Patent Publication Number: US-2023162334-A1

Title: Dynamic Tone Mapping

Description:
BACKGROUND 
     Field 
     This disclosure is generally directed to presenting multimedia content, and more particularly to dynamic tone mapping of video content. 
     Background 
     Content, such as a movie or television (TV) show, is typically displayed on a TV display panel according to the capabilities of the display panel. Such content can be provided to a TV in lower-luminance standard definition range (SDR) or higher-luminance high dynamic range (HDR). SDR video is typically mastered at 48 nits (candelas per square meter (cd/m 2 )) for cinema applications and 100 nits for consumer TV applications, whereas HDR video can be mastered at much higher luminance levels up to 10,000 nits, but most commonly at either 1,000 nits or 4,000 nits. However, modern display panels are rarely capable of producing the high luminance levels of HDR video and are commonly limited to only a few thousand nits at peak level but often even much lower. As a result, a proper mapping from the source content to the display panel is necessary. 
     SUMMARY 
     Provided herein are system, apparatus, article of manufacture, method and/or computer program product embodiments, and/or combinations and sub-combinations thereof, for dynamic tone mapping of video content. The dynamic tone mapping techniques disclosed herein can convert a video signal with a higher dynamic range into a video signal with a lower dynamic range in which the conversion is based on a frame-by-frame analysis of the higher dynamic range video signal. 
     An example embodiment is directed to a computer-implemented method for dynamic tone mapping of video content. The computer-implemented method operates by identifying, by a dynamic tone mapping system executing on a media device, characteristics of a first video signal having a first dynamic range based on a frame-by-frame analysis of the first video signal. The computer-implemented method further operates by modifying, by the dynamic tone mapping system, a tone mapping curve based on the characteristics of the first video signal to generate a modified tone mapping curve. Subsequently, the computer-implemented method operates by converting, by the dynamic tone mapping system, the first video signal based on the modified tone mapping curve to generate a second video signal having a second dynamic range that is less than the first dynamic range. 
     Another example embodiment is directed to a system that includes a memory and at least one processor coupled to the memory and configured to perform operations for dynamic tone mapping of video content. The operations can include identifying characteristics of a first video signal having a first dynamic range based on a frame-by-frame analysis of the first video signal. The operations can further include modifying, by the dynamic tone mapping system, a tone mapping curve based on the characteristics of the first video signal to generate a modified tone mapping curve. Subsequently, the operations can include converting the first video signal based on the modified tone mapping curve to generate a second video signal having a second dynamic range that is less than the first dynamic range. 
     Yet another example embodiment is directed to a non-transitory computer-readable medium having instructions stored thereon that, when executed by a computing device, cause the computing device to perform operations for dynamic tone mapping of video content. The operations can include identifying characteristics of a first video signal having a first dynamic range based on a frame-by-frame analysis of the first video signal. The operations can further include modifying, by the dynamic tone mapping system, a tone mapping curve based on the characteristics of the first video signal to generate a modified tone mapping curve. Subsequently, the operations can include converting the first video signal based on the modified tone mapping curve to generate a second video signal having a second dynamic range that is less than the first dynamic range. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings are incorporated herein and form a part of the specification. 
         FIG.  1    illustrates a block diagram of a multimedia environment, according to some embodiments. 
         FIG.  2    illustrates a block diagram of a streaming media device, according to some embodiments. 
         FIG.  3    illustrates a block diagram of an example dynamic tone mapping system, according to some embodiments. 
         FIG.  4    illustrates dynamic tone mapping data for linear and roll off mapping, according to some embodiments. 
         FIG.  5    illustrates dynamic tone mapping data having a knee point for roll off mapping, according to some embodiments. 
         FIG.  6    illustrates dynamic tone mapping data for domain conversion, according to some embodiments. 
         FIG.  7    illustrates dynamic tone mapping data for dark scene adjustment, according to some embodiments. 
         FIG.  8    illustrates histogram data for dark scene adjustment, according to some embodiments. 
         FIG.  9    illustrates dynamic tone mapping data for bright scene adjustment, according to some embodiments. 
         FIG.  10    illustrates binarized histogram data for local contrast adjustment, according to some embodiments. 
         FIG.  11    illustrates dynamic tone mapping data for local contrast adjustment, according to some embodiments. 
         FIG.  12    is a flowchart illustrating a process for dynamic tone mapping, according to some embodiments. 
         FIG.  13    illustrates an example computer system useful for implementing various embodiments. 
     
    
    
     In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. 
     DETAILED DESCRIPTION 
     Provided herein are system, apparatus, device, method and/or computer program product embodiments, and/or combinations and sub-combinations thereof, for dynamic tone mapping of video content. For instance, the disclosed embodiments may provide for implementing dynamic tone mapping by converting a video signal with a higher dynamic range into a video signal with a lower dynamic range in which the conversion is based on a frame-by-frame analysis of the higher dynamic range video signal. 
     In one illustrative and non-limiting example embodiment, there may exist a mismatch between the luminance range of the source (e.g., broadcasted or streamed video content) and the luminance range supported by the display panel. For instance, the luminance range of the source may be higher than the luminance range of the display panel. As a consequence, a down-conversion, referred to as “tone mapping,” may be necessary in order to represent the content in a proper manner. With exception of the hybrid log gamma (HLG) HDR format, HDR formats often provide metadata describing the characteristics of the content. For HDR10+®, Technicolor®, and Dolby Vision®, this metadata can be updated on frame-by-frame basis, but more often is adjusted on scene-by-scene basis. In contrast, for HDR10, this metadata, called maximum content light level (MaxCLL), is static for the whole program or movie. MaxCLL is a measure of the maximum light level of any single pixel of the entire sequence or movie measured in nits (cd/m 2 ). The scene-based adjustment for some of the HDR formats provides a means to optimally adjust the tone mapping per scene. For HDR10, this is, however, not directly possible, as the scene-based metadata is not provided by the source. Therefore, the tone mapping for HDR10 is substantially sub-optimal. Additionally, the receiver has no control over the source and therefore cannot request extra scene-based metadata. However, the receiver can analyze the content, collecting various statistics, and adjust the tone mapping on a scene-by-scene basis based on those statistics, even in situations where only static metadata has been provided (as is the case for HDR10). For example, the receiver can generate scene-based metadata for HDR10 content by collecting statistics of the last several frames (e.g., history). As such, the receiver can effectively apply an autonomous, or near-autonomous, dynamic tone mapping of HDR10 content. 
     In another example, tone mapping can compress the content, resulting in some compression-based losses. A simple approach would be to truthfully represent all that is possible, and hard clip what is not. However, this approach may be unacceptable because it results in annoying artefacts and a significant loss of details (e.g., in bright picture parts if present in the content). An improved approach is to properly represent the scenes for darker and mid gray levels and start gradually compressing them for higher luminance levels. This approach results in a more graceful degradation of the picture quality and thus the loss of details tends to be less noticeable. If a scene contains luminance within the available luminance range of the display, then no compression may be necessary and therefor no visible losses may occur. However, if another scene contains luminance that exceeds that of the available luminance range of the display, range compression may be necessary, resulting in some losses. When the per-scene characteristics are not known, as is the situation with HDR10 video, the tone mapping may utilize a static (e.g., fixed) curve that implements compression and thereby inherently produces some losses, even for content that can fit within the display luminance range. 
     In contrast, the disclosed embodiments may provide for dynamic tone mapping by identifying characteristics of video content (e.g., HDR10 content) using a frame-by-frame analysis technique and updating or modifying the static tone mapping curve that implements compression to more closely match the current scene of the video content. 
     Various embodiments of this disclosure may be implemented using and/or may be part of a multimedia environment  102  shown in  FIG.  1   . It is noted, however, that multimedia environment  102  is provided solely for illustrative purposes, and is not limiting. Embodiments of this disclosure may be implemented using and/or may be part of environments different from and/or in addition to the multimedia environment  102 , as will be appreciated by persons skilled in the relevant art(s) based on the teachings contained herein. An example of the multimedia environment  102  shall now be described. 
     Multimedia Environment 
       FIG.  1    illustrates a block diagram of a multimedia environment  102 , according to some embodiments. In a non-limiting example, multimedia environment  102  may be directed to streaming media. However, this disclosure is applicable to any type of media (instead of or in addition to streaming media), as well as any mechanism, means, protocol, method and/or process for distributing media. 
     The multimedia environment  102  may include one or more media systems  104 . A media system  104  could represent a family room, a kitchen, a backyard, a home theater, a school classroom, a library, a car, a boat, a bus, a plane, a movie theater, a stadium, an auditorium, a park, a bar, a restaurant, or any other location or space where it is desired to receive and play streaming content. User(s)  132  may operate with the media system  104  to select and consume content. 
     Each media system  104  may include one or more media devices  106  each coupled to one or more display devices  108 . It is noted that terms such as “coupled,” “connected to,” “attached,” “linked,” “combined” and similar terms may refer to physical, electrical, magnetic, logical, etc., connections, unless otherwise specified herein. 
     Media device  106  may be part of a smart TV, to name just one example. Display device  108  may be a display panel that is also a part of the smart TV. In some embodiments, media device  106  can be a part of, integrated with, operatively coupled to, and/or connected to its respective display device  108  such that the media device  106  can obtain display panel information from the display device  108 . 
     Each media device  106  may include a dynamic tone mapping system  107  for performing dynamic tone mapping of content  122  received from the one or more content servers  120 . In some embodiments, there may exist a mismatch between the luminance range provided for by the content  122  (e.g., the source video content) and the luminance range supported by the display device  108 . In such embodiments, the dynamic tone mapping system  107  can utilize a dynamic tone mapping technique to modify the content  122  received from the one or more content servers  120  for output to the display device  108 . In some embodiments, each dynamic tone mapping system  107  may be built into the hardware and software of each media device  106  as described below with reference to  FIG.  3   . 
     Each media device  106  may be configured to communicate with network  118  via a communications device  114 . The communications device  114  may include, for example, a cable modem or satellite TV transceiver. The media device  106  may communicate with the communications device  114  over a communications path  116 , wherein the communications path  116  may include wireless (such as Wi-Fi) and/or wired connections. 
     In various embodiments, the network  118  can include, without limitation, wired and/or wireless intranet, extranet, Internet, cellular, Bluetooth, infrared, and/or any other short range, long range, local, regional, global communications mechanism, means, approach, protocol and/or network, as well as any combination(s) thereof. 
     Media system  104  may include a remote control  110 . The remote control  110  can be any component, part, apparatus and/or method for controlling the media device  106  and/or display device  108 , such as a remote control, a tablet, laptop computer, smartphone, wearable, on-screen controls, integrated control buttons, audio controls, or any combination thereof, to name just a few examples. In an embodiment, the remote control  110  wirelessly communicates with the media device  106  and/or display device  108  using cellular, Bluetooth, infrared, etc., or any combination thereof. The remote control  110  may include a microphone  112 , which is further described below. As used herein, the term “remote control” refers to any device that can be used to control the media device  106 , such as a virtual remote on any client device (e.g., smart phone, tablet, etc.) with features that include, for example, video capture and presentation, audio capture and presentation, chat capture and presentation, and other suitable features. 
     The multimedia environment  102  may include a plurality of content servers  120  (also called content providers or sources). Although only one content server  120  is shown in  FIG.  1   , in practice the multimedia environment  102  may include any number of content servers  120 . Each content server  120  may be configured to communicate with network  118 . 
     Each content server  120  may store content  122  and metadata  124 . Content  122  may include any combination of music, videos, movies, TV programs, multimedia, images, still pictures, text, graphics, gaming applications, advertisements, programming content, public service content, government content, local community content, software, and/or any other content or data objects in electronic form. 
     In some embodiments, metadata  124  includes data about content  122 . For example, metadata  124  may include associated or ancillary information indicating or related to writer, director, producer, composer, artist, actor, summary, chapters, production, history, year, trailers, alternate versions, related content, applications, and/or any other information pertaining or relating to the content  122 . Metadata  124  may also or alternatively include links to any such information pertaining or relating to the content  122 . Metadata  124  may also or alternatively include one or more indexes of content  122 , such as but not limited to a trick mode index. 
     The multimedia environment  102  may include one or more system servers  126 . The system servers  126  may operate to support the media devices  106  from the cloud. It is noted that the structural and functional aspects of the system servers  126  may wholly or partially exist in the same or different ones of the system servers  126 . 
     The media devices  106  may exist in thousands or millions of media systems  104 . Accordingly, the media devices  106  may lend themselves to crowdsourcing and watch party embodiments and, thus, the system servers  126  may include one or more crowdsource servers  128 . 
     For example, using information received from the media devices  106  in the thousands and millions of media systems  104 , the crowdsource server(s)  128  may identify similarities and overlaps between closed captioning requests issued by different users  132  watching a particular movie. Based on such information, the crowdsource server(s)  128  may determine that turning closed captioning on may enhance users’ viewing experience at particular portions of the movie (for example, when the soundtrack of the movie is difficult to hear), and turning closed captioning off may enhance users’ viewing experience at other portions of the movie (for example, when displaying closed captioning obstructs critical visual aspects of the movie). Accordingly, the crowdsource server(s)  128  may operate to cause closed captioning to be automatically turned on and/or off during future streamings of the movie. 
     The system servers  126  may also include an audio command processing module  130 . As noted above, the remote control  110  may include a microphone  112 . The microphone  112  may receive audio data from users  132  (as well as other sources, such as the display device  108 ). In some embodiments, the media device  106  may be audio responsive, and the audio data may represent verbal commands from the user  132  to control the media device  106  as well as other components in the media system  104 , such as the display device  108 . 
     In some embodiments, the audio data received by the microphone  112  in the remote control  110  is transferred to the media device  106 , which is then forwarded to the audio command processing module  130  in the system servers  126 . The audio command processing module  130  may operate to process and analyze the received audio data to recognize the user  132 ’s verbal command. The audio command processing module  130  may then forward the verbal command back to the media device  106  for processing. 
     In some embodiments, the audio data may be alternatively or additionally processed and analyzed by an audio command processing module  216  in the media device  106  (see  FIG.  2   ). The media device  106  and the system servers  126  may then cooperate to pick one of the verbal commands to process (either the verbal command recognized by the audio command processing module  130  in the system servers  126 , or the verbal command recognized by the audio command processing module  216  in the media device  106 ). 
       FIG.  2    illustrates a block diagram of an example media device  106 , according to some embodiments. Media device  106  may include a streaming module  202 , processing module  204 , storage/buffers  208 , and user interface module  206 . As described above, the user interface module  206  may include the audio command processing module  216 . In some embodiments, the media device  106  can further include an ambient light sensor (ALS) configured to detect ambient and generate ambient light measurements. 
     The media device  106  may also include one or more audio decoders  212  and one or more video decoders  214 . Each audio decoder  212  may be configured to decode audio of one or more audio formats, such as but not limited to AAC, HE-AAC, AC3 (Dolby Digital), EAC3 (Dolby Digital Plus), WMA, WAV, PCM, MP3, OGG GSM, FLAC, AU, AIFF, and/or VOX, to name just some examples. Similarly, each video decoder  214  may be configured to decode video of one or more video formats, such as but not limited to MP4 (mp4, m4a, m4v, f4v, f4a, m4b, m4r, f4b, mov), 3GP (3gp, 3gp2, 3g2, 3gpp, 3gpp2), OGG (ogg, oga, ogv, ogx), WMV (wmv, wma, asf), WEBM, FLV, AVI, QuickTime, HDV, MXF (OP1a, OP-Atom), MPEG-TS, MPEG-2 PS, MPEG-2 TS, WAV, Broadcast WAV, LXF, GXF, and/or VOB, to name just some examples. Each video decoder  214  may include one or more video codecs, such as but not limited to H.263, H.264, H.265, HEV, MPEG1, MPEG2, MPEG-TS, MPEG-4, Theora, 3GP, DV, DVCPRO, DVCPRO, DVCProHD, IMX, XDCAM HD, XDCAM HD422, and/or XDCAM EX, to name just some examples. 
     Now referring to both  FIGS.  1  and  2   , in some embodiments, the user  132  may interact with the media device  106  via, for example, the remote control  110 . For example, the user  132  may use the remote control  110  to interact with the user interface module  206  of the media device  106  to select content, such as a movie, TV show, music, book, application, game, etc. The streaming module  202  of the media device  106  may request the selected content from the content server(s)  120  over the network  118 . The content server(s)  120  may transmit the requested content to the streaming module  202 . The media device  106  may transmit the received content to the display device  108  for playback to the user  132 . 
     In streaming embodiments, the streaming module  202  may transmit the content to the display device  108  in real time or near real time as it receives such content from the content server(s)  120 . In non-streaming embodiments, the media device  106  may store the content received from content server(s)  120  in storage/buffers  208  for later playback on display device  108 . 
     Dynamic Tone Mapping 
     Referring to  FIG.  1   , the media devices  106  and display devices  108  may exist in thousands or millions of media systems  104 . The luminance ranges supported by some of the display devices  108  may be less than the luminance ranges of the source content (e.g., content  122 ). Accordingly, the media devices  106  may lend themselves to dynamic tone mapping embodiments to modify, using dynamic tone mapping systems  107  executing in the media devices  106 , the content  122  received from the one or more content servers  120  for output to their respective display devices  108 . 
     For example,  FIG.  3    illustrates a block diagram of a dynamic tone mapping system  300 , according to some embodiments. As shown in  FIG.  3   , the dynamic tone mapping system  300  may include software  310  and hardware  320 . An analysis system  312 , a tone mapping (TM) curve calculation system  314 , and a temporal filtering system  316  can be implemented in the software  310 . A tone mapping curve look-up-table  322  can be implemented in the hardware  320 . 
     In a non-limiting example, the analysis system  312  can analyze histogram data  302  (e.g., collected by hardware  320 ) to determine a value representative for the current brightness of the scene for use as a control point into the TM curve calculation. The analysis system  312  can transmit the determined value to the TM curve calculation system  314 , which can determine a TM curve based on the value received from the analysis system  312  as well as display panel characteristics  304  (e.g., luminance range, etc.) and user settings  306  (e.g., brightness, refresh rate, etc.) associated with the display device  108 . The TM curve calculation system  314  transmits the TM curve to the temporal filtering system  316 , which gradually applies a temporal filter to the TM curve to temporally stabilize the TM curve. The temporal filtering system  316  then sends the final TM curve to the TM curve look-up table (LUT)  322  in the hardware  320 . The temporal filtering system  316  can also be positioned in between the analysis system  312  and the TM curve calculation system  314 . 
     In some embodiments, the analysis system  312  can analyze the histogram data  302  to determine the brightest or “near-brightest” pixel in the picture frame. The histogram can contain the MAX(R, G, B) values from the current frame or any other suitable frame (e.g., previous frame, future frame, etc.). For example, the analysis system  312  can identify the near-brightest pixel by identifying the pixel value which belongs to the top x% of brightest pixels (e.g., by selecting the pixel value below which y% of the pixels values fall). To do so, the analysis system  312  can determine a cumulative histogram based on the histogram data  302 . In some embodiments, the near-brightest pixel, referred to as the scene max S max  value, can be a representative pixel value that defines the maximum target value to be properly displayed. Although potential clipping or loss of details may occur above the scene max S max  value, its impact may be substantially negligible because it is typically limited to a very small percentage (e.g., defined by the threshold). The scene max S max  value may also be limited to a programmable minimum to prevent excessive boosting in dark scenes. 
     In some embodiments, the TM curve determined by the TM curve calculation system  314  can be influenced by the display panel characteristics  304  and the scene characteristics. The display panel characteristics  304  may also be changeable by the user settings  306  (e.g., by reducing the strength of the maximum backlight). As a result, the TM curve calculation system  314  can determine the adjusted maximum luminance of the display device  108 , referred to as the panel max P max  value, based on the display panel characteristics  304  and the user settings  306 . 
     In some embodiments, the TM curve calculation system  314  can optimally represent the current scene within the envelope of the display device  108  (e.g., the envelope may be defined by the adjusted maximum luminance of the display device  108  as represented by the panel max P max  value). For example, if the scene falls fully within the capabilities of the display device  108  (e.g., P max  ≥ S max ), the TM curve calculation system  314  can utilize a “one-to-one” mapping in the linear light domain as shown in input-output graph  402  described with reference to  FIG.  4   . In another example, if the maximum scene luminance as represented by the scene max S max  value is larger than the adjusted panel maximum (e.g., P max  &lt; S max ), the TM curve calculation system  314  can utilize a “roll off” mapping as shown in input-output graph  404  described with reference to  FIG.  4    to substantially prevent hard clipping which could result in a significant loss of details in the brighter picture parts. In some aspects, the scene max S max  value can have a maximum value of up to 10,000 nits (e.g., MaxCLL is limited to 10000 nits) as shown in input-output graph  502  described with reference to  FIG.  5   . 
     In some embodiments, the TM curve calculation system  314  can determine the knee point  504  (described with reference to  FIG.  5   ) at which the roll off (e.g., compression) begins. For example, the TM curve calculation system  314  can determine the coordinates (xknee, )y knee ) of the knee point  504  based upon the relative differences between the panel max P max  value and the scene max S max  value in a perceptual quantizer (PQ) domain according to Equations 1 and 2: 
     
       
         
           
             
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     The TM curve calculation system  314  can define the electro-optical transfer function (EOTF) according to Equation 3 and the opto-electrical transverse function (OETF) according to Equation 4: 
     
       
         
           
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     The TM curve calculation system  314  can define the coefficients as follows: m 1  = 1305/8192; m 2  = 2523/32; c 1  = 107/128; c 2  = 2413/128; and c 3  = 2382/128. 
     In some embodiments, once the TM curve calculation system  314  has determined the knee point  504 , the TM curve calculation system  314  can define a curve (e.g., a three-point Bezier curve) for the roll off between the knee point  504  and the maximum. For example, the TM curve calculation system  314  can define the three control points for the Bezier curve as follows: a knee point P 0  = (xknee, yknee); a mid point P 1  = (Xmid, ymid) that controls the curvature; and an endpoint P 2  = (x end , y end ). The TM curve calculation system  314  can then scale these coordinates within the [0 .. 1] range such that P 2  = (1,1). The TM curve calculation system  314  can define the mid point P 1  = (x mid , y mid ) according to Equation 5: 
     
       
         
           
             
               P 
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             = 
               
             
               
                 
                   x 
                   
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                 + 
                   
                 
                   
                     
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     The TM curve calculation system  314  can define the three-point Bezier curve P according to Equation 6: 
     
       
         
           
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     The TM curve calculation system  314  can define the coordinates xp and y P  of the three-point Bezier curve P according to Equations 7 and 8: 
     
       
         
           
             
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               2 
             
             
               y 
               
                 
                   P 
                   2 
                 
               
             
           
         
       
     
     The TM curve calculation system  314  can resolve Equations 6, 7, and 8 for t = [0 .. 1]. The Bezier curve calculations (Equations 6-8) represent the behavior of the TM curve calculation system  314  in the linear light domain. Since the video input and output may be in a non-linear domain, the TM curve calculation system  314  can perform additional conversions. For example, with the exception of HLG, HDR standards often use the PQ domain, and many display panels expect gamma domain signals. Accordingly, the TM curve calculation system  314  can perform conversion from the PQ domain to the gamma domain together with the tone mapping into a single curve, representing all the necessary conversions as shown in input-output graph  602  described with reference to  FIG.  6   . 
     The axes of the input-output graph  602  represent code values. The horizontal axis represents PQ code words (e.g., input), and the vertical axis represents gamma code words (e.g., output). The scene max S max  value, which is now represented as a code value in the input PQ domain, is aligned with the panel max P max  value, the maximum code word in the output gamma domain. Accordingly, the full gamma range is still being utilized. In some aspects, input pixels with a value larger than the scene max S max  value may be hard clipped, resulting in a loss of details for those pixels and illustrating the need for the TM curve calculation system  314  to determine the scene max S max  value discreetly. 
     In some embodiments, the TM curve calculation system  314  can implement dynamic tone mapping (e.g., tone mapping with dynamic adjustments) by determining additional control points to improve visual performance. 
     For overall darker scenes, the TM curve calculation system  314  can enhance or boost the contrast for better visibility of details in darker picture parts. 
     For overall bright scenes, the TM curve calculation system  314  can limit the roll-off as to better preserve the details in brighter picture parts. 
     The TM curve calculation system  314  can perform smaller, localized contrast adjustments to improve the sharpness impression. 
     In some embodiments, the TM curve calculation system  314  can perform dark scene adjustment. For overall dark scenes, the lower bins of the histograms tend to contain the majority of the pixel count. Therefore, to classify a scene as a dark scene, the cumulative histogram up to a predefined low luminance threshold Th1 can contain a large number of pixels, represented by rwh, where r represents the percentage of pixels, w represents the number of pixels per row (in a frame), and h represents the number of scanning lines. The TM curve calculation system  314  can define the number of dark pixels N DarkPixeis  as shown in Equations 9 and 10: 
     
       
         
           
             
               N 
               
                 DarkPixels 
               
             
               
             &lt; 
               
             r 
             w 
             h 
           
         
       
     
     
       
         
           
             
               N 
               
                 D 
                 a 
                 r 
                 k 
                 P 
                 i 
                 x 
                 e 
                 l 
                 s 
               
             
               
             = 
               
             
               
                 ∑ 
                 
                   i 
                   = 
                   0 
                 
                 k 
               
               
                 H 
                 
                   i 
                 
               
             
           
         
       
     
     Where H represents the histogram (e.g., histogram data  302 ), i represents the index in the histogram, and k represents the matching index just below the low luminance threshold Thl. As an example, r may be equal to 0.99 (99% of the pixels), and Th1 may be a luminance value of 75 on a 10 bits scale. If this condition is satisfied, the TM curve calculation system  314  can identify the scene as a dark scene and apply a dark scene adjustment to the TM curve. 
     Various solutions are possible to realize the desired behavior for darker scenes. For example, the TM curve calculation system  314  can adjust the panel max P max  value (e.g., for the sake of the calculation of the curve only, and thus the true panel max brightness is not adjusted). The TM curve calculation system  314  can recalculate the knee point and Bezier curve based on the adjusted the panel max P max  value. 
     The modified (e.g., lower) panel max P max  value can correspond to the maximum gamma code value (e.g., but still the same scene max S max  value on the PQ axis), and as a result, the scene will become somewhat brighter (e.g., the true panel brightness is not changed and the max gamma code still corresponds to the true panel max value). Consequently, users can see more details and contrast in the darker scene as shown in input-output graph  702  described with reference to  FIG.  7   . The amount of change depends on the “darkness” of the scene and a user controllable factor as shown in Equations 11 and 12: 
     
       
         
           
             
               
                 P 
                 ′ 
               
               
                 max 
               
             
               
             = 
               
             
               P 
               
                 max 
               
             
               
             − 
               
             
               
                 
                   g 
                   
                     100 
                   
                 
               
             
             
               
                 
                   P 
                   
                     max 
                   
                 
                   
                 − 
                   
                 
                   L 
                   
                     dark 
                   
                 
               
             
           
         
       
     
     
       
         
           
             
               L 
               
                 dark 
               
             
               
             &lt; 
               
             
               
                 
                   β 
                   
                     100 
                   
                 
               
             
               
             
               S 
               
                 max 
               
             
           
         
       
     
     Where g represents a user-selectable control in the range [0 .. 100], L dark  represents the luminance value in the PQ domain for which, in one example, 99.5% of the pixels have a pixel value less than or equal to L dark , and β represents a controllable parameter in the range [0 .. 100] that sets a percentage threshold on the maximum value. An example of a histogram reflecting a dark scene is depicted in  FIG.  8   , where most of the pixel values in the frame are located below code level 73, representing a dark scene. 
     In some embodiments, the TM curve calculation system  314  can perform bright scene adjustment. For scenes that are overall bright, the roll off for brighter pixels can have a visible impact as contrast is reduced (e.g., compression). Accordingly, the TM curve calculation system  314  can reduce or limit the roll off by slightly compromising the overall brightness. By doing so, the compression can be spread out over a wider range which can better preserve some of the details in the brighter picture parts (although the overall brightness in the scene may be reduced as a compromise). 
     The TM curve calculation system  314  can detect an overall bright scene by the luminance value for which a programmable percentage of pixels (α) are found to have pixels values above a target luminance value L bright  while at the same time satisfying the inequality L bright  &gt; P max . The TM curve calculation system  314  can calculate this value by accumulating the histogram bins from the higher bins towards the lower bins. A typical value of α may be 25 (25% of the pixels). When the TM curve calculation system  314  determines that at least 25% of the pixels are above the panel max P max  value, the TM curve calculation system  314  can implement a bright scene adjustment by adjusting the panel max P max  value (e.g., only for the sake of the curve calculation) as shown in Equation 13: 
     
       
         
           
             
               
                 P 
                 ′ 
               
               
                 max 
               
             
               
             = 
               
             
               P 
               
                 max 
               
             
               
             − 
               
             
               
                 
                   ρ 
                   
                     100 
                   
                 
               
             
             
               
                 
                   L 
                   
                     bright 
                   
                 
                   
                 − 
                   
                 
                   P 
                   
                     max 
                   
                 
               
             
           
         
       
     
     Where p represents a programmable gain value in the range [0 .. 100]. Accordingly, the maximum gamma code value can be positioned beyond what the display device  108  can represent, and, as a result, all gamma code values are reduced such that the picture becomes darker, leaving more room to preserve detail in brighter picture parts as shown in input-output graph  902  described with reference to  FIG.  9   . 
     In some embodiments, the TM curve calculation system  314  can perform local contrast adjustment. Contrast enhancement can improve the sharpness impression and therefore can be a desired characteristic when properly conducted. The TM curve calculation system  314  can achieve a global contrast enhancement by darkening the dim parts in the scene and brightening the brighter picture parts. The TM curve calculation system  314  can further achieve a local contrast enhancement by stretching the video signal mainly in the mid-tones. However, if some pixels values get stretched out, then other pixels may need to be compressed, resulting in a loss of details. Accordingly, the TM curve calculation system  314  can stretch the pixel values in regions in which substantially no, or very limited, pixels are located. Therefore, the analysis system  312  can analyze the histogram data  302  to identify regions in which significant energy is found next to regions with no significant contribution and output the identified regions to the TM curve calculation system  314 , which can then mark those regions for local stretching as shown as shown in binarized histogram data  1000  described with reference to  FIG.  10   . 
     The TM curve calculation system  314  can select the local contrast adjustment region by moving from left to right and identifying the length of the consecutive “one” bins after binarization. This length can be referred to as η. If at least η/2, and at most 2η, “zero” bins precede the consecutive “one” bins, then these “zero” bins together with the consecutive “one” bins can form the selected local contrast adjustment region. In some aspects, there can be several of these regions within the complete histogram. 
     The TM curve calculation system  314  can perform the tone mapping curve adjustment following the histogram equalization process that is localized only to the selected regions. Assuming that the discrete tone mapping curve is represented by T(i), where i represents the index into the TM curve LUT  322  and H(i) represents the corresponding histogram bin, then the TM curve calculation system  314  can define the local contrast adjustment in the selected region according to Equation 14: 
     
       
         
           
             
               T 
               ′ 
             
             
               i 
             
               
             = 
               
             T 
             
               s 
             
               
             + 
               
             
               
                 
                   
                     H 
                     
                       i 
                     
                       
                     − 
                       
                     H 
                     
                       s 
                     
                   
                   
                     H 
                     
                       e 
                     
                     − 
                     H 
                     
                       s 
                     
                   
                 
               
             
               
             
               
                 T 
                 
                   e 
                 
                   
                 − 
                   
                 T 
                 
                   s 
                 
               
             
           
         
       
     
     Where s and e represent the starting and ending index of the region of interest, respectively. An example of the effect of local contrast adjustment on the tone mapping curve is shown in input-output graph  1102  described with reference to  FIG.  11   . 
     In some embodiments, the temporal filtering system  316  can perform temporal filtering of the TM curves generated by the TM curve calculation system  314 . As the histograms are determined on frame-by-frame basis, differences between histograms can be large from frame to frame. Without the dynamic tone mapping techniques described herein, these differences could result in rather large changes in the tone mapping from frame to frame and produce an annoying flicker. To reduce this unwanted effect, the temporal filtering system  316  can apply a temporal filter to the TM curves generated by the TM curve calculation system  314 . The temporal filter can be, for example, an infinite impulse response (IIR) filter that the temporal filtering system  316  can apply to every point in the LUT as shown in Equation 14: 
     
       
         
           
             
               T 
               
                 filt 
               
             
             
               
                 i 
                 , 
                 n 
               
             
               
             = 
               
             
               
                 T 
                 
                   
                     i 
                     , 
                     n 
                   
                 
                   
                 + 
                   
                 s 
                 
                   
                     
                       T 
                       
                         f 
                         i 
                         l 
                         t 
                       
                     
                     
                       
                         i 
                         , 
                         n 
                         − 
                         1 
                       
                     
                       
                     + 
                       
                     
                       T 
                       
                         f 
                         i 
                         l 
                         t 
                       
                     
                     
                       
                         i 
                         , 
                         n 
                         − 
                         2 
                       
                     
                   
                 
               
               
                 2 
                 s 
                 + 
                 1 
               
             
           
         
       
     
     Where i represents the “bin” position, n represents the frame number, and s represents a programmable strength factor in the range of [0 .. 32]. When s is large, the temporal filtering system  316  can perform a strong temporal filtering and the dampening effect can be strong and adaptation to the scene can be relatively slow. When s is small, the temporal filtering system  316  can perform relatively faster adaptation, but the dampening effect may reduced with a slowly increasing risk of temporal flickering. Accordingly, in some embodiments, the temporal filtering system  316  can utilize temporal filtering that remains constant. In other embodiments, the temporal filtering system  316  can utilize temporal filtering that is reduced to a very low value (or even zero) at a scene change, and increased otherwise. In this way, the adaptation to the new scene can be fast while preserving the dampening effect of the temporal filter. 
     In some embodiments, the dynamic tone mapping system  107  can perform test pattern detection. The dynamic behavior of the tone mapping curve can be a desired feature which improves overall picture quality. However, for certain test patterns (e.g. used by reviewers to measure peak brightness or gamma), it may negatively influence some measurements. Therefore, the dynamic tone mapping system  107  can include a test pattern detector in software  310 . The test pattern detector can detect a test pattern, and once detected, switch the dynamic tone mapping to the static tone mapping. In one example, the test pattern detector can classify a scene as a test pattern if the histogram shows many empty bins (e.g., the energy is concentrated in only a few bins). For instance, if more than 95% of the bins are empty, then the test pattern detector can classify the scene as a test pattern. 
       FIG.  4    illustrates dynamic tone mapping data  400 , according to some embodiments. The dynamic tone mapping data  400  can include input-output graph  402  showing a “one-to-one” mapping in the linear light domain. The dynamic tone mapping data  400  can further include a “roll off” mapping as shown in input-output graph  404 . 
       FIG.  5    illustrates dynamic tone mapping data  500 , according to some embodiments. The dynamic tone mapping data  500  can include input-output graph  502  showing that the scene max S max  value can have a maximum value of up to 10,000 nits (e.g., MaxCLL is limited to 10000 nits). The dynamic tone mapping data  500  can further include knee point  504 , the point at which the roll off (e.g., compression) begins. 
       FIG.  6    illustrates dynamic tone mapping data  600 , according to some embodiments. The dynamic tone mapping data  600  can include input-output graph  602  showing conversion from the PQ domain to the gamma domain together with the tone mapping into a single curve. 
       FIG.  7    illustrates dynamic tone mapping data  700  for dark scene adjustment, according to some embodiments. The dynamic tone mapping data  700  can include input-output graph  702  showing an increase in detail and contrast for a darker scene. 
       FIG.  8    illustrates histogram data  800  for dark scene adjustment, according to some embodiments. The histogram data  800  can reflect a dark scene. 
       FIG.  9    illustrates dynamic tone mapping data  900  for bright scene adjustment, according to some embodiments. The dynamic tone mapping data  900  can include input-output graph  902  showing a reduction in gamma code values such that the picture becomes darker, leaving more room to preserve detail in brighter picture parts. 
       FIG.  10    illustrates binarized histogram data  1000  for local contrast adjustment, according to some embodiments. The binarized histogram data  1000  can be used in the process of selecting regions with significant energy by thresholding the histogram data. To reduce sensitivity to small fluctuations in the histogram  1002 , a down-scaled histogram  1004  can be used. For example, the histogram  1002  can be a 128 bin histogram, and the down-scaled histogram  1004  can be a 64 bin histogram. The threshold can based on the average bin size and a user selectable factor. The binarized histogram can be used to identify the region of interest, which are the transition regions in the binarized histogram (marked as red in the down-scaled histogram  1004 ). 
       FIG.  11    illustrates dynamic tone mapping data  1100  for local contrast adjustment, according to some embodiments. The dynamic tone mapping data  1100  can include input-output graph  1102  that includes a region  1104  showing the effect of local contrast adjustment on the tone mapping curve. 
       FIG.  12    is a flowchart for a method  1200  for dynamic tone mapping, according to an embodiment. Method  1200  can be performed by processing logic that can include hardware (e.g., circuitry, dedicated logic, programmable logic, microcode, etc.), software (e.g., instructions executing on a processing device), or a combination thereof. It is to be appreciated that not all steps may be needed to perform the disclosure provided herein. Further, some of the steps may be performed simultaneously, or in a different order than shown in  FIG.  12   , as will be understood by a person of ordinary skill in the art. Method  1200  shall be described with reference to  FIGS.  1  and  3   . However, method  1200  is not limited to those example embodiments. 
     In  1202 , a dynamic tone mapping system (e.g., dynamic tone mapping system  107 ,  300 ) executing on a media device (e.g., media device  106 ) included in a media system (e.g., media system  104 ) identifies (e.g., using analysis system  312 ) characteristics of a first video signal (e.g., input video signal  307 ) having a first dynamic range based on a frame-by-frame analysis of the first video signal. In some aspects, the characteristics can include histogram data (e.g., histogram data  302 ). In some aspects, the characteristics can include user settings (e.g., user setting  306 ). 
     In  1204 , the dynamic tone mapping system modifies (e.g., using TM curve calculation system  314 ) a tone mapping curve based on the characteristics of the first video signal to generate a modified tone mapping curve. In some aspects, the dynamic tone mapping system can modify the tone mapping curve by temporally filtering (e.g., using temporal filtering system  316 ) the modified tone mapping curve. 
     In  1206 , the dynamic tone mapping system converts (e.g., using TM curve LUT  322 ) the first video signal based on the modified tone mapping curve to generate a second video signal (e.g., output video signal  308 ) having a second dynamic range that is less than the first dynamic range. 
     Optionally, where the characteristic includes a user setting, the dynamic tone mapping system can adapt the second video signal to the user setting. In some aspects, these steps do not have to be sequential. For example, the adjustment based on the user setting can be performed in one step. 
     Optionally, where the characteristic includes an ambient light measurement detected by an ALS, the dynamic tone mapping system can adapt the second video signal based on the ambient light measurement. In some aspects, these steps do not have to be sequential. For example, the adaptation to ALS can be integrated in the calculation of the tone mapping curve. 
     Optionally, the dynamic tone mapping system can generate video quality enhancement data based on the characteristics of the first video signal. The video quality enhancement data can include, for example, dark scene adjustment data, bright scene adjustment data, detail enhancement data, any other suitable data, or any combination thereof. In such aspects, the dynamic tone mapping system can convert the first video signal into the second video signal based on the video quality enhancement data. 
     Example Computer System 
     Various embodiments may be implemented, for example, using one or more well-known computer systems, such as computer system  1300  shown in  FIG.  13   . For example, the media device  106  may be implemented using combinations or sub-combinations of computer system  1300 . Also or alternatively, one or more computer systems  1300  may be used, for example, to implement any of the embodiments discussed herein, as well as combinations and sub-combinations thereof (including, but not limited to, the method  1200 ). 
     Computer system  1300  may include one or more processors (also called central processing units, or CPUs), such as one or more processors  1304 . In some embodiments, one or more processors  1304  may be connected to a communications infrastructure  1306  (e.g., a bus). 
     Computer system  1300  may also include user input/output device(s)  1303 , such as monitors, keyboards, pointing devices, etc., which may communicate with communications infrastructure  1306  through user input/output interface(s)  1302 . 
     One or more of processors  1304  may be a graphics processing unit (GPU). In an embodiment, a GPU may be a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU may have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data utilized for computer graphics applications, images, videos, etc. 
     Computer system  1300  may also include a main memory  1308  (e.g., a primary memory or storage device), such as random access memory (RAM). Main memory  1308  may include one or more levels of cache. Main memory  1308  may have stored therein control logic (e.g., computer software) and/or data. 
     Computer system  1300  may also include one or more secondary storage devices or memories such as secondary memory  1310 . Secondary memory  1310  may include, for example, a hard disk drive  1312 , a removable storage drive  1314  (e.g., a removable storage device), or both. Removable storage drive  1314  may be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and/or any other storage device/drive. 
     Removable storage drive  1314  may interact with a removable storage unit  1318 . Removable storage unit  1318  may include a computer usable or readable storage device having stored thereon computer software (e.g., control logic) and/or data. Removable storage unit  1318  may be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and/ any other computer data storage device. Removable storage drive  1314  may read from and/or write to removable storage unit  1318 . 
     Secondary memory  1310  may include other means, devices, components, instrumentalities or other approaches for allowing computer programs and/or other instructions and/or data to be accessed by computer system  1300 . Such means, devices, components, instrumentalities or other approaches may include, for example, a removable storage unit  1322  and an interface  1320 . Examples of the removable storage unit  1322  and the interface  1320  may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB or other port, a memory card and associated memory card slot, and/or any other removable storage unit and associated interface. 
     Computer system  1300  may further include a communications interface  1324  (e.g., a network interface). Communications interface  1324  may enable computer system  1300  to communicate and interact with any combination of external devices, external networks, external entities, etc. (individually and collectively referenced by reference number  1328 ). For example, communications interface  1324  may allow computer system  1300  to communicate with external devices  1328  (e.g., remote devices) over communications path  1326 , which may be wired and/or wireless (or a combination thereof), and which may include any combination of LANs, WANs, the Internet, etc. Control logic and/or data may be transmitted to and from computer system  1300  via communications path  1326 . 
     Computer system  1300  may also be any of a personal digital assistant (PDA), desktop workstation, laptop or notebook computer, netbook, tablet, smart phone, smart watch or other wearable, appliance, part of the Internet-of-Things, and/or embedded system, to name a few non-limiting examples, or any combination thereof. 
     Computer system  1300  may be a client or server, accessing or hosting any applications and/or data through any delivery paradigm, including but not limited to remote or distributed cloud computing solutions; local or on-premises software (“on-premise” cloud-based solutions); “as a service” models (e.g., content as a service (CaaS), digital content as a service (DCaaS), software as a service (SaaS), managed software as a service (MSaaS), platform as a service (PaaS), desktop as a service (DaaS), framework as a service (FaaS), backend as a service (BaaS), mobile backend as a service (MBaaS), infrastructure as a service (IaaS), etc.); and/or a hybrid model including any combination of the foregoing examples or other services or delivery paradigms. 
     Any applicable data structures, file formats, and schemas in computer system  1300  may be derived from standards including but not limited to JavaScript Object Notation (JSON), Extensible Markup Language (XML), Yet Another Markup Language (YAML), Extensible Hypertext Markup Language (XHTML), Wireless Markup Language (WML), MessagePack, XML User Interface Language (XUL), or any other functionally similar representations alone or in combination. Alternatively, proprietary data structures, formats or schemas may be used, either exclusively or in combination with known or open standards. 
     In some embodiments, a tangible, non-transitory apparatus or article of manufacture including a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon may also be referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system  1300 , main memory  1308 , secondary memory  1310 , removable storage unit  1318 , and removable storage unit  1322 , as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system  1300  or processor(s)  1304 ), may cause such data processing devices to operate as described herein. 
     Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use embodiments of this disclosure using data processing devices, computer systems and/or computer architectures other than that shown in  FIG.  13   . In particular, embodiments can operate with software, hardware, and/or operating system implementations other than those described herein. 
     Conclusion 
     It is to be appreciated that the Detailed Description section, and not any other section, is intended to be used to interpret the claims. Other sections can set forth one or more but not all example embodiments as contemplated by the inventor(s), and thus, are not intended to limit this disclosure or the appended claims in any way. 
     While this disclosure describes example embodiments for example fields and applications, it should be understood that the disclosure is not limited thereto. Other embodiments and modifications thereto are possible, and are within the scope and spirit of this disclosure. For example, and without limiting the generality of this paragraph, embodiments are not limited to the software, hardware, firmware, and/or entities illustrated in the figures and/or described herein. Further, embodiments (whether or not explicitly described herein) have significant utility to fields and applications beyond the examples described herein. 
     Embodiments have been described herein with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined as long as the specified functions and relationships (or equivalents thereof) are appropriately performed. Also, alternative embodiments can perform functional blocks, steps, operations, methods, etc. using orderings different than those described herein. 
     References herein to “one embodiment,” “an embodiment,” “an example embodiment,” or similar phrases, indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it would be within the knowledge of persons skilled in the relevant art(s) to incorporate such feature, structure, or characteristic into other embodiments whether or not explicitly mentioned or described herein. Additionally, some embodiments can be described using the expression “coupled” and “connected” along with their derivatives. These terms are not necessarily intended as synonyms for each other. For example, some embodiments can be described using the terms “connected” and/or “coupled” to indicate that two or more elements are in direct physical or electrical contact with each other. The term “coupled,” however, can also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. 
     The breadth and scope of this disclosure should not be limited by any of the above-described example embodiments, but should be defined only in accordance with the following claims and their equivalents.