Patent Publication Number: US-11049225-B2

Title: Video processing system and video processing method

Description:
CROSS-REFERENCE OF RELATED APPLICATIONS 
     This application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/JP2018/006858, filed on Feb. 26, 2018, which in turn claims the benefit of U.S. Provisional Application No. 62/529,727, filed on Jul. 7, 2017, the entire disclosures of which Applications are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a video processing system and a video processing method for processing a video signal. 
     BACKGROUND ART 
     Patent Literature (PTL) 1 discloses a display apparatus that updates an HDR signal display method based on dynamic HDR metadata in an HDR (High Dynamic Range) video. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Unexamined Patent Application Publication No. 2017-184249 
       
    
     Non-Patent Literature 
     
         
         NPL 1: White Paper Blu-ray Disc Read-Only Format (Ultra HD Blu-ray), Audio Visual Application Format Specifications for BD-ROM Version 3.1, August 2016 (http://www.blu-raydisc.com/Assets/Downloadablefile/BD-ROM_Part3 V3.1_WhitePaper_160729_clean.pdf) 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The present disclosure provides a video processing system or a video processing method that can improve the quality of a video displayed. 
     Solution to Problem 
     A video processing system according to an aspect of the present disclosure includes: a first acquirer that acquires video data including a main video; a second acquirer that acquires a display format that indicates a luminance dynamic range format displayable by a display apparatus; a generator that generates first characteristics information that indicates first dynamic luminance characteristics that correspond to the display format by using the video data when a luminance dynamic range format of the main video indicated by the video data is different from the display format, the first dynamic luminance characteristics being dynamic luminance characteristics that indicate a time-dependent change in luminance characteristics of the main video; and an outputter that outputs the first characteristics information generated by the generator. 
     Advantageous Effect of Invention 
     The present disclosure can provide a video processing system and a video processing method that can improve the quality of a video displayed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating the evolution of imaging technology. 
         FIG. 2  is a diagram illustrating the relationship between video production, delivery methods, and display apparatuses when a new video representation is introduced into content. 
         FIG. 3A  is a diagram showing an example of tone mapping. 
         FIG. 3B  is a diagram showing an example of tone mapping. 
         FIG. 4A  is a diagram showing an example of static tone mapping. 
         FIG. 4B  is a diagram showing an example of dynamic tone mapping. 
         FIG. 5A  is a diagram showing examples of EOTFs (Electro-Optical Transfer Functions) for HDR and SDR. 
         FIG. 5B  is a diagram showing examples of inverse EOTFs for HDR and SDR. 
         FIG. 6  is a diagram showing an example in which graphics are overlaid on a moving image, and the resulting moving image is displayed. 
         FIG. 7  is a diagram showing the influence of dynamic tone mapping when graphics are overlaid on a main video. 
         FIG. 8A  is a main flowchart showing an example of an HDR format checking method. 
         FIG. 8B  is a sub-flowchart of the main flowchart shown in  FIG. 8A  illustrating an example of a format checking method for checking the format of a main video. 
         FIG. 8C  is a sub-flowchart of the main flowchart shown in  FIG. 8A  illustrating an example of a format checking method for checking the format of a video display apparatus. 
         FIG. 9A  is a diagram showing a configuration example of dynamic metadata corresponding to a first option. 
         FIG. 9B  is a diagram showing a configuration example of dynamic metadata corresponding to a second option. 
         FIG. 10  is a block diagram showing a configuration of a video processing system according to Embodiment 1. 
         FIG. 11A  is a flowchart illustrating the operations of a video reproduction apparatus according to Embodiment 1. 
         FIG. 11B  is a flowchart illustrating the operations of a video display apparatus according to Embodiment 1. 
         FIG. 12  is a diagram showing another configuration example of dynamic metadata. 
         FIG. 13  is a block diagram showing a configuration of a video processing system according to Embodiment 2. 
         FIG. 14  is a flowchart illustrating the operations of a video reproduction apparatus according to Embodiment 2. 
         FIG. 15  is a block diagram showing a configuration of a video processing system according to a first example of Embodiment 3. 
         FIG. 16  is a flowchart illustrating the operations of a video display apparatus according to the first example of Embodiment 3. 
         FIG. 17  is a block diagram showing a configuration of a video processing system according to a second example of Embodiment 3. 
         FIG. 18  is a flowchart illustrating the operations of a video display apparatus according to the second example of Embodiment 3. 
         FIG. 19  is a block diagram showing a configuration of a video processing system according to Embodiment 4. 
         FIG. 20  is a block diagram showing a configuration of a tone mapping processor. 
         FIG. 21  is a diagram showing a configuration example of dynamic metadata according to Embodiment 4. 
         FIG. 22A  is a diagram showing a variation in the luminance of subtitles in conventional dynamic tone mapping in the case where graphics are subtitles. 
         FIG. 22B  is a diagram showing a luminance variation in tone mapping. 
         FIG. 23  is a diagram showing a luminance variation in tone mapping. 
         FIG. 24  is a block diagram showing a configuration of video processing system  100 E according to Embodiment 5. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A video processing system according to an aspect of the present invention includes: a first acquirer that acquires video data including a main video; a second acquirer that acquires a display format that indicates a luminance dynamic range format displayable by a display apparatus; a generator that generates first characteristics information that indicates first dynamic luminance characteristics that correspond to the display format by using the video data when a luminance dynamic range format of the main video indicated by the video data is different from the display format, the first dynamic luminance characteristics being dynamic luminance characteristics that indicate a time-dependent change in luminance characteristics of the main video; and an outputter that outputs the first characteristics information generated by the generator. 
     Also, the video data may further include second characteristics information that indicates the dynamic luminance characteristics of the main video, and the generator may generate the first characteristics information by converting a luminance dynamic range format of second dynamic luminance characteristics indicated by the second characteristics information to the display format. 
     Also, the generator may generate the first characteristics information by analyzing the main video of the video data to extract the second dynamic luminance characteristics that indicate the dynamic luminance characteristics of the main video, and converting the luminance dynamic range format of the second dynamic luminance characteristics extracted to the display format. 
     Also, the video processing system may further include: a tone mapping processor that performs a tone mapping process of converting a luminance of the main video based on conversion characteristics according to the first dynamic luminance characteristics indicated by the first characteristics information output from the outputter; and a display that displays the main video that has undergone the tone mapping process. 
     Also, the video processing system may further include: a composer that generates a composite video by overlaying graphics on the main video; and an extractor that extracts luminance characteristics of the graphics. The outputter may further output the composite video and third characteristics information that indicates the luminance characteristics of the graphics. 
     Also, the video processing system may further include: a tone mapping processor that performs a tone mapping process of converting a luminance of the main video based on conversion characteristics according to the first dynamic luminance characteristics indicated by the first characteristics information output from the outputter; and a display that displays the main video that has undergone the tone mapping process. When the composite video is generated by the composer, the tone mapping processor may perform: a first tone mapping process on a first section of the main video in which the first dynamic luminance characteristics indicated by the first characteristics information are greater than or equal to the luminance characteristics of the graphics indicated by the third characteristics information, the first tone mapping process being processing of dynamically changing the luminance of the main video in the first section based on the conversion characteristics according to the first dynamic luminance characteristics in the first section; and a second tone mapping process on a second section of the main video in which the first dynamic luminance characteristics are less than the luminance characteristics of the graphics, the second tone mapping process being processing of changing the luminance of the main video in the second section based on constant conversion characteristics irrespective of the first dynamic luminance characteristics in the second section. 
     Also, a video processing method according an aspect of the present invention is a video processing method in a video processing system, the video processing method including: acquiring video data including a main video; acquiring a display format that indicates a luminance dynamic range format displayable by a display apparatus; generating first characteristics information that indicates first dynamic luminance characteristics that correspond to the display format by using the video data when a luminance dynamic range format of the main video indicated by the video data is different from the display format, the first dynamic luminance characteristics being dynamic luminance characteristics that indicate a time-dependent change in luminance characteristics of the main video; and outputting the first characteristics information generated in the generating of the first characteristics information. 
     1-1. Background 
     First, the transition of imaging technology will be described with reference to  FIG. 1 .  FIG. 1  is a diagram illustrating the evolution of imaging technology. 
     In order to enhance video image quality, the focus has been given to increase the number of pixels displayed. Accordingly, standard definition (SD) videos (720×480 pixels) and high definition (HD) videos (1920×1080 pixels) are now widely used. 
     In recent years, in order to achieve even higher image quality, introduction of ultra-high definition (UHD) videos (3840×1920 pixels), or so-called 4K resolution videos (with a 4K resolution of 4096×2048 pixels) has started. 
     Along with the introduction of 4K resolution videos, consideration is also given to expanding the dynamic range, expanding the color gamut, adding or improving the frame rate, and the like. 
     Among these, with respect to the dynamic range, HDR (High Dynamic Range) rendering is receiving increased attention as a method for representing bright light, such as specular reflection light, that cannot be represented by a currently used television signal to be more close to reality while maintaining low light signal gradation. Specifically, conventional television signals are called SDR (Standard Dynamic Range) signals, and the highest luminance is 100 nits. In contrast, in HDR signals, the highest luminance is expected to be up to 1000 nits or more. For HDR signals, standardization of mastering display standards is currently undertaken by SMPTE (Society of Motion Picture &amp; Television Engineers), ITU-R (International Telecommunications Union Radio communications Sector), and the like. 
     Specific applications of HDR include, as with HD and UHD, broadcasting, packaged media (Blu-ray® disc, and the like), internet delivery, and the like. 
     1-2. Relationship Between Generation of Master, Delivery Methods, and Display Apparatuses 
       FIG. 2  is a diagram illustrating the relationship between video production, delivery methods, and display apparatuses when a new video representation is introduced into content. 
     In the case where a new video representation is introduced (for example, the number of pixels is increased) so as to enhance video image quality, as shown in FIG.  2 , it is necessary to (1) change a master for home entertainment on the video production side. Along with this change, it is also necessary to (2) update the delivery method such as broadcasting, communication, or a packaged medium, and also (3) update the display apparatus such as a television set or a projector for displaying the video. 
     1-3. Tone Mapping 
     Tone mapping is processing for adjusting, based on the relationship between the luminance of an HDR video and the maximum luminance (Display Peak Luminance: DPL) of a video display apparatus, the luminance of the video to be less than or equal to DPL by converting the luminance of the video if the maximum luminance (Maximum Content Luminance Level: MaxCLL) of the video exceeds DPL. Through this processing, the video can be displayed without losing information near the maximum luminance of the video. The conversion depends on the characteristics of the video display apparatus, and also depends on how to display the video, and thus different conversion characteristics are used for each video display apparatus. 
       FIGS. 3A and 3B  are diagrams showing examples of tone mapping.  FIG. 3A  shows a case where DPL is 500 nits, and  FIG. 3B  shows a case where DPL is 1000 nits. Also,  FIGS. 3A and 3B  each show an example of tone mapping performed when a video having a MaxCLL of 1000 nits is displayed and an example of tone mapping performed when a video having a MaxCLL of 4000 nits is displayed. 
     As shown in  FIG. 3A , in the case where DPL is 500 nits, in both videos, the luminance is converted such that the video can be displayed at up to MaxCLL below 500 nits, but the degree of conversion is higher in the video having a higher MaxCLL. 
     As shown in  FIG. 3B , in the case where DPL is 1000 nits, in the video having a MaxCLL of 1000 nits, tone mapping is not performed. In the video having a MaxCLL of 4000 nits, tone mapping is performed so as to convert the luminance from 4000 nits to 1000 nits, and the video is displayed at that luminance. 
     1-4. Dynamic Metadata and Dynamic Tone Mapping 
       FIG. 4A  is a diagram showing an example of tone mapping using static metadata.  FIG. 4B  is a diagram showing an example of dynamic tone mapping using dynamic metadata. 
     As shown in  FIG. 4A , in the case where static metadata (MaxCLL) is used, MaxCLL indicates the highest luminance in a video sequence, and thus the video display apparatus can only perform tone mapping using a fixed curve on the video sequence. In contrast, as shown in (a) in  FIG. 4B , in the case where metadata suitable according to the luminance that varies with time (here, referred to as Dynamic MaxCLL) is used, the video display apparatus does not perform tone mapping when the luminance is low ((b) in  FIG. 4B ), and performs tone mapping when the luminance is high ((c) in  FIG. 4B ). In this way, optimal tone mapping suitable for the luminance that varies with time can be implemented. Dynamic metadata describes the dynamic luminance characteristics that indicate a time-dependent change in the luminance characteristics of the video. The luminance characteristics of the video used in the dynamic metadata may be, for example, the maximum luminance, the average luminance, or the like of each predetermined section of the video. The present disclosure will be described by taking the maximum luminance of the video as an example of the luminance characteristics of the video. As used herein, the term “predetermined section of the video” refers to, for example, a scene, a chapter, a frame, or the like. 
     1-5. EOTF 
     Here, EOTF will be described with reference to  FIGS. 5A and 5B . 
       FIG. 5A  is a diagram showing examples of EOTFs (Electro-Optical Transfer Functions) for HDR and SDR. 
     In general, EOTF is what is called a “gamma curve”, which indicates the correspondence between code values and luminance values so as to convert a code value to a luminance value. That is, EOTF is relationship information that indicates the correspondence relationship between a plurality of code values and luminance values. 
     Also,  FIG. 5B  is a diagram showing examples of inverse EOTFs for HDR and SDR. 
     Inverse EOTF indicates the correspondence between the luminance value and the code value, and is used to convert the luminance value to the code value by quantizing the luminance value inversely to EOTF. That is, inverse EOTF is relationship information that indicates the correspondence relationship between luminance values and a plurality of code values. For example, in the case where the luminance values of an HDR-compatible video are represented by code values on a 10 bit gray scale, luminance values in an HDR luminance range of up to 10000 nits are quantized and mapped to 1024 integer values ranging from 0 to 1023. That is, by performing quantization based on the inverse EOTF, a luminance value in a luminance range of 0 to 10000 nits (the luminance values of the HDR-compatible video) is converted to an HDR signal with 10-bit code value. With HDR-compatible EOTF (hereinafter referred to as “HDR EOTF”) or HDR-compatible inverse EOTF (hereinafter referred to as “HDR inverse-EOTF”), it is possible to represent higher luminance values higher than those of SDR-compatible EOTF (hereinafter referred to as “SDR EOTF”) or SDR-compatible inverse EOTF (hereinafter referred to as SDR inverse-EOTF). For example, in  FIGS. 5A and 5B , the maximum luminance value (peak luminance) is 10000 nits. That is, the HDR luminance range includes the entire SDR luminance range, and the HDR peak luminance is higher than the SDR peak luminance. The HDR luminance range is a luminance range in which the maximum value is increased from 100 nits, which is the maximum value of the SDR luminance range, to 10000 nits. 
     For example, an example of the HDR EOTF and the HDR inverse-EOTF includes SMPTE 2084 standardized by the Society of Motion Picture and Television Engineers (SMPTE) founded in the United States. 
     1-6. Overlaying Graphics on Video 
       FIG. 6  is a diagram showing an example in which graphics such as a menu and subtitles are overlaid on a moving image, and the moving image is displayed on a video display apparatus. Here, an example of Ultra HD Blu-ray is shown. 
     A set of moving images before graphics are overlaid will be referred to as a main video. With Ultra HD Blu-ray, graphics are prepared in HD resolution. A video reproduction apparatus performs HD-UHD conversion on the graphics in HD resolution so as to generate graphics in UHD resolution. Then, the video reproduction apparatus overlays the obtained graphics in UHD resolution with the main video having UHD resolution. Then, the video reproduction apparatus transmits the video resulting from the overlay process to a video display apparatus via HDMI® (High-Definition Multimedia Interface). The video display apparatus displays the transmitted video in HDR. 
     Also, the video reproduction apparatus determines dynamic metadata based on the variation of the luminance of the main video with time, and transmits the dynamic metadata to the video display apparatus via HDMI. The video display apparatus performs dynamic tone mapping on a video signal of the video obtained by overlaying subtitles and menus on the main video based on the transmitted dynamic metadata. 
     The same applies to an HDR video that is displayed through an OTT (over the top) service via broadcasting or communication and in which a menu or subtitles are overlaid on a main video, and the resulting video is displayed on a video display apparatus. 
     1-7. Problem Arising when Performing Dynamic Tone Mapping on Video Data where Graphics are Overlaid on Moving Image 
     In the dynamic metadata method, metadata regarding the luminance of the HDR video such as luminance distribution is designated for each frame, and the metadata is transmitted to the video display apparatus together with the video signal. The video display apparatus performs processing such as luminance conversion based on the transmitted metadata according to the display capabilities of the video display apparatus such as maximum luminance. The dynamic metadata method as described above is receiving increased attention as a method for displaying a video at a constant quality as much as possible irrespective of the display performance of a video display apparatus such as luminance. 
     However, dynamic metadata varies with time, and thus there is a problem in that a video that needs to be displayed stably is not displayed stably. 
     If the video to be displayed is a video or a set of so-called moving images that is simultaneously edited or supervised, processing can be performed considering the state of the video to some degree. When graphics data such as subtitles or a menu whose luminance is essentially constant and does not vary at all is overlaid on a main video composed of a set of moving images as described above and displayed, due to the processing that uses dynamic metadata, a negative effect occurs such as variation of the luminance or color of the graphics that essentially needs to be constant. This negative effect becomes more prominent as the luminance of the main video is higher and the luminance of the video display apparatus is lower. 
       FIG. 7  is a diagram showing the influence of dynamic tone mapping when graphics are overlaid on a main video. It is assumed here that, as shown in (a) in  FIG. 7 , graphics to be overlaid has a luminance of 350 nits. As shown in (b) in  FIG. 7 , in a section of the main video that has a low luminance, tone mapping is not performed, and thus the graphics are displayed on a video display apparatus at a luminance of 350 nits that is the original luminance of the graphics. On the other hand, as shown in (c) in  FIG. 7 , in a section of the main video that has a high luminance, tone mapping is performed, and thus the graphics are displayed on the video display apparatus at a luminance lower than 350 nits. In this way, the graphics luminance that essentially needs to be constant varies with time, resulting in an undesired state. In this example, only the influence on the luminance is considered, but in an actual video display apparatus, the influence may also be exerted on color components, and thus colors may also be affected. 
     1-8. Example of HDR Format Checking Method 
     At present, some HDR formats in which dynamic tone mapping can be performed are currently proposed and standardized. An HDR format is an example of a luminance dynamic range format. Accordingly, the video reproduction apparatus needs to check which HDR format each of the main video, the video reproduction apparatus, and the video display apparatus supports, reproduce the main video supported by the video display apparatus and output the reproduced main video to the video display apparatus. 
       FIGS. 8A to 8C  are flowcharts illustrating an example of an HDR format checking method.  FIG. 8A  is a main flowchart illustrating an example of an HDR format checking method.  FIG. 8B  is a sub-flowchart of the main flowchart shown in  FIG. 8A  illustrating an example of a format checking method for checking the format supported by the main video.  FIG. 8C  is a sub-flowchart of the main flowchart shown in  FIG. 8A  illustrating an example of a format checking method for checking the format supported by the video display apparatus. 
     In an Ultra HD Blu-ray disc, Mandatory HDR and a plurality of Option HDRs are specified as HDR formats. Accordingly, in an Ultra HD Blu-ray disc, a main video that supports only Mandatory HDR, or a main video that supports Mandatory HDR and Option HDR is recorded. In the case where Option HDR is recorded, at least one of the plurality of Option HDRs is recorded. Option HDR videos are higher quality videos than Mandatory HDR videos. 
     As shown in  FIG. 8A , the video reproduction apparatus first checks the luminance dynamic range format of the main video (S 1 ). 
     Specifically, as shown in  FIG. 8B , the video reproduction apparatus checks the flags of the HDR formats listed on a reproduction control list of the main video (S 11 ). In this way, the video reproduction apparatus checks the flags of the HDR formats and determines the HDR format supported by the main video. 
     Next, the video reproduction apparatus checks the HDR format (hereinafter referred to as “display format”) supported by the video display apparatus (S 2 ). That is, the video reproduction apparatus checks the display format that is the luminance dynamic range format displayable by the video display apparatus. 
     Specifically, as shown in  FIG. 8C , the video reproduction apparatus issues a request to transmit EDID of the video display apparatus to the video display apparatus via HDMI (S 21 ). 
     Next, the video reproduction apparatus acquires EDID of the video display apparatus from the video display apparatus via HDMI (S 22 ). 
     Then, the video reproduction apparatus checks the acquired EDID for the display format of the video display apparatus (S 23 ). 
     In this way, by performing steps S 1  and S 2 , the video reproduction apparatus checks, before it reproduces the main video, the HDR format supported by the main video and the HDR format supported by the video display apparatus to which the video reproduction apparatus is connected. That is, here, the video reproduction apparatus checks the Option HDR. 
     After that, referring back to  FIG. 8A , the video reproduction apparatus determines whether or not the HDR format supported by the video reproduction apparatus includes the Option HDR of the main video (S 3 ). 
     If it is determined that the HDR format supported by the video reproduction apparatus includes the Option HDR of the main video (Yes in S 3 ), the video reproduction apparatus determines whether or not the display format of the video display apparatus includes the Option HDR of the main video (S 4 ). In this case, in step S 4 , a determination is made with respect to the HDR format supported by the video reproduction apparatus and the Option HDR included in the main video in step S 3 . 
     If it is determined that the display format of the video display apparatus includes the Option HDR of the main video (Yes in S 4 ), the video reproduction apparatus reproduces the main video in the Option HDR (S 5 ). That is, if all of the main video, the video reproduction apparatus, and the video display apparatus support the same Option HDR, the video reproduction apparatus reproduces the main video in that Option HDR. 
     If, on the other hand, it is determined that the HDR format supported by the video reproduction apparatus does not include the Option HDR of the main video (No in S 3 ), or if it is determined that the display format of the video display apparatus does not include the Option HDR of the main video (No in S 4 ), the video reproduction apparatus reproduces the main video in Mandatory HDR. That is, if any one of the main video, the video reproduction apparatus, and the video display apparatus does not support the Option HDR, the video reproduction apparatus reproduces in Mandatory HDR. It is assumed that HDR-compatible devices support Mandatory HDR. 
     1-9. Problems Arising when Performing Dynamic Tone Mapping in Plurality of HDR Formats 
     Problem 1 
     As described above, in the case where a video reproduction apparatus and a video display apparatus, which do not support Option HDRs, are connected to each other, the main video is reproduced and displayed in Mandatory HDR, and thus there is a problem in that it is not possible to perform dynamic tone mapping. Also, in each Option HDR, some parameters are defined. If there are further options in the parameters, a situation may arise in which a first option is recorded in the main video data, but the video display apparatus does not support the first option, but supports a second option that is different from the first option. However, in such a situation, despite the fact that the main video, the video reproduction apparatus, and the video display apparatus support an Option HDR format, it is not possible to display the video in the Option HDR format depending on the options of the parameters of the Option HDR. Accordingly, in such a video processing system, the main video is reproduced and displayed in Mandatory HDR, and it is therefore not possible to perform dynamic tone mapping. Alternatively, processing is performed only on the mandatory portion of the Option HDR, and thus dynamic tone mapping poorer than desired is performed, and the video is displayed with poor quality. 
       FIGS. 9A and 9B  show examples of different options in an Option HDR.  FIG. 9A  is a diagram showing a configuration example of dynamic metadata corresponding to a first option.  FIG. 9B  is a diagram showing a configuration example of dynamic metadata corresponding to a second option. In  FIGS. 9A and 9B , illustration of the elements that are not relevant to the present disclosure is omitted. 
     As shown in the diagrams, in the first option, for example, the average data value and the value of data value distribution information of the basic tone mapping information are defined by data values. On the other hand, in the second option, they are defined by luminance values. Also, although not shown here, there may be cases where values are expressed in the same unit and have the same definition but the number of values is different. Also, data values or luminance values such as the average data value and the value of data value distribution information of the basic tone mapping information may be expressed in values converted in nit, which is a unit of brightness. 
     Problem 2 
     In the case of metadata based on data values such as an example of dynamic metadata corresponding to the first option shown in  FIG. 9A , it is difficult to perform processing based on the luminance of graphics overlaid on the main video. Specifically, in the case where, depending on the graphics luminance, dynamic tone mapping is not performed when the luminance is lower than or equal to the graphics luminance, because the metadata corresponding to the first option is based on data values, or in other words, RGB values, rather than luminance information, the means that performs dynamic tone mapping needs to perform processing such that the graphics luminance information of the graphics and the luminance information of the metadata are expressed in the same unit. In the case of a Blu-ray disc, in particular, the graphics data on the disc include luminance information and color information, rather than RGB values, and it is therefore more difficult to perform the processing. 
     Problem 3 
     Problem 1 is the problem caused when one Option HDR format includes a plurality of options, but even if the reproduction apparatus supports a plurality of HDR formats in which dynamic tone mapping can be performed, if the video display apparatus does not support a first HDR format supported by the main video to be reproduced, (i) it is not possible to display the video in the first HDR format. Alternatively, if the first HDR format supported by the main video to be reproduced is Option HDR, and the main video includes Mandatory HDR, (ii) the main video is displayed only in the Mandatory HDR format. Accordingly, in such a video processing system, there is a problem in that it is not possible to implement dynamic tone mapping that is a feature of the Option HDR. 
     1-10. Solution 
     In the present disclosure, the following solutions are used. 
     A first method, which is a method for solving Problem 1, will be described. In the first method, in the case where a video display apparatus connected to a video reproduction apparatus via a video signal transmitting means such as an HDMI cable does not support a first option of a predetermined HDR format, but supports a second option of the predetermined HDR format, the video reproduction apparatus generates a second option portion from a first option portion of the dynamic metadata acquired from the main video to be reproduced by the video reproduction apparatus. Then, the video reproduction apparatus (i) replaces the first option portion of the acquired dynamic metadata with the generated second option portion; or (ii) adds the generated second option portion to the acquired dynamic metadata. After that, the video reproduction apparatus transmits the dynamic metadata including the second option portion to the video display apparatus via the video signal transmitting means. The video display apparatus acquires the dynamic metadata including the second option portion, and executes dynamic tone mapping according to the second option of the predetermined HDR format by using the second option portion of the acquired dynamic metadata. 
     Next, a second method, which is a method for solving Problem 1, will be described. In the second method, in the case where a video display apparatus connected to a video reproduction apparatus via a video signal transmitting means such as an HDMI cable does not support a first option of a predetermined HDR format, but supports a second option of the predetermined HDR format, the video reproduction apparatus generates a second option portion of dynamic metadata from the main video to be reproduced by the video reproduction apparatus. Then, the video reproduction apparatus (i) replaces a first option portion of the dynamic metadata of the main video with the generated second option portion; or (ii) adds the generated second option portion to the acquired dynamic metadata. After that, the video reproduction apparatus transmits the dynamic metadata including the second option portion to the video display apparatus via the video signal transmitting means. The video display apparatus acquires the dynamic metadata including the second option portion, and executes dynamic tone mapping according to the second option of the predetermined HDR format by using the second portion of the acquired dynamic metadata. 
     Next, a third method, which is a method for solving Problem 1, will be described. In the third method, the function of generating the second option portion from the first option portion, which was explained in the first method, or the function of generating the second option portion from the main video, which was explained in the second method, is provided to the video display apparatus. That is, in the case where a video display apparatus connected to a video reproduction apparatus via a video signal transmitting means such as an HDMI cable does not have the display processing function of displaying a main video corresponding to a first option of a predetermined HDR format, but has the processing function of processing a main video corresponding to a second option of the predetermined HDR format, the video reproduction apparatus reproduces the main video corresponding to the first option, and outputs a reproduction signal of the main video. The video display (i) generates a second option portion from a first option portion of dynamic metadata transmitted together with the main video, (ii) generates a second option portion from the main video, or generating a second option portion by using both methods (i) and (ii). Then, the video display apparatus executes dynamic tone mapping by using the generated second option portion. 
     Next, a fourth method, which is a method for solving Problem 2, will be described. In the fourth method, in addition to the first method or the second method, the video reproduction apparatus performs inclusion of graphics luminance information at the time of generating the second option portion of the dynamic metadata. That is, the video reproduction apparatus adds, to the second option portion, graphics luminance information of the graphics to be overlaid on the main video. The video display apparatus acquires the dynamic metadata including the second option portion, and performs, on a section in which the luminance of the main video corresponding to the second option is greater than or equal to the graphics luminance, a first tone mapping process of dynamically changing conversion characteristics according to the second option portion of that section by using the acquired dynamic metadata, and performs a second tone mapping process that uses constant conversion characteristics on a section in which the luminance of the main video corresponding to the second option is less (darker) than the graphics luminance. 
     Next, a fifth method, which is a method for solving Problem 3, will be described. In the fifth method, a case will be considered in which the video reproduction apparatus supports a plurality of HDR formats in which dynamic tone mapping can be performed. In the case where the main video supports a first HDR format that is one of a plurality of HDR formats, and the video display apparatus connected to the video reproduction apparatus supports a second HDR format that is another one of the plurality of HDR formats, at the time of reproducing the main video, the video reproduction apparatus dynamically generates, from the main video that is being reproduced, dynamic metadata that is needed in the second HDR format supported by the video display apparatus, and transmits the generated dynamic metadata to the video display apparatus. As a result, the video display apparatus acquires the main video and the dynamic metadata corresponding to the second HDR format, and displays the acquired main video in the second HDR format by using the acquired dynamic metadata. 
     With the method described above, with respect to an HDR video signal transmitted via broadcasting, a packaged medium such as a Blu-ray disc, or internet delivery such as OTT, in the case where there are a plurality of options in an HDR format in which dynamic tone mapping can be performed and that is supported by the HDR video signal, and the HDR video signal supports the first option, and the video display apparatus does not support the first option, but supports the second option, the video reproduction apparatus generates a second option portion from the first option portion of the dynamic metadata or the HDR video signal, and transmits the dynamic metadata including the second option portion to the video display apparatus. Accordingly, the video display apparatus can implement dynamic tone mapping provided by the HDR format by using the second option portion supported by the video display apparatus. 
     Also, when performing dynamic tone mapping, the video display apparatus can, by using the second option, reduce the influence of the dynamic tone mapping on graphics such as a menu and subtitles, with which it is difficult to cope by using the first option, and thus can display subtitles and a menu in a stable manner. 
     Also, in the case where there are a plurality of HDR formats in which dynamic tone mapping can be performed, and the HDR video signal supports a first HDR format, and the video display apparatus supports a second HDR format, the video reproduction apparatus generates dynamic metadata in the second HDR format from the first HDR format or the HDR video signal. Accordingly, the video display apparatus can implement dynamic tone mapping in the second HDR format. 
     2. Embodiment 1 
     In the present embodiment, in the case where a video display apparatus connected to a video reproduction apparatus via a video signal transmitting means such as an HDMI cable does not support a first option of a predetermined HDR format, but supports a second option of the predetermined HDR format, the video reproduction apparatus generates a second option portion from a first option portion of dynamic metadata acquired from a main video to be reproduced, and (i) replaces the first option portion of the acquired dynamic metadata with the generated second option portion; or (ii) adds the second option portion to the acquired dynamic metadata. After that, the video reproduction apparatus transmits the dynamic metadata including the second option portion to the video display apparatus via the video signal transmitting means. The video display apparatus acquires the dynamic metadata including the second option portion, and executes dynamic tone mapping according to the second option of the predetermined HDR format by using the second portion of the acquired dynamic metadata. 
     [2-1. Configuration of Video Processing System] 
       FIG. 10  is a block diagram showing a configuration of video processing system  100  according to Embodiment 1. Video processing system  100  shown in  FIG. 10  includes video reproduction apparatus  101  and video display apparatus  102 . 
     Video reproduction apparatus  101  reproduces a video, and outputs the obtained video to video display apparatus  102 . Video reproduction apparatus  101  includes acquirer  111 , demultiplexer  112 , main video decoder  113 , subtitles decoder  114 , menu decoder  115 , metadata acquirer  116 , format acquirer  117 , generator  118 , graphics composer  119 , main video composer  120 , and video transmitter  121 . 
     Acquirer  111  acquires a video signal. For example, in the case where video reproduction apparatus  101  is a disc reproduction apparatus, acquirer  111  acquires a video signal by reproducing a disc. In the case where video reproduction apparatus  101  is a broadcast reception apparatus, acquirer  111  acquires a video signal by receiving a broadcast wave. In the case where video reproduction apparatus  101  is an internet broadcast reception apparatus, acquirer  111  acquires a video signal by receiving an internet broadcast. 
     Demultiplexer  112  outputs a main video signal, a subtitles signal, and a menu signal that have been encoded and included in the video signal to main video decoder  113 , subtitles decoder  114 , and menu decoder  115 , respectively. 
     Main video decoder  113  decodes the encoded main video signal output from demultiplexer  112 . 
     Subtitles decoder  114  decodes the encoded subtitles signal output from demultiplexer  112 . Also, subtitles decoder  114  determines whether or not to display subtitles based on a user&#39;s operation or the like, and selects the type of subtitles to be displayed. Subtitles decoder  114  outputs the selected subtitles to graphics composer  117  when displaying the subtitles. 
     Menu decoder  115  decodes the encoded menu signal output from demultiplexer  112 . Also, menu decoder  115  determines whether or not to display a menu based on a user&#39;s operation or the like, and selects the type of menu to be displayed. Menu decoder  115  outputs the selected menu to graphics composer  117  when displaying the menu. Menu decoder  115  may overlay and display a menu by using, not only information from the video signal, but also a program that runs on video reproduction apparatus  101 . 
     Metadata acquirer  116  acquires main video dynamic metadata. For example, metadata acquirer  116  generates main video dynamic data based on information included in the main video signal. The description will be given assuming that main video dynamic metadata corresponding to the first option is acquired by metadata acquirer  116 . 
     Format acquirer  117  acquires, from video display apparatus  102 , a display format indicating a luminance dynamic range format displayable by video display apparatus  102 . Here, the option of the HDR format supported by the display format of video display apparatus  102  is a second option, and thus format acquirer  117  acquires a display format indicating the second option. 
     The format (first option) supported by the main video dynamic metadata acquired by metadata acquirer  116  and the display format (second option) acquired by format acquirer  117  are different, and thus generator  118  generates a second option portion from the first option portion of the main video dynamic metadata. Then, generator  118  replaces the first option portion of the main video dynamic metadata with the generated second option portion, or adds the generated second option portion to the main video dynamic metadata. In this way, in the case where the luminance dynamic range format of the video indicated by the video data is different from the display format of the video display apparatus, generator  118  converts the format of the main video dynamic metadata to the display format. 
     Graphics composer  119  generates graphics information by composing subtitles and menus. As described above, graphics composer  119  may convert the resolution of subtitles and menus. For example, in the case of Ultra HD Blu-ray, graphics composer  119  may convert subtitles and menus in HD resolution to subtitles and menus in UHD resolution. 
     Also, graphics composer  119  generates graphics information. In the case where the generated graphics information is overlaid on the main video, graphics composer  119  sets graphics luminance information as a value other than “0” or a “value indicating that there are graphics”, and transmits the graphics luminance information to video transmitter  121 . In the case where the generated graphics information is not overlaid on the main video, graphics composer  119  sets graphics luminance information as “0” or a “value indicating that there are no graphics”, and transmits the graphics luminance information to video transmitter  121 . The graphics luminance information may be generated by a program installed on video reproduction apparatus  101 , or by any other means. 
     Main video composer  120  generates a video signal by overlaying the graphics information generated by graphics composer  119  on the main video obtained by main video decoder  113 . 
     Video transmitter  121  transmits the video signal generated by main video composer  120  and dynamic metadata to video display apparatus  102  via the video signal transmitting means such as an HDMI cable. The dynamic metadata includes the main video dynamic metadata acquired by metadata acquirer  116  and the graphics luminance information generated by graphics composer  119 . That is, video transmitter  121  outputs the main video dynamic metadata including the second option portion generated by generator  118  to video display apparatus  102 . 
     Next, a configuration of video display apparatus  102  will be described. Video display apparatus  102  includes video receiver  131 , metadata acquirer  132 , tone mapping processor  133 , display  134 , and notifier  135 . 
     Video receiver  131  receives the video signal and the dynamic metadata transmitted from video reproduction apparatus  101 . Video receiver  131  separates the video signal from the dynamic metadata, and transmits the video signal to tone mapping processor  133  and the dynamic metadata to metadata acquirer  132 . Metadata acquirer  132  transmits the main video dynamic metadata included in the dynamic metadata and the graphics luminance information to tone mapping processor  133  as a control signal. 
     Tone mapping processor  133  performs a tone mapping process on the video signal in accordance with the main video dynamic metadata. Tone mapping processor  133  performs a tone mapping process of converting the luminance of the main video by using conversion characteristics according to the second option portion of the dynamic metadata supported by the output display format. Specifically, when the graphics luminance information indicates “0” or a “value indicating that there are no graphics”, tone mapping processor  133  performs a tone mapping process (dynamic tone mapping process) on the video signal in accordance with the main video dynamic metadata. On the other hand, when the graphics luminance information indicates a value other than “0” or a “value indicating that there are graphics”, tone mapping processor  133  performs a tone mapping process so as to reduce the influence of dynamic tone mapping on the overlaid graphics. Display  134  displays the video signal that has undergone the tone mapping process. 
     Notifier  135  transmits EDID including the display format of video display apparatus  102  to video reproduction apparatus  101 . For example, upon receiving a request to transmit EDID from video reproduction apparatus  101 , notifier  135  transmits EDID to video reproduction apparatus  101  via the video signal transmitting means such as an HDMI cable. 
     [2-2. Operations of Video Processing System] 
     In the case where the first option portion and the second option portion of the dynamic metadata are configured as shown in  FIGS. 9A and 9B , metadata acquirer  116  acquires the main video dynamic metadata including the first option portion and the mandatory portion of Option HDR based on the information included in the main video. 
     A flow of operations of video processing system  100  performed in this case will be described.  FIG. 11A  is a flowchart illustrating the operations of video reproduction apparatus  101  according to Embodiment 1. 
     After the reproduction of a video starts, in video reproduction apparatus  101 , metadata acquirer  116  extracts, for each frame of the main video, the mandatory portion and the first option portion of the dynamic metadata from the main video (S 31 ). 
     Then, generator  118  generates a second option portion from the first option portion of the dynamic metadata extracted by metadata acquirer  116  (S 32 ). 
     Next, generator  118  replaces the first option portion of the main video dynamic metadata with the generated second option portion, or adds the generated second option portion to the main video dynamic metadata (S 33 ). After that, generator  118  transmits the main video dynamic metadata including the mandatory portion and the second option portion to video transmitter  121 . Then, video transmitter  121  transmits the main video dynamic metadata together with the main video to video display apparatus  102  via the video signal transmitting means. 
     Then, video reproduction apparatus  101  determines whether the reproduction of the video is completed or an operation to stop the reproduction of the video is performed (S 34 ). If it is determined that the reproduction of the video is completed or an operation to stop the reproduction of the video is performed, video reproduction apparatus  101  ends the reproduction of the video. That is, video reproduction apparatus  101  repeats the processing operations of steps S 31  to S 34  until the reproduction of the video is completed or an operation to stop the reproduction of the video is performed. For example, the processing operations are repeatedly performed for each frame or every plurality of frames. 
       FIG. 11B  is a flowchart illustrating the operations of video display apparatus  102  according to Embodiment 1. 
     In video display apparatus  102 , video receiver  131  receives the video signal and the dynamic metadata (S 41 ). Video receiver  131  transmits the received video signal as the main video to tone mapping processor  133  and the dynamic metadata to metadata acquirer  132 . 
     Metadata acquirer  132  acquires the main video dynamic metadata including the second option portion (S 42 ). 
     Then, tone mapping processor  133  starts a tone mapping process according to the second option portion at the same time when the display of the video starts (S 43 ). 
     After that, display  134  displays the video that has undergone the tone mapping process of tone mapping processor  133  (S 44 ). 
     Then, video display apparatus  102  determines whether or not the reception of the video is completed or an operation to turn off the display is performed (S 45 ). If it is determined that the reception of the video is completed or an operation to turn off the display is performed, video display apparatus  102  ends the display of the video. That is, video display apparatus  102  repeats the processing operations in steps S 41  to S 45  until the reception of the video is completed or an operation to turn off the display is performed. For example, the processing operations are repeatedly performed for each frame or every plurality of frames. 
       FIG. 12  is a diagram showing another configuration example of dynamic metadata. In  FIG. 12 , illustration of the elements that are not relevant to the present disclosure is omitted. 
     The configuration example of dynamic metadata shown in  FIG. 12  is different from those of  FIGS. 9A and 9B  in that the mandatory portion, the first option portion, and the second option portion are specified by the item record position. In the case of the configuration example shown in  FIG. 12 , in the metadata as the first option portion, the second option portion has a value of “0” or a “value indicating invalidity”. In the metadata as the second option portion, the first option portion has a value of “0” or a “value indicating invalidity”. The first option portion and the second option portion may both have effective values. 
     Also, the generation of the second option portion from the first option portion of the dynamic metadata can be performed by, for example, converting the value of the first option to a value corresponding to the second option by using the data value distribution and the average data value based on the video specifications of the main video (the use of the main video corresponding to the first option and the use of the main video corresponding to the second option). In the case where RGB values are designated as data values in the first option portion, the first option portion can be completely converted to the second option portion. In both the dynamic metadata configuration shown in  FIGS. 9A and 9B  and the dynamic metadata configuration shown in  FIG. 12 , the number of distribution information elements of the first option and the number of distribution information elements of the second option may not match. Even in such a case, if at least distribution information that is necessary to generate the second option portion is included in the first option portion, the first option portion can be converted directly to the second option portion. On the other hand, if distribution information that is necessary to generate the second option portion is not included in the first option portion, by using distribution information obtained by supplementing necessary distribution information from the distribution information of the first option, the first option portion can be converted to the second option portion. 
     3. Embodiment 2 
     Embodiment 2 will be described. Embodiment 1 is configured such that the second option portion corresponding to the display format of the video display apparatus is generated from the first option portion of the dynamic metadata of the main video, but the configuration is not limited thereto. In Embodiment 2, an example will be described in which the second option portion is generated from the main video. That is, in the present embodiment, in the case where a video display apparatus connected to a video reproduction apparatus via a video signal transmitting means such as an HDMI cable does not support a first option of a predetermined HDR format, but supports a second option of the predetermined HDR format, the video reproduction apparatus generates a second option portion of dynamic metadata from the main video to be reproduced by the video reproduction apparatus. Then, the video reproduction apparatus (i) replaces the first option portion of the dynamic metadata of the main video with the generated second option portion; or (ii) adds the generated second option portion to the acquired dynamic metadata. After that, the video reproduction apparatus transmits the dynamic metadata including the second option portion to the video display apparatus via the video signal transmitting means. The video display apparatus acquires the dynamic metadata including the second option portion, and executes dynamic tone mapping according to the second option of the predetermined HDR format by using the second portion of the acquired dynamic metadata. 
     [3-1. Configuration of Video Processing System] 
       FIG. 13  is a block diagram showing a configuration of video processing system  100 A according to Embodiment 2. Video reproduction apparatus  101 A according to the present embodiment is different from video reproduction apparatus  101  according to Embodiment 1 in that the function of generator  118 A is different. Other structural elements of video reproduction apparatus  101 A are the same as those of video reproduction apparatus  101  according to Embodiment 1, and thus a detailed description thereof will be omitted. 
     The format (first option) supported by the main video dynamic metadata acquired by metadata acquirer  116  and the display format (second option) acquired by format acquirer  117  are different, and thus generator  118 A generates a second option portion of dynamic metadata from the main video output from main video decoder  113 . Then, generator  118 A replaces the first option portion of the main video dynamic metadata with the generated second option portion, or adds the generated second option portion to the main video dynamic metadata. In this way, generator  118 A extracts the dynamic metadata of the main data by analyzing the main video, and converts the luminance dynamic range format of the extracted dynamic metadata to the display format. 
     [3-2. Operations of Video Processing System] 
     In the case where the first option portion and the second option portion of the dynamic metadata are configured as shown in  FIGS. 9A and 9B , metadata acquirer  116  acquires the main video dynamic metadata including the first option portion and the mandatory portion of Option HDR. 
     A flow of operations of video processing system  100 A performed in this case will be described.  FIG. 14  is a flowchart illustrating the operations of video reproduction apparatus  101 A according to Embodiment 2. The operations of video reproduction apparatus  101 A according to Embodiment 2 are different from the operations of video reproduction apparatus  101  according to Embodiment 1 in that step S 32 A is performed instead of step S 32 . Accordingly, only step S 32 A will be described, and a description of other steps will be omitted. 
     In video processing system  100 A, after step S 31 , generator  118 A analyzes the luminance characteristics of the main video output from main video decoder  113 , and generates dynamic metadata corresponding to the second option (or in other words, a second option portion) from the result of the analysis (S 32 A). 
     After that, video reproduction apparatus  101 A performs the same processing operations as those of step S 33  and the subsequent steps shown in  FIG. 11A . 
     As in the case of another configuration example of dynamic metadata shown in  FIG. 12 , in the metadata as the first option portion, the second option portion has a value of “0” or a “value indicating invalidity”. In the metadata as the second option portion, the first option portion has a value of “0” or a “value indicating invalidity”. The first option portion and the second option portion may both have effective values. 
     Also, the generation of the second option portion of dynamic metadata from the main video can be performed by, for example, for each frame of the main video, acquiring the luminance values of all pixel data of the main video, obtaining the distribution thereof through statistical processing, and performing calculation according to the specification of the second option. 
     In the data of the main video, in the case where the values of the second option are defined as code values indicating the luminance values of displayed luminance, the second option portion of dynamic metadata may be determined in the manner described below. In this case, the data of the main video includes code values associated with predetermined luminance values in input/output characteristics (EOTF: Electro-Optical Transfer Function) specified by the HDR format when display processing is performed in accordance with EOTF. Accordingly, first, the processing in accordance with EOTF is performed so as to convert the code values of the main video to luminance values, and statistical processing is performed using the luminance values obtained by the conversion. Then, calculation is performed in accordance with the specification of the second option by using the result of the statistical processing so as to obtain a second option portion of dynamic metadata. 
     4. Embodiment 3 
     Embodiment 3 will be described. Embodiments 1 and 2 are configured such that the second option portion corresponding to the display format of the video display apparatus is generated by the video reproduction apparatus, but in Embodiment 3, an example will be described in which the second option portion is generated by the video display apparatus. That is, in the present embodiment, in the case where a video display apparatus connected to a video reproduction apparatus via a video signal transmitting means such as an HDMI cable does not have the display processing function of displaying a main video corresponding to a first option of a predetermined HDR format, but has the processing function of processing a main video corresponding to a second option of the predetermined HDR format, the video reproduction apparatus reproduces the main video corresponding to the first option, and outputs a reproduction signal of the main video. The video display apparatus (i) generates a second option portion from the first option portion of the dynamic metadata transmitted together with the main video, (ii) generates a second option portion from the main video, or generates a second option portion by using the two methods (i) and (ii). Then, the video display apparatus executes dynamic tone mapping using the generated second option portion. 
     [4-1. Configuration of Video Processing System of First Example] 
       FIG. 15  is a block diagram showing a configuration of video processing system  100 B according to a first example of Embodiment 3. 
     Video reproduction apparatus  101 B according to the first example of the present embodiment is different from video reproduction apparatus  101  according to Embodiment 1 in that video reproduction apparatus  101 B does not include format acquirer  117  and generator  118 . Accordingly, video transmitter  121  transmits the video signal generated by main video composer  120  and the dynamic metadata including the first option portion to video display apparatus  102 B via a video signal transmitting means such as an HDMI cable. Other structural elements of video reproduction apparatus  101 B are the same as those of video reproduction apparatus  101  according to Embodiment 1, and thus a detailed description thereof is omitted here. 
     Also, video display apparatus  102 B according to the first example of the present embodiment is different from video display apparatus  102  according to Embodiment 1 in that video display apparatus  102 B further includes generator  136  but does not include notifier  135 . Other structural elements of video display apparatus  102 B are the same as those of video display apparatus  102  according to Embodiment 1, and thus a detailed description thereof is omitted here. 
     The format (first option) supported by the main video dynamic metadata acquired by metadata acquirer  132  and the display format (second option) are different, and thus generator  136  generates a second option portion from the first option portion of the main video dynamic metadata. Then, generator  136  replaces the first option portion of the main video dynamic metadata with the generated second option portion. In this way, in the case where the luminance dynamic range format of the video indicated by the video data is different from the display format of the video display apparatus, generator  136  converts the format of the main video dynamic metadata to the display format. 
     [4-2. Operations of Video Processing System of First Example] 
     First, video reproduction apparatus  101 B transmits the main video dynamic metadata including the first option portion, together with the main video, to video display apparatus  102 B via a video signal transmitting means such as an HDMI cable. 
       FIG. 16  is a flowchart illustrating the operations of video display apparatus  102 B according to the first example of Embodiment 3. The operations of video display apparatus  102 B according to the first example of Embodiment 3 are different from those of video display apparatus  102  according to Embodiment 1 in that steps S 51  to S 53  are performed instead of step S 42 . Accordingly, only steps S 51  to S 53  will be described, and a description of other steps will be omitted. 
     In video display apparatus  102 B, after step S 41 , metadata acquirer  132  acquires the main video dynamic metadata including the first option portion (S 51 ). 
     Next, generator  136  generates a second option portion from the first option portion of the main video dynamic metadata (S 52 ). 
     Then, generator  136  outputs main video dynamic data including the second option portion to tone mapping processor  133  (S 53 ). 
     After that, steps S 43  to S 45  of video display apparatus  102  according to Embodiment 1 are performed. Video display apparatus  102 B repeats the processing operations in steps S 41 , S 51  to S 53 , and S 43  to S 45  until the reception of the video is completed or an operation to turn off the display is performed. For example, the processing operations are repeatedly performed for each frame or every plurality of frames. 
     [4-3. Configuration of Video Processing System of Second Example] 
       FIG. 17  is a block diagram showing a configuration of video processing system  100 C according to a second example of Embodiment 3. 
     Video processing system  100 C according to the second example of the present embodiment is different from video display apparatus  102 B of video processing system  100 C according to the first embodiment in that generator  136 C of video display apparatus  102 C has a different function. Other structural elements of video display apparatus  102 C are the same as those of video display apparatus  102 B according to the first example, and thus a detailed description thereof will be omitted. 
     The format (first option) supported by the main video dynamic metadata acquired by metadata acquirer  132  and the display format (second option) are different, and thus generator  136 C generates a second option portion of the dynamic metadata from the main output from video receiver  131 . Then, generator  136 C replaces the first option portion of the main video dynamic metadata with the generated second option portion. In this way, generator  136 C extracts the dynamic metadata of the main video by analyzing the main video, and converts the luminance dynamic range format of the extracted dynamic metadata to the display format. 
     [4-4. Operations of Video Processing System of Second Example] 
       FIG. 18  is a flowchart illustrating the operations of video display apparatus  102 C according to a second example of Embodiment 3. The operations of video display apparatus  102 C according to the second example of Embodiment 3 are different from those of video display apparatus  102 B according to the first example in that step S 52 C is performed instead of step S 52 . Accordingly, only step S 52 C will be described, and a description of other steps will be omitted. 
     In video display apparatus  102 C, after step S 51 , generator  136 C analyzes the luminance characteristics of the main video output from video receiver  131 , and generates dynamic metadata corresponding to the second option (or in other words, a second option portion) from the result of the analysis (S 52 C). 
     After that, video display apparatus  102 C performs the same processing operations as those of step S 53  and the subsequent steps shown in  FIG. 16 . 
     5. Embodiment 4 
     Embodiment 4 will be described. In Embodiment 4, in addition to Embodiment 1 or 2, the video reproduction apparatus performs inclusion of graphics luminance information at the time of generating the second option portion of the dynamic metadata. That is, the video reproduction apparatus adds, to the second option portion, graphics luminance information of the graphics to be overlaid on the main video. The video display apparatus acquires the dynamic metadata including the second option portion, and performs, on a section in which the luminance of the main video corresponding to the second option is greater than or equal to the graphics luminance, a first tone mapping process of dynamically changing conversion characteristics according to the second option portion of that section by using the acquired dynamic metadata, and performs a second tone mapping process that uses constant conversion characteristics on a section in which the luminance of the main video corresponding to the second option is less (darker) than the graphics luminance. 
     5-1. Configuration of Video Processing System 
       FIG. 19  is a block diagram showing a configuration of video processing system  100 D according to Embodiment 4. Video reproduction apparatus  101 D according to the present embodiment is different from video reproduction apparatus  101  according to Embodiment 1 in that video reproduction apparatus  101 D further includes extractor  122 . Other structural elements of video reproduction apparatus  101 D are the same as those of video reproduction apparatus  101  according to Embodiment 1, and thus a detailed description thereof will be omitted. 
     Extractor  122  extracts graphics luminance characteristics. 
     Also, video display apparatus  102 D according to the present embodiment is different from video display apparatus  102  according to Embodiment 1 in that tone mapping processor  133 D has a different function. Other structural elements of video display apparatus  102 D are the same as those of video display apparatus  102  according to Embodiment 1, and thus a detailed description thereof will be omitted. 
       FIG. 20  is a block diagram showing a configuration of tone mapping processor  133 D. 
     Tone mapping processor  133 D includes coefficient calculator  141 , coefficient storage  142 , tone mapper  143 , coefficient composer  144 , and switch SW 2 . 
     The video signal from video receiver  131  is transmitted to tone mapper  143 . The main video dynamic metadata from metadata acquirer  132  is transmitted to coefficient calculator  141 . 
     Coefficient calculator  141  calculates a tone mapping coefficient used in the tone mapping process performed by tone mapper  143  according to video display capabilities such as the luminance of video display apparatus  102 D. Coefficient storage  142  stores the tone mapping coefficient calculated by coefficient calculator  141 . As used herein, the tone mapping coefficient refers to the coefficient included in a function that indicates conversion characteristics used in the tone mapping process. That is, the conversion characteristics are determined based on the tone mapping coefficient. 
     Switch SW 2  selects one from a tone mapping coefficient (A) calculated by coefficient calculator  141  and a tone mapping coefficient (B) stored in coefficient storage  142 , and inputs the selected tone mapping coefficient to coefficient storage  142 . That is, switch SW 2  switches between (A) updating the tone mapping coefficient stored in coefficient storage  142  with the tone mapping coefficient newly calculated by coefficient calculator  141  and (B) continuously storing the currently stored tone mapping coefficient. 
     Coefficient composer  144  performs a dynamic tone mapping process by using the tone mapping coefficient calculated by coefficient calculator  141  when the graphics luminance information indicates “0” or a “value indicating that there are no graphics”. On the other hand, when the graphics luminance information indicates a value other than “0” or a “value indicating that there are graphics”, or in other words, when the graphics luminance information indicates that graphics are overlaid, coefficient composer  144  compares the graphics luminance indicated by the graphics luminance information and the luminance indicated by the second option portion of the dynamic metadata. Then, when the luminance of the main video corresponding to the second option is greater than or equal to the graphics luminance, coefficient composer  144  performs a first tone mapping process of dynamically changing the conversion characteristics according to the second option portion. When the luminance of the main video corresponding to the second option is less (darker) than the graphics luminance, coefficient composer  144  performs any one of the following processing operations of: (1) fixing tone mapping; (2) not performing a tone mapping process; (3) suppressing variation of tone mapping; and (4) making the influence of tone mapping imperceptible to human. As used herein, the graphics luminance refers to a luminance higher than, for example, the maximum luminance value used in graphics. With this configuration, the variation of tone mapping in the luminance range used in graphics is suppressed. Also, in the processing described above, in order to maintain continuity between the conversion characteristics conversion characteristics greater than or equal to the border luminance level and the conversion characteristics less than the border luminance level, coefficient composer  144  may correct the conversion characteristics in these border regions such that the conversion characteristics vary smoothly. 
     With this configuration, a portion on which graphics are overlaid can be displayed stably. 
     Also, the configuration described here is merely an example, and thus tone mapping processor  133 D may be configured to, when the graphics luminance information indicates that graphics are overlaid, fix the tone mapping coefficient at a specific luminance or less, or not perform a tone mapping process. 
     That is, with respect to a first section of the video in which the second option portion of dynamic metadata as first dynamic luminance characteristics has a luminance greater than or equal to the graphics luminance, tone mapping processor  133 D performs a first tone mapping process of dynamically changing the luminance of the main video in the first section based on the conversion characteristics according to the first dynamic luminance characteristics in the first section. Also, with respect to a second section of the video in which the second option portion of dynamic metadata has a luminance less than the graphics luminance characteristics, tone mapping processor  133 D performs a second tone mapping process of changing the luminance of the main video in the second section based on constant conversion characteristics irrespective of the graphics luminance in the second section. 
       FIG. 21  is a diagram showing a configuration example of dynamic metadata according to Embodiment 4. In  FIG. 21 , illustration of the elements that are not relevant to the present disclosure is omitted. 
     The configuration example of dynamic metadata shown in  FIG. 21  is different from that shown in  FIGS. 9A, 9B, and 12  in that graphics luminance information is added. The value of the graphics luminance information indicates the effective maximum luminance of graphics (or in other words, subtitles or a menu) overlaid on the main video. When the graphics luminance information indicates “0” or a “value indicating that there are no graphics”, video display apparatus  102 D performs dynamic tone mapping according to the dynamic metadata. On the other hand, when the graphics luminance information indicates a value other than “0” or a “value indicating that there are graphics”, video display apparatus  102 D performs dynamic tone mapping on a section of the main video that has a luminance greater than or equal to the luminance of the graphics luminance information, and fixes tone mapping on a section of the main video that has a luminance less than the graphics luminance. 
     The graphics luminance information may be a portion of the luminance value distribution of the tone mapping information of the second option. As the graphics luminance information, for example, a luminance value that is defined as the knee point may be used. In this case, a graphics process and a normal dynamic tone mapping process can be made common by video display apparatus  102 D. That is, at a luminance less than or equal to the luminance designated by the knee point, not performing tone mapping is set as an expected value, and thus video display apparatus  102 D does not perform tone mapping at a luminance less than or equal to the graphics luminance. Accordingly, even when graphics are overlaid, video display apparatus  102 D can display a portion on which the graphics are overlaid at a stable luminance. 
     5-2. Advantageous Effects 
       FIG. 22A  is a diagram showing a variation in the luminance of subtitles in conventional dynamic tone mapping in the case where graphics are subtitles. In the case of the subtitles luminance level being 200 nits or less, when the tone mapping varies with time, as can be seen from  FIG. 22A , the luminance at a level from 0 to near 200 nits also varies, and the subtitles luminance that essentially needs to be constant varies. 
     In contrast, by setting a predetermined luminance to a fixed value and performing tone mapping on a luminance that exceeds the predetermined luminance, the occurrence of variation in tone mapping with time can be prevented with respect to a luminance less than or equal to the predetermined border luminance. Accordingly, as can be seen from  FIG. 22B , there is no variation with time below a level of 200 nits, which is the subtitles luminance, and thus the subtitles are displayed at a stable luminance level. Here, the predetermined luminance is, for example, a fixed value that is higher than the luminance level of ordinary subtitles, and the knee point of the conversion characteristics is also fixed. 
     However, when the predetermined luminance level is fixed, a problem arises in that the range of variation of dynamic tone mapping is limited, and advantageous effects of dynamic tone mapping on the main video are reduced. The problem becomes prominent particularly when the maximum luminance (DPL) of video display apparatus  102  is low. It is of course possible to enhance the advantageous effects of dynamic tone mapping by devising the dynamic tone mapping method such as setting the luminance of graphics data to a predetermined value or less in video display apparatus  102 . However, in this case, there is a problem in that, when graphics data having a luminance higher than the set luminance is displayed, the display of the graphics data is susceptible to the influence of dynamic tone mapping. 
     To address this, in order to change the predetermined luminance based on the subtitles luminance information, as shown in  FIG. 23 , dynamic tone mapping having an even higher degree of freedom can be applied to the main video.  FIG. 23  shows a case where the actual subtitles luminance is 100 nits. As shown in  FIG. 23 , in this case, dynamic tone mapping having an even higher degree of freedom can be implemented as compared with the case where processing is performed by fixing the border luminance to 200 nits as shown in  FIG. 22B . Such an advantageous effect increases as the maximum luminance of video display apparatus  102 D to which the video reproduction apparatus is connected is lower. 
     6. Embodiment 5 
     Embodiment 5 will be described. In Embodiment 5, a case will be considered in which a video reproduction apparatus supports a plurality of HDR formats in which dynamic tone mapping can be performed. In the case where the main video supports a first HDR format that is one of a plurality of HDR formats, and a video display apparatus connected to the video reproduction apparatus supports a second HDR format that is another one of the plurality of HDR formats, at the time of reproducing the main video, the video reproduction apparatus dynamically generates, from the main video that is being reproduced, dynamic metadata that is needed in the second HDR format supported by the video display apparatus, and transmits the generated dynamic metadata to the video display apparatus. As a result, the video display apparatus acquires the main video and the dynamic metadata corresponding to the second HDR format, and displays the acquired main video in the second HDR format by using the acquired dynamic metadata. 
     [6-1. Configuration of Video Processing System] 
       FIG. 24  is a block diagram showing a configuration of video processing system  100 E according to Embodiment 5. Video reproduction apparatus  101 E according to the present embodiment is different from video reproduction apparatus  101 A according to Embodiment 2 in that generator  118 E has a different function. Other structural elements of video reproduction apparatus  101 E are the same as those of video reproduction apparatus  101 A according to Embodiment 2, and thus a detailed description thereof will be omitted. Also, video display apparatus  102  has the same configuration as that of video display apparatus  102  according to Embodiments 1 and 2, and thus a detailed description thereof will be omitted. 
     First, the present embodiment will be described assuming that metadata acquirer  116  acquires main video dynamic metadata corresponding to the first HDR format. It is also assumed that format acquirer  117  acquires the display format indicated by the second HDR format because the HDR format supported by the display format of video display apparatus  102  is second HDR format. 
     The format (first HDR format) supported by the main video dynamic metadata acquired by metadata acquirer  116  and the display format (second HDR format) acquired by format acquirer  117  are different, and thus generator  118 E generates dynamic metadata in the second HDR format from the main video output from main video decoder  113 . Then, generator  118 E replaces the dynamic metadata in the first HDR format with the generated main video dynamic metadata in the second HDR format, or adds the generated dynamic metadata in the second HDR format to the main video dynamic metadata. In this way, generator  118 E extracts the dynamic metadata of the main video corresponding to the display format by analyzing the main video. 
     7. Variation 
     The details of Blu-ray and Ultra HD Blu-ray are disclosed in, for example, Non-Patent Literature (NPL)  1 . 
     The HDR video acquired by acquirer  111  may be a video on, for example, a Blu-ray disc, a DVD, a moving image delivery site on the Internet, a broadcast, or a HDD (Hard Disk Drive). 
     The video reproduction apparatus described above may be an apparatus that decodes a compressed video signal transmitted from a recording medium, a broadcast, or the Internet, and transmits the decoded video signal to a video display apparatus. Examples of the video reproduction apparatus include a disc player, a disc recorder, a set top box, a television set, a personal computer, and a smartphone. Also, video display apparatus  102  may have some or all of the functions of the video reproduction apparatus. For example, among the processors included in the video reproduction apparatus, video display apparatus  102  may include the processors other than acquirer  111 . Also, video receiver  131 , metadata acquirer  132 , and tone mapping processor  133  or  133 D included in video display apparatus  102  or  102 D may be incorporated in the video reproduction apparatus. Also, among the processors included in tone mapping processor  133 D, the video reproduction apparatus may include the processors other than tone mapper  143 . 
     The video signal transmitting means that transmits the video signal from the video reproduction apparatus to the video display apparatus may be a means that transmits the video signal in an uncompressed state such as HDMI, DVI, or DP, or may be a means that transmits the video signal in a compressed form such as transmission via a network. 
     The maximum luminance information or the tone mapping information of the video display apparatus can be set in the video reproduction apparatus by a user inputting the information into the video reproduction apparatus via a remote controller or the like, or via an operating apparatus included in the video reproduction apparatus. Alternatively, the user may acquire these information via the Internet or any other means, store the acquired information in a portable storage medium, and transmit the information to the video reproduction apparatus via the portable storage medium. Alternatively, the video reproduction apparatus may be connected directly to the Internet such that the video reproduction apparatus can acquire these information from a database on a server. Furthermore, the video reproduction apparatus may display a test pattern on the video display apparatus such that these information can be acquired or stored, with the user confirming the characteristics of the video display apparatus by using the displayed test pattern. 
     The video reproduction apparatus may generate graphics luminance information (including subtitles luminance information and menu luminance information) by detecting the luminance of graphics (subtitles or a menu) from the data of the graphics, or may acquire the luminance of graphics created in advance during production of the video data. For example, the graphics luminance may be recorded in a disc, or may be transmitted as metadata via broadcasting or the Internet. The video reproduction apparatus reads the graphics luminance, and transmits the read graphics luminance to the video display apparatus as a portion of the dynamic metadata. Alternatively, the luminance information of graphics (subtitles or a menu) may be recorded in a database on a server that is connected to the Internet as information regarding the content to be reproduced such that the video reproduction apparatus can acquire the graphics luminance information from the database, and transmit the acquired graphics luminance information to the video display apparatus. 
     The metadata of the first option and the metadata of the second option may be provided in different descriptions that are different from the bit number and the number of items of the configuration examples, such as a coordinate system of a unit system of the values of the first option being different from a coordinate system of a unit system of the values of the second option. 
     In Embodiments 1 to 4, a case has been described in which the first option and the second option of the HDR format are different. However, the expression the HDR format being different also encompasses that the first option and the second option are different. That is, the first option of the HDR format may be defined as a first HDR format, and the second option of the HDR format may be defined as a second HDR format. Also, Mandatory HDR may be an HDR format that is different from the first option of the HDR format and the second option of the HDR format. 
     Up to here, the video processing systems according to the embodiments of the present disclosure have been described, but the present disclosure is not limited to the embodiments. 
     Also, the processors included in the video processing systems according to the embodiments described above are typically implemented as LSIs, which are integrated circuits. They may be individual single chips, or a part or all of them may be configured in a single chip. 
     Also, implementation of an integrated circuit is not limited to an LSI, and may be implemented by a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array) that can be programmed after LSI production or a reconfigurable processor that enables reconfiguration of the connection and setting of circuit cells in the LSI. 
     Also, in each of the embodiments described above, the structural elements may be configured using dedicated hardware, or may be implemented by executing a software program suitable for the structural elements. The structural elements may be implemented by a program executor such as a CPU or a processor reading and executing a software program recorded in a recording medium such as a hard disk or a semiconductor memory. 
     Also, the present disclosure may be implemented as a method executed by the video processing system. 
     Also, the functional blocks shown in the block diagrams are merely examples. Accordingly, it is possible to implement a plurality of functional blocks as a single functional block, or divide a single functional block into a plurality of blocks. Alternatively, some functions may be transferred to other functional blocks. Also, the functions of a plurality of functional blocks that have similar functions may be processed by a single piece of hardware or software in parallel or by time division. 
     Also, the order in which the steps of each flowchart are performed is merely an example provided to specifically describe the present disclosure. Accordingly, the order is not limited to that described above. Also, one or more of the steps described above may be performed simultaneously with (in parallel to) other steps. 
     A video processing system according to one or more aspects has been described by way of embodiments above, but the present disclosure is not limited to the embodiments given above. Embodiments obtained by making various modifications that can be conceived by a person having ordinary skill in the art to the above embodiments as well as embodiments implemented by any combination of the structural elements of different embodiments without departing from the gist of the present disclosure may also be encompassed within the scope of one or more aspects. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to a video processing system, a video reproduction apparatus, or a video display apparatus.