Patent Publication Number: US-2021176471-A1

Title: Processing an image

Description:
1. FIELD 
     At least one embodiment relates generally to a processing an video or image. 
     2. BACKGROUND 
     The present section is intended to introduce the reader to various aspects of art, which may be related to various aspects of at least one embodiment that is described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of at least one embodiment. 
     The advent of the High Efficiency Video Coding (HEVC) standard (ITU-T H.265 Telecommunication standardization sector of ITU (02/2018), series H: audiovisual and multimedia systems, infrastructure of audiovisual services—coding of moving video, High efficiency video coding, Recommendation ITU-T H.265) enables the deployment of new video services with enhanced viewing experience, such as Ultra HD services. In addition to an increased spatial resolution, Ultra HD format can bring a wider color gamut (WCG) and a higher dynamic range (HDR) than respectively the Standard Color Gamut (SCG) and the Standard Dynamic Range (SDR) of High Definition format currently deployed. 
     Different solutions for the representation and coding of HDR/WCG video have been proposed such as the perceptual transfer function Perceptual Quantizer (PQ) (SMPTE ST 2084, “High Dynamic Range Electro-Optical Transfer Function of Mastering Reference Displays, or Diaz, R., Blinstein, S. and Qu, S. “Integrating HEVC Video Compression with a High Dynamic Range Video Pipeline”, SMPTE Motion Imaging Journal, Vol. 125, Issue 1. February, 2016, pp 14-21). Typically, SMPTE ST 2084 allows representing HDR video signal of up to 10 000 cd/m 2  peak luminance with only 10 or 12 bits. 
     SDR backward compatibility with a decoding and rendering apparatus is an important feature in some video distribution systems, such as broadcasting or multicasting systems. A solution based on a single-layer coding/decoding process may be backward compatible, for example SDR compatible, and may leverage legacy distribution networks and services already in place. 
     Such a single-layer based distribution solution enables both high quality HDR rendering on HDR-enabled Consumer Electronic (CE) devices, while also offering high quality SDR rendering on SDR-enabled CE devices. Such a solution is based on an encoded signal, for example SDR signal, and associated metadata (typically only using a few bytes per video frame or scene) that can be used to reconstruct another signal, for example either SDR or HDR signal, from a decoded signal. 
     An example of a single-layer based distribution solution may be found in the ETSI technical specification TS 103 433-1 V1.2.1 (August 2017). Such a single-layer based distribution solution is denoted SL-HDR1 in the following. 
     Additionally, HDR distribution systems (workflows, but also decoding and rendering apparatus) may already be deployed. Indeed, there are a number of global video services providers which include HDR content. However, distributed HDR material may be represented in a format or with characteristics which do not match consumer end-device characteristics. Usually, the consumer end-device adapts the decoded material to its own characteristics. However, the versatility of technologies employed in the HDR TV begets important differences in terms of rendition because of the differences between the consumer end-device characteristics compared to the mastering display used in the production environment to grade the original content. For a content producer, artistic intent fidelity and its rendition to the consumer are of the utmost importance. Thus, “display adaptation” metadata can be generated either at the production stage during the grading process, or under the control of a quality check operator before emission. The metadata enable the conveyance of the artistic intent to the consumer when the decoded signal is to be adapted to end-device characteristics. 
     An example of a single-layer based distribution solution implements a display adaptation may be found in ETSI technical specification TS 103 433-2 V1.1.1 (January 2018). Such a single-layer based distribution solution is denoted SL-HDR2 in the following. 
     Such a single-layer based distribution solution, SL-HDR1 or SL-HDR2, generates metadata as parameters used for the reconstruction or adaptation of the signal. Metadata may be either static or dynamic. 
     Static metadata means parameters representative of the video content or its format that remain the same for, for example, a video (set of images) and/or a program. 
     Static metadata are valid for the whole video content (scene, movie, clip . . . ) and may depend on the image content per se or the representation format of the image content. The static metadata may define, for example, image format, color space, or color gamut. For instance, SMPTE ST 2086:2014, “Mastering Display Color Volume Metadata Supporting High Luminance and Wide Color Gamut Images” defines static metadata that describes the mastering display used to grade the material in a production environment. The Mastering Display Colour Volume (MDCV) SEI (Supplemental Enhanced Information) message corresponds to ST 2086 for both H.264/AVC (“ Advanced video coding for generic audiovisual Services ”, SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS, Recommendation ITU-T H.264, Telecommunication Standardization Sector of ITU, April 2017) and HEVC video codecs. 
     Dynamic metadata is content-dependent information, so that metadata could change with the image/video content, for example for each image or for each group of images. As an example, SMPTE ST 2094:2016, “Dynamic Metadata for Color Volume Transform” defines dynamic metadata typically generated in a production environment. SMPTE ST 2094-30 can be distributed in HEVC and AVC coded video streams using, for example, the Colour Remapping Information (CRI) SEI message. 
     3. SUMMARY 
     The following presents a simplified summary of at least one embodiment in order to provide a basic understanding of some aspects of at least one embodiment. This summary is not an extensive overview of an embodiment. It is not intended to identify key or critical elements of an embodiment. The following summary merely presents some aspects of at least one embodiment in a simplified form as a prelude to the more detailed description provided elsewhere in the application. 
     According to a general aspect of at least one embodiment, there is provided a method and device that compares a first set of bits of formatted metadata with at least one given second set of bits identifying a particular formatting of said formatted metadata. The formatted metadata associated with first image data are both received from an uncompressed interface. The method and device further reconstructs second image data from said first image data and parameters obtained by parsing said formatted metadata according to a particular formatting identified from the result of said comparison. 
     One or more of the present embodiments also provide a computer program comprising instructions which when executed by one or more processors cause the one or more processors to carry out the above method. One or more of the present embodiments also provide a computer readable storage medium comprising instructions which when executed by a computer cause the computer to carry out the above method. One or more of the present embodiments also provide a computer readable medium containing data content generated according to the above method. 
     The specific nature of at least one embodiment as well as other objects, advantages, features and uses of at least one embodiment will become evident from the following description of examples taken in conjunction with the accompanying drawings. 
    
    
     
       4. BRIEF DESCRIPTION OF DRAWINGS 
       In the drawings, examples of at least one embodiment are illustrated. It shows: 
         FIG. 1  shows a high-level representation of an end-to-end workflow supporting content delivery for displaying image/video in accordance with at least one embodiment; 
         FIG. 2  shows an example of the end-to-end workflow of  FIG. 1  supporting delivery to HDR and SDR CE displays in accordance with a single-layer based distribution solution; 
         FIG. 3  shows a particular implementation of the workflow of  FIG. 2 ; 
         FIG. 4 a    shows an illustration of an example of perceptual transfer function; 
         FIG. 4 b    shows an example of a piece-wise curve used for mapping; 
         FIG. 4 c    shows an example of a curve used for converting a perceptual uniform signal to a linear-light domain; 
         FIG. 5  illustrates a block diagram of an example of a system in which various aspects and embodiments are implemented; 
         FIG. 6  shows a diagram of the steps of a method in accordance with at least one embodiment. 
         FIG. 7  illustrates an example of a HDR dynamic Metadata Extended InfoFrame structure; and 
     
    
    
     Similar or same elements are referenced with the same reference numbers. 
     5. DESCRIPTION OF AT LEAST ONE EMBODIMENT 
     At least one embodiment is described more fully hereinafter with reference to the accompanying figures, in which examples of at least one embodiment are shown. An embodiment may, however, be embodied in many alternate forms and should not be construed as limited to the examples set forth herein. Accordingly, it should be understood that there is no intent to limit embodiments to the particular forms disclosed. On the contrary, the disclosure is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this application as defined by the claims. 
     The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including” when used in this specification, specify the presence of stated, for example, features, integers, steps, operations, elements, and/or components but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Moreover, when an element is referred to as being “responsive” or “connected” to another element, it can be directly responsive or connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly responsive” or “directly connected” to other element, there are no intervening elements present. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements are not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the teachings of this application. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows. Some examples are described with regard to block diagrams and operational flowcharts in which each block represents a circuit element, module, or portion of code which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in other implementations, the function(s) noted in the blocks may occur out of the indicated order. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending on the functionality involved. Reference herein to “in accordance with an example” or “in an example” means that a particular feature, structure, or characteristic described in connection with the example can be included in at least one implementation. The appearances of the expression “in accordance with an example” or “in an example” in various places in the specification are not necessarily all referring to the same example, nor are separate or alternative examples necessarily mutually exclusive of other examples. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims. Although not explicitly described, the present examples and variants may be employed in any combination or sub-combination. 
     In the following, image data refer to data, for example, one or several arrays of samples (for example, pixel values) in a specific image/video format, which specifies information pertaining to the pixel values of an image (or a video) and/or information which may be used by a display and/or any other apparatus to visualize and/or decode an image (or video) for example. An image typically includes a first component, in the shape of a first array of samples, usually representative of luminance (or luma) of the image, and a second component and a third component, in the shape of other arrays of samples, usually representative of the chrominance (or chroma) of the image. Some embodiments represent the same information using a set of arrays of color samples, such as the traditional tri-chromatic RGB representation. 
     A pixel value is represented in one or more embodiments by a vector of C values, where C is the number of components. Each value of a vector is typically represented with a number of bits which can define a dynamic range of the pixel values. 
     Standard Dynamic Range images (SDR images) are images whose luminance values are typically represented with a smaller number of bits (typically 8) than in High Dynamic Range images (HDR images). The difference between the dynamic ranges of SDR and HDR images is therefore relative, and SDR images can have, for example, more than 8 bits. Because of the smaller number of bits, SDR images often do not allow correct rendering of small signal variations or do not cover high range of luminance values, in particular in dark and bright luminance ranges. In HDR images, the signal representation is typically extended to maintain a higher accuracy of the signal over all or part of its range. For example, at least one embodiment represents an HDR image using 10-bits for luminance, and provides 4 times as many values than an 8-bit representation. The additional values allow a greater luminance range to be represented, and can also allow finer differences in luminance to be represented. In HDR images, pixel values are usually represented in floating-point format (typically at least 10 bits per component, namely float or half-float), the most popular format being openEXR half-float format (for example 48 bits per pixel) or in integers with a long representation, typically at least 16 bits when the signal is linear-light encoded (10 bits at least when it us encoded non-uniformly using the recommendation ST 2084 for example). 
     Typically, two different images have a different dynamic range of the luminance. The dynamic range of the luminance of an image is the ratio of the maximum over the minimum of the luminance values of the image. 
     Typically, when the dynamic range of the luminance of an image is below 1000 (for example 500: for example, 100 cd/m 2  over 0.2 cd/m 2 ), the image is denoted as a Standard Dynamic Range (SDR) image and when the dynamic range of the luminance of an image is equal to or greater than 1000 (for example 10000: for example, 1000 cd/m 2  over 0.1 cd/m 2 ) the image is denoted as an HDR image. Luminance is expressed by the unit candela per square meter (cd/m 2 ). This unit supersedes the term “nit” which may also be used. 
     At least one embodiment is described for pre-processing, encoding, decoding, and post-processing an image but extends to pre-processing, encoding, decoding, and post-processing a sequence of images (video) because each image of the sequence is sequentially pre-processed, encoded, decoded, and post-processed as described below. 
     In the following, a component C n   m  designates a component m of an image n. These components {C n   m } with m=1, 2, 3, represent an image I n  in a specific image format. Typically, an image format is characterized by a color volume (for example chromaticity and dynamic range), and a color encoding system (for example RGB, YCbCr . . . ). 
       FIG. 1  shows a high-level representation of an end-to-end workflow supporting content delivery for displaying image/video in accordance with at least one embodiment. 
       FIG. 1  includes apparatuses A1, A2 and A3. 
     The remote apparatuses A1 and A2 are communicating over a distribution network NET that is configured at least to provide a bitstream from apparatus A1 to apparatus A2. 
     In accordance with an example, the distribution network NET is a broadcast network, adapted to broadcast still images or video images from apparatus A1 to a plurality of apparatuses A2. DVB-based and ATSC-based networks are examples of such broadcast networks. 
     In accordance with another example, the distribution network NET is a broadband network adapted to deliver still images or video images from apparatus A1 to a plurality of apparatuses A2. Internet-based networks, GSM networks, or TV over IP networks are examples of such broadband networks. 
     In an alternate embodiment, the distribution network NET is replaced by a physical packaged media on which the encoded image or video stream is stored. 
     Physical packaged media include, for example, optical packaged media such as Blu-ray disc and Ultra-HD Blu-ray, and memory-based package media such as used in OTT and VoD services. 
     The apparatus A1 includes at least one device configured to pre-process an input image/video and to encode, in the transmitted bitstream, an image/video and associated formatted metadata resulting of said pre-processing. 
     The apparatus A2 includes at least one device configured to decode a image/video from a received bitstream and to transmit to the apparatus A3 said decoded image/video and the associated formatted metadata over an uncompressed digital interface such as HDMI or Displayport for example. 
     The apparatus A3 includes at least one device configured to receive the decoded image/video and associated formatted metadata obtained from the bitstream. The at least one device included in apparatus A3 is also configured to obtain parameters by parsing said associated formatted metadata, to reconstruct another image/video by post-processing the decoded image/video (received from apparatus A2) using said parameters. 
     The at least one device of apparatuses A1, A2 and A3 belongs to a set of devices including, for example, a mobile device, a communication device, a game device, a tablet (or tablet computer), a computer device such as a laptop, a still image camera, a video camera, an encoding chip, a still image server, and a video server (for example a broadcast server, a video-on-demand server, or a web server), a computer device, a set top box, a TV set (or television), a tablet (or tablet computer), a display, a head-mounted display and a rendering/displaying chip. 
     The format of the metadata is different according to the format of the transmitted bitstream that depends on the data encoding. Typically, the metadata obtained from the transmitted bitstream are extracted and conveyed on an uncompressed interface such as specified in CTA-861-G (e.g. as an extended infoFrame). Typically, when coded image/picture are conveyed within an HEVC bitstream, the metadata are embedded in an HEVC SEI message. For example, such an SEI message is defined in Annex A of ETSI TS 103 433-1. When conveyed within an AVC bitstream, the metadata are embedded in an AVC SEI message as defined in Annex B of ETSI TS 103 433-1. 
     The scope of the at least one embodiment is not limited to HEVC or AVC formatted SEI message but extends to any message covering the same intent as an SEI message such as “extension data” defined in AVS2 (second generation of Audio Video Standard, GY/T 299.1-2016 or IEEE P1857.4 part 1) for example. 
     Typically, there is no signaling in the data transmitted on the uncompressed digital interface that indicates whether the formatted metadata associated with the decoded image/video comply with a format of a specific SEI messages, that is that complies with AVC/H.264 or HEVC/H.265 format for example. 
     Consequently, when metadata, transported with a specific formatting, are carried through the uncompressed interface with an associated and decoded image/video stream, the apparatus A3 cannot identify the formatting of those metadata. For example, the apparatus A3 can not determine if the format of metadata is carried on a AVC SEI message or HEVC SEI message. This can create interoperability issues as the apparatus A3 may assume a particular format to be parsed while the metadata are not formatted according to said particular format. Then, the parsed metadata may be totally corrupted and not usable or if used may beget a very altered image/video reconstructed from the received decoded image/video and those altered metadata. 
     A straightforward approach may be to fix the format of metadata to a uniquely predetermined format. This can be set as a recommendation or a guideline document followed by stakeholders. But, this means that if the formatting of the metadata is not the fixed one then a translation/conversion mechanism shall occur in the apparatus A2 to adapt the formatting of metadata to an expected formatting carried on the uncompressed interface. This requires extra processing in the apparatus A2 that is against the initial intent of directly transmitting formatted metadata over the uncompressed interface. If the formatting conversion is not operated, metadata carriage is disrupted. 
     Another approach may be to signal the formatting of the metadata so that the apparatus A3 can operate the parsing responsive to the signaling information. This can be implemented in a specification revision or amendment of CTA-861-G specification for example. But, this approach possibly requires updating every specification or document or product that specifies carriage between the apparatus A3 (also denoted Sink device) and the apparatus A2 (also denoted source device). 
     According to at least one embodiment, there is provided a device included in the apparatus A3 that is configured to compare a first set of bits of a payload of received formatted metadata with at least one given second set of bits identifying a particular formatting of said received formatted metadata, and to reconstruct an image/video from image data associated with said formatted metadata and parameters obtained by parsing said received formatted metadata according to a particular formatting identified from the result of said comparison. 
     Such a device then determines/identifies the formatting of the metadata carried on uncompressed interface to be parsed by comparing sets of bits. 
     This solution is an efficient implementation because it involves few logics, few comparisons and it is included at the very beginning of the parsing process. This solution requires a minor firmware update (CE-friendly) and is compatible with existing interface specifications, avoiding thus any update/amendment of said specification(s). 
       FIG. 2  shows an example of the end-to-end workflow of  FIG. 1  supporting delivery to HDR and SDR CE displays in accordance with a single-layer based distribution solution. Distribution and parsing part of the end-to-end workflow of  FIG. 1  are not explicitly shown in  FIG. 2 . 
     Such a single-layer based distribution solution may address SDR direct backward compatibility. That is, the solution leverages SDR distribution networks and services already in place and enables high-quality HDR rendering on HDR-enabled CE devices including high-quality SDR rendering on SDR CE devices. 
     SL-HDR1 is one example of such a single-layer based distribution solution. 
     Such a single-layer based distribution solution may also relate to a solution used on distribution networks for which display adaptation dynamic metadata are delivered. This allows, for example, the content to be adapted to a user&#39;s display characteristics. For example, dynamic metadata can be delivered along with a PQ HDR video signal. PQ means “Perceptual Quantization” as specified in Rec. ITU-R BT.2100 “Recommendation ITU-R BT.2100-1, Image parameter values for high dynamic range television for use in production and international programme exchange”. 
     The workflow shown in  FIG. 2  involves a single-layer based distribution solution with associated SL-HDR metadata. Such a method illustrates an example of the use of a method for reconstructing three components {C 30   m } representative of three components {C 10   m } of an input image. Such a reconstruction is based on three decoded components { } representative of a decoded image and the metadata as specified, for example, in SL-HDR1 or SL-HDR2. 
     An information data ID determines which of the single-layer based distribution solutions (for example SL-HDR1 or SL-HDR2) is used. Usually, in practice only one single-layer based distribution solution is used and the information data ID is a given (predetermined) value. If more than one single-layer based distribution solution can be used, then the information data ID indicates which of these single-layer based distribution solutions is used. 
     Typically, SL-HDR1 and SL-HDR2 may be used and the information data ID indicates if either SL-HDR1 or SL-HDR2 has to be used. 
     As shown, the single-layer based distribution solution shown in  FIG. 2  includes a pre-processing step  20 , an encoding step  23 , decoding steps  25  and  26 , and a post-processing step  28 . 
     The input and the output of the pre-processing step  20  are triplets of components {C 1   m } and {C 12   m } respectively, and the input and the output of the post-processing step  28  are triplets of components {C 2   m } and {C 3   m } respectively. 
     The single-layer based distribution solution shown in  FIG. 2  may include optional format adaptation steps  21 ,  22 ,  27 ,  29  to adapt the format of three components {C n   m } to the input of a further processing to be applied on these components. 
     For example, in step  21  (optional), the format of the three components {C n   m } may be adapted to a format fitting an input format of the pre-processing step  20  or an input format of an encoding step  23 . In step  22  (optional), the format of the three components {C 12   m } may be adapted to a format fitting the input format of the encoding step  23 . 
     In step  27  (optional), the format of the three components { } may be adapted to a format fitting the input of the post-processing step  28 , and in step  29 , the format of the three components {C 3   m } may be adapted to a format that may be defined from at least one characteristic of a targeted apparatus  30  (for example a Set-Top-Box, a connected TV, HDR/SDR enabled CE device, an Ultra HD Blu-ray disc player). 
     The format adaptation steps ( 21 ,  22 ,  27 ,  29 ) may include color space conversion and/or color gamut mapping (and/or inverse color gamut mapping). Inverse color gamut mapping may be used, for example, when the three decoded components { } and the three components {C 30   m } of an output image or the three components {C 10   m } of an input image are represented in different color spaces and/or gamuts. 
     Usual format adapting processes may be used such as R′G′B′-to-Y′CbCr or Y′CbCr-to-R′G′B′ conversions, BT.709-to-BT.2020 or BT.2020-to-BT.709, down-sampling or up-sampling chroma components, etc. 
     For example, SL-HDR1 may use format adapting processes and inverse gamut mapping as specified in Annex D of the ETSI technical specification TS 103 433-1 V1.2.1 (August 2017). 
     The input format adaptation step  21  may also include adapting the bit depth of the three components {C 10   m } to bit depth such as 10 bits for example, by applying a transfer function on the three components {C 10   m } such as a PQ or HLG transfer function or its inverse. The Recommendation Rec. ITU-R BT.2100 provides examples of such transfer functions. 
     In the pre-processing step  20 , the three components {C 1   m } are equal either to the three components {C 10   m } when the format has not been adapted in step  21  or equal to adapted versions of these three components {C 10   m } when the format of these components has been adapted in step  21 . These three input components are decomposed into three components {C 12   m } and a set of parameters SP formed by parameters coming from step  21 ,  200 ,  201  and/or  203 . The format of the three components {C 12   m } may be optionally adapted during step  22  to get the three components {C 120   m }. A switching step  24  determines if the three components {C 20   m } equals either the three components {C 120   m } or the three components {C 1   m }. 
     In step  23 , the three components {C 20   m } may be encoded with any video codec and the output is a signal including the bitstream B. The output signal is carried throughout a distribution network. 
     According to variant of step  23 , the set of parameters SP and/or the information data ID are conveyed as associated static and/or dynamic metadata in the bitstream B, or out-of-band (that is not in the bitstream B but either as predetermined values known by the receiver or as a part of another stream on another communication channel, for example using SIP or H.323 protocoles). 
     According to a variant, the set of parameters SP and/or the information data ID are conveyed as associated static and/or dynamic metadata on a specific channel. 
     At least one signal, intended to be decoded by the apparatus A2 of  FIG. 1 , carries the bitstream B which can include the accompanying metadata. 
     In a variant, the bitstream B is stored on a storage medium such as a (UltraHD) Blu-ray disk or a hard disk or a memory of a Set-Top-Box for example. 
     In a variant, at least some accompanying associated metadata is stored on a storage medium such as an (UltraHD) Blu-ray disk or a hard disk or a memory of a Set-Top-Box for example. 
     In at least one implementation, in step  23 , a sequence of at least one triplet of components {C 20   m }, each representing an image, and possibly associated metadata, are encoded with a video codec such as an H.265/HEVC codec or an H.264/AVC codec. 
     In step  25 , the set of parameters SP is obtained at least partially either from the bitstream B or from another specific channel. At least one of the parameters of the set of parameters SP may also be obtained from a separate storage medium. 
     In step  26 , the three decoded components { } are obtained from the bitstream B. 
     The post-processing step  28  is a functional inverse, or substantially a functional inverse, of the pre-processing step  20 . In the post-processing step  28 , the three components {C 30   m } are reconstructed from the three decoded components { } and the obtained set of parameters SP. 
     In more detail, the pre-processing step  20  includes steps  200 - 203 . 
     In step  200 , a component C 1,pre   1  is obtained by applying a mapping function on the component C 1   1  of the three components {C 1   m }. The component C 1   1  represents the luminance of the input image. 
     Mathematically speaking, 
         C   1,pre   1   =MF ( C   1   1 )  (1)
 
     with MF being a mapping function that may reduce or increase the dynamic range of the luminance of an image. Note that its inverse, denoted IMF, may increase or reduce, respectively, the dynamic range of the luminance of an image. 
     In step  202 , a reconstructed component   is obtained by applying an inverse-mapping function on the component C 1,pre   1 : 
         = IMF ( C   1,pre   1 )  (2)
 
     where IMF is the functional inverse of the mapping function MF. The values of the reconstructed component   belong thus to the dynamic range of the values of the component C 1   1 . 
     In step  201 , the components C 12   3  and C 12   3  are derived by correcting the components C 1   2  and C 1   3  representing the chroma of the input image according to the component C 1,pre   1  and the reconstructed component  . 
     This step  201  allows control of the colors obtained from the three components {C 12   m } and allows perceptual matching to the colors of the input image. The correction of the components C 1   2  and C 1   2  (usually denoted chroma components) may be maintained under control by tuning the parameters of the chroma correcting and inverse mapping steps. The color saturation and hue obtained from the three components {C 12   m } are thus under control. Such a control is not possible, usually, when a non-parametric mapping function (step  200 ) is used. 
     Optionally, in step  203 , the component C 1,pre   1  may be adjusted to further control the perceived saturation, as follows: 
         C   12   1   =C   1,pre   1 −max(0, a·C   12   2   +b·C   12   3 )  (3)
 
     where a and b are two parameters. 
     This step  203  allows control of the luminance (represented by the component C 12   2 ) to allow a perceived color matching between the colors (saturation and hue) obtained from the three components {C 12   m } and the colors of the input image. 
     The set of parameters SP may include information data related to the mapping function or its inverse (steps  200 ,  202  and  282 ), information data related to the chroma correcting (steps  201  and  281 ), information data related to the saturation adjusting function, in particular their parameters a and b (step  203 ), and/or information related to the optional conversion used in the format adapting stages  21 ,  22 ,  27 ,  29  (for example gamut mapping and/or inverse gamut mapping parameters). 
     The set of parameters SP may also include the information data ID and information characteristics of the output image, for example the format of the three components {C 30   m } representative of the output image (steps  29  of  FIGS. 2 and 3, 284  of  FIG. 3 ). 
     In more details, the post-processing step  28  includes steps  280 - 282  which take as input at least one parameter of the set of parameters SP. 
     In optional step  280 , the component C 2   1  of the three components {C 2   m }, output of step  27 , may be adjusted as follows: 
         C   2,post   1   =C   2   1 +max(0, a·C   2   2   +b·C   2   3 )  (4)
 
     where a and b are two parameters of the set of parameters SP. 
     For example, the step  280  is executed when the information data ID indicates that SL-HDR1 has to be considered and not executed when it indicates that SL-HDR2 has to be considered. 
     In step  282 , the component C 3   1  of the three components {C 3   m } is obtained by applying a mapping function on the component CZ or, optionally, C 2,post   1 : 
         C   3   1   =MF 1( C   2,post   1 )  (5)
 
     where MF1 is a mapping function derived from at least one parameter of the set of parameters SP. 
     In step  281 , the components C 3   2 , C 3   3  of the three components {C 3   m } are derived by inverse correcting the components C 2   2 , C 2   3  of the three components {C 2   m } according to the component C 2   1  or, optionally, C 2,post   1 . 
     According to an embodiment, the components C 2   2  and C 2   3  are multiplied by a chroma correcting function β(·) as defined by parameters of the set of parameters SP and whose value depends on the component C 2   1  or, optionally, C 2,post   1 . 
     Mathematically speaking, the components C 3   2 , C 3   3  are given by: 
     
       
         
           
             
               
                 
                   
                     
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                               2 
                             
                           
                         
                         
                           
                             
                               C 
                               3 
                               3 
                             
                           
                         
                       
                       ] 
                     
                     = 
                     
                       
                         
                           β 
                            
                           
                             ( 
                             
                               C 
                               2 
                               1 
                             
                             ) 
                           
                         
                          
                         
                           [ 
                           
                             
                               
                                 
                                   C 
                                   2 
                                   2 
                                 
                               
                             
                             
                               
                                 
                                   C 
                                   2 
                                   3 
                                 
                               
                             
                           
                           ] 
                         
                       
                        
                       
                           
                       
                        
                       or 
                        
                       
                           
                       
                        
                       optionally 
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       [ 
                       
                         
                           
                             
                               C 
                               3 
                               2 
                             
                           
                         
                         
                           
                             
                               C 
                               3 
                               3 
                             
                           
                         
                       
                       ] 
                     
                     = 
                     
                       
                         β 
                          
                         
                           ( 
                           
                             C 
                             
                               2 
                               , 
                               post 
                             
                             1 
                           
                           ) 
                         
                       
                        
                       
                         [ 
                         
                           
                             
                               
                                 C 
                                 2 
                                 2 
                               
                             
                           
                           
                             
                               
                                 C 
                                 2 
                                 3 
                               
                             
                           
                         
                         ] 
                       
                     
                   
                    
                   
                       
                   
                 
               
               
                 
                   ( 
                   
                     6 
                      
                     bis 
                   
                   ) 
                 
               
             
           
         
       
     
       FIG. 3  represents a hardware-friendly version of a single layer-based solution of  FIG. 2 . The version includes two additional steps  283  and  284  and allows a reduction in complexity for hardware implementations by reducing buses bitwidth use. 
     In step  283 , three components denoted (R 1 , G 1 , B 1 ) are obtained from components C 3,post   2  and C 3,post   3 , outputs of the step  281 , by taking into account parameters of the set of parameters SP: 
     
       
         
           
             
               [ 
               
                 
                   
                     
                       R 
                       1 
                     
                   
                 
                 
                   
                     
                       G 
                       1 
                     
                   
                 
                 
                   
                     
                       B 
                       1 
                     
                   
                 
               
               ] 
             
             = 
             
               
                 [ 
                 
                   
                     
                       1 
                     
                     
                       0 
                     
                     
                       
                         m 
                         0 
                       
                     
                   
                   
                     
                       1 
                     
                     
                       
                         m 
                         1 
                       
                     
                     
                       
                         m 
                         2 
                       
                     
                   
                   
                     
                       1 
                     
                     
                       
                         m 
                         3 
                       
                     
                     
                       0 
                     
                   
                 
                 ] 
               
               × 
               
                 [ 
                 
                   
                     
                       
                         S 
                         0 
                       
                     
                   
                   
                     
                       
                         C 
                         
                           3 
                           , 
                           post 
                         
                         2 
                       
                     
                   
                   
                     
                       
                         C 
                         
                           3 
                           , 
                           post 
                         
                         3 
                       
                     
                   
                 
                 ] 
               
             
           
         
       
     
     where m 0 , m 1 , m 2 , m 3  are parameters of the set of parameters SP and S 0  is derived from the components C 3,post   2  and C 3,post   3  and other parameters of the set of parameters SP. 
     In step  284 , the three components {C 3   m } are then obtained by scaling the three components (R 1 , G 1 , B 1 ) according to a component C 3,post   1 , output of step  282 . 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             C 
                             3 
                             1 
                           
                           = 
                           
                             
                               C 
                               
                                 3 
                                 , 
                                 post 
                               
                               1 
                             
                             × 
                             
                               R 
                               1 
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             C 
                             3 
                             2 
                           
                           = 
                           
                             
                               C 
                               
                                 3 
                                 , 
                                 post 
                               
                               1 
                             
                             × 
                             
                               G 
                               1 
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             C 
                             3 
                             3 
                           
                           = 
                           
                             
                               C 
                               
                                 3 
                                 , 
                                 post 
                               
                               1 
                             
                             × 
                             
                               B 
                               1 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     where C 3,post   1 =MF1(C 2,post   1 ) (step  282 ). 
     According to a first embodiment of the end-to-end workflow of  FIG. 2  or  FIG. 3 , the information data ID indicates that SL-HDR1 has to be considered. 
     The mapping function MF(·) in eq. (1) reduces the dynamic range of the luminance of the input image, its inverse IMF(·) in eq. (2) increases the dynamic range of the component C 1,pre   1 , and the mapping function MF1(·) in eq. (5) increases the dynamic range of the component C 2,post   1 . 
     According to a first variant of the first embodiment, the component C 1   1  is a non-linear signal, denoted luma in literature, which is obtained (step  21 ) from the gamma-compressed RGB components of the input image by: 
     
       
         
           
             
               
                 
                   
                     C 
                     1 
                     1 
                   
                   = 
                   
                     
                       A 
                       1 
                     
                      
                     
                       [ 
                       
                         
                           
                             
                               R 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                         
                           
                             
                               G 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                         
                           
                             
                               B 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     where γ may be a gamma factor, equal to 2.4 in some implementations. 
     According to the first variant, the component C 1   2 , C 1   3  are obtained (step  21 ), by applying a gamma compression to the RGB components of the input image: 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             C 
                             1 
                             2 
                           
                         
                       
                       
                         
                           
                             C 
                             1 
                             3 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               A 
                               2 
                             
                           
                         
                         
                           
                             
                               A 
                               3 
                             
                           
                         
                       
                       ] 
                     
                      
                     
                       [ 
                       
                         
                           
                             
                               R 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                         
                           
                             
                               G 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                         
                           
                             
                               B 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     where A=[A 1  A 2  A 3 ] T  is the canonical 3×3 R′G′B′-to-Y′CbCr conversion matrix (for example Recommendation ITU-R BT.2020-2 or Recommendation ITU-R BT.709-6 depending on the color space), A 1 , A 2 , A 3  being 1×3 matrices where 
         A   1 =[ A   11    A   12    A   13 ] 
         A   2 =[ A   21    A   22    A   23 ] 
         A   3 =[ A   31    A   32    A   33 ] 
     where A mn  (m=1, . . . , 3, n=1, . . . 3) are matrix coefficients. 
     In step  201 , according to the first variant, the components C 1   2  and C 1   3  are corrected from the ratio between the component C 1,pre   1  over the product of the gamma-compressed reconstructed component   by Ω(C 1,pre   1 ): 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             C 
                             12 
                             2 
                           
                         
                       
                       
                         
                           
                             C 
                             12 
                             3 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         C 
                         
                           1 
                           , 
                           pre 
                         
                         1 
                       
                       
                         
                           Ω 
                            
                           
                             ( 
                             
                               C 
                               
                                 1 
                                 , 
                                 pre 
                               
                               1 
                             
                             ) 
                           
                         
                         · 
                         
                           
                             1 
                             / 
                             γ 
                           
                         
                       
                     
                     · 
                     
                       [ 
                       
                         
                           
                             
                               C 
                               1 
                               2 
                             
                           
                         
                         
                           
                             
                               C 
                               1 
                               3 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     where Ω(C 1,pre   1 ) is a value that depends on the component C 1,pre   1  but may also be a constant value depending on the color primaries of the three components {C 1   m }·Ω(C 1,pre   1 ) may equal to 1.2 for Rec. BT.2020 for example. Possibly, Ω(C 1,pre   1 ) may also depend on parameters as specified in ETSI TS 103 433-1 V.1.2.1 clause C.2.3·Ω(C 1,pre   1 ) may also be a parameter of the set of parameters SP. 
     Further, according to the first variant, the three components {C 120   m } may represent a Y′CbCr 4:2:0 gamma transfer characteristics video signal. 
     For example, the control parameters relative to the mapping function MF and/or its inverse IMF and/or the mapping function MF1(·) may be determined as specified in Clause C.3.2 (ETSI technical specification TS 103 433-1 V1.2.1). The chroma correcting function β(·) and their parameters may be determined as specified in Clause C.2.3 and C.3.4 (ETSI technical specification TS 103 433-1 V1.2.1). Information data related to the control parameters, information data related to the mapping functions or their inverse, and information data related to the chroma correcting function β(·) and their parameters, are parameters of the set of parameters SP. Examples of numerical values of the parameters of the set of parameters SP may be found, for example, in Annex F (Table F.1 of ETSI technical specification TS 103 433-1 V1.2.1). 
     The parameters m 0 , m 1 , m 2 , m 3  and S 0  may be determined as specified in Clause 6.3.2.6 (matrixCoefficient[i] are defining m 0 , m 1 , m 2 , m 3 ) and Clause 6.3.2.8 (kCoefficient[i] are used to construct S 0 ) of ETSI technical specification TS 103 433-1 V1.2.1 and their use for reconstruction may be determined as specified in Clause 7.2.4 (ETSI technical specification TS 103 433-1 V1.2.1). 
     According to a second variant of the first embodiment, the component C 1   1  is a linear-light luminance component L obtained from the RGB component of the input image I 1  by: 
     
       
         
           
             
               
                 
                   
                     C 
                     1 
                     1 
                   
                   = 
                   
                     L 
                     = 
                     
                       
                         A 
                         1 
                       
                        
                       
                         [ 
                         
                           
                             
                               R 
                             
                           
                           
                             
                               G 
                             
                           
                           
                             
                               B 
                             
                           
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     According to the second variant, the component C 1   2 , C 1   3  are derived (step  21 ) by applying a gamma compression to the RGB components of the input image I 1 : 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             C 
                             1 
                             2 
                           
                         
                       
                       
                         
                           
                             C 
                             1 
                             3 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               A 
                               2 
                             
                           
                         
                         
                           
                             
                               A 
                               3 
                             
                           
                         
                       
                       ] 
                     
                      
                     
                       [ 
                       
                         
                           
                             
                               R 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                         
                           
                             
                               G 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                         
                           
                             
                               B 
                               
                                 1 
                                 / 
                                 γ 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     According to the second variant, the component C 12   2 , C 12   3  are derived (step  201 ) by correcting the components C 1   2 , C 1   3  from the ratio between the first component C 1,pre   1  over the product of the gamma-compressed reconstructed component   by Ω(C 1,pre   1 ) 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           
                             C 
                             12 
                             2 
                           
                         
                       
                       
                         
                           
                             C 
                             12 
                             3 
                           
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         C 
                         
                           1 
                           , 
                           pre 
                         
                         1 
                       
                       
                         
                           Ω 
                            
                           
                             ( 
                             
                               C 
                               
                                 1 
                                 , 
                                 pre 
                               
                               1 
                             
                             ) 
                           
                         
                         · 
                         
                           
                             1 
                             / 
                             γ 
                           
                         
                       
                     
                      
                     
                       [ 
                       
                         
                           
                             
                               C 
                               1 
                               2 
                             
                           
                         
                         
                           
                             
                               C 
                               1 
                               3 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     where Ω(C 1,pre   1 ) is a value that depends on the component C 1,pre   1  and, is possibly, obtained from parameters as specified in ETSI TS 103 433-1 V.1.2.1 clause C.3.4.2 where 
     
       
         
           
             
               Ω 
                
               
                 ( 
                 
                   C 
                   
                     1 
                     , 
                     pre 
                   
                   1 
                 
                 ) 
               
             
             = 
             
               1 
               
                 Max 
                  
                 
                   ( 
                   
                     
                       
                         R 
                         sgf 
                       
                        
                       
                         : 
                       
                        
                       255 
                     
                     ; 
                     
                       
                         R 
                         sgf 
                       
                       · 
                       
                         g 
                          
                         
                           ( 
                           
                             Y 
                             n 
                           
                           ) 
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
     
     in equation (22). 
     Ω(C 1,pre   1 ) may also be a parameter of the set of parameters SP. 
     Further, according to the second variant, the three components {C 120   m } may represent a Y′CbCr 4:2:0 gamma transfer characteristics video signal. 
     For example, the control parameters related to the mapping function MF and/or its inverse IMF and/or the mapping function MF1(·) may be determined as specified in Clause C.3.2 (ETSI technical specification TS 103 433-1 V1.2.1). The chroma correcting function β(·) and their parameters may be determined as specified in Clause 7.2.3.2 (ETSI technical specification TS 103 433-2 V1.1.1) eq. (25) where f sgf (Y n )=1. Information data related to the control parameters, information data related to the mapping functions or their inverse, and information data related to the chroma correcting function β(·) and their parameters, are parameters of the set of parameters SP. 
     The parameters m 0 , m 1 , m 2 , m 3  and S 0  may be determined as specified in Clause 6.3.2.6 (matrixCoefficient[i] are defining m 0 , m 1 , m 2 , m 3 ) and Clause 6.3.2.8 (kCoefficient[i] are used to construct S 0 ) of ETSI technical specification TS 103 433-1 V1.2.1. Use of the parameters for reconstruction may be determined as specified in Clause 7.2.4 (ETSI technical specification TS 103 433-1 V1.2.1). 
     According to a second embodiment of the end-to-end workflow of  FIG. 2  or  FIG. 3 , the information data ID indicates that SL-HDR2 has to be considered. 
     In the second embodiment, the three components {C 1   m } may be represented as a Y′CbCr4:4:4 full range PQ10 (PQ 10 bits) video signal (specified in Rec. ITU-R BT.2100). The three components {C 20   m }, which represent PQ 10-bit image data and associated parameter(s) computed from the three components {C 1   m } (typically 10, 12 or 16 bits), are provided. The provided components are encoded (step  23 ) using, for example an HEVC Main 10 profile encoding scheme. Those parameters are set to the set of parameters SP. 
     The mapping function MF1(·) in eq. (5) may increase or reduce the dynamic range of the component C 2,post   1  according to variants. 
     For example, the mapping function MF1(·) increases the dynamic range when the peak luminance of the connected HDR CE displays is above the peak luminance of the content. The mapping function MF1(·) decreases the dynamic range when the peak luminance of the connected HDR or SDR CE displays is below the peak luminance of the content. For example, the peak luminances may be parameters of the set of parameters SP. 
     For example, the control parameters related to the mapping function MF1 may be determined as specified in Clause C.3.2 (ETSI technical specification TS 103 433-1 V1.2.1). The chroma correcting function β(·) and their parameters may be determined as specified in Clause 7.2.3.2 (ETSI technical specification TS 103 433-2 V1.1.1) eq. (25) where f sgf (Y n )=1. Information data related to the control parameters, information data related to the mapping function, and information data related to the chroma correcting function β(·) and their parameters, are parameters of the set of parameters SP. Examples of numerical values of the parameters of the set of parameters SP may be found, for example, in Annex F (Table F.1) (ETSI technical specification TS 103 433-2 V1.1.1). 
     The parameters m 0 , m 1 , m 2 , m 3  (defined by matrixCoefficient[i] in ETSI technical specification TS 103 433-2 V1.1.1) and S 0  (constructed with kCoefficient[i] in ETSI technical specification TS 103 433-2 V1.1.1) may be determined as specified in Clause 7.2.4 (ETSI technical specification TS 103 433-2 V1.1.1). 
     According to a first variant of the second embodiment, the three components {C 30   m } representative of the output image are the three components { }. 
     According to a second variant of the second embodiment, in the post-processing step  28 , the three components {C 3   m } are reconstructed from the three components { } and parameters of the set of parameters SP after decoding (step  25 ). 
     The three components {C 3   m } are available for either an SDR or HDR enabled CE display. The format of the three components {C 3   m } are possibly adapted (step  29 ) as explained above. 
     The mapping function MF(·) or MF1(·) is based on a perceptual transfer function. The goal of the perceptual transfer function is to convert a component of an input image into a component of an output image, thus reducing (or increasing) the dynamic range of the values of their luminance. The values of a component of the output image belong thus to a lower (or greater) dynamic range than the values of the component of an input image. The perceptual transfer function uses a limited set of control parameters. 
       FIG. 4 a    shows an illustration of an example of a perceptual transfer function that may be used for mapping luminance components but a similar perceptual transfer function for mapping the luminance component may be used. The mapping is controlled by a mastering display peak luminance parameter (equal to 5000 cd/m 2  in  FIG. 4 a   ). To better control the black and white levels, a signal stretching between content-dependent black and white levels is applied. Then the converted signal is mapped using a piece-wise curve constructed out of three parts, as illustrated in  FIG. 4 b   . The lower and upper sections are linear, the steepness is determined by the shadowGain control and highlightGain control parameters respectively. The mid-section is a parabola providing a continuous and smooth bridge between the two linear sections. The width of the cross-over is determined by the midToneWidthAdjFactor parameter. All the parameters controlling the mapping may be conveyed as metadata for example by using an SEI message as specified in ETSI TS 103 433-1 Annex A.2 metadata. 
       FIG. 4 c    shows an example of the inverse of the perceptual transfer function TM ( FIG. 4 a   ) to illustrate how a perceptually optimized luminance signal may be converted back to the linear-light domain based on a targeted legacy display maximum luminance, for example 100 cd/m 2 . 
     In step  25  ( FIG. 2 or 3 ), the set of parameters SP is obtained to reconstruct the three components {C 3   m } from the three components {Ĉ 20   m }. These parameters may be obtained from metadata obtained from a bitstream, for example the bitstream B. 
     ETSI TS 103 433-1 V1.2.1 clause 6 and Annex A.2 provide an example of syntax of the metadata. The syntax of this ETSI recommendation is described for reconstructing an HDR video from an SDR video but this syntax may extend to the reconstruction of any image from any decoded components. As an example, TS 103 433-2 V1.1.1 uses the same syntax for reconstructing a display adapted HDR video from an HDR video signal (with a different dynamic range). 
     According to ETSI TS 103 433-1 V1.2.1, the dynamic metadata may be conveyed according to either a so-called parameter-based mode or a table-based mode. The parameter-based mode may be of interest for distribution workflows that have a goal of, for example, providing direct SDR backward compatible services with very low additional payload or bandwidth usage for carrying the dynamic metadata. The table-based mode may be of interest for workflows equipped with low-end terminals or when a higher level of adaptation is required for representing properly both HDR and SDR streams. In the parameter-based mode, dynamic metadata to be conveyed include luminance mapping parameters representative of the inverse mapping function to be applied at the post-processing step, that is tmnputSignalBlackLevelOffset; tmnputSignalWhiteLeveOffset; shadowGain; highlightGain; midToneWidthAdjFactor tmOutputFine Tuning parameters. 
     Moreover, other dynamic metadata to be conveyed include color correction parameters (saturationGainNumVal, saturationGainX(i) and saturationGainY(i)) used to fine-tune the default chroma correcting function β(·) as specified in ETSI TS 103 433-1 V1.2.1 clauses 6.3.5 and 6.3.6. The parameters a and b may be respectively carried in the saturationGain function parameters as explained above. These dynamic metadata may be conveyed using, for example, the HEVC SL-HDR Information (SL-HDRI) user data registered SEI message (see ETSI TS 103 433-1 V1.2.1 Annex A.2) or another extension data mechanism such as specified in the AVS2/IEEE1857.4 specification. Typical dynamic metadata payload size is less than 100 bytes per picture or scene. 
     Back to  FIG. 3 , in step  25 , the SL-HDRI SEI message is parsed to obtain at least one parameter of the set of parameters SP. 
     In step  282  and  202 , the inverse mapping function (so-called lutMapY) is reconstructed (or derived) from the obtained mapping parameters (see ETSI TS 103 433-1 V1.2.1 clause 7.2.3.1 for more details; same clause for TS 103 433-2 V1.1.1). 
     In step  282  and  202 , the chroma correcting function β(·) (so-called lutCC) is also reconstructed (or derived) from the obtained color correction parameters (see ETSI TS 103 433-1 V1.2.1 clause 7.2.3.2 for more details; same clause for TS 103 433-2 V1.1.1). 
     In the table-based mode, dynamic data to be conveyed include pivots points of a piece-wise linear curve representative of the mapping function. For example, the dynamic metadata are luminanceMappingNumVal that indicates the number of the pivot points, luminanceMappingX that indicates the abscissa (x) values of the pivot points, and luminanceMappingY that indicates the ordinate (y) values of the pivot points (see ETSI TS 103 433-1 V1.2.1 clauses 6.2.7 and 6.3.7 for more details). Moreover, other dynamic metadata to be conveyed may include pivots points of a piece-wise linear curve representative of the chroma correcting function β(·). For example, the dynamic metadata are colorCorrectionNumVal that indicates the number of pivot points, colorCorrectionX that indicates the x values of pivot points, and colorCorrectionY that indicates the y values of the pivot points (see ETSI TS 103 433-1 V1.2.1 clauses 6.2.8 and 6.3.8 for more details). These dynamic metadata may be conveyed using, for example, the HEVC SL-HDRI SEI message (mapping between clause 6 parameters and annex A distribution metadata is provided in Annex A.2.3 of ETSI TS 103 433-1 V1.2.1). 
     In step  25 , the SL-HDRI SEI message is parsed to obtain the pivot points of a piece-wise linear curve representative of the inverse mapping function and the pivot points of a piece-wise linear curve representative of the chroma correcting function β(·), and the chroma to luma injection parameters a and b. 
     In step  282  and  202 , the inverse mapping function is derived from those pivot points relative to a piece-wise linear curve representative of the inverse mapping function ITM (see ETSI TS 103 433-1 V1.2.1 clause 7.2.3.3 for more details; same clause for ETSI TS 103 433-2 V1.1.1). 
     In step  281  and  201 , the chroma correcting function β(·), is also derived from those of the pivot points relative to a piece-wise linear curve representative of the chroma correcting function β(·) (see ETSI TS 103 433-1 V1.2.1 clause 7.2.3.4 for more details; same clause for TS 103 433-2 V1.1.1). 
     Note that static metadata also used by the post-processing step may be conveyed by SEI message. For example, the selection of either the parameter-based mode or table-based mode may be carried by the payloadMode information as specified by ETSI TS 103 433-1 V1.2.1 (clause A.2.2). Static metadata such as, for example, the color primaries or the maximum mastering display luminance are conveyed by a Mastering Display Colour Volume (MDCV) SEI message as specified in AVC, HEVC or embedded within the SL-HDRI SEI message as specified in ETSI TS 103 433-1 V1.2.1 Annex A.2. 
     According to an embodiment of step  25 , the information data ID is explicitly signaled by a syntax element in a bitstream and thus obtained by parsing the bitstream. For example, the syntax element is a part of an SEI message such as sl_hdr_mode_value_minus1 syntax element contained in an SL-HDRI SEI message. 
     According to an embodiment, the information data ID identifies the processing that is to be applied to the input image to process the set of parameters SP. According to this embodiment, the information data ID may then be used to deduce how to use the parameters to reconstruct the three components {C 3   m } (step  25 ). 
     For example, when equal to 1, the information data ID indicates that the set of parameters SP has been obtained by applying the SL-HDR1 pre-processing step (step  20 ) to an input HDR image, and that the three components { } are representative of an SDR image. When equal to 2, the information data ID indicates that the parameters have been obtained by applying the SL-HDR2 pre-processing step (step  20 ) to an HDR 10 bits image (input of step  20 ), and that the three components { } are representative of an HDR10 image. 
       FIG. 6  shows a diagram of the steps of a method in accordance with at least one embodiment. 
     In step  610 , a module M1 compares a first set of bits of formatted metadata with at least one second set of bits identifying (or allowing identifying of) a particular formatting of said formatted metadata. 
     The formatted metadata are associated with first image data received from an uncompressed interface and said at least one second set of bits may be received from another channel for example or obtained from a local storage mean. 
     According to an embodiment of step  610 , comparing a first set of bits of formatted metadata with at least one second set of bits comprises steps  611 - 613 . 
     In step  611 , the first set of bits is obtained from formatted metadata. 
     According to an embodiment, the position of at least one bit of the first set of bits obtained from the formatted metadata is a first given value. 
     In a variant, said first given value depends on information associated with a second set of bits of a given (predetermined) second sets of bits library. 
     For example, the position of the first bit of a second set of bits identifying a specific metadata determines the position of the first bit to check in the formatted metdata. 
     According to an embodiment, the number of bits of the first set of bits obtained from the formatted metadata is a second given value. 
     In a variant, said second given value depends on information associated with a second set of bits of a given (predetermined) second sets of bits library. 
     For example, the number of bits of a second set of bits identifying a specific metadata determines the number of bits of the first set of bits to be obtained from the formatted metadata. 
     In step  612 , a second set of bits is obtained form said given (predetermined) second sets of bits library. Each second set of bits identifies (or allows identifying of) a particular formatting of said formatted metadata. Each given second set of bits may be representative of a particular formatting of the metadata. There might be several second set of bits associated to a same formatting of the metadata (for example HEVC formatting of the metadata may have the bit patter 0xB5 0x00 or 0xB5 0x00 0x3A 0x00). 
     In step  613 , the first set of bits of formatted metadata is compared with each given second set of bits of said given (predetermined) second sets of bits library (loop over given second sets of bits from the given sets of bits library). 
     The method stops when a match is found (identification is positive) or when every given second set of bits has been tried but no match occurred. 
     In the former case, the parser, to parse the formatted metadata, is configured according to the formatting identified by the given second set of bits that matches the first set of bits of formatted metadata. 
     In the latter case (no match), according to a variant, metadata may be recovered thanks, for example, to a recovery procedure/mode and values specified, for example, in annex F of ETSI TS 103 433-1. 
     An alternative may be to assume a default formatting (e.g. HEVC SEI message formatting). 
     An alternative may be to consider contextual information relative to capabilities of the apparatus A3 (for example a TV may be configured in Chinese then use AVS2 formatting). 
     An alternative may be that the apparatus A2 provides information that it can only decode a distribution format/codec type (for example the apparatus A2 can only decode HEVC stream and not AVC nor AVS2 stream so that the TV can assume that the metadata can only be with HEVC SEI message formatting). 
     Possibly, the first set of bits of formatted metada and a given second set of bits identifying a particular formatting have not the same number of bits. 
     Then, according to an embodiment, only the number of bits of the shortest set of bits is used in the comparison. 
     According to an embodiment, the comparison is a bitwise comparison in which a particular formatting is identified when each bit of the first set of bits of formatted metadata equal each bit of a given second set of bits identifiying said particular formatting. 
     In a variant, only a percentage of bits of the first set of bits equals the bits of the second set of bits and the two set of bits match when this percentage exceeds a given threshold. 
     According to an embodiment, the comparison succeeds when the position of at least one bit in the formatted metadata is compared with the position of at least one bit of a second set of bits in metadata that would be formatted according to the formatting identified by said second set of bits. 
     According to an embodiment, the comparison succeeds when the number of bits of the first set of bits equals the number of bits of a second set of bits. 
     In step  620 , a module M2 obtains parameters by parsing said formatted metadata according to a particular formatting identified from the result of said comparison. 
     In step  630 , a module M3 reconstructs (post-process) second image data from said first image data and said obtained parameters. 
     According to an embodiment of the method, a single-layer based distribution solution of  FIG. 2 or 3  is used, such as SL-HDR1 or SL-HDR2. 
     Parameters (SP) are generated and carried as metadata as described in relation with  FIG. 2 or 3 . In step  630 , the module M3 reconstructs an HDR image from an SDR image (SL-HDR1 case) or an HDR image (SL-HDR2 case) received from the uncompressed interface and parameters as described in relation with the post-processing step  28  of  FIG. 2 or 3 . 
     According to an embodiment, CTA-861-G document specifies the carriage of the metadata on uncompressed digital interface as illustrated in  FIG. 7 . The syntax element denoted ExtendedInfoFrame Type is set to 0x0002 HDR Dynamic to signal that metadata generated by either SL-HDR1 or SL-HDR2 are carried in an Extended InfoFrame (going from apparatus A2 to apparatus A3) as Supplemental Enhancement Information (SEI) messages. Then, the set of bits of the payload of formatted metadata used in step  610  is a fixed/predetermined bit pattern portion of the payload of the Extended InfoFrame denoted “Data Byte 1”, . . . , “Data Byte n” of the HDR Dynamic Metadata Extended InfoFrames in  FIG. 7  typically 7 first Data Bytes, or the Data Byte 3 and Databyte 6, or only Data Byte 6. 
     According to an embodiment, a given second set of bits identifying a particular formatting of formatted metadata may be the terminal_provider_oriented_code_message_idc and/or itu_t35_country_code and/or payloadType and/or payloadSize syntax elements values as specified respectively in AVC and HEVC specifications. 
     According to an embodiment, a given second set of bits identifying a particular formatting of formatted metadata may be either the n-first bytes or the n-first bytes from the m-th byte from the start or a concatenation of discriminating bytes of sl_hdr_info( ) SEI message payload (more discriminating) as specified in annex B and annex A of ETSI TS 103 433-1, or TS 103 433-2. 
     Typically, the two bytes of sei_message( ) (section 7.3.5 of HEVC specification) and four first bytes of sl_hdr_info( ) enable discrimination/identification of whether the bitstream is related to the formatting of AVC, HEVC or whatever else. 
     As an example, the following ordered byte/bits patterns mark with HEVC for Extended InfoFrame Type Code 0x0002: 
     Data byte 1: 0x04 (payloadType) 
     Data byte 2: 0x?? (payloadSize, variable not discriminating) 
     Data byte 3: 0xB5 (itu_t_t35_country_code) 
     Data byte 4: 0x00 (terminal_provider_code byte 1) 
     Data byte 5: 0x3A (terminal_provider_code byte 2) 
     Data byte 6: 0x00 (terminal_provider_oriented_code_message_idc) The given set of bits identifying a HEVC formatting of formatted metadata may be 0x04, 0x??, 0xB5, 0x, 0x3A, 0x, or 0xB5 x00 (that is a concatenation of 3rd byte and 6th byte). 
     As an example, the following ordered byte/bits patterns mark with AVC for Extended InfoFrame Type Code 0x002: 
     Data byte 1: 0x04 (payloadType) 
     Data byte 2: 0x?? (payloadSize, variable not discriminating) 
     Data byte 3: 0xB5 (itu_t_t35_country_code) 
     Data byte 4: 0x00 (terminal_provider_code byte 1) 
     Data byte 5: 0x3A (terminal_provider_code byte 2) 
     Data byte 6: 0x01 (terminal_provider_oriented_code_message_idc) The given set of bits identifying a AVC formatting of formatted metadata may be 0x04, 0x??, 0xB5, 0x, 0x3A, x01 or 0xB5 0x01 (that is concatenation of 3rd byte and 6th byte). 
     AVS2 bitstream is different from HEVC and AVC bitstreams. One may determine the similarly to HEVC/AVC method described above: from typical syntax elements values of the data extension (data extension is equivalent in AVS2 to SEI messaging in HEVC/AVC) that is from n-first bytes, from n-bytes from the m-th byte from the start or from the concatenation of discriminating bytes. 
     Thus, considering the above examples, the metadata formatting carried in an Extended InfoFrame Type Code set to x0002 could be identified by comparing, as an example, the four MSB of the third byte of the metadata ‘1011’ (“0xB”) with the AVS2 set of bits ‘1110’ (“0xE”) and by comparing the third and sixth bytes of the metadata (for example 0xB5 0x00) with two sets of bits (that is HEVC: 0xB5 0x0, AVC: 0xB5 0x01). In that case, one may determine that the metadata are HEVC formatted. 
     On  FIGS. 1-4   c  and  6 - 7  the modules are functional units. In various embodiments, all, some, or none of these functional units correspond to distinguishable physical units. For example, these modules or some of them may be brought together in a unique component or circuit or contribute to functionalities of a software. As another example, some modules may be composed of separate physical entities. Various embodiments are implemented using either pure hardware, for example using dedicated hardware such as an ASIC or an FPGA or VLSI, respectively «Application Specific Integrated Circuit», «Field-Programmable Gate Array», «Very Large Scale Integration», or from several integrated electronic components embedded in an apparatus, or from a blend of hardware and software components. 
       FIG. 5  illustrates a block diagram of an example of a system in which various aspects and embodiments are implemented. System  5000  can be embodied as a device including the various components described below and is configured to perform one or more of the aspects described in this application. Examples of such devices, include, but are not limited to, various electronic devices such as personal computers, laptop computers, smartphones, tablet computers, digital multimedia set top boxes, digital television receivers, personal video recording systems, connected home appliances, and servers. Elements of system  5000 , singly or in combination, can be embodied in a single integrated circuit, multiple ICs, and/or discrete components. For example, in at least one embodiment, the processing and encoder/decoder elements of system  5000  are distributed across multiple ICs and/or discrete components. In various embodiments, the system  5000  is communicatively coupled to other similar systems, or to other electronic devices, via, for example, a communications bus or through dedicated input and/or output ports. In various embodiments, the system  5000  is configured to implement one or more of the aspects described in this document. 
     The system  5000  includes at least one processor  5010  configured to execute instructions loaded therein for implementing, for example, the various aspects described in this document. Processor  5010  can include embedded memory, input output interface, and various other circuitries as known in the art. The system  5000  includes at least one memory  5020  (e.g., a volatile memory device, and/or a non-volatile memory device). System  5000  includes a storage device  5040 , which can include non-volatile memory and/or volatile memory, including, but not limited to, EEPROM, ROM, PROM, RAM, DRAM, SRAM, flash, magnetic disk drive, and/or optical disk drive. The storage device  5040  can include an internal storage device, an attached storage device, and/or a network accessible storage device, as non-limiting examples. 
     System  5000  includes an encoder/decoder module  5030  configured, for example, to process data to provide an encoded video or decoded video, and the encoder/decoder module  5030  can include its own processor and memory. The encoder/decoder module  5030  represents module(s) that can be included in a device to perform the encoding and/or decoding functions. As is known, a device can include one or both of the encoding and decoding modules. Additionally, encoder/decoder module  5030  can be implemented as a separate element of system  5000  or can be incorporated within processor  5010  as a combination of hardware and software as known to those skilled in the art. 
     Program code to be loaded onto processor  5010  or encoder/decoder  5030  to perform the various aspects described in this document can be stored in storage device  5040  and subsequently loaded onto memory  5020  for execution by processor  5010 . In accordance with various embodiments, one or more of processor  5010 , memory  5020 , storage device  5040 , and encoder/decoder module  5030  can store one or more of various items during the performance of the processes described in this document. Such stored items can include, but are not limited to, the input video, the decoded video or portions of the decoded video, a bitstream, matrices, variables, and intermediate or final results from the processing of equations, formulas, operations, and operational logic. 
     In several embodiments, memory inside of the processor  5010  and/or the encoder/decoder module  5030  is used to store instructions and to provide working memory for processing that is needed during encoding or decoding. 
     In other embodiments, however, a memory external to the processing device (for example, the processing device can be either the processor  5010  or the encoder/decoder module  5030 ) is used for one or more of these functions. The external memory can be the memory  5020  and/or the storage device  5040 , for example, a dynamic volatile memory and/or a non-volatile flash memory. In several embodiments, an external non-volatile flash memory is used to store the operating system of a television. In at least one embodiment, a fast external dynamic volatile memory such as a RAM is used as working memory for video coding and decoding operations, such as for MPEG-2, HEVC, or WC (Versatile Video Coding). 
     The input to the elements of system  5000  can be provided through various input devices as indicated in block  5030 . Such input devices include, but are not limited to, (i) an RF portion that receives an RF signal transmitted, for example, over the air by a broadcaster, (ii) a Composite input terminal, (iii) a USB input terminal, and/or (iv) an HDMI input terminal. 
     In various embodiments, the input devices of block  5030  have associated respective input processing elements as known in the art. For example, the RF portion can be associated with elements necessary for (i) selecting a desired frequency (also referred to as selecting a signal, or band-limiting a signal to a band of frequencies), (ii) down-converting the selected signal, (iii) band-limiting again to a narrower band of frequencies to select (for example) a signal frequency band which can be referred to as a channel in certain embodiments, (iv) demodulating the down-converted and band-limited signal, (v) performing error correction, and (vi) demultiplexing to select the desired stream of data packets. The RF portion of various embodiments includes one or more elements to perform these functions, for example, frequency selectors, signal selectors, band-limiters, channel selectors, filters, downconverters, demodulators, error correctors, and demultiplexers. The RF portion can include a tuner that performs various of these functions, including, for example, down-converting the received signal to a lower frequency (for example, an intermediate frequency or a near-baseband frequency) or to baseband. 
     In one set-top box embodiment, the RF portion and its associated input processing element receives an RF signal transmitted over a wired (for example, cable) medium, and performs frequency selection by filtering, down-converting, and filtering again to a desired frequency band. 
     Various embodiments rearrange the order of the above-described (and other) elements, remove some of these elements, and/or add other elements performing similar or different functions. 
     Adding elements can include inserting elements in between existing elements, such as, for example, inserting amplifiers and an analog-to-digital converter. In various embodiments, the RF portion includes an antenna. 
     Additionally, the USB and/or HDMI terminals can include respective interface processors for connecting system  5000  to other electronic devices across USB and/or HDMI connections. It is to be understood that various aspects of input processing, for example, Reed-Solomon error correction, can be implemented, for example, within a separate input processing IC or within processor  5010  as necessary. Similarly, aspects of USB or HDMI interface processing can be implemented within separate interface ICs or within processor  5010  as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor  5010 , and encoder/decoder  5030  operating in combination with the memory and storage elements to process the data stream as necessary for presentation on an output device. 
     Various elements of system  5000  can be provided within an integrated housing. Within the integrated housing, the various elements can be interconnected and transmit data therebetween using suitable connection arrangement, for example, an internal bus as known in the art, including the  12 C bus, wiring, and printed circuit boards. 
     The system  5000  includes communication interface  5050  that enables communication with other devices via communication channel  5060 . The communication interface  5050  can include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel  5060 . The communication interface  5050  can include, but is not limited to, a modem or network card and the communication channel  5060  can be implemented, for example, within a wired and/or a wireless medium. 
     Data is streamed to the system  5000 , in various embodiments, using a Wi-Fi network such as IEEE 802.11. The Wi-Fi signal of these embodiments is received over the communications channel  5060  and the communications interface  5050  which are adapted for Wi-Fi communications. The communications channel  5060  of these embodiments is typically connected to an access point or router that provides access to outside networks including the Internet for allowing streaming applications and other over-the-top communications. 
     Other embodiments provide streamed data to the system  5000  using a set-top box that delivers the data over the HDMI connection of the input block  5030 . 
     Still other embodiments provide streamed data to the system  5000  using the RF connection of the input block  5030 . 
     It is to be appreciated that signaling can be accomplished in a variety of ways. For example, one or more syntax elements, flags, and so forth are used to signal information to a corresponding decoder in various embodiments. 
     The system  5000  can provide an output signal to various output devices, including a display  5100 , speakers  5110 , and other peripheral devices  5120 . The other peripheral devices  5120  include, in various examples of embodiments, one or more of a stand-alone DVR, a disk player, a stereo system, a lighting system, and other devices that provide a function based on the output of the system  5000 . 
     In various embodiments, control signals are communicated between the system  5000  and the display  5100 , speakers  5110 , or other peripheral devices  5120  using signaling such as AV.Link, CEC, or other communications protocols that enable device-to-device control with or without user intervention. 
     The output devices can be communicatively coupled to system  5000  via dedicated connections through respective interfaces  5070 ,  5080 , and  5090 . 
     Alternatively, the output devices can be connected to system  5000  using the communications channel  5060  via the communications interface  5050 . The display  5100  and speakers  5110  can be integrated in a single unit with the other components of system  5000  in an electronic device such as, for example, a television. 
     In various embodiments, the display interface  5070  includes a display driver, such as, for example, a timing controller (T Con) chip. 
     The display  5100  and speaker  5110  can alternatively be separate from one or more of the other components, for example, if the RF portion of input  5130  is part of a separate set-top box. In various embodiments in which the display  5100  and speakers  5110  are external components, the output signal can be provided via dedicated output connections, including, for example, HDMI ports, USB ports, or COMP outputs. 
     Implementations of the various processes and features described herein may be embodied in a variety of different equipment or applications. Examples of such equipment include an encoder, a decoder, a post-processor processing output from a decoder, a pre-processor providing input to an encoder, a video coder, a video decoder, a video codec, a web server, a set-top box, a laptop, a personal computer, a cell phone, a PDA, any other device for processing an image or a video, and any other communication apparatus. As should be clear, the equipment may be mobile and even installed in a mobile vehicle. 
     Additionally, the methods may be implemented by instructions being performed by a processor, and such instructions (and/or data values produced by an implementation) may be stored on a computer readable storage medium. A computer readable storage medium can take the form of a computer readable program product embodied in one or more computer readable medium(s) and having computer readable program code embodied thereon that is executable by a computer. A computer readable storage medium as used herein is considered a non-transitory storage medium given the inherent capability to store the information therein as well as the inherent capability to provide retrieval of the information therefrom. A computer readable storage medium can be, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. It is to be appreciated that the following, while providing more specific examples of computer readable storage media, is merely an illustrative and not exhaustive listing as is readily appreciated by one of ordinary skill in the art: a portable computer, a floppy disk; a hard disk; a read-only memory (ROM); an erasable programmable read-only memory (EPROM or Flash memory); a portable compact disc read-only memory (CD-ROM); an optical storage device; a magnetic storage device; or any suitable combination of the foregoing. 
     The instructions may form an application program tangibly embodied on a processor-readable medium (also referred to as a computer readable medium or a computer readable storage medium). Instructions may be, for example, in hardware, firmware, software, or a combination. Instructions may be found in, for example, an operating system, a separate application, or a combination of the two. A processor may be characterized, therefore, as, for example, both an apparatus configured to carry out a process and an apparatus that includes a processor-readable medium (such as a storage apparatus) having instructions for carrying out a process. Further, a processor-readable medium may store, in addition to or in lieu of instructions, data values produced by an implementation. 
     As will be evident to one of skill in the art, implementations may produce a variety of signals formatted to carry information that may be, for example, stored or transmitted. The information may include, for example, instructions for performing a method, or data produced by one of the described implementations. For example, a signal may be formatted to carry as data the rules for writing or reading the syntax of a described example, or to carry as data the actual syntax-values written by a described example. Such a signal may be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal. The formatting may include, for example, encoding a data stream and modulating a carrier with the encoded data stream. The information that the signal carries may be, for example, analog or digital information. The signal may be transmitted over a variety of different wired or wireless links, as is known. The signal may be stored on a processor-readable medium. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, elements of different implementations may be combined, supplemented, modified, or removed to produce other implementations. Additionally, one of ordinary skill will understand that other structures and processes may be substituted for those disclosed and the resulting implementations will perform at least substantially the same function(s), in at least substantially the same way(s), to achieve at least substantially the same result(s) as the implementations disclosed. Accordingly, these and other implementations are contemplated by this application.