Patent Publication Number: US-2022224975-A1

Title: Transmission method, reception method, transmitting device, and receiving device

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a transmission method for transmitting an image or a reception method for receiving the image. 
     2. Description of the Related Art 
     In recent years, widening the dynamic range of luminance of video from the standard dynamic range (SDR) to the high dynamic range (HDR) has been considered (for example, see non-patent literature (NPL) 1: White Paper Blu-ray (registered trademark) Disc Read-Only Format (Ultra HD Blu-ray) Audio Visual Application Format Specifications for BD-ROM Version 3.0 July 2015, Blu-ray Disc Association). A broadcast station not only transmits video through normal broadcasting (basic broadcasting), but also transmits text, graphics, etc., through data broadcasting. 
     SUMMARY 
     When an HDR image and an SDR image in NPL 1 are transmitted through broadcasting or the like, however, a receiving device is not capable of displaying these images appropriately. 
     Thus, a non-limiting and exemplary embodiment disclosed herein provides a transmission method and the like that make it possible for a receiving device that received an HDR image and an SDR image transmitted through broadcasting or the like to display these images appropriately. 
     The transmission method according to one aspect of the present disclosure includes: obtaining an image and image signal characteristics information indicating one of an opto-electrical transfer function (OETF) or an electro-optical transfer function (EOTF) as image signal characteristics of the image; and transmitting a signal including the image and the image signal characteristics information. 
     Note that these general and specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a compact disc read-only memory (CD-ROM), or any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     Additional benefits and advantages of the disclosed embodiment will be apparent from the specification and drawings. The benefits and advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and advantages. 
     According to the transmission method in the present disclosure, the receiving device that received the HDR image and the SDR image transmitted through broadcasting or the like can display these images appropriately. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG. 1  illustrates one example of the configuration of a transmitting and receiving system and one example of the screen displayed on a receiving device according to an embodiment; 
         FIG. 2  illustrates an example in which a receiving device according to an embodiment displays an HDR primary video and an SDR secondary video simultaneously; 
         FIG. 3A  is a block diagram illustrating one example of the configuration of a transmitting device according to an embodiment; 
         FIG. 3B  is a block diagram illustrating another example of the configuration of a transmitting device according to an embodiment; 
         FIG. 4  illustrates an example in which a receiving device according to an embodiment displays a basic broadcast video, a data broadcast video, etc., simultaneously; 
         FIG. 5  is a block diagram illustrating another example of the configuration of a transmitting device according to an embodiment; 
         FIG. 6  is a block diagram illustrating another example of the configuration of a transmitting device according to an embodiment; 
         FIG. 7  illustrates an HDR EOTF and an SDR EOTF according to an embodiment; 
         FIG. 8  illustrates an example in which a receiving device according to an embodiment displays a basic broadcast caption and another video simultaneously; 
         FIG. 9  is a block diagram illustrating one example of the configuration of a receiving device according to an embodiment; 
         FIG. 10  is a flowchart illustrating one example of operations performed by a receiving device according to an embodiment; 
         FIG. 11  illustrates an example of transition in an image that is displayed by a receiving device according to an embodiment; 
         FIG. 12  is a block diagram illustrating another example of the configuration of a receiving device according to an embodiment; 
         FIG. 13  is a flowchart illustrating another example of operations performed by a receiving device according to an embodiment; 
         FIG. 14A  is a flowchart illustrating a transmission method according to one aspect of the present disclosure; 
         FIG. 14B  is a block diagram illustrating the configuration of a transmitting device according to one aspect of the present disclosure; 
         FIG. 15A  is a flowchart illustrating a reception method according to one aspect of the present disclosure; and 
         FIG. 15B  is a block diagram illustrating the configuration of a receiving device according to one aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     (Underlying Knowledge Forming Basis of the Present Disclosure) 
     In relation to NPL 1 described in the “BACKGROUND” section, the inventors have found the problem indicated below. 
     In NPL 1, it is presumed that graphics are created with the SDR, and when video on which the graphics are to be superimposed is an HDR video, the dynamic range of the graphics is converted from the SDR into the HDR, and the graphics are displayed with the HDR. 
     At present, SDR videos are more often provided than HDR videos as video on which graphics are to be superimposed. Therefore, it is reasonable that graphics created with the SDR be provided and only when video on which the graphics are to be superimposed is an HDR video, the dynamic range of the graphics be converted from the SDR into the HDR. 
     However, as HDR videos become common, the frequency of the dynamic range of graphics being converted into the HDR and the graphics being displayed with the HDR may become higher than the frequency of graphics being displayed with the SDR. Generally, rather than converting graphics created with the SDR into HDR graphics and displaying the graphics with the HDR, it is preferable that graphics created with the HDR be displayed with the HDR because such graphics are displayed as a creator of the graphics intended. 
     Thus, there is the possibility that along with the spread of HDR videos, graphics created originally with the HDR will be provided as well in the future. 
     The inventors noticed the above possibility, took the opportunity to start conducting in-depth research, found various problems occurring in a conventionally unexpected environment in which provision of graphics created with the SDR and provision of graphics created with the HDR are mixed, and found solutions for the problems, which will be described in the embodiment below. 
     In order to solve such various problems, the transmission method according to one aspect of the present disclosure includes: obtaining an image and image signal characteristics information indicating one of an opto-electrical transfer function (OETF) or an electro-optical transfer function (EOTF) as image signal characteristics of the image; and transmitting a signal including the image and the image signal characteristics information. 
     Thus, according to whether the dynamic range of an image (for example, graphics) for data broadcasting is the SDR or the HDR, a data broadcast signal including image signal characteristics information indicating the corresponding OETF or EOTF is transmitted through data broadcasting. In other words, even in an environment in which provision of graphics created with the SDR through data broadcasting and provision of graphics created with the HDR through data broadcasting are mixed, the corresponding OETF or EOTF is transmitted together with such graphics through data broadcasting. Therefore, even in such an environment, a receiving device, such as a television, can display an image, such as graphics, for data broadcasting with an appropriate dynamic range by using the corresponding OETF or EOTF. 
     Furthermore, in the obtaining of the image signal characteristics information, when the image is one of text or a graphic, the image signal characteristics information that indicates one of an offset or a scale factor for each code value included in the image, instead of the one of the OETF or the EOTF, may be obtained. 
     Accordingly, the receiving device can easily convert the image signal characteristics, such as the dynamic range, of an image for the data broadcasting by using the offset or scale factor thereof. 
     Furthermore, the image may be an image for data broadcasting, and the signal may be a data broadcast signal, in the transmitting of the signal, the data broadcast signal may be transmitted through the data broadcasting, and the transmission method may further include: obtaining video for basic broadcasting different from the data broadcasting; converting, when the image signal characteristics of the image for the data broadcasting and image signal characteristics of the video for the basic broadcasting are different, the image signal characteristics of at least one of the image for the data broadcasting and the video for the basic broadcasting to obtain matched image signal characteristics of the image for the data broadcasting and the video for the basic broadcasting; and transmitting, through the basic broadcasting, a basic broadcast signal including the video for the basic broadcasting and image signal characteristics information indicating the matched image signal characteristics. The image signal characteristics information included in the data broadcast signal may indicate one of the OETF or the EOTF as the matched image signal characteristics. 
     Accordingly, the image signal characteristics, i.e., OETF or EOTF, of the image for the data broadcasting and the video for the basic broadcasting are unified, and the image signal characteristics information indicating the unified image signal characteristics is transmitted both through basic broadcasting and through data broadcasting. Therefore, the receiving device does not need to switch the OETF or the ETF for each of the image for the data broadcasting and the video for the basic broadcasting, that is, not need to switch the display process, to display these image and video simultaneously. As a result, it is possible to facilitate mounting of the receiving device. Furthermore, since the image signal characteristics information indicating the unified image signal characteristics is transmitted both through basic broadcasting and through data broadcasting, there is no need of linkage for image signal characteristics between the reception process for basic broadcast and the reception process for data broadcast in the receiving device. As a result, it is possible to facilitate mounting of the receiving device. 
     For example, the video for the basic broadcasting may be one of a primary video, a secondary video, or a caption corresponding to the primary video. Furthermore, for example, the image signal characteristics information may indicate one of the OETF or the EOTF and at least one of a dynamic range, a color gamut, and a white point as the image signal characteristics. 
     Furthermore, the reception method according to one aspect of the present disclosure includes: receiving a first image and first image signal characteristics information indicating image signal characteristics of the first image; receiving a second image and second image signal characteristics information indicating image signal characteristics of the second image; converting, when the first image signal characteristics information and the second image signal characteristics information are different, the image signal characteristics of at least one of the first image and the second image to obtain matched image signal characteristics of the first image and the second image; and simultaneously displaying the first image and the second image having the matched image signal characteristics. For example, each of the first image signal characteristics information and the second image signal characteristics information indicates at least one of an opto-electrical transfer function (OETF), an electro-optical transfer function (EOTF), a dynamic range, a color gamut, and a white point as the image signal characteristics. 
     Accordingly, when the image signal characteristics of the first image are SDR OETF or EOTF, for example, and the image signal characteristics of the second image are HDR OETF or EOTF, for example, the first and second images having the same OETF or EOTF are displayed simultaneously. Thus, it is possible to make the first and second images more eye-friendly. 
     Furthermore, the above reception method may further include: when, while the first image and the second image are being displayed simultaneously, only the image signal characteristics indicated in the second image signal characteristics information among the first image signal characteristics information and the second image signal characteristics information that are being received switch, converting the image signal characteristics of the second image after the switch or stopping conversion that is being performed on the image signal characteristics of the second image before the switch, to obtain matched image signal characteristics of the first image and the second image; and simultaneously displaying the first image and the second image having the matched image signal characteristics after the conversion of the image signal characteristics of the second image is performed or stopped. 
     Accordingly, even when only the image signal characteristics of the second image switch, the image signal characteristics of the first and second images being displayed can remain the same before and after the switch. Thus, the feeling of visual discomfort due to the switch can be suppressed. 
     Furthermore, in the receiving of the first image and the first image signal characteristics information, the first image and the first image signal characteristics information transmitted through data broadcasting may be received, and in the receiving of the second image and the second image signal characteristics information, the second image and the second image signal characteristics information transmitted through basic broadcasting different from the data broadcasting may be received. 
     Accordingly, for example, even when the first image for the data broadcasting is displayed with the SDR and the image signal characteristics of the second image for the basic broadcasting displayed at the same time as the first image switch from the SDR to the HDR, the second image is continuously displayed with the SDR. Thus, the feeling of visual discomfort due to the switch can be suppressed. 
     Furthermore, in the receiving of the first image and the first image signal characteristics information, the first image and the first image signal characteristics information transmitted through communication via a communication network may be received, and in the receiving of the second image and the second image signal characteristics information, the second image and the second image signal characteristics information transmitted through broadcasting may be received. 
     Accordingly, for example, even when the first image for the communication is displayed with the SDR and the image signal characteristics of the second image for broadcasting displayed at the same time as the first image switch from the SDR to the HDR, the second image is continuously displayed with the SDR. Thus, the feeling of visual discomfort due to the switch can be suppressed. 
     Note that these general and specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer readable recording medium such as a compact disc read-only memory (CD-ROM), or any combination of systems, methods, integrated circuits, computer programs, or recording media. 
     Hereinafter, an embodiment will be specifically described with reference to the drawings. 
     Note that each embodiment described below shows a general or specific example. The numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, steps, the processing order of the steps etc. shown in the following embodiment are mere examples, and are not intended to limit the scope of the present disclosure. Furthermore, among the structural elements in the following embodiment, structural elements not recited in the independent claims indicating the broadest concepts of the present disclosure are described as arbitrary structural elements. 
     Embodiment 
       FIG. 1  illustrates one example of the configuration of a transmitting and receiving system and one example of the screen displayed on a receiving device according to the present embodiment. 
     The transmitting and receiving system includes transmitting device  100  which is a broadcast station and receiving device  200  which is a television or the like placed in a house, for example. 
     Transmitting device  100  transmits broadcast content to receiving device  200  through broadcasting via a broadcasting network including a satellite. Furthermore, transmitting device  100  transmits communication content to receiving device  200  through communication via a communication network such as the Internet. The broadcast content and the communication content include an image or audio. The image is video, captions, text, or graphics, for example. The broadcasting includes basic broadcasting and data broadcasting, which are different from each other. 
     Receiving device  200  receives broadcast content and communication content and reproduces the broadcast content and the communication content. As a result of this reproduction, receiving device  200  simultaneously displays a plurality of images included in these contents on the screen of a display device such as a display. 
     For example, receiving device  200  displays video  1  and video  2 , which are basic broadcast primary video and secondary video, data broadcast video  3 , data broadcast text or graphics, communication video  4 , and communication text or graphics simultaneously. Note that the primary video and the secondary video are videos displayed simultaneously in a picture-in-picture display. 
     Note that the image included in the content to be transmitted includes an image having luminance in a conventional standard dynamic range (SDR) and an image having luminance in a high dynamic range (HDR) which is several to 100 times wider than the standard dynamic range. 
     The present embodiment relates to a method and a device for displaying an HDR video and an SDR video simultaneously on the screen of receiving device  200 . 
       FIG. 2  illustrates an example in which receiving device  200  displays an HDR primary video and an SDR secondary video simultaneously. 
     When transmitting device  100  according to the present embodiment superimposes a plurality of images different in the dynamic range, which is one of image signal characteristics, on one another and sends out the plurality of images as a broadcast signal, transmitting device  100  unifies the image signal characteristics of these images including the opto-electrical transfer function (OETF) or the electro-optical transfer function (EOTF). Transmitting device  100  sends out the plurality of images superimposed on one another and image signal characteristics information including the OETF/EOTF of these images. In the present embodiment, the OETF and EOTF or the OETF or EOTF is referred to as OETF/EOTF. 
     This eliminates the need for receiving device  200  to switch the display process according to the image signal characteristics for each screen region to display the HDR primary video and the SDR secondary video simultaneously, as illustrated in  FIG. 2 . Specifically, it is not necessary to switch the OETF/EOTF to be applied to each image. As a result, it is possible to facilitate mounting of receiving device  200 . 
     In the present embodiment, the image signal characteristics and the image signal characteristics information corresponding to an image are referred to as video signal characteristics and video signal characteristics information regardless of whether or not the image is video. The video signal characteristics information indicates characteristics of an images signal (i.e., video signal characteristics), and the characteristics are at least one of the OETF/EOTF, the dynamic range, the color gamut, the white point, and the like. 
     In the present embodiment, as long as the video signal characteristics of each of the primary video and the secondary video are unified, either the following method (1) or (2) may be performed: (1) converting the video signal characteristics so as to match the video signal characteristics of the primary video; and (2) converting the video signal characteristics into HDR. 
     By configuring the settings that the video signal characteristics are fixed to one of the video signal characteristics, that is, the HDR or the SDR, within a certain period of time such as one program, it is possible to reduce the frequency of switching of the display process in receiving device  200 , and distortion of images due to the switch can be suppressed. 
       FIG. 3A  is a block diagram illustrating one example of the configuration of transmitting device  100  according to the present embodiment. 
     Transmitting device  100  includes converters  101  and  105 , synthesizer  102 , sender  103 , and controller  104 . 
     Controller  104  obtains primary video signal characteristics information, which is video signal characteristics information of the primary video, and secondary video signal characteristics information, which is video signal characteristics information of the secondary video. Subsequently, in accordance with the primary video signal characteristics information and the secondary video signal characteristics information, controller  104  outputs, to converter  101 , a control signal for converting the video signal characteristics of the primary video into the video signal characteristics of the secondary video. Alternatively, in accordance with the primary video signal characteristics information and the secondary video signal characteristics information, controller  104  outputs, to converter  105 , a control signal for converting the video signal characteristics of the secondary video into the video signal characteristics of the primary video. Alternatively, in accordance with the primary video signal characteristics information and the secondary video signal characteristics information, controller  104  outputs, to converter  101  or  105 , a control signal for converting the video signal characteristics of each of the primary video and the secondary video into the HDR or the SDR. 
     Furthermore, controller  104  outputs, to sender  103 , video signal characteristics information indicating the unified video signal characteristics of both the primary video and the secondary video, that is, the video signal characteristics common to the primary video and the secondary video. 
     Converter  101  obtains the primary video and converts the video signal characteristics of the primary video on the basis of the control signal output from controller  104 . Similarly, converter  105  Obtains the secondary video and converts the video signal characteristics of the secondary video on the basis of the control signal output from controller  104 . 
     Synthesizer  102  synthesizes (or superimposes on one another) the primary video and the secondary video output from converters  101  and  104  and outputs the synthesized primary video and secondary video to sender  103 . 
     Sender  103  transmits, as a basic broadcast signal through broadcasting (specifically, the basic broadcasting), a signal including the synthesized primary video and secondary video and the unified video signal characteristics information output from controller  104 . Note that sender  103  is a transmitter. 
     The transmitting and receiving system according to the present embodiment may include a transmitting device having another configuration, as illustrated in  FIG. 3B , instead of transmitting device  100 . 
       FIG. 3B  is a block diagram illustrating another example of the configuration of the transmitting device according to the present embodiment. 
     Transmitting device  100 A has a function the same as or similar to that of transmitting device  100  described above and includes synthesizer  102   a , sender  103 , controller  104   a , and converter  105 . 
     Controller  104   a  obtains primary video signal characteristics information and secondary video signal characteristics information. Subsequently, in accordance with the primary video signal characteristics information and the secondary video signal characteristics information, controller  104  outputs, to converter  105 , a control signal for converting the video signal characteristics of the secondary video into the video signal characteristics of the primary video. 
     Converter  105  obtains the secondary video and converts the video signal characteristics of the secondary video on the basis of the control signal output from controller  104   a.    
     Synthesizer  102   a  obtains the primary video, synthesizes (or superimposes on one another) the primary video and the secondary video output from converter  105 , and outputs the synthesized primary video and secondary video to sender  103 . 
     Sender  103  transmits, as a basic broadcast signal through broadcasting (specifically, the basic broadcasting), a signal including the synthesized primary video and secondary video and the primary video signal characteristics information. This primary video signal characteristics information indicates the unified video signal characteristics of both the primary video and the secondary video, that is, the video signal characteristics common to the primary video and the secondary video. 
     In such transmitting devices  100  and  100 A, converter  101  or  105  converts a primary or secondary video signal from an SDR signal into an HDR signal or from an HDR signal into an SDR signal according to the control signal. 
       FIG. 4  illustrates an example in which receiving device  200  displays a basic broadcast video, a data broadcast video, etc., simultaneously. 
     Receiving device  200  displays, for example, video  1  and video  2 , which are basic broadcast primary video and secondary video, data broadcast video  3 , and data broadcast text or graphics simultaneously. 
     Here, there are cases where the basic broadcast primary video, the basic broadcast secondary video, and the data broadcast image (video, text, or graphics) are different in the video signal characteristics such as the dynamic range. 
     In such a case, the transmitting and receiving system according to the present embodiment may include a transmitting device that unifies the video signal characteristics by changing the video signal characteristics of each image other than the basic broadcast primary video into the video signal characteristics of the basic broadcast primary video, as illustrated in  FIG. 5 , instead of transmitting device  100  or  100 A. This eliminates the need for receiving device  200  to switch the video signal characteristics information for each type of broadcasting, making it possible to facilitate mounting of receiving device  200 . 
       FIG. 5  is a block diagram illustrating another example of the configuration of the transmitting device according to the present embodiment. 
     Transmitting device  100 B includes senders (transmitters)  111  and  116 , controllers  112 ,  114 , and  117 , and converters  113 ,  115 , and  118 . 
     Controller  112  obtains primary video signal characteristics information and secondary video signal characteristics information. Subsequently, in accordance with the primary video signal characteristics information and the secondary video signal characteristics information, controller  112  outputs, to converter  113 , a control signal for converting the video signal characteristics of the secondary video into the video signal characteristics of the primary video. 
     Converter  113  obtains the secondary video and converts the video signal characteristics of the secondary video on the basis of the control signal output from controller  112 . 
     Sender  111  obtains the primary video, the primary video signal characteristics information, and the secondary video output from converter  113 , and transmits a signal including these as a basic broadcast signal through the basic broadcasting. 
     Controller  114  obtains data broadcast video signal characteristics information, which is video signal characteristics information of the data broadcast video, and the primary video signal characteristics information. Subsequently, in accordance with the data broadcast video signal characteristics information and the primary video signal characteristics information, controller  112  outputs, to converter  115 , a control signal for converting the video signal characteristics of the data broadcast video into the video signal characteristics of the primary video. 
     Converter  115  obtains a data broadcast video, which is video for data broadcasting, and converts the video signal characteristics of the data broadcast video on the basis of the control signal output from controller  114 . 
     Controller  117  obtains data broadcast graphic signal characteristics information, which is video signal characteristics information of data broadcast text or graphics, and primary video signal characteristics information. Subsequently, in accordance with the data broadcast graphic signal characteristics information and the primary video signal characteristics information, controller  117  outputs, to converter  118 , a control signal for converting the video signal characteristics of the data broadcast text or graphics into the video signal characteristics of the primary video. 
     Converter  118  obtains data broadcast graphics, which are text or graphics for data broadcasting, and converts the video signal characteristics of the data broadcast graphics on the basis of the control signal output from controller  117 . 
     Sender  116  obtains the primary video signal characteristics information, the data broadcast video output from converter  115 , and the data broadcast graphics output from converter  118 , and transmits a signal including these as a data broadcast signal through the data broadcasting. 
     As described above, transmitting device  100 B according to the present embodiment includes the video signal characteristics information in each of the basic broadcast signal and the data broadcast signal. This eliminates the need of linkage for video signal characteristics between the process of receiving the basic broadcast signal and the process of receiving the data broadcast signal in receiving device  200 , making it possible to facilitate mounting of receiving device  200 . 
     In the case where receiving device  200  can always receive and process the basic broadcast signal and the data broadcast signal in pairs, transmitting device  100 B may omit the video signal characteristics information included in the data broadcast signal. In this case, the transmission method according to the present embodiment includes: obtaining an image for the data broadcasting and video for the basic broadcasting different from the data broadcasting; converting, when the image signal characteristics of the image for the data broadcasting and the image signal characteristics of the video for the basic broadcasting are different, the image signal characteristics of at least one of the image for the data broadcasting and the video for the basic broadcasting to obtain matched image signal characteristics of the image for the data broadcasting and the video for the basic broadcasting; transmitting, through the data broadcasting, a data broadcast signal including the image for the data broadcasting; and transmitting, through the basic broadcasting, a basic broadcast signal including the video for the basic broadcasting and image signal characteristics information indicating the matched image signal characteristics. 
     The transmitting and receiving system according to the present embodiment may include a transmitting device having another configuration, as illustrated in  FIG. 6 , instead of transmitting device  100 B. 
       FIG. 6  is a block diagram illustrating another example of the configuration of the transmitting device according to the present embodiment. 
     Transmitting device  100 C includes senders (transmitters)  111  and  116   a , controllers  112 ,  114 , and  117   a , and converters  113  and  115 . 
     Controller  117   a  obtains data broadcast graphic signal characteristics information, which is video signal characteristics information of data broadcast text or graphics, and primary video signal characteristics information. Subsequently, in accordance with the data broadcast graphic signal characteristics information and the primary video signal characteristics information, controller  117   a  outputs, to sender  116   a , conversion information for converting the video signal characteristics of the data broadcast text or graphics into the video signal characteristics of the primary video. The conversion information is, specifically, an offset, a scale factor, or the like. 
     Sender  116   a  obtains the conversion information output from controller  117   a , the primary video signal characteristics information, the data broadcast video output from converter  115 , and the data broadcast graphics, and transmits a signal including these as a data broadcast signal through the data broadcasting. 
     In transmitting device  100 C, the conversion information (such as an offset or a scale factor) is transmitted without conversion of the video signal characteristics of data broadcast text or graphics. This allows receiving device  200  to easily convert the video signal characteristics (for example, the dynamic range) of the data broadcast text or graphics so as to match the video signal characteristics of the basic broadcast primary video. 
     As described above, in the transmission method according to the present embodiment, the image for the data broadcasting and the image signal characteristics information indicating one of the OETF or the EOTF as the image signal characteristics of the image are obtained. Subsequently, the data broadcast signal including the image for the data broadcasting and the image signal characteristics information is transmitted through the data broadcasting. Here, in the obtaining of the image signal characteristics information, when the image is one of text or graphics, the image signal characteristics information that indicates one of an offset or a scale factor for each code value included in the image, instead of the one of the OETF or the EOTF, may be obtained. 
     Furthermore, in the transmission method according to the present embodiment, the video for the basic broadcasting different from the data broadcasting is further obtained. When the image signal characteristics of the image for the data broadcasting and the image signal characteristics of the video for the basic broadcasting are different, the image signal characteristics of at least one of the image for the data broadcasting and the video for the basic broadcasting is converted to obtain matched image signal characteristics of the image for the data broadcasting and the video for the basic broadcasting. Next, the basic broadcast signal including the video for the basic broadcasting and image signal characteristics information indicating the matched image signal characteristics is transmitted through the basic broadcasting. Here, the image signal characteristics information included in the data broadcast signal indicates the OETF or the EOTF as the matched image signal characteristics. 
     Here, the conversion of the video signal characteristics is specifically described below. 
       FIG. 7  illustrates an HDR EOTF and an SDR EOTF. 
     When each of the above-described converters converts the dynamic range, which is one of the video signal characteristics of an image, from the SDR into the HDR, the converter converts a code value of an SDR EOTF included in the image into a code value of an HDR EOTF.  FIG. 7  illustrates a conversion example of code values when the dynamic range is converted from the SDR having the peak luminance of 100 nit into the HDR having the peak luminance of 1,000 nit. 
     In the example illustrated in  FIG. 7 , each of the above converters converts the code value of an SDR EOTF into a code value of an HDR EOTF so that the luminance range (the dynamic range) of an SDR image is converted into the luminance value of an HDR image. Each of the above converters, however, may convert the code value of an SDR EOTF into a code value of an HDR EOTF so that the luminance range of an SDR image is not converted. In this case, each of the above converters converts the code value of the SDR EOTF so that the luminance corresponding to the code value of an SDR EOTF before the conversion becomes the same as the luminance corresponding to the code value of an HDR EOTF after the conversion. In other words, each of the above converters converts the code value of the SDR EOTF by horizontally projecting a point in the SDR EOTF onto a curve of the HDR EOTF. 
     As a result of such conversion of the code value, the video signal characteristics of the image are converted. Furthermore, the video signal characteristics of a plurality of images are unified by such conversion. As a result, in receiving device  200 , the EOTF/OETF (the video signal characteristics information) to be applied to these images are also unified. Consequently, there is no need for receiving device  200  to switch the display process according to the image signal characteristics for each screen region to display the HDR primary video and the SDR secondary video simultaneously, as illustrated in  FIG. 2 . Specifically, it is not necessary to switch the OETF/EOTF to be applied to each image. As a result, it is possible to facilitate mounting of receiving device  200 . 
     Here, the peak luminance for the HDR may be either an absolute value or a relative value such as a scaling factor to dynamic range SDR. Furthermore, the peak luminance may be included in auxiliary information of a multiplexing layer for data broadcasting. 
     As the multiplexing layer, the MPEG-2 transport stream (TS), the MPEG-H MMT (MPEG Media Transport), or the like is used. The auxiliary information is stored by a section of the TS or a descriptor in a message of the MMT, for example. Furthermore, when the dynamic range is switched in units of programs, the transmitting device may indicate, in program information such as an event information table (EIT), whether a program has the SDR or the HDR. 
     The peak luminance for the HDR in converting of the dynamic range into the HDR may be a default value preset in receiving device  200  or may be a value obtained using the default value. For example, when data transmitted through broadcasting, communication, or the like includes conversion information indicating, for example, the peak luminance to be used in conversion into the HDR, receiving device  200  converts the dynamic range into the HDR according to the peak luminance. When such conversion information is not included, receiving device  200  may convert the dynamic range into the HDR according to a default value that is set therein or a value obtained using the default value. Receiving device  200  can convert the dynamic range from the HDR into the SDR likewise as well. 
     As the HDR EOTF, it is possible to use a hybrid EOTF which allows the same code value to be applied to both the HDR and the SDR. For example, when receiving device  200  superimposes image  2  having the SDR on image  1  of the hybrid type having the HDR and outputs these images as SDR images, it is possible to superimpose the images assuming that the pixel values of both image  1  and image  2  are in the SDR. Therefore, the transmitting device may add, as an HDR attribute of the primary video, the secondary video, the data broadcast image, or the like, information for identifying whether or not such video or image is of the hybrid type. 
       FIG. 8  illustrates an example in which receiving device  200  displays a basic broadcast caption and another video simultaneously. 
     Receiving device  200  displays, for example, video  1 , which is a basic broadcast primary video, caption  1 , which is a caption for the basic broadcast primary video, data broadcast video  3 , and data broadcast text or graphics simultaneously. In the present embodiment, the video for the basic broadcasting is the primary video, the secondary video, or the caption corresponding to the primary video. 
     The transmitting device (any one of transmitting devices  100  and  100 A to  1000  described above) transmits the basic broadcast caption independently of video such as the primary video and the secondary video. Before sending the caption, the transmitting device changes the video signal characteristics of a caption so that these video signal characteristics and the video signal characteristics of the video on which the caption is to be superimposed are unified. 
     The caption is described in an extensible markup language (XML)-based language such as the timed text markup language (TTML) of the world wide web consortium (W3C), and the color or the luminance value of the caption is represented by RGB values. Therefore, information for identifying whether the RGB value designated in the XML corresponds to the OETF/EOTF for the SDR or the HDR may be added to the XML document or may be transmitted as video signal characteristics information of the whole caption. 
     The data broadcast is configured by an application such as the hypertext markup language (HTML). Video signal characteristics information in the data broadcast may indicate the SDR or the HDR as the video signal characteristics of the whole application. Furthermore, using an HTML tag or the like, the video signal characteristics information in the data broadcast may indicate whether each of moving images, still images, and text to be referred to by the HTML has the SDR or the HDR. 
     Examples of the video signal characteristics of a plurality of images including captions to be displayed simultaneously include not only the dynamic range, but also the color gamut. Especially, in a high-resolution image having 4K resolution or the like, it is assumed that not only the existing BT. 709 (Recommendation ITU-R BT. 709), but also BT. 2020 (Recommendation ITU-R BT. 2020) which enables representation of a wider color gamut than that in BT. 709 will be used. When receiving device  200  displays images different in the color gamut simultaneously, it is necessary to change the color gamut of one of the images into that of the other to unify the color gamut. In this case as well, on the basis of criteria similar to those for the dynamic range (or the OETF/EOTF), the transmitting device (or receiving device  200 ) can determine the color gamut that is to be chosen as the unified color gamut. 
       FIG. 9  is a block diagram illustrating one example of the configuration of receiving device  200  according to the present embodiment. 
     Receiving device  200  includes broadcast receiver  201 , communication receiver  202 , controller  203 , converter  204 , and display  205 . 
     Broadcast receiver  201  receives a basic broadcast signal and outputs video included in the basic broadcast signal to display  205 . At this time, broadcast receiver  201  may apply, to the video, video signal characteristics information included in the basic broadcast signal, thereby converting the data format of the video into a format supported by display  205 . For example, broadcast receiver  201  applies the EOM to convert a code value included in the video into luminance. Broadcast receiver  201  outputs such video in the converted data format to display  205 . Furthermore, broadcast receiver  201  outputs, as basic broadcast video signal characteristics information to controller  203 , the video signal characteristics information included in the basic broadcast signal. 
     Communication receiver  202  receives a communication signal, outputs video included in the communication signal to converter  204  as a communication video, and outputs video signal characteristics information included in the communication signal to controller  203  as communication video signal characteristics information. The communication signal is a signal transmitted through communication via a communication network such as the Internet. 
     Controller  203  obtains the basic broadcast video signal characteristics information and the communication video signal characteristics information. Subsequently, on the basis of the basic broadcast video signal characteristics information and the communication video signal characteristics information, controller  104  outputs, to converter  204 , a control signal for converting the video signal characteristics of the communication video into the video signal characteristics of the basic broadcast video. 
     Converter  204  obtains the communication video from communication receiver  202  and converts the video signal characteristics of the communication video on the basis of the control signal output from controller  203 . Furthermore, converter  204  may obtain the basic broadcast video signal characteristics information from broadcast receiver  201  via controller  203  and apply the basic broadcast video signal characteristics information to the communication video having the converted video signal characteristics. By this application, converter  204  converts the data format of the communication video into a data format supported by display  205 . For example, converter  204  applies the EOTF to convert a code value included in the communication video into luminance. Note that “luminance” herein is not limited to the weighted sum of RGB components and may be the intensity of each of the RGB components, may be the degree of brightness of light, or may be the intensity of light. Converter  204  outputs such a communication video in the converted data format to display  205 . 
     Display  205  is a display device and displays the basic broadcast video output from broadcast receiver  201  and the communication video output from converter  204  simultaneously. 
     There are cases where even when the video signal characteristics of the basic broadcast and the data broadcast are unified by transmitting device  100  described above or the like, these video signal characteristics do not match the video signal characteristics for the communication (for example, the OETF/EOTF or the dynamic range). In such a case, receiving device  200  according to the present embodiment converts the video signal characteristics of the communication video so that the video signal characteristics of the communication matches the video signal characteristics of the broadcast, and displays the communication video after the conversion. Thus, it is possible to make the communication video more eye-friendly. 
     Note that regarding any of these images, it is sufficient that the video signal characteristics thereof be unified; the video signal characteristics of the images may be unified on the basis of the data broadcast image, the communication image, or the like. 
     Receiving device  200  may change the video signal characteristics (such as brightness, hue, or contrast) of an on-screen display (OSD) such as the channel selection information or sound volume to be displayed on display  205 , according to the video signal characteristics of the basic broadcast. For example, when the dynamic range of the basic broadcast video is the HDR, receiving device  200  can increase the contrast of the OSD such as the channel selection information or the sound volume in displaying the video so that the visibility thereof is improved. 
       FIG. 10  is a flowchart illustrating operations performed by receiving device  200  according to the present embodiment. 
     Controller  203  of receiving device  200  determines whether or not the basic broadcast video signal characteristics information and the communication video signal characteristics information are the same (Step S 101 ). Here, when controller  203  determines that these are the same (YES in Step S 101 ), controller  203  outputs, to converter  204 , a control signal that does not convert the video signal characteristics of the communication video (Step S 102 ). When controller  203  determines that those are not the same (NO in Step S 101 ), controller  203  outputs, to converter  204 , a control signal instructing to convert the video signal characteristics of the communication video (Step S 103 ). 
     As described above, in the reception method according to the present embodiment, a first image and first image signal characteristics information indicating the image signal characteristics of the first image are received. Next, a second image and second image signal characteristics information indicating the image signal characteristics of the second image are received. Subsequently, when the first image signal characteristics information and the second image signal characteristics information are different, the image signal characteristics of at least one of the first image and the second image is converted to obtain matched image signal characteristics of the first image and the second image. Furthermore, the first image and the second image having the matched image signal characteristics are displayed simultaneously. Here, the first image signal characteristics information and the second image signal characteristics information each indicate at least one of the OETF, the EOTF, the dynamic range, the color gamut, and the white point as image signal characteristics. Here, in the above reception of the first image and the first image signal characteristics information, the first image and the first image signal characteristics information transmitted through communication via a communication network are received. In the above reception of the second image and the second image signal characteristics information, the second image and the second image signal characteristics information transmitted through broadcasting are received. Alternatively, in the above reception of the first image and the first image signal characteristics information, the first image and the first image signal characteristics information transmitted through data broadcasting may be received. Likewise, in the above reception of the second image and the second image signal characteristics information, the second image and the second image signal characteristics information transmitted through basic broadcasting different from data broadcasting may be received. 
       FIG. 11  illustrates an example of transition in an image that is displayed by the receiving device according to the present embodiment. 
     For example, there are cases where, while the receiving device is displaying a plurality of videos simultaneously, the dynamic range of part of the videos switches from the SDR to the HDR or from the HDR to the SDR or the like. As a characteristic example, it is assumed that the dynamic range of a primary video program switches while the receiving device is displaying a data broadcast image. At this time, if the dynamic range of the luminance of the primary video switches while the data broadcast image is being displayed, visual discomfort would be felt due to a difference in brightness between the video before the switch and the same video after the switch. 
     Thus, the transmitting and receiving system according to the present embodiment may include receiving device  200 A instead of receiving device  200 . In receiving device  200 N the dynamic range is fixed while the data broadcast image is being displayed. 
     For example, while receiving device  200 A is displaying a data broadcast image (specifically, video  3  and text, graphics, etc.) and program  1 , which is a basic broadcast primary video, as illustrated in (a) of  FIG. 11 , the primary video switches from program  1  to program  2  as illustrated in (b) of  FIG. 11 . Here, the dynamic range of program  1  is the SDR, the dynamic range of program  2  is the HDR, and the dynamic range of the data broadcast image has been the SDR since when program  1  was reproduced. 
     Receiving device  200 A according to the present embodiment displays program  2 , which is a primary video, with the SDR while the data broadcast image is being displayed with the SDR, as illustrated in (b) of  FIG. 11 , even after the primary video switches from program  1  having the SDR to program  2  having the HDR. Specifically, receiving device  200 A converts the video signal characteristics of program  2  into video signal characteristics for the SDR and applies the SDR EOTF/OETF to program  2 . Subsequently, as illustrated in (c) of  FIG. 11 , receiving device  200 A displays program  2  with the HDR after the display of the data broadcast image is ended. Specifically, receiving device  200 A does not convert the video signal characteristics of program  2  and applies the HDR EOTF/OETF to program  2 . 
     In this way, in the case where during display of a plurality of videos, the dynamic range of part of the videos upon reception switches, receiving device  200 A according to the present embodiment determines whether the video is to be displayed with the HDR or the SDR so that the dynamic range of the video being already displayed does not switch. In other words, receiving device  200 A controls whether or not to convert the video signal characteristics of the video being already displayed. 
     Note that in order that the dynamic range of the basic broadcast primary video being displayed does not switch while the data broadcast image is being displayed, receiving device  200 A controls conversion of the video signal characteristics of the primary video. Such control is, however, not limited to the data broadcast image and the basic broadcast primary video; receiving device  200 A may perform the above-described control on a plurality of any images. For example, receiving device  200 A may perform the above-described control on the communication video and the basic broadcast video. 
       FIG. 12  is a block diagram illustrating another example of the configuration of receiving device  200 A according to the present embodiment. 
     Receiving device  200 A includes broadcast receiver  201 , communication receiver  202 , controller  203   a , converters  204  and  206 , and display  205 . 
     Broadcast receiver  201  receives a basic broadcast signal and outputs video included in the basic broadcast signal to converter  206 . Furthermore, broadcast receiver  201  outputs, as basic broadcast video signal characteristics information to controller  203   a , the video signal characteristics information included in the basic broadcast signal. 
     Communication receiver  202  receives a communication signal, outputs video included in the communication signal to converter  204  as a communication video, and outputs video signal characteristics information included in the communication signal to controller  203   a  as communication video signal characteristics information. 
     Controller  203   a  obtains the basic broadcast video signal characteristics information and the communication video signal characteristics information. Subsequently, on the basis of the basic broadcast video signal characteristics information and the communication video signal characteristics information, controller  203   a  outputs a control signal to converters  204  and  206 . This control signal is for converting both the video signal characteristics of the basic broadcast video and the video signal characteristics of the communication video into the HDR or the SDR. Specifically, in the case where during display of the basic broadcast video and the communication video, the video signal characteristics of one of the videos switch, that is, these videos have different video signal characteristics, controller  203   a  outputs a control signal for converting the video signal characteristics of the one of the videos. As a result of this conversion, the video signal characteristics of one of the videos are the same before and after the switch, and the video signal characteristics of both the videos are maintained in the same state. 
     Note that in the case where when the video signal characteristics of one of the above-described videos are being converted, that video signal characteristics switch, controller  203   a  may cause converter  204  or  206  to stop the conversion so that the video signal characteristics of both the videos are maintained in the same state. Specifically, as a result of converter  204  converting the video signal characteristics of the communication video from the SDR to the HDR, both the basic broadcast video and the communication video are displayed with the HDR. In such a situation, when the video signal characteristics of the video being received by communication receiver  202  switch from the SDR to the HDR, controller  203   a  causes converter  204  to stop the conversion being performed by converter  204 . Thus, both the basic broadcast video and the communication video can be continuously displayed with the HDR before and after the switch of the video signal characteristics. 
     Converter  204  obtains the communication video from communication receiver  202  and converts the video signal characteristics of the communication video on the basis of the control signal output from controller  203   a . Furthermore, converter  204  may obtain, from controller  203   a , video signal characteristics information corresponding to the converted video signal characteristics, and apply the video signal characteristics information to the communication video having the converted video signal characteristics. By this application, converter  204  converts the data format of the communication video into a data format supported by display  205 . For example, converter  204  applies the EOTF to convert a code value included in the communication video into luminance. Converter  204  outputs such a communication video in the converted data format to display  205 . 
     Converter  206  obtains the basic broadcast video from broadcast receiver  201  and converts the video signal characteristics of the basic broadcast video on the basis of the control signal output from controller  203   a . Furthermore, converter  206  may obtain, from controller  203   a , video signal characteristics information corresponding to the converted video signal characteristics, and apply the video signal characteristics information to the basic broadcast video having the converted video signal characteristics. By this application, converter  206  converts the data format of the basic broadcast video into a data format supported by display  205 . For example, converter  206  applies the EOTF to convert a code value included in the basic broadcast video into luminance. Converter  206  outputs such a basic broadcast video in the converted data format to display  205 . 
     Display  205  is a display device and simultaneously displays the basic broadcast video output from converter  206  and the communication video output from converter  204 . 
       FIG. 13  is a flowchart illustrating operations performed by receiving device  200 A according to the present embodiment. 
     First, controller  203   a  of receiving device  200 A determines whether or not the video signal characteristics of any of the plurality of videos being displayed have switched (Step S 100 ). Here, when the video signal characteristics are determined to have switched (YES in Step S 100 ), controller  203   a  outputs, to converter  204  or  206 , a control signal instructing to convert or not to convert the video signal characteristics so that the video signal characteristics are the same before and after the switch. 
     When the video signal characteristics are determined to have not switched (NO in Step S 100 ), controller  203   a  determines whether or not the basic broadcast video signal characteristics information and the communication video signal characteristics information are the same (Step S 101 ). Here, when controller  203   a  determines that these are the same (YES in Step S 101 ), controller  203   a  outputs, to converters  204  and  206 , a control signal that does not convert the video signal characteristics (Step S 102 ). When controller  203   a  determines that those are not the same (NO in Step S 101 ), controller  203   a  outputs, to converter  204  and converter  206 , a control signal instructing to convert the video signal characteristics of at least one of the basic broadcast video and the communication video (Step S 103 ). 
     As described above, in the reception method according to the present embodiment, when, while the first image and the second image are being displayed simultaneously, only the image signal characteristics indicated in the second image signal characteristics information among the first image signal characteristics information and the second image signal characteristics information that are being received switch, the image signal characteristics of the second image after the switch is converted, or conversion that is being performed on the image signal characteristics of the second image before the switch is stopped, to obtain matched image signal characteristics of the first image and the second image. The first image and the second image having the matched image signal characteristics are displayed simultaneously after the conversion of the image signal characteristics of the second image is performed or stopped. 
     Accordingly, even when only the image signal characteristics of the second image switch, the image signal characteristics of the first and second images being displayed can remain the same before and after the switch. Thus, the feeling of visual discomfort due to the switch can be suppressed. 
     (Summary) 
       FIG. 14A  is a flowchart illustrating a transmission method according to one aspect of the present disclosure. 
     The transmission method according to one aspect of the present disclosure includes Step S 11  and Step S 12 . In Step S 11 , an image for the data broadcasting and image signal characteristics information indicating the OETF or the EOTF as the image signal characteristics of the image are obtained. In Step S 12 , a data broadcast signal including the image for the data broadcasting and the image signal characteristics information is transmitted through the data broadcasting. 
       FIG. 14B  is a block diagram illustrating the configuration of a transmitting device according to one aspect of the present disclosure. 
     Transmitting device  10  according to one aspect of the present disclosure includes obtainer  11  and transmitter  12 . Obtainer  11  obtains an image for the data broadcasting and image signal characteristics information indicating the OETF or the EOTF as the image signal characteristics of the image. Transmitter  12  transmits a data broadcast signal including the image for the data broadcasting and the image signal characteristics information through the data broadcasting. 
     Thus, according to whether the dynamic range of an image (for example, graphics) for the data broadcasting is the SDR or the HDR, a data broadcast signal including image signal characteristics information indicating the corresponding OETF or EOTF is transmitted through the data broadcasting. In other words, even in an environment in which provision of graphics created with the SDR through the data broadcasting and provision of graphics created with the HDR through the data broadcasting are mixed, the corresponding OETF or EOTF is transmitted together with such graphics through the data broadcasting. Therefore, even in such an environment, a receiving device, such as a television, can display an image, such as graphics, for data broadcasting with an appropriate dynamic range by using the corresponding OETF or EOTF. 
       FIG. 15A  is a flowchart illustrating a reception method according to one aspect of the present disclosure. 
     The reception method according to one aspect of the present disclosure includes Steps S 21  to S 24 . 
     In Step S 21 , a first image and first image signal characteristics information indicating the image signal characteristics of the first image are received. In Step S 22 , a second image and second image signal characteristics information indicating the image signal characteristics of the second image are received. In Step S 23 , when the first image signal characteristics information and the second image signal characteristics information are different, the image signal characteristics of at least one of the first image and the second image is converted to obtain matched image signal characteristics of the first image and the second image. In Step S 24 , the first image and the second image having the matched image signal characteristics are displayed simultaneously. 
       FIG. 15B  is a block diagram illustrating the configuration of a receiving device according to one aspect of the present disclosure. 
     Receiving device  20  according to one aspect of the present disclosure includes first receiver  21 , second receiver  22 , converter  23 , and display  24 . 
     First receiver  21  receives a first image and first image signal characteristics information indicating the image signal characteristics of the first image. Second receiver  22  receives a second image and second image signal characteristics information indicating the image signal characteristics of the second image. When the first image signal characteristics information and the second image signal characteristics information are different, converter  23  converts the image signal characteristics of at least one of the first image and the second image to obtain matched image signal characteristics of the first image and the image signal characteristics of the second image. Display  24  simultaneously displays the first image and the second image having the matched image signal characteristics. 
     Accordingly, when the image signal characteristics of the first image are SDR OETF or EOTF, for example, and the image signal characteristics of the second image are HDR OETF or EOTF, for example, the first and second images having the same OETF or EOTF are displayed simultaneously. Thus, it is possible to make the first and second images more eye-friendly. 
     Note that in the embodiment described above, each of the structural elements may be configured in the form of an exclusive hardware product or may be realized by executing a software program suitable for each of the structural elements. Each of the structural elements may be realized by means of a program executing unit, such as a central processing unit (CPU) and a processor, reading and executing the software program recorded on a recording medium such as a hard disk or a semiconductor memory. Here, software for implementing the transmitting device or the receiving device according to the above embodiment is a program which causes a computer to execute the steps included in the flowchart illustrated in  FIG. 10 , FIG,  13 ,  FIG. 14A , or  FIG. 15A . 
     Although the transmitting device and the receiving device according to one or more aspects are described thus far based on the embodiment, the present disclosure is not limited to this embodiment. Various modifications of the present embodiment as well as embodiments resulting from combinations of structural elements of the different embodiments that may be conceived by those skilled in the art may be included within the scope of one or more aspects as long as these do not depart from the essence of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure produces the advantageous effect of displaying an image appropriately and can be used, for example, as a transmitting device which transmits images such as a television video, a caption, text, or graphics through broadcasting or communication and a receiving device, such as a television, which receives and displays such images.