METHOD AND APPARATUS FOR COLOR gamut mapping, signal having an SDR video and parameter values used for gamut mapping and processor-readable media
Patent Information
- Application Number
- BR112019022968
- Authority / Receiving Office
- BR · BR
- Patent Type
- Patents
- Current Assignee / Owner
- Publication Date
- 2026-08-11
Smart Images
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Figure 00000044_0000 
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Abstract
Description
"METHOD AND DEVICE FOR COLOR GAMMA MAPPING, SIGNAL HAVING AN SDR VIDEO AND PARAMETER VALUES USED FOR "Gamma Mapping and Processor-Readable Media" 1. Field.
[001] These principles generally relate to image / video encoding / decoding. Particularly, but not exclusively, the technical field of these principles relates to color gamut mapping of an image whose pixel values belong to a high dynamic range and inverse color gamut mapping of an image whose pixel values belong to a low dynamic range. 2. Fundamentals.
[002] This section is intended to introduce the reader to various aspects of the technique, which may be related to various aspects of the present principles described and / or claimed below. It is believed that this discussion will be useful in providing the reader with background information to facilitate a better understanding of the various aspects of the present principles. Therefore, it should be understood that these statements should be read in this light, and not as admissions of the prior art.
[003] Next, an image contains one or more sample matrices (pixel values) in a specific image / video format that specifies all the information relating to the pixel values of an image (or video) and all the information that can be used by a viewer and / or any other device to view and / or decode an image (or video), for example. An image comprises at least one component, in the form of a first sample matrix, usually a luma (or luminance) component, and possibly at least one other component, in the form of at least one other sample matrix, usually a chroma component. Or, equivalently, the same Petition 870260066244, dated 06 / 07 / 2026, page 8 / 93 2 / 38 Information can also be represented by a set of color sample matrices, such as the traditional three-color RGB representation.
[004] A pixel value is represented by a vector of values C, where C is the number of components. Each value in the vector is represented with a number of bits that defines a maximum dynamic range of pixel values.
[005] Low dynamic range images (LDR images) are images whose luminance values are represented with a limited number of bits (usually 8 or 10). This limited representation does not allow for the correct rendering of small signal variations, especially in dark and bright luminance ranges. In high dynamic range images (HDR images), the signal representation is extended to maintain high signal accuracy across the entire range. In HDR images, the pixel values representing luminance levels are usually represented in floating-point format (32 bits or 16 bits for each component, i.e., floating or half-floating), with the most popular format being the openEXR half-floating format (16 bits per RGB component, i.e., 48 bits per pixel) or in integers with a long representation, usually with at least 16 bits.
[006] The arrival of the High Efficiency Video Coding (HEVC) standard (ITU-T H.265 Telecommunication standardization sector of ITU (10 / 2014), series H: audiovisual and multimedia systems, infrastructure of audiovisual services - coding of moving video, High efficiency video coding, Recommendation ITU-TH.265) allows the deployment of new video services with enhanced viewing experience, such as Ultra HD broadcast services. In addition to higher spatial resolution, Ultra HD can offer a wider color gamut (WCG) and a higher dynamic range (HDR) than the standard dynamic range HD TV (SDR) currently deployed. Different solutions for HDR / WCG video representation and encoding have been proposed (SMPTE 2014, “High Dynamic Range Electro-Optical Transfer”). Petition 870260066244, dated 06 / 07 / 2026, page 9 / 93 3 / 38 Function of Mastering Reference Visors, or SMPTE ST 2084, 2014, 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 Feb. 2016, pp 14-21).
[007] Backward compatibility with SDR decoding and rendering devices is an important feature in some video distribution systems, such as broadcast or multicast systems.
[008] Dual-layer encoding is one solution to support this feature. However, due to its multi-layered design, this solution is not suited to all distribution workflows.
[009] An alternative is a single-layer HDR distribution solution, as defined by ETSI Recommendation TS 103 433. The reader may also refer to the IBC 2016 paper (“A single-Layer HDR video coding framework with SDR compatibility”, E. François and L. Van de Kerkhof, IBC 2016) for further details. This single-layer distribution solution is SDR compatible and leverages existing SDR distribution networks and services. It enables high-quality HDR rendering on HDR-compatible CE (Consumer Electronics) devices, as well as high-quality SDR rendering on SDR CE devices.
[010] This single-layer distribution solution is based on a single-layer encoding / decoding process and is codec-independent (a 10-bit codec is recommended).
[011] This single-layer distribution solution uses side metadata (a few bytes per video frame or scene) that can be used in a post-processing stage to reconstruct the HDR signal from a decoded SDR signal.
[012] When the decoded SDR signal and the reconstructed HDR signal do not have the same color space, an inverse gamma mapping (being the dual function of Petition 870260066244, dated 06 / 07 / 2026, page 10 / 93 4 / 38 a gamut mapping in a pre-processing stage in HDR encoding) can be used in this post-processing stage. In practice, color gamuts can be defined by standards such as NTSC, ITU-R BT rec.709 (rec. 709), ITU-R BT rec. 2020 (rec. 2020), Adobe RGB, DCI-P3, or any other present or future color reproduction standard or any other restriction on the range of colors. In the case of single-layer HDR / WCG distribution, color gamut mapping is the process of mapping or redistributing colors from the wider color gamut (source colors) to colors of a narrower color gamut (target colors).When attempting to define a method of mapping source colors within a source color gamut (with its own source boundary) to target colors, which are located within a target color gamut (with its own target boundary), in order to utilize the entire color range in the target color gamut, it is known to define the color gamut mapping according to different conditions, among which is a boundary mapping condition: any source boundary color must be mapped to a target boundary color. However, this color gamut mapping is problematic because it results in faded colors, as illustrated in Fig. 1a. Figs. 1a and 1b illustrate a color gamut mapping on a hue sheet according to the previous technique. A hue sheet is a flat section of the color gamut at a constant hue (yellow in Fig. 1a, blue in Fig. 1b).The mapping of the boundary color band is performed by scaling the chroma value to a constant lightness value. Fig. 1a illustrates the case where the source cusp color (source yellow) is brighter than the target cusp color, meaning that, in this hue sheet, the lightness of the source color with maximum chroma (source yellow) is greater (brighter) than the lightness of the target color (target cusp color) with maximum chroma. Experts in the art will appreciate that if the source cusp color, source yellow in Fig. 1a, corresponds to the primary yellow of the source band, the target cusp color... Petition 870260066244, dated 06 / 07 / 2026, p. 11 / 93 5 / 38 may not necessarily correspond to the primary yellow of the target band, just as the primary yellow of the source band and the primary yellow of the target band may have different hues. As shown in Fig. 1a, without lightness mapping, the source yellow is mapped to a faded yellow (yellow mapped with constant lightness), being a mixture of yellow and white. Furthermore, some colors in the source boundary with increasing chroma and lightness values (in segment S0) are thus mapped to colors in the target boundary with decreasing chroma and increasing lightness values (in segment S1). This is particularly visually confusing. Fig. 1b illustrates the case where the color of the source cusp, blue in Fig.Figure 1b shows that the source color with maximum chroma (source blue) is darker than the corresponding target cusp color, meaning that in this hue sheet, the lightness of the source color with maximum chroma (source blue) is lower (darker) than the lightness of the target color (target cusp color) with maximum chroma. As shown in Fig. 1b, without lightness mapping, the source blue (corresponding to the maximum chroma color) is mapped to a blue (mapped blue with constant lightness) with the same brightness, but does not correspond to the maximum chroma color in the target range. The source cusp color (source blue) is not mapped to the most saturated color (target cusp color) of this hue sheet in the target range, as shown in Fig. 1b. Thus, without lightness mapping, the source blue is mapped to a blue (mapped blue with constant lightness) with the same brightness, but desaturated.However, another color (source color) in the source color gamut, representing a faded blue compared to the source blue, is mapped to the most saturated color (target cusp color) of this hue sheet in the target gamut, as shown in Fig. 1b, so that the mapped color (target cusp color) in the target image is perceived as very saturated relative to the mapped blue with a constant luminosity. This is a saturation inversion. In fact, the source color segment... Petition 870260066244, dated 06 / 07 / 2026, page 12 / 93 6 / 38 (S2) and the mapped color segment (S3) have inverted saturation slopes with known chroma mapping methods. The same problem arises for the yellow hue sheet. Similarly, in the target image, the yellow mapped to a constant luminosity will be perceived as insufficiently saturated relative to the mapped color (target cusp color). One possible solution to avoid saturation inversion, illustrated in Fig. 1c, is to apply a preliminary luminosity mapping to align the luminosity of the source cusp color with the luminosity of the target cusp color. However, this solution would increase the luminosity of the mapped color to the source blue. This alters the contrast of the images after color gamut mapping and therefore the artistic intent: in the example, the blue becomes lighter while the yellow becomes darker.
[013] An invertible color gamut mapping method that avoids or at least reduces saturation inversion, better preserving image contrast, is therefore desirable for improving HDR signal rendering. 3. Summary.
[014] The following is a simplified summary of these principles in order to provide a basic understanding of some aspects of these principles. This summary is not a comprehensive overview of these principles. It is not intended to identify key or critical elements of these principles. The following summary presents only some aspects of these principles in a simplified way, as a prelude to the more detailed description provided below.
[015] These principles propose a reversible chroma mapping that reduces the saturation inversion made by chroma mapping to a constant luminosity. This is achieved by performing a new chroma mapping that respects the slopes of the original color range. Two modalities corresponding to the modification of a larger part are disclosed. Petition 870260066244, dated 06 / 07 / 2026, p. 13 / 93 7 / 38 brighter or darker than the target band.
[016] According to a first aspect, a method is disclosed for mapping a color range from a first color range (source range) to a second color range (target range).The method comprises, in a constant hue plane, obtaining a target color at the second color gamut limit, where the luminosity of the target color is greater than or equal to the luminosity of a color with maximum chroma from the first color gamut (source cusp color) and where the luminosity of the target color is less than the luminosity of a color with maximum chroma from the second color gamut (target cusp color); and in the case where the luminosity of the current color is greater than the luminosity of the target color, mapping the chroma of a color at the first color gamut limit to constant luminosity using a decreasing chroma function applied to the luminosity, where the respective outputs of the decreasing function applied to the luminosity of the target color and the luminosity of white are the chroma of the target color and the chroma of white. This first specific modality is applicable in the case where the brightness of the color of the destination cusp is greater than the brightness of the color of the source cusp.
[017] According to a specific feature, the method additionally comprises determining for color, the color at the first color band boundary with constant luminosity; and in the case where the luminosity of the color is greater than the luminosity of the target color, performing a chroma mapping at constant luminosity of the color in relation to the color determined at the first color band boundary mapped with the decreasing function. This specific feature allows mapping any color on the hue sheet, not just the colors at the first color band boundary.
[018] According to another specific feature, the method additionally comprises obtaining intermediate target colors and determining the decreasing function of chroma applied to luminosity as a response to the target colors, white and colors. Petition 870260066244, dated 06 / 07 / 2026, p. 14 / 93 8 / 38 of intermediate destinations. This specific feature allows for a better definition of the decreasing function.
[019] According to another specific feature, the target color is at the second color gamut limit and the target color luminosity is a linear interpolation between the source cusp color luminosity and the target cusp color luminosity. This specific feature allows for an adaptive exchange between the saturation inversion range and the mapped color splitting in the second gamut.
[020] According to another specific characteristic, the target color is at the limit of the second color gamut and the luminosity of the target color is equal to the luminosity of the source cusp color. This specific characteristic allows avoiding saturation inversion.
[021] According to another specific feature, the source cusp color is selected from a group of primary and secondary colors. This specific feature allows reducing the number of target colors to be provided. Experts in the technique will understand that for a tint sheet between tint sheets of primary and secondary colors, the target color is interpolated.
[022] According to another specific feature, obtaining the target color involves receiving metadata regarding the parameters used for invertible gamma mapping.
[023] According to a second specific embodiment, in the case where the luminosity of the target cusp color is less than the luminosity of the source cusp color, the method comprises obtaining a target color at the limit of the second color band, wherein the luminosity of the target color is greater than the luminosity of a maximum chroma color of the second color band (target cusp color) and wherein the luminosity of the target color is less than or equal to the luminosity of a maximum chroma color of the first color band (cusp color). Petition 870260066244, dated 06 / 07 / 2026, p. 15 / 93 9 / 38 of origin) In the case where the luminosity of the color is less than the luminosity of the target color, chroma mapping comprises mapping, with constant luminosity, the chroma of a color at the limit of the first color band by an increasing chroma function applied to the luminosity, wherein the respective outputs of the increasing function applied to the luminosity of the target color and to the luminosity of black are the chroma of the target color and the chroma of black. Any of the specific characteristics described for the first embodiment is applicable to this second embodiment, mutatis mutandis.
[024] According to a second aspect, a device is disclosed for gamut mapping from a first color gamut to a second color gamut.The device comprises a processor configured, in a constant hue plane, to obtain a target color at the second color gamut boundary, wherein the luminosity of the target color is greater than or equal to the luminosity of a maximum chroma color of the first color gamut (source cusp color) and wherein the luminosity of the target color is less than the luminosity of a maximum chroma color of the second color gamut (target cusp color); and in the case where the luminosity of the current color is greater than the luminosity of the target color, the processor is further configured to map with constant luminosity the chroma of a color at the first color gamut boundary by a chroma-decreasing function applied to the luminosity, wherein the respective outputs of the decreasing function applied to the luminosity of the target color and the luminosity of white are the chroma of the target color and the chroma of white.
[025] According to a third aspect, a signal is disclosed having an SDR video and parameter values used for invertible color gamut mapping. The signal is further formatted to understand targetCroppingMode, crpWeightFactor, to implement invertible color gamut mapping.
[026] According to a fourth aspect, a processor-readable medium does not Petition 870260066244, dated 06 / 07 / 2026, page 16 / 93 10 / 38 transient, whose content stores an SDR video and metadata regarding the parameters used for invertible color gamut mapping, the non-transient processor-readable medium additionally comprises targetCroppingMode, crpWeightFactor to implement invertible color gamut mapping.
[027] According to a fifth aspect, a computer program product is disclosed comprising program code instructions for executing the steps of any of the disclosed methods when this program is run on a computer.
[028] According to a sixth aspect, a processor-readable medium is disclosed that contains instructions stored therein to cause a processor to execute at least the steps of any of the disclosed methods.
[029] According to a seventh aspect, a non-transient, computer-readable program storage device is disclosed, which tangibly embodies a program of instructions executable by the computer to perform any of the disclosed methods.
[030] Although not explicitly described, the present embodiments may be employed in any combination or subcombination. Furthermore, any feature or embodiment described for a method is compatible with a device intended to process the disclosed method and with a computer-readable storage medium that stores program instructions. 4. Brief description of the drawings.
[031] The drawings illustrate examples of the present principles. This shows:
[032] - Fig. 1a illustrates a color gamut mapping on a hue sheet according to the previous technique;
[033] - Fig. 1b illustrates a color gamut mapping on another hue sheet, according to the previous technique; Petition 870260066244, dated 06 / 07 / 2026, page 17 / 93 11 / 38
[034] - Fig. 1c illustrates a color gamut mapping on a hue sheet, according to the previous technique;
[035] - Fig. 2 shows an end-to-end workflow, supporting the production and delivery of content for HDR and SDR displays;
[036] - Fig. 3a shows the preprocessing stage in more detail;
[037] - Fig. 3b shows the HDR to SDR decomposition in more detail;
[038] - Fig. 4a shows the post-processing stage in more detail;
[039] - Fig. 4b shows the HDR reconstruction process in more detail;
[040] - Fig. 5 shows a block diagram of the steps of a method for invertible color gamut mapping, according to examples of the present principles;
[041] - Fig. 6a, Fig. 6b, Fig. 6c and Fig. 6d illustrate chroma mapping on a hue sheet, according to examples of the present principles;
[042] - Fig. 7 shows an example of a device architecture in accordance with an example of the present principles; and
[043] - Fig. 8 shows two remote devices communicating through a communication network according to an example of the present principles;
[044] Similar or identical elements are referenced with the same reference numbers. 5. Description of the Example of the present principles.
[045] These principles will be described in more detail hereafter with reference to the accompanying figures, which show examples of these principles. These principles may, however, be incorporated in many alternative forms and should not be interpreted as limited to the examples presented here. Therefore, although these principles are susceptible to various modifications and alternative forms, specific examples thereof are shown by way of examples in the drawings and will be described herein. Petition 870260066244, dated 06 / 07 / 2026, page 18 / 93 12 / 38 in detail. It should be understood, however, that there is no intention to limit these principles to the particular forms disclosed, but, on the contrary, the disclosure should cover all modifications, equivalents and alternatives that fall within the spirit and scope of these principles, as defined by the claims.
[046] The terminology used in this document is intended to describe only particular examples and is not intended to limit the present principles. As used herein, the singular forms a, an, and / or are also intended to include the plural forms, unless the context clearly indicates otherwise. It will be further understood that the terms comprise, including, include, and / or including, when used in this specification, specify the presence of declared resources, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more resources, integers, steps, operations, elements, components, and / or groups thereof. Furthermore, when an element is referred to as responsive or connected to another element, it may be directly responsive to or connected to the other element, or intervening elements may be present.On the other hand, when an element is referred to as directly responsive or directly connected to another 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 listed associated items and may be abbreviated as / .
[047] It will be understood that, although the terms first, second, etc. may be used here to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be called a second element, and similarly, a second element may be called a first element without departing from the teachings of the present principles. Petition 870260066244, dated 06 / 07 / 2026, page 19 / 93 13 / 38
[048] Although some of the diagrams include arrows in the communication paths to show a primary direction of communication, it should be understood that communication can occur in the opposite direction to the arrows shown.
[049] Some examples are described with regard to operational block diagrams and flowcharts in which each block represents an element, module, or part of the circuit code comprising one or more executable instructions to implement the specified logical functions. It should also be noted that in other implementations, the function(s) observed in the blocks may occur out of the order mentioned. For example, two blocks shown in succession may, in fact, be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order, depending on the functionality involved.
[050] The reference herein to "according to an example" or "in an example" means that a specific feature, structure, or characteristic described in connection with the example may be included in at least one implementation of these principles. The appearances of the phrase "according to an example" or "in an example" in various places in the specification do not necessarily all refer to the same example, nor are separate or alternative examples necessarily mutually exclusive of other examples.
[051] The reference numbers appearing in the claims are merely illustrative and will not have a limiting effect on the scope of the claims.
[052] Although not explicitly described, the present examples and variants may be employed in any combination or subcombination.
[053] These principles are described for decoding an image, but they extend to decoding a sequence of images (video) because each image in the sequence is sequentially encoded / decoded, as described below.
[054] Fig. 2 shows an end-to-end workflow that supports the Petition 870260066244, dated 06 / 07 / 2026, page 20 / 93 14 / 38 Production and delivery of content for HDR and SDR displays. It involves single-layer SDR / HDR encoding and decoding with side metadata, as defined, for example, in the ETSI recommendation, ETSI TS 103 433. The reader can also consult the IBC 2016 article (“A single-Layer HDR video coding framework with SDR compatibility”, E. François and L. Van de Kerkhof, IBC 2016) for more details.
[055] In the pre-processing stage, an incoming HDR video is decomposed into an SDR video and metadata. The SDR video is then encoded with any SDR video codec and an SDR bitstream is transported over an existing SDR distribution network with the accompanying metadata transported on a dedicated channel or embedded in the SDR bitstream.
[056] Preferably, the encoded video is an HEVC codec, such as the H.265 / HEVC or H.264 / AVC codec.
[057] Metadata is typically transported by SEI messages when used in conjunction with an H.265 / HEVC or H.264 / AVC codec.
[058] The SDR bitstream is decoded and a decoded SDR video is made available to a Consumer Electronics (CE) SDR display.
[059] Next, in a post-processing stage, which is functionally the reverse of the pre-processing stage, the HDR video is reconstructed from the decoded SDR video and the metadata obtained from a specific channel or SDR bitstream.
[060] Fig. 3a shows the preprocessing stage in more detail.
[061] The main component of the pre-processing stage is the decomposition of HDR to SDR which generates an SDR video and metadata from the HDR video.
[062] More precisely, HDR to SDR decomposition aims to convert an HDR video represented in a specific input format to an SDR video. Petition 870260066244, dated 06 / 07 / 2026, page 21 / 93 15 / 38 represented in a specific output format according to the embodiment disclosed below, but the present principles are not limited to a specific input / output format (color space or gamut).
[063] Optionally, the HDR video format, respectively the SDR video format, can be adapted to the aforementioned specific input format, respectively to the specific output format.
[064] The aforementioned input / output format adaptation may include color space conversion and / or color gamut mapping. Common format adaptation processes may be used, such as RGB to YUV or YUV to RGB conversion, BT.709-to-BT.2020 or BT.2020-to-BT.709, downsampling or upsampling of chroma components, etc.
[065] HDR to SDR decomposition aims to convert a 4:4:4 linear light input RGB HDR video into an SDR-compatible version. The process uses static metadata, such as the primary colors and gamma of the HDR and SDR images.
[066] Optionally, the HDR video format can be pre-adapted to the predetermined input format of the pre-processing stage and / or a gamma mapping can be used when the HDR video (input of the HDR decomposition stage) and the SDR video (output of the HDR decomposition stage) are represented in different color spaces.
[067] Fig. 3b shows the HDR to SDR decomposition in more detail.
[068] Next, HDR video samples are represented in the RGB color space (specific input format) and SDR video samples are represented in the RGB color space (specific output format).
[069] In step 1, the HDR video is analyzed frame by frame in order to derive a set of mapping parameters that will later be used to convert the HDR video into SDR video. Petition 870260066244, dated 06 / 07 / 2026, page 22 / 93 16 / 38
[070] In step 2, the luminance component L of an actual HDR video image to be decomposed is mapped to an SDR luminance component. Yi. The resulting signal is the SDR (the luma SDR component Yt) provided by: fl G B. (1) Yl— TM[L](2) where A — [A1A2A3]T is the canonical 3x3 conversion matrix from R'G'B' to Y'CbCr (for example, as specified in ITU-R Rec. BT.2020 or ITU-R Rec. BT.709 (depending on the color space), A1A2A3 being 1x3 matrices.
[071] In step 3 of Fig. 3b, the chroma components are derived as follows. First, the R, G, B values of the input HDR video are scaled by the ratio (Yi / L), resulting in a linear light SDR version of RGB. Then, a square root is applied, to reproduce a transfer function close to the ITU-R Rec. BT.709 OETF (Optoelectric Transfer Function). Note that using a square root ensures the process is reversible.
[072] The resulting R, G, B signal is converted into the chroma components Ut, V: [Uzl IvJA2 YR See (3) .VB.
[073] In step 4, a final color correction is applied to match the SDR colors to the HDR video colors. First, the chroma components are adjusted by a scaling factor of 1 / β(Yι), where β(Yι) is a function that allows control of the color saturation and hue of the resulting SDR video. USDR .VSDR. -----* β(Chi) V]<4)
[074] This step allows control of SDR colors and ensures their matching with HDR colors.
[075] In step 6, an invertible gamma mapping process can be applied when the input SDR image of the SDR reconstruction process to HDR is provided in a BT.709 color gamut (as specified by the variable). Petition 870260066244, dated 06 / 07 / 2026, p. 23 / 93 17 / 38 prePicColourSpace) and is different from the target BT.2020 color gamut of the HDR image (as specified by the recPicColourSpace variable). Backward color compatibility is defined so that the SDR CE receiver only supports the BT.709 color space, while the video to be distributed using SLHDR1 can support the BT.2020 color space. When recPicColourSpace is not equal to prePicColourSpace, on the HDR-to-SDR decomposition side, the WCG HDR video must be converted to a standard color gamut SDR video (plus metadata), while the reverse process on the HDR reconstruction side reverses this conversion by rendering the WCG HDR video from the standard color gamut SDR video (plus metadata). The cascade of these two color processes must be visually lossless, while the standard color gamut SDR video must fully preserve the artistic intent of the original WCG HDR video with minimal loss.The color reconstruction (inverse gamma mapping) and compression (gamma mapping) conversions are specified as reciprocals.
[076] In step 5, the metadata relating to luminance mapping (step 2), color correction (step 4) and invertible color gamut mapping (step 6) are transported to the post-processing stage. The metadata is transported as static metadata (if the parameters are not changed with the figure) or dynamic metadata (if the parameters are changed with the figure as for luminance mapping).
[077] This metadata allows fine control of the texture and colors of the SDR version and ensures a good fit to the intention of HDR.
[078] Fig. 4a shows the post-processing stage in more detail. The main component of the post-processing stage is SDR to HDR reconstruction, which reconstructs an HDR video from an SDR video (decoded) and metadata.
[079] More precisely, HDR reconstruction aims to convert SDR video. Petition 870260066244, dated 06 / 07 / 2026, page 24 / 93 18 / 38 represented in a specific input format in an HDR video represented in a specific output format according to the modality disclosed below, but the present principles are not limited to specific input / output formats (color space or gamma).
[080] Adapting the aforementioned input or output format may include color space conversion and / or color gamut mapping. Common format adaptation processes may be used, such as RGB to YUV or YUV to RGB conversion, BT.709 to BT-2020 or BT.2020 to BT-709, etc. For example, see Appendix D of ETSI Recommendation TS 103 433 which provides use cases for inverse gamut mapping.
[081] Optionally, the format of the reconstructed HDR video can be adapted to specific system characteristics (e.g., a set-top box, a connected TV) and / or an inverse gamma mapping can be used when the decoded SDR video (HDR reconstruction stage input) and the reconstructed HDR video (HDR reconstruction stage output) are represented in different color spaces and / or gamuts.
[082] Fig. 4b shows the HDR reconstruction process in more detail.
[083] HDR reconstruction is the functional inverse of HDR decomposition to SDR (Fig. 3b). However, for reasons of implementation complexity, some operations are concatenated or applied in a different order.
[084] In step 31, dynamic and / or static metadata is obtained, for example, from the SDR bitstream or from a specific channel.
[085] In step 32, a lutMapY luminance mapping lookup table (a 1D lookup table) is derived from the obtained metadata. This luminance mapping lookup table corresponds to the inverse of the square root of the luminance mapping curve.
[086] In step 33, a lutCC color correction lookup table is Petition 870260066244, dated 06 / 07 / 2026, page 25 / 93 19 / 38 derived from the obtained dynamic metadata. The lutCC color correction lookup table is linked to the βρ(Yβ) preprocessing color correction (equation 4) and the lutMapY luminance mapping lookup table by the following equation: β[Y] = 2B x lutMapY[Y] x lutCC[Y](5) where B is the bit depth of the luma component of the decoded SDR image.
[087] In step 34, an image from the reconstructed HDR video (linear light HDR video) is reconstructed by applying an HDR reconstruction to an image from the decoded SDR video using the luma-related lookup table derived from lutMapY and the color correction lookup table derived from lutCC. In step 36, the color reconstruction or inverse gamma mapping process allows the generation of a wide color gamut image from a standard color gamut image with associated metadata. This process is defined for a 4:4:4 chroma sampling and a full-range YUV linear light signal. The input YUV signal comes from converting an input RGB linear light signal (output of the SDR to HDR 34 reconstruction process) into a YUV color space due to the canonical R'G'B' to Y'CbCr matrix (computed due to SMPTE RP 177 [i.8]).This process may also include a chroma remapping according to the modalities described, a luminosity remapping (if applicable), and a hue remapping.
[088] Post-processing operates on a lutMapY luminance mapping lookup table (step 32), a lutCC color correction lookup table (step 33), and inverse gamma mapping parameters (step 35) defining chroma mapping that preserves saturation slopes. According to a highlighted idea, the disclosed chroma mapping operates with constant luminance and uses a clipped version of the target color gamut so that the luminance of the color with maximum chroma in the source gamut is nearly the same. Petition 870260066244, dated 06 / 07 / 2026, page 26 / 93 20 / 38 which is the brightness of the color with the maximum chroma in the clipped version of the target color gamut. Furthermore, the same slope to the threshold is determined for the source and destination threshold. Consequently, parameters are defined that determine the chroma mapping mode and the amount of gamut clipping required for the primary and secondary colors. The table and the respective parameters are derived from the metadata (step 31).
[089] Metadata can be transported (step 5) as dynamic metadata according to the so-called parameter-based mode or table-based mode, in order to derive the lutMapY luminance mapping lookup table (step 32) and the lutCC color correction lookup table (step 33) from dynamic metadata obtained (step 31). Metadata relating to inverse color gamut mapping can be transported (step 5) as static metadata. Some metadata to be transported in step 5 are chroma mapping parameters representative of the chroma mapping method and a target color required by primary and / or secondary colors (ETSI recommendation ETSI TS 103 433, clause 6.3.10). Thus, the following parameters are described: targetCroppingMode and crpWeightFactor. targetCroppingMode TargetCroppingMode Value Setting 0 Target cropping disabled 1 Target cropping applied to each primary and secondary color 2 Target cropping applied to cool colors (colors with their cusp value in the wide gamut lower than the cusp value in the standard gamut) 3 Target cropping with weighting factor applied to each primary and secondary color crpWeightFactor
[090] This array of six variables specifies the weighting to be applied to each primary and secondary color during the target range cropping process. This array should only be invoked when targetCroppingMode is equal to 3. The value Petition 870260066244, dated 06 / 07 / 2026, page 27 / 93 21 / 38 of the c index equal to 0 should correspond to primary red, c equal to 1 should correspond to secondary magenta, c equal to 2 should correspond to primary blue, c equal to 3 should correspond to secondary cyan, c equal to 4 should correspond to primary green, c equal to 5 should correspond to secondary yellow. The value of crpWeightFactor [c] is in the range limited [0 / 128... 135 / 128] by the 9 / 128 step.
[091] These parameters are renamed croppingModeSCG and cmWeightFactor, respectively, in the latest version of the ESTI recommendation.
[092] This metadata can be transmitted using the SEI message registered by the HEVC Color Volume Reconstruction Information (CVRI) user data, whose syntax is based on the SMPTE ST 2094-20 specification (ETSI recommendation ETSI TS 103 433 Annex A. 3).
[093] In step 31, the SEI CVRI message is analyzed to obtain the luminance mapping parameters, color correction parameters and inverse gamma parameters.
[094] In step 32, the lutMapY luminance mapping lookup table is reconstructed (derived) from the obtained luminance mapping parameters (see section 7.2.3.1 of ETSI TS 103 433 for more details).
[095] In step 33, the lutCC color correction lookup table is reconstructed (derived) from the obtained color correction parameters (see section 7.2.3.2 of ETSI TS 103 433 for more details).
[096] In step 35, the resources for chroma mapping (mainly the target color) are determined (derived) from the inverse gamma mapping parameters obtained, as described below with the color gamma mapping method. The chroma mapping parameters offer the possibility of either performing a global chroma mapping for all colors, or only mapping cool colors (such as blue, cyan, and green) corresponding to the colors in which the color Petition 870260066244, dated 06 / 07 / 2026, page 28 / 93 22 / 38 of the source cusp is darker than the destination cusp color) or weight the chroma mapping at constant luminosity of each individual primary and secondary color.
[097] This metadata can be transmitted as dynamic metadata using the HEVC Color Remapping Information (CRI) SEI message whose syntax is based on the SMPTE ST 2094-30 specification (ETSI recommendation ETSI TS 103 433 Appendix A.4).
[098] Note that static metadata can also be used by the post-processing stage and transmitted via the SEI message. For example, targetCroppingMode and crpWeightFactor can be carried by the SEI message registered by TS 103 433 Information (TSI) user data (payloadMode), as defined by ETSI TS 103 433 (section A.2.2). Static metadata, such as primary colors or maximum display mastering luminance, are transmitted via a Mastering Display Colour Volume (MDCV) SEI message, as defined in AVC, HEVC.
[099] Fig. 5 shows a block diagram of the steps of a method for invertible gamma mapping, according to examples from the present principles. This method is compatible with any HDR to SDR decomposition process, producing an SDR image and metadata. For illustrative purposes, the gamma mapping method is part (step 6) of the HDR to SDR decomposition process, as described in relation to Fig. 3b. This process is particularly suited when wide color gamut HDR video needs to be converted into standard color gamut SDR video. Advantageously, constant luminance chroma mapping according to the present principles avoids or reduces saturation inversion in order to obtain better preservation of the original color intent of the HDR image. As shown in Figs. 6a, 6b, 6c, and 6d, the output of Petition 870260066244, dated 06 / 07 / 2026, page 29 / 93 23 / 38 chroma mapping is clipped in the gray area of the target color gamut. However, since this method is fully invertible, it is also compatible with any SDR-to-HDR reconstruction process that produces an HDR image. For illustrative purposes, the gamma mapping method is also part (step 36) of the SDR-to-HDR reconstruction process, as described in relation to Fig. 4b. This process is especially suited when standard color gamut SDR video needs to be converted back into a wide color gamut HDR video. Advantageously, inverse gamma mapping reverses the chroma correction applied on the encoder side. The chroma is corrected while keeping the hue and brightness unchanged. However, the method is also compatible with any process involving color gamut mapping from a first color gamut to a second color gamut.HDR video samples and SDR video samples can be represented in any color space, such as YUV, CIELUV, L*a*b*, or IPT. For illustrative purposes, an HDR video sample, called a color, is represented on a plane with a constant hue, known as a hue sheet, as shown in Fig. 6a, Fig. 6b, Fig. 6c, and Fig. 6d.
[0100] In a preliminary step 51, a target color is obtained for a color at the limit of the first range (source range). According to the first variant illustrated in Fig. 6a, the luminosity (L2) of the target color is equal to the luminosity (L2) of a maximum chroma color from the first color band (source cusp color) and the luminosity (L2) of the target color is less than the luminosity (L3) of a maximum chroma color from the second color band (target cusp color). According to the second variant illustrated in Fig. 6b, the luminosity (L2) of the target color is equal to the luminosity (L2) of a maximum chroma color from the first color band (source cusp color) and the luminosity (L2) of the target color is greater than the luminosity (L3) of a maximum chroma color from the second color band (target cusp color). According to the third variant illustrated in Fig. 6d, the Petition 870260066244, dated 06 / 07 / 2026, p. 30 / 93 24 / 38 The luminosity (L5) of the target color is greater than the luminosity (L2) of a maximum chroma color from the first color band (source cusp color), and the luminosity (L5) of the target color is less than the luminosity (L3) of a maximum chroma color from the second color band (target cusp color). Although not illustrated, in a fourth variant, the luminosity of the target color is greater than the luminosity of a maximum chroma color from the second color band (target cusp color), and the luminosity of the target color is less than the luminosity of a maximum chroma color from the first color band (source cusp color).Advantageously, as shown below, the first and second variants avoid any saturation inversion, while the third and fourth variants limit saturation inversion to colors whose luminosity belongs to the range between the luminosity (L2) of the color at the limit of the first range with maximum chroma, called the source cusp color, and the luminosity of the target color (L5). In contrast, in the methods of the prior art, saturation inversion occurs for colors whose luminosity belongs to the range between the luminosity (L2) of the source cusp color and the luminosity of the target cusp color (L3). The source cusp color (respectively the target cusp color) belongs to the limit of the first color band / source (respectively the second color band / target) and has a maximum chroma, as shown in Fig. 6a and Fig. 6b.The target color represents the amount of chroma correction to be applied to colors where the luminosity is greater than the luminosity of the target color, in the case where the luminosity of the target cusp color is greater than the luminosity of the source cusp color, or to colors where the luminosity is less than the luminosity of the target color, in the case where the luminosity of the target cusp color is less than the luminosity of the source cusp color. According to the first and second variants, the intersection between the limit of the second range and the luminosity line (L2) of the source cusp color defines the target color. In the third variant, the target color is not. Petition 870260066244, dated 06 / 07 / 2026, p. 31 / 93 25 / 38 determined by the lightness of the source cusp color, but is determined at the second gamut limit (target gamut) for a lightness (L5) responsive to the lightness (L3) of the target cusp color and the lightness (L2) of the source cusp color, as shown in Fig. 6d. For example, the lightness (L5) of the target color is a linear combination of the lightness (L3) of the target cusp color and the lightness (L2) of the source cusp color. This variant does not prevent saturation inversion, but limits it to the range of colors whose lightness is comprised between the lightness of the source cusp color and the lightness of the target color. Advantageously, this variant is a trade-off between saturation inversion and second gamut coverage (as the mapped colors belong to a larger part of the second gamut).According to another non-limiting example, the luminosity value of the target color (L5) is obtained from a weighting factor, which is a ratio (or percentage) of the difference in luminosity values between the luminosity (L3) of a second cusp color (source cusp color) and the luminosity (L2) of the second cusp color, for example, 0.3 or 30%, but is usually in a range [0 - 1] or [0% - 100%]. According to a specific characteristic, the color is a primary color selected from a group of primary and secondary colors. As explained earlier with respect to the targetCroppingMode variable, chroma mapping is applied to each primary and secondary color, or only to parts of them, such as primary colors green and blue and secondary color cyan, or with a weighting factor applied to each primary and secondary color. The weighting factors define the lightness (L5) of the target color in the provided hue sheet.According to a non-limiting example, a factor of 100% is applied to the primary colors green and blue and the secondary color cyan, and a factor of 50% is applied to the secondary colors yellow and magenta and the primary red. In this example, as shown in Fig. 6a, the lightness (L2) of the target color corresponds to the lightness of the source color at the limit of the first gamut with. Petition 870260066244, dated 06 / 07 / 2026, p. 32 / 93 26 / 38 maximum chroma (source cusp color) on the same hue sheet. According to another non-limiting example, a factor of 50% is applied to the primary colors green and blue and the secondary color cyan, and a factor of 0% is applied to the secondary colors yellow and magenta and the primary color red. In this example, as shown in Fig. 6d, the lightness (L5) of the target color corresponds to the arithmetic mean ((L2 + L3) / 2) of the lightness of the source cusp color and the target cusp color on the same hue sheet. In other words, the weighting factor defines a linear interpolation between the lightness (L3) of the target cusp color and the lightness (L2) of the source cusp color. The parameters for obtaining the target color are advantageously sent / received for the primary colors, thus limiting the size of the metadata.According to the characteristic where the color is any color (meaning it is not a primary color), the target color values are interpolated from the corresponding values for the primary colors. According to these examples, lightness mapping is advantageously limited to a few hues, for example, where the lightness of the cusp color is lower in the source color range than in the target color range, as shown in Fig. 1a. In yet another fifth variant illustrated in Fig. 6c, N (N being an integer greater than 1) target colors are carefully determined as respective N chroma values mapped to N colors on the boundary of the first range (source range) with the same lightness. These N target colors allow refining the ascending or descending function used in chroma mapping.In an HDR-to-SDR decomposition process, the primary colors and their corresponding target colors are defined and encoded as parameters for invertible gamma mapping, as described above. The chroma mapping parameters used for invertible gamma mapping are then sent metadata for inverse gamma mapping. In the SDR-to-HDR reconstruction process, the metadata relating to the parameters used for the... Petition 870260066244, dated 06 / 07 / 2026, page 33 / 93 27 / 38 invertible gamma mapping is received, and the primary colors and corresponding target color are derived from the received parameters.
[0101] In step 52, a chroma mapping of the color from the first color band to the second color band at constant luminosity is applied. Advantageously, the method is compatible with known methods that map colors while maintaining constant hue and luminosity, meaning that the output color is on the same constant luminosity line and the same constant hue sheet as the original color. The chroma mapping method according to the present principles is now explained for the first variant of Fig. 6a and the third variant of Fig. 6d. Experts in the art will easily adapt the description to other variants, such as the variant of Fig. 6b. In the first and third variants where the target cusp color is brighter than the source cusp color (the target color is in the middle), a decreasing function, representative of a cut target band (dashed line in Fig.1a), is defined such that the chroma values generated by the function applied to the increasing luminosity value are decreasing chroma values and such that the boundary of the cut target band passes through the target color and white. In other words, the output of the function applied to the luminosity of the target color results in the chroma of the target color and the output of the function applied to the luminosity of white results in the chroma of white (being zero). Thus, mapping (523) to a constant luminosity of the chroma of a color in the first color band boundary comprises applying the decreasing function to the luminosity of the color in the case where the luminosity of the color is greater than the luminosity of the target color (and up to the luminosity of white). For other colors in the first color band boundary, that is, in the case where the luminosity of the color is less than the luminosity of the target color (and up to the luminosity of the back), the known chroma mapping is applied.Thus, the limit of the cut-off destination range follows the decrease in the limit of the origin range to clearer values. Na. Petition 870260066244, dated 06 / 07 / 2026, p. 34 / 93 28 / 38 Additional variant where the luminosity of the target color corresponds to the luminosity of the source cusp color, the disclosed method avoids saturation inversion, thus avoiding any preliminary luminosity mapping. Experts in the technique will understand that, for colors that are not at the first gamut limit, the mapping involves determining, for the color, the color at the first gamut limit of color with constant luminosity; and if the luminosity of the color is greater than the luminosity (L5) of the target color, performing a chroma mapping at constant luminosity of the color in relation to the color determined at the first gamut limit of color mapped with the decreasing function. More generally, for any color, the chroma mapping with a constant luminosity of the color is performed in relation to the chroma mapped of the color determined at the first gamut limit of color.According to a particular embodiment, a linear chroma scale is used that maps the colors on each line of constant luminosity (Li, L2, L3, L4), so that the source color with the highest chroma value on this line (L2) is mapped on this same line of constant luminosity (L2) to the color determined at the first color gamut limit mapped with the decreasing function in case the color luminosity is greater than the luminosity (L5) of the target color, or to the color at the target gamut limit on this same line of constant luminosity (L2) in case the color luminosity is less than the luminosity (L5). In the case of the primary color blue, as shown in Fig. 6a, since the lower part of the target range is linear, an increasing function applied to the chroma is an affine function corresponding to the target range.Furthermore, a color on the first color band boundary between the source cusp color and white is mapped with a decreasing chroma function between the target color and white at a constant luminosity. In the case of the primary color blue, as shown in Fig. 6a, since the target band is piecewise linear, the decreasing function applied to the chroma is also an affine function linking the target color and white. Advantageously, in... Petition 870260066244, dated 06 / 07 / 2026, p. 35 / 93 29 / 38 In a linear color space, in each constant hue sheet, the mapped colors are distributed only within a triangle defined by black, white, and the target color corresponding to the source cusp color. In other words, the mapped color gamut is clipped so that, at its boundaries, saturation does not increase with lightness for lightness values greater than the lightness of the source cusp color. The shape of the mapped gamut is therefore closer to the shape of the source color gamut (since, at the boundary of the source color gamut, saturation does not increase with lightness for lightness values greater than the lightness of the cusp color). For simplicity, affine functions are described in the example, but the present principles are compatible with any other function. In another example, the function used in each constant hue sheet is a quadratic function. According to a variant shown in Fig.6c, a portion of the upper segment of the target color band or the entire segment (the line connecting white to the target cusp color) is replaced by a parabola tangent to that segment and connecting the N intermediate target colors.
[0102] For the sake of completeness, the entire chroma mapping is briefly explained. In a preliminary test 521, the variant in which the darkest or brightest part of the gamma boundary is cut is determined. Therefore, if the brightness of the target cusp color is greater than the brightness of the source cusp color, the brightest part of the target band is cut with the decreasing function 523 corresponding to the variants in Fig. 6a, Fig. 6c, and Fig. 6d. If the brightness of the target cusp color is less than the brightness of the source cusp color, the darkest part of the target band is cut with the increasing function 522 corresponding to the variant in Fig. 6b.
[0103] Even if the disclosed method does not allow the use of a preliminary luminosity mapping, the method is compatible with luminosity mapping to achieve a satisfactory color shift distribution in the gamut. Petition 870260066244, dated 06 / 07 / 2026, page 36 / 93 30 / 38 of the target and in the contrast change. Therefore, a luminosity mapping can be used to map the source cusp color to an intermediate target color with a luminosity closer to the target cusp color. This corresponds to applying the proposed method after luminosity mapping, using the color gamut mapped from the luminosity instead of the source color gamut.
[0104] Experts in the technique will understand that the method is fully invertible, since for inverse gamma mapping, source and destination gamma limits are inverted. In fact, the color mapped by inverse chroma is obtained using the same ascending or descending function used during direct gamma mapping.
[0105] This method is based on any HDR reconstruction process that requires an SDR image and dynamic metadata.
[0106] For illustrative purposes, the HDR reconstruction process may be the HDR reconstruction process as described in relation to Fig. 4b. In this case, the HDR image is reconstructed from a decoded SDR image. However, the SDR image used to reconstruct an HDR image may also be stored with compression and obtained without the need for decoding.
[0107] Next, the method obtains, for example, by decoding an SDR bitstream, an SDR image (decoded) whose dynamic range of luminance values is smaller than the dynamic range of luminance values of the HDR image to be reconstructed.
[0108] In Fig. 2-5, modules are functional units, which may or may not be related to distinguishable physical units. For example, these modules, or some of them, may be assembled into a single component or circuit or contribute to the functionality of a software. Conversely, some modules may potentially be composed of separate physical entities. The devices Petition 870260066244, dated 06 / 07 / 2026, page 37 / 93 31 / 38 that are compatible with the present principles are implemented using either pure hardware, for example, using dedicated hardware such as ASIC or FPGA or VLSI, respectively "Application-Specific Integrated Circuit", "Field Programmable Gate Array", "Very Large Scale Integration", or several integrated electronic components incorporated into a device or a mixture of hardware and software components.
[0109] Fig. 7 represents an exemplary architecture of a device 60 that can be configured to implement a method described in relation to Fig. 2-5.
[0110] Device 60 comprises the following elements which are linked together by a data and address bus 61: - a 62 microprocessor (or CPU), which is, for example, a DSP (or Digital Signal Processor); - a ROM (or Read-Only Memory) 63; - a 64-bit RAM (or Random Access Memory); - an I / O interface 65 for receiving data to be transmitted from an application; and - a 66 battery
[0111] According to an example, battery 66 is external to the device. In each of the memories mentioned, the word "register" used in the specification can correspond to a small capacity area (a few bits) or a very large area (for example, an entire program or a large amount of received or decoded data). ROM 63 comprises at least one program and parameters. ROM 63 can store algorithms and instructions to execute techniques according to described modalities. When powered on, CPU 62 loads the program into RAM and executes the corresponding instructions.
[0112] RAM 64 contains, in a register, the program executed by Petition 870260066244, dated 06 / 07 / 2026, page 38 / 93 32 / 38 CPU 62 is loaded after switching device 60, input data is stored in a register, intermediate data in different states of the method is stored in a register, and other variables used for the execution of the method are stored in a register.
[0113] The implementations described in this document can be implemented in, for example, a method or process, a device, a software program, a data stream, or a signal. Even if discussed only in the context of a single implementation form (for example, discussed only as a method or device), the implementation of the discussed features can also be implemented in other forms (for example, a program). A device can be implemented in, for example, appropriate hardware, software, and firmware. Methods can be implemented in, for example, a device such as, for example, a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device.Processors also include communication devices, such as computers, mobile phones, portable / personal digital assistants (PDAs), and other devices that facilitate the communication of information between end users.
[0114] According to an encoding example or encoder, the HDR video or an HDR image from an HDR video is obtained from a source. For example, the source belongs to a set comprising: - a local memory (63 or 64), for example, a video memory or a RAM (or random access memory), a flash memory, a ROM (or read-only memory), a hard disk; - a storage interface (65), for example, an interface with mass storage, RAM, flash memory, ROM, optical disk or magnetic media; - a communication interface (65), for example, a wired interface Petition 870260066244, dated 06 / 07 / 2026, page 39 / 93 33 / 38 (for example, a bus interface, a wide area network interface, a local area network interface) or a wireless interface (such as an IEEE 802.11 interface or a Bluetooth® interface); and - an image capture circuit (for example, a sensor such as, for example, a CCD (or charge-coupled device) or CMOS (or complementary metal-oxide semiconductor)).
[0115] According to a decoding or decoder example, the decoded SRD video or reconstructed HDR video is sent to a destination; specifically, the destination belongs to a set comprising: - a local memory (63 or 64), for example, a video memory or RAM, a flash memory, a hard drive; - a storage interface (65), for example, an interface with mass storage, RAM, flash memory, ROM, optical disk or magnetic media; - a communication interface (65), for example, a wired interface (for example, a bus interface (for example, USB (or Universal Serial Bus)), a wide area network interface, a local area network interface, an HDMI (High Definition Multimedia Interface) interface or a wireless interface (such as an IEEE 802.11, WiFi® or Bluetooth® interface); and - a display.
[0116] According to encoding examples or encoder, the SDR bitstream and / or the other bitstream carrying the metadata are sent to a destination. As an example, one or both of these bitstreams are stored in local or remote memory, for example, video memory (64) or RAM (64), a hard disk (63). In a variant, one or both bitstreams are sent to a storage interface (65), for example, an interface with mass storage, flash memory, ROM, an optical disk or a Petition 870260066244, dated 06 / 07 / 2026, page 40 / 93 34 / 38 magnetic support and / or transmitted through a communication interface (65), for example, an interface for a point-to-point link, a communication bus, a point-to-multipoint link or a broadcast network.
[0117] According to decoding or decoder examples, the SDR bitstream and / or other bitstream carrying metadata is obtained from a source. For example, the bitstream is read from local memory, for example, video memory (64), RAM (64), ROM (63), flash memory (63) or a hard disk (63). In a variant, the bitstream is received from a storage interface (65), for example, an interface with mass storage, RAM, ROM, flash memory, optical disk or magnetic media and / or received from a communication interface (65), for example, an interface to a point-to-point link, a bus, a point-to-multipoint link or a broadcast network.
[0118] According to examples, device 60 being configured to implement an encoding method as described above, belongs to a set comprising: - a mobile device; - a communication device; - a gaming device; - a tablet (or tablet computer); - a laptop; - a still image camera; - a video camera; - an encoding chip; - a static image server; and - a video server (for example, a broadcast server, a video-on-demand server, or a web server). Petition 870260066244, dated 06 / 07 / 2026, page 41 / 93 35 / 38
[0119] According to examples, device 60 being configured to implement a decoding method as described above, belongs to a set comprising: - a mobile device; - a communication device; - a gaming device; - a set-top box; - a TV set; - a tablet (or tablet computer); - a laptop; - a screen and - a decoding chip.
[0120] According to an example of the present principles, illustrated in Fig. 7, in a transmission context between two remote devices A and B through a NET communication network, device A comprises a processor with respect to RAM and ROM memory configured to implement a method for encoding an image as described above and device B comprises a processor with respect to RAM and ROM memory that are configured to implement a method for decoding as described above.
[0121] According to an example, the network is a transmission network, adapted to transmit still images or video images from device A to decoding devices, including device B.
[0122] A signal, intended to be transmitted by device A, carries the SDR bitstream and / or the other bitstream that carries the metadata. The SDR bitstream comprises an encoded SDR video, as explained previously. This signal additionally comprises metadata relating to the parameter values used to reconstruct an HDR video from said decoded SDR video. Petition 870260066244, dated 06 / 07 / 2026, p. 42 / 93 36 / 38
[0123] The implementations of the various processes and resources described in this document can be incorporated into a variety of different equipment or applications. Examples of such equipment include an encoder, a decoder, a post-processor output from a decoder, a pre-processor that provides input to an encoder, a video encoder, a video decoder, a video codec, a web server, a set-top box, laptop, personal computer, mobile phone, PDA, and any other device for processing an image or video or other communication devices. As should be clear, the equipment can be mobile and even installed in a mobile vehicle.
[0124] Furthermore, methods can be implemented by instructions being executed by a processor, and these instructions (and / or data values produced by an implementation) can be stored in a computer-readable storage medium. A computer-readable storage medium can take the form of a computer-readable program product embedded in one or more computer-readable media and with computer-readable program code embedded therein that is executable by a computer. A computer-readable storage medium, as used herein, is considered a non-transient storage medium, given its inherent ability to store the information contained therein, as well as its inherent ability to provide retrieval of information from it.A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. It should be appreciated that, while providing more specific examples of computer-readable storage media to which the present principles may apply, it is merely an illustrative and not exhaustive list, as is easily seen. Petition 870260066244, dated 06 / 07 / 2026, page 43 / 93 37 / 38 appreciated by one skilled in the art: a portable computer 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 thereof.
[0125] The instructions can form an application program tangibly embedded in a processor-readable medium.
[0126] Instructions can be found, for example, in hardware, firmware, software, or a combination thereof. Instructions can be found in, for example, an operating system, a separate application, or a combination of both. A processor can therefore be characterized as, for example, a device configured to execute a process and a device that includes a processor-readable medium (such as a storage device) having instructions to execute a process. Furthermore, a processor-readable medium may store, in addition to or instead of instructions, data values produced by an implementation.
[0127] As will be evident to a person skilled in the art, implementations can produce a variety of formatted signals to carry information that can, for example, be stored or transmitted. The information can include, for example, instructions to execute a method or data produced by one of the described implementations. For example, a signal can be formatted to carry as data the rules for writing or reading the syntax of a described example of the present principles, or to carry as data the actual syntax values written by a described example of the present principles. This signal can be formatted, for example, as an electromagnetic wave (for example, using a portion of the radio frequency spectrum) or as a signal of Petition 870260066244, dated 06 / 07 / 2026, page 44 / 93 38 / 38 baseband. 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 through a variety of different links, wired or wireless, as is known. The signal may be stored on a processor-readable medium.
[0128] Several implementations have been described. However, 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. Furthermore, one skilled in the art 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), at least substantially in the same manner(s), to achieve at least substantially the same result(s) as the disclosed implementations. Therefore, these and other implementations are contemplated by this application.
Claims
1. Method comprising gamut mapping of a current color from a first color gamut to a second color gamut, the gamut mapping comprising, on a constant hue plane, mapping the chroma of the current color from the first color gamut to the second color gamut at constant lightness, the method being CHARACTERIZED in that the chroma mapping further comprises: obtaining (51) a target color at the boundary of the second color gamut, wherein the lightness (L5) of the target color is greater than or equal to the lightness (L2) of a maximum chroma color from the first color gamut and wherein the lightness (L5) of the target color is less than the lightness (L3) of a maximum chroma color from the second color gamut;in the case where the luminosity of the current color is greater than the luminosity of the target color, map (523) at constant luminosity the chroma of a color at the first color gamut limit by a decreasing chroma function applied to the luminosity, wherein the respective outputs of the decreasing function applied to the luminosity of the target color and to the luminosity of white are the chroma of the target color and the chroma of white.; 2. Method, according to claim 1, CHARACTERIZED in that it further comprises, in the constant hue plane: determining for the current color, the color at the first color gamut limit with constant luminosity; and in the case where the luminosity of the current color is greater than the luminosity of the target color, performing a chroma mapping at constant luminosity of the color in relation to the color determined at the first color gamut limit mapped with the decreasing function.
3. Method, according to claim 1 or 2, CHARACTERIZED by Petition 870260066244, dated 06 / 07 / 2026, p. 46 / 93 2 / 4, in that it further comprises obtaining intermediate target colors and determining the decreasing chroma function applied to the luminosity in response to the target color, white, and intermediate target colors.
4. Method comprising gamut mapping of a current color from a first color gamut to a second color gamut, the gamut mapping comprising, on a constant hue plane, mapping the chroma of the current color from the first color gamut to the second color gamut at constant luminosity, the method being CHARACTERIZED in that the chroma mapping further comprises: obtaining (51) a target color at the boundary of the second color gamut, wherein the luminosity of the target color is greater than the luminosity of a maximum chroma color from the second color gamut and wherein the luminosity of the target color is less than or equal to the luminosity of a maximum chroma color from the first color gamut;in the case where the luminosity of the current color is less than the luminosity of the target color, map (522) with constant luminosity the chroma of a color at the first color band limit by an increasing chroma function applied to the luminosity, wherein the respective outputs of the increasing function applied to the luminosity of the target color and to the luminosity of black are the chroma of the target color and the chroma of black.; 5. Method, according to any one of claims 1 to 4, CHARACTERIZED in that the brightness of the target color is a linear interpolation between the brightness (L2) of the maximum chroma color of the first color band and the brightness (L3) of the maximum chroma color of the second color band.
6. Method, according to any one of claims 1 to 4, CHARACTERIZED in that the brightness of the target color is equal to the brightness (L2) of the maximum chroma color of the first color band.
7. Method, according to any one of claims 1 to 6, Petition 870260066244, dated 06 / 07 / 2026, p. 47 / 93 3 / 4 CHARACTERIZED in that said maximum chroma color of the first color band is selected from a group of primary and secondary colors.
8. A method, according to any one of claims 1 to 7, characterized in that said increasing or decreasing function is a piecewise affine function.
9. Device comprising means for gamut mapping of a current color from a first color gamut to a second color gamut in a constant hue plane, CHARACTERIZED in that the device further comprises • means for obtaining a target color at the boundary of the second color gamut, wherein the lightness (L5) of the target color is greater than or equal to the lightness (L2) of a maximum chroma color from the first color gamut and wherein the lightness (L5) of the target color is less than the lightness (L3) of a maximum chroma color from the second color gamut;and • means for performing chroma mapping of the current color from the first color band to the second color band at constant luminosity, wherein in the case where the luminosity of the current color is greater than the luminosity of the target color, map (523) at constant luminosity the chroma of a color at the limit of the first color band by a decreasing chroma function applied to the luminosity, wherein the respective outputs of the decreasing function applied to the luminosity of the target color and to the luminosity of white are the chroma of the target color and the chroma of white.; 10. Device according to claim 9, CHARACTERIZED in that the brightness of the target color is a linear interpolation between the brightness (L2) of the maximum chroma color of the first color band and the brightness (L3) of the maximum chroma color of the second color band. Petition 870260066244, dated 06 / 07 / 2026, p. 48 / 93 4 / 4 11. Device according to claim 9, CHARACTERIZED in that the brightness of the target color is equal to the brightness (L2) of the maximum chroma color of the first color band.
12. Device, according to any one of claims 9 to 11, CHARACTERIZED in that said maximum chroma color of the first color band is selected from a group of primary and secondary colors.
13. Device according to any one of claims 9 to 12, CHARACTERIZED in that said increasing or decreasing function is a piecewise affine function.
14. Signal having an SDR video and parameter values used for gamma mapping, CHARACTERIZED in that said parameters used for gamma mapping allow for gamma mapping as defined in claim 1 or 4.
15. Processor-readable media CHARACTERIZED in that it is disclosed that it contains stored instructions to cause a processor to execute at least the steps of the method as defined in any one of claims 1 to 8.