Patent Description:
Patent Literature (PTL) <NUM> and <NUM> disclose methods and systems for mapping graphics on an image of an HDR (High Dynamic Range) video. In particular, PTL <NUM> relates to transmitting static and/or dynamic HDR meta data to the display device to display the video in accordance with the luminance range of the display. Flag information is used to indicate whether meta data are stored. Moreover, PTL <NUM> discloses aspects concerning the usage of subtitles with SDR (Standard Dynamic Range) and HDR videos, in which the video may be combined with subtitles so as to generate an overlaid image.

The present disclosure provides a video display apparatus and a video display method that can improve the quality of a video displayed.

This is achieved by the features of the independent claims, with preferred embodiments being specified in the dependent claims. Embodiments <NUM>,<NUM> and <NUM> fall outside the scope of the invention.

The present disclosure can provide a video display apparatus and a video display method that can improve the quality of a video displayed.

First, the transition of imaging technology will be described with reference to <FIG> 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 (<NUM> × <NUM> pixels) and high definition (HD) videos (<NUM> × <NUM> pixels) are now widely used.

In recent years, in order to achieve even higher image quality, introduction of ultra high definition (UHD) videos (<NUM> × <NUM> pixels), or so-called <NUM> resolution videos (with a <NUM> resolution of <NUM> × <NUM> pixels) has started.

Along with the introduction of <NUM> 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 <NUM> nits. In contrast, in HDR signals, the highest luminance is expected to be up to <NUM> nits or more. For HDR signals, standardization of mastering display standards is currently undertaken by SMPTE (Society of Motion Picture & 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.

<FIG> 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>, it is necessary to (<NUM>) change a master for home entertainment on the video production side. Along with this change, it is also necessary to (<NUM>) update the delivery method such as broadcasting, communication, or a packaged medium, and also (<NUM>) update the display apparatus such as a television set or a projector for displaying the video.

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.

<FIG> are diagrams showing examples of tone mapping. <FIG> shows a case where DPL is <NUM> nits, and <FIG> shows a case where DPL is <NUM> nits. Also, <FIG> each show an example of tone mapping performed when a video having a MaxCLL of <NUM> nits is displayed and an example of tone mapping performed when a video having a MaxCLL of <NUM> nits is displayed.

As shown in <FIG>, in the case where DPL is <NUM> nits, in both videos, the luminance is converted such that the video can be displayed at up to MaxCLL below <NUM> nits, but the degree of conversion is higher in the video having a higher MaxCLL.

As shown in <FIG>, in the case where DPL is <NUM> nits, in the video having a MaxCLL of <NUM> nits, tone mapping is not performed. In the video having a MaxCLL of <NUM> nits, tone mapping is performed so as to convert the luminance from <NUM> nits to <NUM> nits, and the video is displayed at that luminance.

<FIG> is a diagram showing an example of tone mapping using static metadata. <FIG> is a diagram showing an example of dynamic tone mapping using dynamic metadata.

As shown in <FIG>, 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>, 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>), and performs tone mapping when the luminance is high ((c) in <FIG>). In this way, optimal tone mapping suitable for the luminance that varies with time can be implemented.

<FIG> 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 on 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.

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> 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>, graphics to be overlaid has a luminance of <NUM> nits. As shown in (b) in <FIG>, in a section in which the luminance of the main video is low, tone mapping is not performed, and thus the graphics are displayed on a video display apparatus at a luminance of <NUM> nits that is the original luminance of the graphics. On the other hand, as shown in (c) in <FIG>, in a section in which the luminance of the main video is high, tone mapping is performed, and thus the graphics are displayed on the video display apparatus at a luminance lower than <NUM> 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.

As a means for avoiding the problem described above, a method may be conceived in which the position information of graphics to be overlaid is transmitted to the video display apparatus, and dynamic metadata is not used in an area where the graphics are displayed. However, it is very difficult to implement this method because it is necessary to transmit information that indicates whether graphics are displayed in the entire region of the display screen, and also necessary to make determinations for each display pixel in the processing performed by the video display apparatus.

In the present disclosure, the following solution is used. According to a first method, the video reproduction apparatus transmits a "graphics overlay flag" that indicates whether or not graphics are overlaid on the main video to the video display apparatus as dynamic metadata information. Graphics include a menu and subtitles, and thus the video reproduction apparatus may transmit a "menu overlay flag" and a "subtitles overlay flag" to the video display apparatus as the "graphics overlay flag".

The video display apparatus switches dynamic tone mapping between on and off or changes the intensity of dynamic tone mapping according to the state of the menu overlay flag. With this configuration, the influence of dynamic tone mapping on the overlaid graphics can be reduced.

According to the invention in addition to the first method, the video reproduction apparatus transmits graphics maximum luminance information regarding the graphic maximum luminance of the graphics to be overlaid as the dynamic metadata information to the video display apparatus. As with the overlay flag, the graphics maximum luminance information may include subtitles maximum luminance information and menu maximum luminance information.

The video display apparatus can more finely control dynamic tone mapping according to the graphics overlay flag and the graphics maximum luminance information.

According to a third method, the video display apparatus detects graphics to be displayed constantly by using inter-frame correlation or the like, and does not perform dynamic tone mapping on the detected portion.

According to a fourth method, an HDR video reproduction apparatus such as an Ultra HD Blu-ray reproduction apparatus, a broadcast reception apparatus, or an internet broadcast reception apparatus changes the luminance of graphics to be overlaid according to the maximum luminance information of a video display apparatus to which the HDR video reproduction apparatus is connected, so as to reduce the influence of tone mapping performed by the video display apparatus. The video reproduction apparatus may acquire the maximum luminance of the video display apparatus from settings set by an operator, or may acquire the same from the video display apparatus based on EDID stored in HDMI connected to the video reproduction apparatus.

There are various methods for tone mapping performed in a video display apparatus, and thus the graphics luminance can be adjusted within a predetermined range. As the method for adjusting the graphics luminance, it is possible to use a method in which an operator sets the graphics luminance, a method in which the graphics luminance is adjusted based on information acquired from the database of each video display apparatus, or the like.

According to a fifth method, the HDR video reproduction apparatus assumes a dynamic tone mapping method performed by a video display apparatus that displays an HDR video on which graphics are overlaid, and performs inverse conversion of the dynamic tone mapping performed by the video display apparatus on the graphics to be overlaid before the graphics are overlaid. As a result, the overlaid graphics can be displayed with the original luminance and color after the dynamic tone mapping has been performed.

The video reproduction apparatus may use the following method as the method for assuming the dynamic tone mapping method performed by the video display apparatus to which the video reproduction apparatus is connected. The video reproduction apparatus may assume the dynamic tone mapping method simply based on video luminance information corresponding to, for example, <NUM>% of the maximum luminance of the video display apparatus as the maximum luminance that is free from influence. To be more specific, the video reproduction apparatus may acquire the method from a database. Alternatively, the video reproduction apparatus may perform measurement by using a test pattern, and set the method based on the result of measurement.

With the methods described above, the influence of dynamic tone mapping on graphics such as a menu or subtitles can be reduced when dynamic tone mapping is performed on an HDR video signal transmitted via broadcasting, a packaged medium such as a Blu-ray disc, or internet delivery such as OTT. As a result, it is possible to display subtitles or a menu in a stable manner, and obtain advantageous effects of dynamic tone mapping according to the maximum luminance (DPL) of the video display apparatus and the maximum luminance of the moving images.

Also, in particular, in the case where the luminance of the video display apparatus is lower than the luminance of a video, HDR effects can be increased, and a menu and subtitles can be displayed with high quality as high as that of static tone mapping.

Also, different processing operations are performed on subtitles and a menu, and thus the influence of dynamic tone mapping can be further reduced as a result of performing different processing operations suitable for subtitles and a menu. Specifically, the luminance of a menu varies while the luminance of subtitles is substantially constant. Also, when subtitles are displayed while the main video is reproduced, the subtitles are displayed in synchronization with the main video from the beginning to the end of the main video. On the other hand, a menu is displayed only when an operation is performed, and thus it does not synchronize the main video. In this way, processing can be performed in consideration of the difference in the properties of subtitles and menus.

In the present embodiment, the video reproduction apparatus embeds the graphics overlay flag, which indicates whether graphics are overlaid on the main video, into a portion of the dynamic metadata, and transmits the dynamic metadata to the video display apparatus. The video display apparatus switches dynamic tone mapping that uses the dynamic metadata between on and off or changes the intensity of dynamic tone mapping according to the state of the graphics overlay flag. With this configuration, the influence of dynamic tone mapping on the overlaid graphics can be reduced. The graphics overlay flag may be composed of two flags: a subtitles overlay flag that indicates whether or not there are subtitles to be displayed; and a menu overlay flag that indicates whether or not there is a menu to be displayed.

<FIG> is a block diagram showing a configuration of video display system <NUM> according to the present embodiment. Video display system <NUM> shown in <FIG> includes video reproduction apparatus <NUM> and video display apparatus <NUM>.

Video reproduction apparatus <NUM> reproduces a video, and outputs the obtained video to video display apparatus <NUM>. Video reproduction apparatus <NUM> includes acquirer <NUM>, demultiplexer <NUM>, main video decoder <NUM>, subtitles decoder <NUM>, menu decoder <NUM>, metadata acquirer <NUM>, graphics composer <NUM>, main video composer <NUM>, and video transmitter <NUM>.

Acquirer <NUM> acquires a video signal. For example, in the case where video reproduction apparatus <NUM> is a disc reproduction apparatus, acquirer <NUM> acquires a video signal by reproducing a disc. In the case where video reproduction apparatus <NUM> is a broadcast reception apparatus, acquirer <NUM> acquires a video signal by receiving a broadcast wave. In the case where video reproduction apparatus <NUM> is an internet broadcast reception apparatus, acquirer <NUM> acquires a video signal by receiving an internet broadcast.

Demultiplexer <NUM> 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 <NUM>, subtitles decoder <NUM>, and menu decoder <NUM>, respectively.

Main video decoder <NUM> decodes the encoded main video signal output from demultiplexer <NUM>.

Subtitles decoder <NUM> decodes the encoded subtitles signal output from demultiplexer <NUM>. Also, subtitles decoder <NUM> determines whether or not to display subtitles based on a user's operation or the like, and selects the type of subtitles to be displayed. Subtitles decoder <NUM> outputs the selected subtitles to graphics composer <NUM> when displaying the subtitles.

Menu decoder <NUM> decodes the encoded menu signal output from demultiplexer <NUM>. Also, menu decoder <NUM> determines whether or not to display a menu based on a user's operation or the like, and selects the type of menu to be displayed. Menu decoder <NUM> outputs the selected menu to graphics composer <NUM> when displaying the menu. Menu decoder <NUM> 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 <NUM>.

Metadata acquirer <NUM> acquires main video dynamic metadata. For example, metadata acquirer <NUM> generates main video dynamic data based on information included in the main video signal.

Graphics composer <NUM> generates graphics information by configuring subtitles and a menu. As described above, graphics composer <NUM> may convert the resolutions of the subtitles and the menu. For example, in the case of Ultra HD Blu-ray, graphics composer <NUM> converts the subtitles and the menu in HD format to UHD format.

Also, in the case where graphics composer <NUM> generates graphics information and overlays the generated graphics information on the main video, graphics composer <NUM> sets the graphics overlay flag to ON, and transmits the graphics overlay flag to video transmitter <NUM>. In the case where graphics composer <NUM> does not overlay the graphics information on the main video, graphics composer <NUM> sets the graphics overlay flag to OFF, and transmits the graphics overlay flag to video transmitter <NUM>. The graphics overlay flag may be generated by a program in video reproduction apparatus <NUM>, or by any other means.

Main video composer <NUM> generates a video signal by overlaying the graphics information generated by graphics composer <NUM> on the main video obtained by main video decoder <NUM>.

Video transmitter <NUM> transmits the video signal generated by main video composer <NUM> and the dynamic metadata to video display apparatus <NUM> via a video signal transmitting means such as an HDMI cable. The dynamic metadata includes the main video dynamic metadata acquired by metadata acquirer <NUM> and the graphics overlay flag generated by graphics composer <NUM>.

<FIG> is a diagram showing a configuration example of the main video dynamic metadata and the graphics overlay flag transmitted from video reproduction apparatus <NUM> to video display apparatus <NUM>. As shown in <FIG>, the main video dynamic metadata shows the maximum luminance and the average luminance of the main video. For example, the main video dynamic metadata shows the maximum luminance and the average luminance per frame or more frames.

<FIG> is a diagram showing another configuration example of the main video dynamic metadata and the graphics overlay flag. As shown in <FIG>, the graphics overlay flag may include a subtitles overlay flag that indicates whether subtitles are overlaid on the main video and a menu overlay flag that indicates whether a menu is overlaid on the main video.

Next, a configuration of video display apparatus <NUM> will be described. Video display apparatus <NUM> includes video receiver <NUM>, metadata acquirer <NUM>, tone mapping processor <NUM>, and display <NUM>.

Video receiver <NUM> receives the video signal and the dynamic metadata transmitted from video reproduction apparatus <NUM>. Video receiver <NUM> separates the video signal from the dynamic metadata, and transmits the video signal to tone mapping processor <NUM> and the dynamic metadata to metadata acquirer <NUM>. Metadata acquirer <NUM> transmits the main video dynamic metadata and the graphics overlay flag included in the dynamic metadata to tone mapping processor <NUM> as a control signal.

Tone mapping processor <NUM> performs a tone mapping process on the video signal in accordance with the main video dynamic metadata. Specifically, tone mapping processor <NUM> performs a tone mapping process (dynamic tone mapping process) on the video signal in accordance with the main video dynamic metadata in the case where the graphics overlay flag is set to OFF On the other hand, in the case where the graphics overlay flag is set to ON, tone mapping processor <NUM> performs a tone mapping process with reduced influence of dynamic tone mapping on the overlaid graphics. Display <NUM> displays the video signal that has undergone the tone mapping process.

Tone mapping processor <NUM> will be described in detail. <FIG> is a block diagram showing a configuration of tone mapping processor <NUM>. Tone mapping processor <NUM> includes coefficient calculator <NUM>, coefficient storage <NUM>, tone mapper <NUM>, and switches SW1 and SW2.

The video signal from video receiver <NUM> is transmitted to tone mapper <NUM>. The main video dynamic metadata from metadata acquirer <NUM> is transmitted to coefficient calculator <NUM>.

Coefficient calculator <NUM> calculates a tone mapping coefficient used in the tone mapping process performed by tone mapper <NUM> according to the video display capabilities such as the luminance of video display apparatus <NUM>. Coefficient storage <NUM> stores the tone mapping coefficient calculated by coefficient calculator <NUM>. As used herein, the tone mapping coefficient refers to a 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 SW1 selects one from the tone mapping coefficient (A) calculated by coefficient calculator <NUM> and the tone mapping coefficient (B) stored in coefficient storage <NUM>, and transmits the selected tone mapping coefficient to tone mapper <NUM>. Switch SW2 selects one from the tone mapping coefficient (A) calculated by coefficient calculator <NUM> and the tone mapping coefficient (B) stored in coefficient storage <NUM>, and inputs the selected tone mapping coefficient to coefficient storage <NUM>. That is, switch SW2 switches between (A) updating the tone mapping coefficient stored in coefficient storage <NUM> with the tone mapping coefficient newly calculated by coefficient calculator <NUM> and (B) continuously storing the currently stored tone mapping coefficient.

Switches SW1 and SW2 work in conjunction with each other. In the case where the graphics overlay flag is set to OFF, switches SW1 and SW2 are both connected to A. In the case where the graphics overlay flag is set to ON, switches SW1 and SW2 are both connected to B. With this configuration, dynamic tone mapping based on the dynamic metadata is fixed in the case where graphics are overlaid.

Also, in the case where the graphics overlay flag includes a subtitles overlay flag and a menu overlay flag, the processing of the tone mapping coefficient input to tone mapper <NUM> may be changed according to the combination. As an example, in the case where the graphics overlay flag is set to ON, the tone mapping coefficient is fixed (switches SW1 and SW2 are connected to B). When only the menu overlay flag is set to ON, a normal tone mapping coefficient is used (switches SW1 and SW2 are connected to A).

The configuration described here is merely an example, and thus tone mapping processor <NUM> may be configured to, in the case where the graphics overlay flag is set to ON, fix the tone mapping coefficient at a specific luminance or less, or not perform a tone mapping process.

<FIG> is a diagram showing a configuration of tone mapping processor 123A that is configured to fix the tone mapping coefficient at a specific luminance or less. Tone mapping processor 123A includes coefficient composer <NUM> in place of switch SW1.

According to the invention, in the case where the graphics overlay flag is set to ON, coefficient composer <NUM> performs a dynamic tone mapping process on a luminance greater than or equal to a border luminance level that is a predetermined luminance. However, coefficient composer <NUM> performs the following processing on a luminance less than the border luminance: (<NUM>) fixing the tone mapping; (<NUM>) not performing a tone mapping process; (<NUM>) suppressing variation of tone mapping; or (<NUM>) making the influence of tone mapping imperceptible to human. As used herein, the border luminance level refers to, for example, a luminance higher than the maximum luminance value used in the graphics. With this configuration, the variation of tone mapping in the luminance range used in the graphics is suppressed. Also, in the processing described above, in order to maintain continuity between the conversion characteristics greater than or equal to the border luminance level and the conversion characteristics less than the border luminance level, coefficient composer <NUM> may correct the conversion characteristics in these border regions such that the conversion characteristics varies smoothly.

Here, the configuration has been described using only a video, subtitles, and a menu, but video reproduction apparatus <NUM> and video display apparatus <NUM> are configured to also process, transmit, and output an audio signal and the like. These are irrelevant to the present disclosure, and thus a description thereof is omitted here and in the following description.

Also, in the case where the graphics overlay flag includes a subtitles overlay flag and a menu overlay flag, coefficient composer <NUM> shown in <FIG> uses different overlay methods depending on the state of the subtitles overlay flag and the menu overlay flag. For example, coefficient composer <NUM> sets the border luminance level to different values between when the graphics overlay flag is set to ON and when only the menu overlay flag is set to ON.

Coefficient composer <NUM> sets the border luminance level by taking into consideration the highest luminance of display <NUM> and other video-related characteristics. In general, the luminance level of a menu is higher than the luminance level of subtitles. Accordingly, in the case where the menu overlay flag is set to ON, coefficient composer <NUM> sets the border luminance level to be higher than that in the case where only the subtitles overlay flag is set to ON.

Whether to overlay a menu is determined by a user, and thus importance may be placed on tone mapping of the main video rather than the influence of dynamic tone mapping on the menu. Accordingly, in the case where the menu overlay flag is set to ON, coefficient composer <NUM> may set the border luminance level to be lower than that in the case where the graphics overlay flag is set to ON.

A flow of operations performed in the video display system will be described. <FIG> is a flowchart illustrating the operations of video reproduction apparatus <NUM>. After the reproduction of a video starts, video reproduction apparatus <NUM> determines, based on the graphics (subtitles and a menu) processing state, whether graphics are overlaid on the main video (S101). If it is determined that graphics are overlaid on the main video (Yes in S101), video reproduction apparatus <NUM> sets the graphics overlay flag to ON (S102). If, on the other hand, it is determined that graphics are not overlaid on the main video (No in S101), video reproduction apparatus <NUM> sets the graphics overlay flag to OFF (S103). Then, video reproduction apparatus <NUM> repeatedly performs the processing operations of steps S101 to S103 until the reproduction of the video is completed or an operation to stop the reproduction of the video is performed (S104). For example, the processing operations are repeatedly performed for each frame or every plurality of frames.

<FIG> is a flowchart illustrating the operations of video display apparatus <NUM>. Video display apparatus <NUM> starts a tone mapping process at the same time as it starts displaying the video. At this time, video display apparatus <NUM> determines whether the graphics overlay flag is set to ON or OFF (S111). If it is determined that the graphics overlay flag is set to OFF (No in S111), video display apparatus <NUM> connects switches SW1 and SW2 to A so as to perform a tone mapping process based on the main video dynamic metadata and update the tone mapping (S112). That is, coefficient calculator <NUM> calculates the tone mapping coefficient based on the main video dynamic metadata at the current time, and tone mapper <NUM> performs a tone mapping process on the video at the current time by using the calculated tone mapping coefficient. At this time, coefficient storage <NUM> stores the newly calculated tone mapping coefficient.

When the graphics overlay flag is set to ON (Yes in Sill), video display apparatus <NUM> connects switches SW1 and SW2 to B so as to fix the tone mapping (S113). Specifically, as a result of the input terminal of coefficient storage <NUM> being connected to the output terminal of coefficient storage <NUM>, coefficient storage <NUM> stores the tone mapping coefficient immediately before switch SW2 is switched from A to B. Also, switch SW1 is connected to B, and thus the tone mapping coefficient used by tone mapper <NUM> is fixed. Accordingly, the variation of tone mapping with time is eliminated.

Also, when the graphics overlay flag is set to OFF (No in S111), the variation of the tone mapping coefficient with time starts (S112). The processing operations in steps S111 to S113 are repeatedly performed until the reception of the video is completed or an operation to turn off the display is performed (S114). For example, the processing operations are repeatedly performed for each frame or every plurality of frames.

As described above, video display system <NUM> according to the present embodiment includes tone mapping processor <NUM> that performs a tone mapping process of converting the luminance of a video by using conversion characteristics according to the maximum luminance of the video and display <NUM> that displays the video that has undergone the tone mapping process. Tone mapping processor <NUM> switches between the first tone mapping process of dynamically changing the conversion characteristics according to the time-dependent change in the maximum luminance of the video (S112) and the second tone mapping process that is performed using constant conversion characteristics irrespective of the time-dependent change in the maximum luminance of the video (S113).

With this configuration, the processing can be switched according to, for example, the type of video or the like between dynamically changing the conversion characteristics for use in tone mapping and fixing the same. Accordingly, by either performing optimal tone mapping at each point in time or fixing tone mapping according to the type of video or the like, switching can be performed between suppressing and not suppressing the variation in the luminance of the video that essentially needs to be constant. In this way, video display system <NUM> can improve the quality of a video displayed.

Also, video display system <NUM> further includes a composer (main video composer <NUM> and graphics composer <NUM>) that overlays graphics on the main video to generate the final output video. If graphics are not overlaid on the main video (No in S111), tone mapping processor <NUM> performs the first tone mapping process (S112). If graphics are overlaid on the main video (Yes in S111), tone mapping processor <NUM> performs the second tone mapping process (S113). With this configuration, the variation in the luminance of the graphics can be suppressed.

Also, the composer generates a first flag (graphics overlay flag) that indicates whether or not graphics are overlaid on the main video. Tone mapping processor <NUM> determines, according to the first flag, which of the first tone mapping process and the second tone mapping process is to be performed.

Also, graphics include subtitles and a menu, and the first flag includes a second flag (subtitles overlay flag) that indicates whether or not subtitles are overlaid on the main video and a third flag (menu overlay flag) that indicates whether or not a menu is overlaid on the main video. With this configuration, it is possible to perform a tone mapping process suitable for each of the cases where subtitles are overlaid and where a menu is overlaid.

For example, when switching from the first tone mapping process to the second tone mapping process, tone mapping processor <NUM> continuously uses the conversion characteristics used immediately before the switching in the second tone mapping process. With this configuration, it is possible to suppress a significant variation in the luminance when switching is performed from the first tone mapping process to the second tone mapping process.

According to the invention, as shown in <FIG>, in the second tone mapping process, with respect to a luminance greater than or equal to the border luminance level, tone mapping processor 123A dynamically changes the conversion characteristics according to the time-dependent change in the maximum luminance of the video. With respect to a luminance less than the border luminance level, tone mapping processor 123A uses constant conversion characteristics irrespective of the time-dependent change in the maximum luminance of the video.

With this configuration, with respect to a luminance greater than or equal to the border luminance level, optimal tone mapping can be performed at each point in time, and at the same time, with respect to a luminance less than the border luminance level, it is possible to suppress the luminance variation.

Also, video display apparatus <NUM> according to the present embodiment includes tone mapping processor <NUM> that performs a tone mapping process of converting the luminance of a video by using conversion characteristics according to the maximum luminance of the video and display <NUM> that displays the video that has undergone the tone mapping process. Tone mapping processor <NUM> switches between the first tone mapping process of dynamically changing the conversion characteristics according to the time-dependent change in the maximum luminance of the video (S112) and the second tone mapping process that is performed using constant conversion characteristics irrespective of the time-dependent change in the maximum luminance of the video (S113).

With this configuration, the processing can be switched according to, for example, the type of video or the like between dynamically changing the conversion characteristics for use in tone mapping and fixing the same. Accordingly, by either performing optimal tone mapping at each point in time or fixing tone mapping according to the type of video or the like, switching can be performed between suppressing and not suppressing the variation in the luminance of the video that essentially needs to be constant. In this way, video display apparatus <NUM> can improve the quality of a video displayed.

If it is determined that the video does not contain graphics (No in S111), tone mapping processor <NUM> performs the first tone mapping process (S112). If it is determined that the video contains graphics (Yes in S111), tone mapping processor <NUM> performs the second tone mapping process (S113). With this configuration, it is possible to suppress the variation in the luminance of the graphics.

Also, tone mapping processor <NUM> determines which of the first tone mapping process and the second tone mapping process is to be performed according to the first flag (graphics overlay flag) that indicates which of the first tone mapping process and the second tone mapping process is to be performed.

Also, the first flag includes a second flag (subtitles overlay flag) that indicates whether or not the video contains subtitles and a third flag (menu overlay flag) that indicates whether the video contains a menu. With this configuration, it is possible to perform a tone mapping process suitable for each of the cases where subtitles are overlaid and where a menu is overlaid.

In the present embodiment, in addition to the processing of Embodiment <NUM>, video reproduction apparatus <NUM> embeds graphics luminance information of the graphics to be overlaid on the main video into a portion of the dynamic metadata. Video display apparatus <NUM> switches dynamic tone mapping between on and off or changes the intensity of dynamic tone mapping according to the state of the menu overlay flag and the graphics luminance information. With this configuration, the influence of dynamic tone mapping on the overlaid graphics can be reduced.

Video reproduction apparatus <NUM> according to the present embodiment is different from that of Embodiment <NUM> in terms of the following points. In the case where graphics information is overlaid on the main video, graphics composer <NUM> shown in <FIG> sets the graphics overlay flag to ON, extracts graphics luminance information that is information regarding the luminance of the graphics, and then transmits the extracted graphics luminance information to video transmitter <NUM>. Video transmitter <NUM> transmits the graphics luminance information to video display apparatus <NUM> as a portion of the dynamic metadata. Graphics composer <NUM> may use a pre-set fixed value as the graphics luminance information, or extract luminance information from the graphics information as needed, or acquire the graphics luminance information by referring to metadata provided by other means.

Also, the graphics luminance information may include subtitles luminance information and menu luminance information.

Video display apparatus <NUM> according to the present embodiment is different from that of Embodiment <NUM> in terms of the following points. Metadata acquirer <NUM> shown in <FIG> acquires the graphics luminance information in addition to the main video dynamic metadata and the graphics overlay flag, and transmits these information to tone mapping processor <NUM>. Specifically, tone mapping processor <NUM> has, for example, the configuration shown in <FIG>, and includes coefficient composer <NUM>. In addition to the graphics overlay flag, the graphics luminance information is input to coefficient composer <NUM>, and coefficient composer <NUM> performs processing of composing the tone mapping coefficient by using the graphics luminance information. For example, coefficient composer <NUM> does not change tone mapping with time with respect to a luminance less than or equal to the graphics luminance information. That is, coefficient composer <NUM> uses the graphics luminance information as the border luminance of Embodiment <NUM>.

Also, in Embodiments <NUM> and <NUM>, coefficient composer <NUM> may adjust the border luminance level based on the settings of video display apparatus <NUM>, or the like. Likewise, video reproduction apparatus <NUM> may, instead of transmitting the graphics luminance information directly to video display apparatus <NUM>, adjust the graphics luminance information based on the environment, the type of video reproduced, users' preference or the like, and then transmit the graphics luminance information to video display apparatus <NUM>. By doing so, it is possible to adjust the degree of influence of dynamic tone mapping on the graphics and the degree of adaptation to the main video.

The graphics luminance information may include subtitles luminance information and menu luminance information. In this case, as in Embodiment <NUM>, coefficient composer <NUM> may change the method of composing dynamic tone mapping depending on the subtitles or the menu.

<FIG> is a diagram showing a configuration example of the main video dynamic metadata, the graphics overlay flag, and the graphics luminance information transmitted from video reproduction apparatus <NUM> to video display apparatus <NUM> in the present embodiment. The graphics luminance information shows the maximum luminance of the graphics used. For example, the main video dynamic metadata shows the maximum luminance and the average luminance per frame or more frames.

<FIG> is a diagram showing another configuration example of the main video dynamic metadata, the graphics overlay flag, and the graphics luminance information. As shown in <FIG>, the graphics luminance information may include maximum subtitles luminance and maximum menu luminance.

Also, the graphics luminance information may include the application of the graphics overlay flag. For example, a portion or a specific value of the graphics luminance information may indicate that the graphics overlay flag is set to OFF, and other values may indicate that the graphics overlay flag is set to ON.

<FIG> is a diagram showing a configuration example of the main video dynamic metadata and the graphics luminance information transmitted from video reproduction apparatus <NUM> to video display apparatus <NUM> in this case. In the example shown in <FIG>, the graphics luminance information is <NUM> bit, and indicates a luminance of <NUM> to <NUM> nits. A value of <NUM> indicates that graphics are present, but the luminance is not known. A value of <NUM> indicates that graphics are not present, and other values indicate brightness levels of <NUM> nits to <NUM> nits, with an increment of <NUM> nits. The bit configuration of the graphics luminance information, the brightness range, and the definitions of the value of <NUM>, the value of <NUM> and other values are not limited thereto, and can be changed according to the system requirements.

Also, as shown in <FIG>, the same applies to the case where the graphics luminance information includes subtitles luminance information and menu luminance information.

<FIG> 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 <NUM> nits or less, when the tone mapping varies with time, as can be seen from <FIG>, the luminance at a level from <NUM> to near <NUM> nits also varies, and the subtitles luminance that essentially needs to be constant varies.

In contrast, in Embodiment <NUM>, the occurrence of variation in tone mapping with time can be prevented with respect to a luminance less than or equal to a predetermined border luminance. Accordingly, as can be seen from <FIG>, there is no variation with time below a level of <NUM> nits, which is the subtitles luminance, and thus the subtitles are displayed at a stable luminance level. Here, the border 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 border 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 <NUM> 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 expecting the luminance of graphics data to a predetermined value or less in video display apparatus <NUM>. However, in this case, there is a problem in that, when graphics data having a luminance higher than expected is displayed, the display of the graphics data is susceptible to the influence of dynamic tone mapping.

To address this, Embodiment <NUM> is configured such that the border luminance can be changed based on the subtitles luminance information. Accordingly, as shown in <FIG>, dynamic tone mapping having an even higher degree of freedom can be applied to the main video. <FIG> shows a case where the actual subtitles luminance is <NUM> nits. As shown in <FIG>, 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 level to <NUM> nits as shown in <FIG>. Such an advantageous effect increases as the maximum luminance of video display apparatus <NUM> to which the video reproduction apparatus is connected is lower.

In the present embodiment, video reproduction apparatus <NUM> is configured to embed the graphics luminance information of the graphics to be overlaid on the main video into a portion of the dynamic metadata. Thus, an example of the method for embedding the information will be described.

In the case of reproducing a video on a packaged medium such as a Blu-ray disc, one continuous reproduction path is defined in a file called a playlist and recorded on the disc. In the playlist, reproduction management information such as which of the video streams on the disc is to be reproduced, the start position and the end position of the video stream to be reproduced, and reproduction duration is recorded.

In the playlist, graphics luminance information of the graphics displayed together with the main video, or upper limit information of the luminance range is recorded. With this configuration, video reproduction apparatus <NUM> can easily acquire the graphics luminance information of the graphics displayed together with the main video, or the upper limit information of the luminance range, and transmit the acquired information to video display apparatus <NUM>.

The graphics luminance information may include subtitles luminance information and menu luminance information. Also, in the case where subtitles or a menu can be selected from a plurality of languages or a plurality of versions, the graphics luminance information may include a plurality of subtitles luminance information or a plurality of menu luminance information corresponding to the plurality of languages or the plurality of versions. In this case, the plurality of subtitles luminance information or the plurality of menu luminance information may be recorded in the playlist.

Furthermore, the graphics luminance information may indicate not only the maximum luminance during reproduction of the playlist, but also the maximum luminance per scene or per unit time, together with the reproduction time information.

The graphics luminance information stored in the playlist may be MaxSLL shown in <FIG>. MaxSLL is at least one of the graphics maximum luminance of the graphics to be overlaid on the main video and the minimum luminance of dynamic tone mapping on the main video.

The details of Blu-ray and Ultra HD Blu-ray are disclosed in, for example, Non-Patent Literature (NPL) <NUM>.

As described above, in the present embodiment, tone mapping processor 123A sets the border luminance according to the graphics luminance. As a result, an appropriate border luminance can be set according to the type of graphics or the like, and it is therefore possible to expand the luminance range to which dynamic tone mapping can be applied.

Embodiments <NUM>,<NUM> and <NUM> do not fall under the invention. The description thereof may however be useful for the understanding.

In addition to the processing of video display apparatus <NUM> of Embodiment <NUM>, video display apparatus <NUM> according to the present embodiment detects the position of graphics overlaid on the main video by using an inter-frame correlation or the like. Video display apparatus <NUM> performs tone mapping that does not vary with time on the pixels where graphics are overlaid, without performing dynamic tone mapping. With this configuration, the influence of dynamic tone mapping on the graphics can be reduced.

Hereinafter, a configuration of video display system <NUM> according to the present embodiment will be described. Video reproduction apparatus <NUM> has the same configuration as that of Embodiment <NUM>. Video reproduction apparatus <NUM> does not need to have a function of transmitting the graphics overlay flag to video display apparatus <NUM>.

Tone mapping processor 123B included in video display apparatus <NUM> has a configuration different from that of Embodiment <NUM>. <FIG> is a block diagram showing a configuration of tone mapping processor 123B according to the present embodiment. Tone mapping processor 123B shown in <FIG> includes graphics detector <NUM> in addition to the structural elements of tone mapping processor 123A shown in <FIG>.

A video signal is input to graphics detector <NUM>. Graphics detector <NUM> detects the positions of pixels on which graphics are overlaid by using an inter-frame correlation or the like. Then, graphics detector <NUM> outputs per-pixel information that indicates whether graphics are overlaid to coefficient composer <NUM>.

In the case where the graphics overlay flag is set to ON, with respect to the pixels where graphics are not overlaid, coefficient composer <NUM> outputs the tone mapping coefficient calculated based on the main video dynamic metadata to tone mapper <NUM>. With respect to the pixels on which graphics are overlaid, coefficient composer <NUM> outputs the tone mapping coefficient that does not vary with time to tone mapper <NUM>.

Also, in the case where the graphics overlay flag is not transmitted from video reproduction apparatus <NUM>, coefficient composer <NUM> performs processing of composing a tone mapping coefficient by using the per-pixel information that indicates whether graphics are overlaid, which was detected by graphics detector <NUM>. That is, coefficient composer <NUM> may generate a graphics overlay flag based on the output signal of graphics detector <NUM>.

For example, if graphics detector <NUM> detects that graphics are present on one or a pre-set number of pixels in a frame or a frame group to be processed, coefficient composer <NUM> sets the graphics overlay flag to ON and performs processing, assuming that graphics are overlaid.

In this case, tone mapper <NUM> performs processing by taking into consideration a time delay due to the processing time of graphics detector <NUM>. For example, the time delay is set in tone mapper <NUM> in advance.

Also, tone mapper <NUM> may determine that graphics are present if it is determined that the number of pixels detected as graphics exceeds a threshold value. With this configuration, it is possible to suppress an erroneous detection of graphics. The threshold value may be changed by a user.

As described above, tone mapping processor 123B detects a graphics region in the video where graphics are overlaid, and then performs the second tone mapping process on the graphics region and performs the first tone mapping process on a region in the video other than the graphics region. With this configuration, tone mapping can be fixed with respect to the graphics, and dynamic tone mapping can be performed on a region other than the graphics.

Unlike Embodiment <NUM>, the present embodiment is configured such that video reproduction apparatus 101A does not generate the graphics overlay flag, and video display apparatus <NUM> does not have the function of changing dynamic tone mapping based on the graphics overlay flag. Instead, video reproduction apparatus 101A performs processing of converting the graphics luminance.

Specifically, maximum luminance information of video display apparatus <NUM> connected to video reproduction apparatus 101A is set in video reproduction apparatus 101A. Video reproduction apparatus 101A changes the graphics luminance of graphics to be overlaid according to the maximum luminance information so as to minimize the influence of tone mapping performed in video display apparatus <NUM>. With this configuration, the influence of dynamic tone mapping on the overlaid graphics can be reduced.

Video reproduction apparatus 101A may acquire the maximum luminance information of video display apparatus <NUM> from settings set by an operator, or may acquire the same from video display apparatus <NUM> based on EDID stored in HDMI connected to video reproduction apparatus 101A. There are various methods for tone mapping performed in video display apparatus <NUM>, and thus video reproduction apparatus 101A adjusts the graphics luminance within a predetermined range. Video reproduction apparatus 101A may perform the adjustment based on an operation performed by an operator, or based on information acquired from the database of each video display apparatus <NUM>.

Hereinafter, a configuration of video reproduction apparatus 101A according to the present embodiment will be described. <FIG> is a block diagram showing the configuration of video reproduction apparatus 101A according to the present embodiment. Video reproduction apparatus 101A shown in <FIG> includes maximum luminance setter <NUM> and luminance converter <NUM> in addition to the structural elements of video reproduction apparatus <NUM> according to Embodiment <NUM>.

Maximum luminance setter <NUM> acquires and stores the maximum luminance information of video display apparatus <NUM>. For example, the maximum luminance information may be set based on an operation performed by a user, or may be acquired via a video signal transmission apparatus as attribute information of video display apparatus <NUM> connected to video reproduction apparatus 101A. For example, maximum luminance setter <NUM> may acquire the maximum luminance information of video display apparatus <NUM> as EDID of HDMI. Alternatively, maximum luminance setter <NUM> may acquire the attribute information of video display apparatus <NUM> from a database in a server on a network.

The graphics information generated by graphics composer <NUM> is input to luminance converter <NUM>. Luminance converter <NUM> converts the luminance of the graphics information based on the maximum luminance information of video display apparatus <NUM> stored in maximum luminance setter <NUM>, and transmits the graphics information that has undergone conversion to main video composer <NUM>. Main video composer <NUM> overlays the graphics information that has undergone conversion on the main video.

For example, in the case where the maximum luminance of video display apparatus <NUM> is <NUM> nits, and the maximum luminance of the graphics information is <NUM> nits, luminance converter <NUM> converts the maximum luminance of the graphics information to <NUM> nits, which is <NUM>% of the maximum luminance of video display apparatus <NUM>. As a result, it is possible to reduce the influence of tone mapping in video display apparatus <NUM>.

The conversion condition and proportion (<NUM>% described above) are not limited to those described above. Also, these may be changed by a user, or may be changed according to the characteristics of video display apparatus <NUM> to which the video reproduction apparatus is connected.

As described above, video display system <NUM> according to the present embodiment includes display <NUM>, luminance converter <NUM> that generates a second video by converting the luminance of a first video according to the maximum luminance of display <NUM>, and tone mapping processor <NUM> that performs a tone mapping process of generating a third video by converting the luminance of the second video by using conversion characteristics according to the maximum luminance of the second video. Display <NUM> displays the third video. With this configuration, it is possible to suppress a luminance variation caused by variation of tone mapping.

Specifically, luminance converter <NUM> generates the second video by converting the luminance of graphics included in the first video according to the maximum luminance of display <NUM>. With this configuration, it is possible to suppress a variation in the luminance of the graphics.

Unlike Embodiment <NUM>, the present embodiment is configured such that video reproduction apparatus 101B assumes a dynamic tone mapping method in video display apparatus <NUM>, and performs, on graphics to be overlaid, inverse conversion of the dynamic tone mapping in video display apparatus <NUM> before the graphics are overlaid. With this configuration, after dynamic tone mapping has been performed, the overlaid graphics can be displayed at the original luminance and color of the graphics.

For example, video reproduction apparatus 101B assumes the dynamic tone mapping method in video display apparatus <NUM> to which video reproduction apparatus 101B is connected, by using the following means. Video reproduction apparatus 101B assumes the dynamic tone mapping method simply based on video luminance information corresponding to, for example, <NUM>% of the maximum luminance of video display apparatus <NUM> as the maximum luminance that is free from influence. To be more specific, video reproduction apparatus 101B acquires the dynamic tone mapping method in video display apparatus <NUM> from a database. Alternatively, video reproduction apparatus 101B may perform measurement by using a test pattern, and estimates the dynamic tone mapping method based on the result of measurement.

Hereinafter, a configuration of video reproduction apparatus 101A according to the present embodiment will be described. <FIG> is a block diagram showing a configuration of video reproduction apparatus 101B according to the present embodiment.

Video reproduction apparatus 101B shown in <FIG> is different from video reproduction apparatus 101A according to Embodiment <NUM> shown in <FIG> in that video reproduction apparatus 101B includes tone mapping information storage <NUM> in place of maximum luminance setter <NUM>. Also, the main video dynamic metadata output from metadata acquirer <NUM> is transmitted to luminance converter <NUM>.

Tone mapping information storage <NUM> stores tone mapping information related to the tone mapping process performed in video display apparatus <NUM>. Luminance converter <NUM> performs, on the graphics information, inverse conversion of the tone mapping performed in video display apparatus <NUM> by using the tone mapping information and the main video dynamic metadata, and outputs the graphics information that has undergone the inverse conversion to main video composer <NUM>. Main video composer <NUM> overlays, on the main video, the graphics that have undergone the inverse conversion of the tone mapping.

With this configuration, when tone mapping is performed in video display apparatus <NUM> that has received a video signal, the graphics portion that has undergone the inverse conversion of the tone mapping is displayed as original graphics. Accordingly, the influence of tone mapping of video display apparatus <NUM> can be reduced.

<FIG> a diagram showing an example of tone mapping used in video display apparatus <NUM>. <FIG> is a diagram showing an example of tone mapping information used in this case. For example, the tone mapping information includes the luminance information of video display apparatus <NUM> and the tone mapping information of video display apparatus <NUM>. The luminance information of video display apparatus <NUM> indicates the maximum luminance of video display apparatus <NUM> and the maximum full-display luminance that is the maximum luminance that can be displayed simultaneously in all pixels. Also, the tone mapping information of video display apparatus <NUM> indicates inflection points in the tone mapping, and indicates, for example, luminance values at the inflection points or an increase of a slope between inflection points.

The configuration of the tone mapping information is not limited to that described above. For example, the tone mapping information may include only a portion of information shown in <FIG>.

The condition or proportion (for example, <NUM>% described above) of the inverse conversion of the tone mapping in video display apparatus <NUM> may be changed by a user, or may be changed for each video display apparatus <NUM> to which the video reproduction apparatus is connected.

Also, video reproduction apparatus 101B may acquire the tone mapping information of video display apparatus <NUM> from settings set by a user, or may acquire via a video signal transmission apparatus as attributes of video display apparatus <NUM> connected to video reproduction apparatus 101B. For example, video reproduction apparatus 101B may acquire the tone mapping information as EDID of HDMI. Alternatively, video reproduction apparatus 101B may acquire the attribute information of video display apparatus <NUM> to which video reproduction apparatus 101B is connected from a database in a server on a network.

As described above, video display system <NUM> according to the present embodiment includes luminance converter <NUM> that generates a second video by converting the luminance of a first video, tone mapping processor <NUM> that performs a tone mapping process of generating a third video by converting the luminance of the second video by using conversion characteristics according to the maximum luminance of the second video, and display <NUM> that displays the third video. Luminance converter <NUM> converts the luminance of the first video according to the tone mapping process performed by tone mapping processor <NUM>. With this configuration, it is possible to suppress a luminance variation caused by variation of tone mapping.

Specifically, luminance converter <NUM> converts the luminance of the first video based on the maximum luminance of the first video and the conversion characteristics used in the tone mapping process performed by tone mapping processor <NUM>.

The HDR video acquired by acquirer <NUM> 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 <NUM> 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 <NUM> may include the processors other than acquirer <NUM>. Also, video receiver <NUM>, metadata acquirer <NUM>, and tone mapping processor <NUM> included in video display apparatus <NUM> may be incorporated in the video reproduction apparatus. Also, among the processors included in tone mapping processor <NUM>, the video reproduction apparatus may include the processors other than tone mapper <NUM>.

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.

In Embodiment <NUM>, an example has been shown in which the tone mapping information of the video display apparatus is defined by two inflection points, but may be defined by three or more inflection points, or may be defined by a curved line.

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.

Also, the processors included in the video display 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 display system.

Claim 1:
A video display apparatus (<NUM>), comprising:
a tone mapping processor (<NUM>) adapted to perform a tone mapping process of converting a luminance of a video by using conversion characteristics according to a maximum luminance of the video; and
a display (<NUM>) adapted to display the video that has undergone the tone mapping process;
characterized in that the tone mapping processor (<NUM>) is adapted
(i) to switch, according to a first flag (graphics overlay flag), between
(a) a first tone mapping process of dynamically changing the conversion characteristics according to a time-dependent change in the maximum luminance of the video and
(b) a second tone mapping process that is performed
using, with respect to a luminance less than a border luminance level,
constant conversion characteristics irrespective of the change in the maximum luminance of the video, and
dynamically changing, with respect to a luminance greater than or equal to the border luminance level, the conversion characteristics according to the time-dependent change in the maximum luminance of the video;
wherein the first flag (graphics overlay flag) indicates whether or not graphics are overlaid on a main video in a generating of the video;
(ii) to perform the first tone mapping process when the first flag (graphics overlay flag) indicates that graphics are not overlaid on the main video; and
(iii) to perform the second tone mapping process when the first flag (graphics overlay flag) indicates that graphics are overlaid on the main video.