTV.

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

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

  As shown in FIG. 10B, when displaying an HDR video, if the display device is an SDRTV, the maximum value (peak luminance (DPL: example 300 nit)) of the luminance range of the SDRTV to be displayed exceeds 100 nits. 10B is 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) in FIG. 10B. If the signal obtained by performing "brightness conversion" using DPL (eg, 300 nit) and performing "brightness conversion" can be directly input to the "display device" of SDRTV, the same effect as that of HDRTV can be obtained by using SDRTV. Can be realized.

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

  FIG. 10C is a diagram illustrating an example of a display process of performing HDR display using an HDR-compatible playback device and an SDRTV connected to each other via a standard interface.

  As shown in FIG. 10C, normally, it is necessary to input a signal capable of obtaining the effect of FIG. 10B to the SDRTV using an input interface (HDMI (registered trademark, the same applies hereinafter) or the like) provided in the SDRTV. In SDRTV, a signal input via an input interface sequentially passes through “EODR conversion of SDR”, “luminance conversion for each mode”, and “display device”, and an image adjusted to the maximum luminance range of the display device. Is displayed. For this reason, a signal (pseudo HDR signal) that can cancel “EODR conversion of SDR” and “luminance conversion for each mode” that passes immediately after the input interface by SDRTV in an HDR-compatible Blu-ray device. Generate. That is, within the HDR-compatible Blu-ray device, immediately after “HDR EOTF conversion” and “luminance conversion” using the peak luminance (DPL) of SDRTV, “inverse luminance conversion for each mode” and “inverse SDR EOTF conversion ", the same effect as in the case where the signal immediately after the" luminance conversion "is input to the" display device "(broken arrow in FIG. 10C) is realized in a pseudo manner.

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

  As shown in FIG. 11, the conversion apparatus 100 includes an HDR EOTF converter 101, a luminance converter 102, an inverse luminance converter 103, and an inverse SDR EOTF converter 104. The display device 200 includes a display setting unit 201, an EOTF conversion unit 202 for SDR, a luminance 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 HDR luminance range (0 to HPL [nit]) is referred to as a “first luminance range”. The luminance range (0 to DPL [nit]) of the display is referred to as “second luminance range”. The SDR luminance range (0 to 100 [nit]) is referred to as “third luminance range”.

[1-12. Conversion Method and Display Method]
A 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 an HDR video on which inverse HDR EOTF conversion has been performed. The HDR EOTF conversion unit 101 of the conversion device 100 performs HDR EOTF conversion on the obtained HDR video HDR signal (S101). Thereby, HDR EOTF conversion section 101 converts the obtained HDR signal into a linear signal indicating a luminance value. The HDR EOTF is, for example, SMPTE 2084.

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

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

  More specifically, in step S101, the HDR EOTF conversion unit 101 uses the acquired HDR signal and the HDR EOTF to determine an HDR code value as a first code value indicated by the acquired HDR signal. Determine the HDR luminance value associated with the HDR code value in the HDR EOTF. Note that the HDR signal is obtained by quantizing the luminance value of a video (content) using an HDR inverse EOTF that associates a luminance value in the HDR luminance range with a plurality of HDR code values. Shows the HDR code value.

  Also, in step S102, the luminance conversion unit 102 determines a display luminance value corresponding to the luminance range of the display, which is related to the luminance value of HDR determined in step S101 in advance, and The first luminance conversion is performed to convert the HDR luminance value corresponding to the luminance range of the display into a display luminance value corresponding to the luminance range of the display.

  Also, before step S102, the conversion apparatus 100 has content luminance information including at least one of a maximum value of the luminance of the video (content) (CPL: Content Peak Luminance) and an average luminance value of the video (CAL: Content Average Luminance). Is obtained as information on the HDR signal. The CPL (first maximum luminance value) is, for example, the maximum value of the luminance values for a plurality of images constituting the HDR video. CAL is, for example, an average luminance value which is an average of luminance values of a plurality of images constituting an HDR video.

  Further, the conversion device 100 has acquired the display characteristic information of the display device 200 from the display device 200 before step S102. Note that the display characteristic information includes the maximum value (DPL) of the luminance that can be displayed by the display device 200, the display mode (see below) of the display device 200, and the input / output characteristics (EOTF corresponding to the display device). This is information indicating display characteristics.

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

  Next, the inverse luminance conversion unit 103 of the conversion device 100 performs inverse luminance conversion according to the display mode of the display device 200. Accordingly, the inverse luminance conversion unit 103 performs the second luminance conversion for converting the luminance value corresponding to the display luminance range, which is the second luminance range, to the luminance value corresponding to the SDR luminance range, which is the third luminance range. Perform (S103). Details will be described later. That is, the inverse luminance conversion unit 103 sets the display luminance value obtained in step S102 as a third luminance value corresponding to the SDR luminance range having a maximum value of 100 nits, which is related to the display luminance value in advance. A luminance value corresponding to the SDR (hereinafter, referred to as “a luminance value of the SDR”) is determined, and a display luminance value corresponding to the luminance range of the display is converted to a luminance value of the SDR corresponding to the luminance range of the SDR. A second luminance conversion is performed.

  Then, the inverse SDR EOTF conversion unit 104 of the conversion device 100 performs the inverse SDR EOTF conversion to generate a pseudo HDR video (S104). That is, the inverse SDR EOTF conversion unit 104 performs inverse EOTF (Electro-Optical) of SDR (Standard Dynamic Range), which is the third relation information relating the luminance value in the luminance range of HDR and a plurality of third code values. Using Transfer Function, the determined SDR luminance value is quantized, a 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 the signal into 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 obtained by quantizing the luminance value of the video using the inverse EOTF of the SDR that associates the luminance value in the luminance range of the SDR with the code values of the plurality of SDRs. It is represented by a code value. Then, conversion device 100 outputs the pseudo HDR signal (SDR signal) generated in step S104 to display device 200.

  The conversion apparatus 100 generates the SDR luminance value corresponding to the pseudo HDR by performing the first luminance conversion and the second luminance conversion on the HDR luminance value obtained by dequantizing the HDR signal. Then, the SDR signal corresponding to the pseudo HDR is generated by quantizing the luminance value of the SDR using the EOTF of the SDR. The luminance value of SDR is a numerical value within a luminance range of 0 to 100 nit corresponding to SDR. However, since the conversion based on the luminance range of the display is performed, the HDR EOTF and SDR Is a numerical value different from a luminance value in a luminance range of 0 to 100 nit corresponding to SDR obtained by performing luminance conversion using EOTF.

  Next, a 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 display settings of the display device 200 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 display settings recommended for the display device, and information indicating how to EOTF the pseudo HDR video and which setting can display a beautiful video (i.e., This is information for switching the display setting of the display device 200 to the optimal display setting. The setting information includes, for example, gamma curve characteristics at the time of output on the display device, display modes such as a living mode (normal mode) and a dynamic mode, and numerical values of a backlight (brightness). Further, a message that prompts the user to change the display settings of the display device 200 by a manual operation may be displayed on the display device 200 (hereinafter, also referred to as “SDR display”). Details will be described later.

  Note that 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 before step S105.

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

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

  Then, the brightness conversion unit 203 of the display device 200 performs brightness conversion according to the display mode set for the display device 200. Thereby, the brightness conversion unit 203 converts the SDR brightness value corresponding to the SDR brightness range (0 to 100 [nit]) into the display brightness value corresponding to the display brightness range (0 to DPL [nit]). Is performed (S107). Details will be described later.

  From the above, the display device 200 determines the third code value indicated by the acquired SDR signal (pseudo HDR signal) in step S106 and step S107 using the setting information acquired in step S105, using the display luminance range ( 0 to DPL [nit]).

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

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

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

[1-13. First luminance conversion]
Next, 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 describing an example of the first luminance conversion.

  The brightness conversion unit 102 of the conversion device 100 performs a first brightness conversion for converting the linear signal (HDR brightness value) obtained in step S101 using the display characteristic information and the HDR video content brightness information. . 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 the 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 a dark image on the SDR display and a dynamic mode for displaying a bright image. When the display mode is, for example, the maximum brightness of the SDR display is 1,500 nit and the display mode is a mode in which the brightness is 50% of the maximum brightness, the DPL is 750 nit. Here, the DPL (second maximum luminance value) is a maximum value of luminance 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 using the display characteristic information that is the information indicating the display characteristic of the SDR display.

  Also, in the first luminance conversion, CAL and CPL of the content luminance information are used, luminance values below CAL are the same before and after the conversion, and luminance values are changed only for luminance values above CPL. I do. That is, as shown in FIG. 13A, in the first luminance conversion, when the luminance value of the HDR is equal to or less than CAL, the luminance value of the HDR is not converted, and the luminance value of the HDR is determined as a display luminance value. When the HDR luminance value is equal to or higher than the CPL, the DPL as the second maximum luminance value is determined as the display luminance value.

  In the first luminance conversion, the peak luminance (CPL) of the HDR video in the luminance information is used, and when the luminance value of the HDR is CPL, 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 be clipped to a value not exceeding DPL. By performing such a luminance conversion, the processing in the conversion device 100 can be simplified, and the device can be reduced in size, the power consumption can be reduced, and the processing speed can be increased. FIG. 13B is a diagram for describing another example of the first luminance conversion.

[1-14. Second luminance conversion]
Next, 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 describing the second luminance conversion.

  The inverse luminance conversion unit 103 of the conversion device 100 performs the inverse luminance conversion according to the display mode on the display luminance value of the display luminance range (0 to DPL [nit]) converted by the first luminance conversion in step S102. Apply. In the reverse luminance conversion, when the luminance conversion processing (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]) of the display after the processing of step S102 is obtained. This is a process for making it possible. That is, the second luminance conversion is an inverse luminance conversion of the third luminance conversion.

  By the above processing, the second luminance conversion is performed by changing 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) of the SDR luminance range, which is the third luminance range. Value).

  In the second brightness conversion, the conversion formula is switched according to the display mode of the SDR display. For example, when the display mode of the SDR display is the normal mode, the luminance is converted into a directly proportional value that is directly proportional to the display display luminance value. In the second luminance conversion, when the display mode of the SDR display is a dynamic mode in which the high luminance pixels are brighter and the low luminance pixels are darker than the normal mode, the inverse function is used to obtain the low luminance pixels. Is converted to a value higher than a directly proportional value directly proportional to the display luminance value, and the SDR luminance value of the high luminance pixel is converted to a value lower than a directly 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 using the luminance relation information corresponding to the display characteristic information that is the information indicating the display characteristic of the SDR display. The luminance value is determined as the luminance value of the SDR, and the luminance conversion processing is switched according to the display characteristic information. Here, the luminance-related information according to the display characteristic information includes, for example, a display luminance value (input luminance value) determined for each display parameter (display mode) of the SDR display and an SDR This is information relating a luminance value (output luminance value).

[1-15. Display Settings]
Next, details of the display setting in step S105 will be described with reference to FIG. FIG. 15 is a flowchart showing the 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 the EOTF set for the SDR display (EODR for SDR display) matches the EOTF assumed when the pseudo HDR video (SDR signal) is generated. A determination is made (S201).

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

  When determining that the display can be switched, the display setting unit 201 switches the EOTF for SDR display to an appropriate EOTF using the setting information (S203).

  In steps S201 to S203, in the display setting (S105), the EOTF set on the SDR display is set to the recommended EOTF according to the acquired setting information. In this way, in step S106 performed after step S105, the luminance value of SDR can be determined using the recommended EOTF.

  If the system determines that the switching is not possible (No in S202), a message prompting the user to change the EOTF by manual operation is displayed on the screen (S204). For example, a message “set display gamma to 2.4” is displayed on the screen. That is, if the EOTF set for the SDR display cannot be switched in the display setting setting (S105), the display setting unit 201 switches the EOTF set for the SDR display (EODR for SDR display) to the recommended EOTF. Is displayed on the SDR display.

  Next, on the SDR display, a pseudo HDR video (SDR signal) is displayed. Before displaying the pseudo HDR video, it is determined whether the display parameters of the SDR display match the setting information using the setting information (S205).

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

  When determining 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 in accordance with the setting information (S207).

  From steps S204 to S207, in the display setting (S105), the display parameters set in the SDR display are set to the recommended display parameters according to the acquired setting information.

  If the system determines that the switching is not possible (No in S206), a message that prompts the user to manually change the display parameters set in the SDR display is displayed on the screen (S208). For example, a message “Please change the display mode to the dynamic mode and maximize the backlight” is displayed on the screen. That is, in the setting (S105), if the display parameters set in the SDR display cannot be switched, a message for prompting the user to switch the display parameters set in the SDR display to the recommended display parameters is displayed on the SDR display. To be displayed.

[1-16. Third luminance conversion]
Next, 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 describing the third luminance conversion.

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

  In the third brightness conversion, the conversion formula is switched according to 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 directly proportional value that is directly proportional to the SDR luminance value. . 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 the normal mode, the display luminance value of the low-luminance pixels is equal to that of the SDR. The display brightness value of the high-brightness pixel is converted into a value higher than a directly proportional value directly proportional to the SDR brightness value to a value lower than the directly proportional value directly proportional to the brightness value. That is, in the third luminance conversion, the luminance value of the SDR determined in step S106 is determined by using the luminance-related information corresponding to the display parameter indicating the display setting of the SDR display, and the luminance value previously associated with the SDR luminance value. The value is determined as the display luminance value, and the luminance conversion processing is switched according to the display parameter. Here, the luminance-related information corresponding to the display parameters includes, for example, an SDR luminance value (input luminance value) determined for each display parameter (display mode) of the SDR display and a display luminance as shown in FIG. This is information that is associated with a value (output luminance value).

[1-17. Effects]
A normal SDRTV has an input signal of 100 nits, but has an ability to express a video of 200 nits or more in accordance with a viewing environment (dark room: cinema mode, bright room: dynamic mode, etc.). However, since the upper limit of the luminance of the input signal to the SDRTV was set to 100 nit, the ability could not be used directly.

  When displaying an HDR video in SDRTV, utilizing the fact that the peak luminance of the displayed SDRTV exceeds 100 nit (usually 200 nit or more), instead of converting the HDR video to an SDR video of 100 nit or less, the luminance exceeding 100 nit is used. “HDR → pseudo HDR conversion processing” is performed so as to maintain the range of gradations to some extent. For this reason, it is possible to display the pseudo HDR video close to the original HDR on the SDRTV.

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

  Therefore, it has been considered that an HDR-compatible TV is required to watch an HDR video, but a pseudo HDR video that can realize an HDR-like effect can be viewed on an existing SDRTV. As a result, the spread of HDR-compatible Blu-ray can be expected.

  An HDR signal transmitted by broadcast, package media such as Blu-ray, or Internet distribution such as OTT is converted into a pseudo HDR signal by performing an HDR-pseudo HDR conversion process. This makes it possible to display the HDR signal as a pseudo HDR video on an existing SDRTV.

(Other embodiments)
As described above, the embodiments have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which changes, replacements, additions, omissions, and the like are made as appropriate. Further, it is also possible to form a new embodiment by combining the components described in the above embodiment.

  Therefore, other embodiments will be described below.

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

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

  The display device 200 (SDR display unit) is, for example, a television, a personal computer, and 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 protocol. The display characteristic information acquired by the conversion device 100 may acquire the display characteristic information included in the model information of the display device 200 via the Internet. Alternatively, the user may perform a manual operation to set the display characteristic information in the conversion device 100. Further, the acquisition of the display characteristic information of the conversion device 100 may be performed immediately before the generation of the pseudo HDR video (steps S101 to S104), or may be performed at the time of initial setting of the device or at the time of connecting the display. For example, the acquisition of the display characteristic information may be performed immediately before the conversion to the display luminance value, or may be performed at a timing when the conversion device 100 is first connected to the display device 200 via the HDMI cable.

  Also, one CPL or CAL of HDR video may be provided for one content, or may exist for each scene. That is, in the conversion method, the first maximum luminance value is luminance information corresponding to each of a plurality of scenes of a video, and is a maximum value of luminance values for a plurality of images constituting the scene for each of the scenes. And luminance information (CPL, CAL) including at least one of an average luminance value that is an average of luminance values for a plurality of images forming the scene. 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.

  Also, the CPL and CAL may be bundled with the same medium (Blu-ray disc, DVD, etc.) as the HDR video, or may be obtained from a location different from the HDR video, such as the conversion device 100 obtaining from the Internet. May be. That is, luminance information including at least one of CPL and CAL may be obtained as video meta information, or may be obtained via a network.

  Further, in the first luminance conversion (HPL → DPL) of the conversion device 100, a fixed value may be used without using CPL, CAL, and display peak luminance (DPL). Further, the fixed value may be externally changeable. Further, CPL, CAL, and DPL may be switched in several types. For example, DPL may be only three types, 200 nit, 400 nit, and 800 nit, and a value closest to the display characteristic information may be used. You may make it.

  Also, the HDR EOTF may not be SMPTE 2084, and another type of HDR EOTF may be used. Also, the maximum luminance (HPL) of the HDR video need not be 10,000 nits, and may be, for example, 4,000 nits or 1,000 nits.

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

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

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

  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. The setting information may be flag information indicating whether or not the image is a pseudo HDR image. For example, when the image is a pseudo HDR image, the setting may be changed to a setting for displaying the brightest image. That is, in the setting of the display setting (S105), when the acquired setting information indicates a signal indicating the pseudo HDR video converted using the DPL, the brightness setting of the display device 200 is set to be the brightest. May be switched to.

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

  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 0-1. As in the example of FIG. 13A, CAL is set to 300 nits, CPL is set to 2,000 nits, DPL is set to 750 nits, conversion is not performed up to CAL + 50 nits, and conversion is performed for 350 nits or more. It becomes such a value.

S1 = 350/10000
S2 = 2000 / 10,000
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 luminance value of the HDR corresponds to the luminance value of the HDR using the natural logarithm. Determine the display brightness value.

  By converting the HDR video using information such as the content peak luminance and the average content luminance of the HDR video, the conversion formula can be changed according to the content, and the HDR video can be converted to keep the HDR gradation as much as possible. Becomes Further, adverse effects such as too dark and too bright can be suppressed. Specifically, the gradation is kept as much as possible by mapping the content peak luminance of the HDR video to the display peak luminance. Also, by not changing the pixel values below the average luminance, the overall brightness is not changed.

  Also, by converting the HDR video using the peak luminance value and the display mode of the SDR display, the conversion formula can be changed according to the display environment of the SDR display. The video (pseudo HDR video) can be displayed with the same gradation and brightness as the original HDR video. Specifically, the display peak brightness is determined according to the maximum brightness and the display mode of the SDR display, and the HDR video is converted so as not to exceed the peak brightness value. The display is performed with almost no reduction in gradation, and the brightness value that cannot be displayed is reduced to the displayable brightness.

  As described above, undisplayable brightness information can be reduced, and display can be performed in a form close to the original HDR video without reducing the displayable brightness gradation. For example, for a display with a peak luminance of 1,000 nits, the overall brightness is maintained by converting to a pseudo HDR image with a peak luminance of 1,000 nits, and the luminance value changes depending on the display mode of the display. For this reason, the conversion formula of the luminance is changed according to the display mode of the display. If a luminance higher than the peak luminance of the display is allowed in the pseudo HDR image, the large luminance may be replaced with the peak luminance on the display side and displayed. In this case, the whole image is darker than the original HDR image. Become. Conversely, when a luminance smaller than the peak luminance of the display is converted as the maximum luminance, the small luminance is replaced with the peak luminance on the display side, and the whole becomes brighter than the original HDR video. In addition, since the brightness is smaller than the peak luminance on the display side, the performance regarding the gradation of the display is not used to the utmost.

  On the display side, by switching the display setting using the setting information, it is possible to display the pseudo HDR video better. For example, when the brightness is set to be dark, high-luminance display cannot be performed, and the HDR feeling is impaired. In that case, by changing the display setting or displaying a message urging the user to change the display setting, the performance of the display is maximized and a high-gradation image can be displayed.

  In content such as Blu-ray, a video signal and a graphics signal such as a caption or a menu are multiplexed as independent data. At the time of reproduction, each is individually decoded, and the decoding results are combined and displayed. Specifically, a subtitle or menu plane is superimposed on a 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 conversions (a) and (b) are possible.

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

(B) Performing HPL → DPL conversion before graphics synthesis The graphics EOTF is converted from the SDR EOTF to the HDR EOTF.
2. HPL → DPL conversion is performed on the video.
3. The graphics after the EOTF conversion and the video after the DPL conversion are combined.

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

  In either of the methods (a) and (b), the graphics peak luminance is 100 nits. For example, when the DPL is high luminance such as 1000 nits, the graphics luminance remains at 100 nits. , The luminance of graphics may be reduced with respect to the video after the HPL → DPL conversion. In particular, adverse effects such as darkening of subtitles superimposed on video are assumed. Therefore, the brightness of graphics may be converted according to the value of DPL. For example, the subtitle luminance may be set in advance to what 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 a similar manner.

  The operation of reproducing an HDR disc storing only HDR signals has been described above.

  Next, the multiplexed data stored in the dual disc 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 describing multiplexed data stored on a dual disk.

  In the dual disc, as shown in FIG. 18, the HDR signal and the SDR signal are stored as different multiplexed streams. For example, in an optical disc such as a Blu-ray, data of a plurality of media such as video, audio, subtitles, and graphics is stored as one multiplexed stream by an MPEG-2 TS-based multiplexing method called M2TS. These multiplexed streams are referred to from playback control metadata such as a playlist, and at the time of playback, a multiplexed stream that is played by a player by analyzing the metadata, or an individual language stored in the multiplexed stream. Select the data. This example shows a case where playlists for HDR and SDR are individually stored, and each playlist refers to an HDR signal or an SDR signal. Also, identification information indicating that both the HDR signal and the SDR signal are stored may be separately indicated.

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

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

  FIG. 19 is a flowchart showing a reproducing operation of the dual disk.

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

  According to the conversion method of the present disclosure, when displaying an HDR video in an SDRTV, the HDR video is converted into an SDR video of 100 nit or less by using the fact that the peak luminance of the displayed SDRTV exceeds 100 nit (usually 200 nit or more). Instead, the “HDR → pseudo HDR conversion processing” that can be converted so as to maintain the gradation of an area exceeding 100 nit to some extent, converted to a pseudo HDR video close to the original HDR, and displayed on an SDRTV is realized.

  Further, in the conversion method, the conversion method of “HDR → pseudo HDR conversion processing” may be switched according to the display characteristics (maximum luminance, input / output characteristics, and display mode) of the SDRTV.

  The display characteristic information can be acquired by (1) automatically acquiring the information through HDMI or a network, (2) generating the information by allowing the user to input information such as a manufacturer name and a product number, and (3) producing a manufacturer name and a product number. It is conceivable that the information is obtained from a cloud or the like by using the information of.

  In addition, the acquisition timing of the display characteristic information of the conversion apparatus 100 includes: (1) acquisition immediately before pseudo HDR conversion, and (2) first connection with the display apparatus 200 (such as SDRTV) (when connection is established). ).

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

  For example, the conversion device 100 can acquire the luminance information of the HDR video by (1) acquiring it as meta information attached to the HDR video, (2) acquiring the title information of the content by the user, And (3) acquiring from a cloud or the like using input information that is influential to the user.

  The details of the conversion method include (1) conversion so as not to exceed DPL, (2) conversion so that CPL becomes DPL, (3) CAL and the luminance below the CAL without changing, 4) Conversion is performed using natural logarithm, and (5) clip processing is performed by DPL.

  Further, in the conversion method, in order to enhance the effect of the pseudo HDR, display settings such as the display mode of SDRTV and display parameters can be transmitted to the display device 200 and switched, for example, prompting the user to perform 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.

  As described above, the display method and the display device according to one or more aspects of the present disclosure have been described based on the embodiments, but the present disclosure is not limited to the embodiments. Unless departing from the gist of the present disclosure, various modifications conceivable to those skilled in the art may be applied to the present embodiment, and a form constructed by combining components in different embodiments may be one or more of the present disclosure. 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 that can appropriately convert luminance from a first luminance range to a second luminance range in which the luminance range is reduced.

REFERENCE SIGNS LIST 100 conversion device 101 conversion unit 102 luminance conversion unit 103 inverse luminance 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 (1)

A conversion method for converting the brightness of an image to be displayed on a display device,
The luminance of the image includes luminance values in a first luminance range,
Obtaining a first luminance signal indicating a code value obtained by quantizing the luminance value of the image;
A second luminance, which is smaller than the maximum value of the first luminance range and is larger than 100 nit, is determined based on the luminance range of the display device, and determines a code value indicated by the acquired first luminance signal. A conversion method for converting to a second luminance value corresponding to the range.