Method, device, computer program and signal for avoiding chrominance clipping in a tone mapper with flexible brightness, saturation and hue preservation

Abstract

A method comprising: obtaining a first picture in a first dynamic range; obtaining parameters defining a first color correction function preventing clipping of color components of a second picture resulting from a tone mapping of the first picture in a second dynamic range; signaling parameters defining a tone mapping function in metadata, the parameters of the tone mapping function being derived from the parameters defining the first color correction function; signaling parameters defining a second color correction function in the metadata, the parameters defining the second color correction function being obtained from default values; signaling a third picture in the second dynamic range obtained using the signaled parameters of the tone mapping function and the signaled parameters of the second color correction function in video data along with the metadata.

Description

[0001]2023PF00945 METHOD, DEVICE AND APPARATUS FOR AVOIDING UV SDR CLIPPING IN A SL-HDR1 TONE MAPPER WITH FLEXIBLE BRIGHTNESS, SATURATION AND HUE PRESERVATION 1. TECHNICAL FIELD At least one of the present embodiments generally relates to the field of distribution of HDR (High Dynamic Range) video using a SL-HDR1 system and more particularly to a method, a device and an equipment for avoiding U and V components of SDR (Standard Dynamic Range) pictures clipping while maintaining as much as possible a saturation and a hue of SDR pictures. 2. BACKGROUND Recent advancements in display technologies are beginning to allow for an extended dynamic range of color, luminance and contrast in images to be displayed. The term image refers here to an image content that can be for example a video or a still picture or image. High-dynamic-range video (HDR video) describes video having a dynamic range greater than that of standard-dynamic-range video (SDR video). HDR video involves capture, production, content / encoding, and display. HDR capture and displays are capable of brighter whites and deeper blacks. To accommodate this, HDR encoding standards allow for a higher maximum luminance. While technically "HDR" refers strictly to a ratio between the maximum and minimum luminance, the term "HDR video" is commonly understood to imply wide color gamut as well. Although a number of HDR display devices have appeared, as well as image and video cameras capable of capturing images with an increased dynamic range, there is still a very limited number of HDR contents available. In addition, a majority of current content distribution systems are designed for transporting SDR contents. The standard SL-HDR1 (ETSI TS 103433-1 V1.4.1) provides direct backwards compatibility by using metadata allowing reconstructing a HDR signal from a SDR video stream. One advantage of SL-HDR1 is to allow using SDR distribution networks and services already in place for distributing HDR contents. Moreover, SL-HDR1 2023PF00945 allows for HDR rendering on HDR devices and SDR rendering on SDR devices using a single layer video stream. In some typical SL-HDR1 systems, the luma part of a SDR signal (i.e. the SDR luma) is computed applying a tone mapping operation on the luminance of an original HDR signal computed from original HDR RGB components or computed applying a tone mapping operation on the luma of an original HDR signals computed from a gammatized versions of HDR RGB components of the original HDR signal (i.e. HDR luma). The chroma part of the SDR signal (i.e. the SDR chroma) is computed from a gammatized versions of HDR RGB components of the original HDR signal and from a color correction factor that depends on the computed SDR luma. In some cases, generated SDR chroma components are clipped to a maximum possible value. The clipping is directly at the origin of reconstruction errors when reconstructing the HDR signal from the SDR signal. To get rid of the SDR chroma components clipping, some methods are modifying a saturation of the computed SDR chroma components. However, these methods produce very desaturated SDR images that are no more consistent in terms of colors (i.e., in terms of hue) with the original HDR signal. It is desirable to overcome the above drawbacks. It is particularly desirable to define a method allowing to avoid the SDR chroma components clipping while maintaining saturation and preserving hue of the derived SDR signal. 3. BRIEF SUMMARY In a first aspect, one or more of the present embodiments provide a method comprising: obtaining a first picture in a first dynamic range; obtaining parameters defining a first color correction function preventing clipping of color components of a second picture resulting from a tone mapping of the first picture in a second dynamic range; signaling parameters defining a tone mapping function in metadata, the parameters of the tone mapping function being derived from the parameters defining the first color correction function; 2023PF00945 signaling parameters defining a second color correction function in the metadata, the parameters defining the second color correction function being obtained from default values; and signaling a third picture in the second dynamic range obtained using the signaled parameters of the tone mapping function and the signaled parameters of the second color correction function in video data along with the metadata. In an embodiment, the parameters defining the tone mapping function define a fine-tuning function and the obtaining of the parameters defining the tone mapping function comprises a conversion of the parameters defining the first color correction function from a gamma signal to a perceptual uniform signal. In an embodiment, the parameters defining the first color correction function are points defining a piece wise saturation gain function and the obtaining of the parameters defining the tone mapping function comprises an interpolation of the piece wise saturation gain function from the points. In an embodiment, the obtaining of the parameters defining a first color correction function comprises: segmenting a range of luminance values of an initial luma component of the first picture in partial luminance ranges, each frontier between two consecutive partial luminance ranges depending on a first coordinate of one of initial tuples defining an initial color correction function; estimating an attenuation value for initial chroma components of the first picture in at least one partial luminance range, each attenuation value allowing lowering the initial chroma components to avoid a clipping of said initial chroma component; determining a global attenuation value for the initial chroma components using the estimated attenuation values; computing a factor for each partial luminance range allowing maintaining a saturation in each partial luminance range based on the global attenuation value and the attenuation value associated to said partial luminance range; 2023PF00945 for each frontier between two consecutive luminance ranges, computing a minimum factor representing a minimum of the factors computed for these two consecutive partial luminance ranges; computing a final correction factor for each frontier between two consecutives partial luminance ranges based on the minimum factor corresponding to said frontier and the global attenuation value; and modifying a second coordinate of at least one of the initial tuples using the final correction factors to obtain new tuples, the new tuples being the parameters defining the first color correction function. In an embodiment, the parameters defining the second color correction function are also obtained from the parameters defining the first color correction function. In an embodiment, a level of use of the parameters defining the first color correction function for computing the parameters of the tone mapping function and the parameters of the second color correction function depends on a single value. In a second aspect, one or more of the present embodiments provide a device comprising electronic circuitry configured for: obtaining a first picture in a first dynamic range; obtaining parameters defining a first color correction function preventing clipping of color components of a second picture resulting from a tone mapping of the first picture in a second dynamic range; signaling parameters defining a tone mapping function in metadata, the parameters of the tone mapping function being derived from the parameters defining the first color correction function; signaling parameters defining a second color correction function in the metadata, the parameters defining the second color correction function being obtained from default values; and signaling a third picture in the second dynamic range obtained using the signaled parameters of the tone mapping function and the signaled parameters of the second color correction function in video data along with the metadata. 2023PF00945 In an embodiment, the parameters defining the tone mapping function define a fine-tuning function and the obtaining of the parameters defining the tone mapping function comprises a conversion of the parameters defining the first color correction function from a gamma signal to a perceptual uniform signal. In an embodiment, the parameters defining the first color correction function are points defining a piece wise saturation gain function and the obtaining of the parameters defining the tone mapping function comprises an interpolation of the piece wise saturation gain function from the points. In an embodiment, the obtaining of the parameters defining a first color correction function comprises: segmenting a range of luminance values of an initial luma component of the first picture data in partial luminance ranges, each frontier between two consecutive partial luminance ranges depending on a first coordinate of one of initial tuples defining an initial color correction function; estimating an attenuation value for initial chroma components of the first picture data in at least one partial luminance range, each attenuation value allowing lowering the initial chroma components to avoid a clipping of said initial chroma component; determining a global attenuation value for the initial chroma components using the estimated attenuation values; computing a factor for each partial luminance range allowing maintaining a saturation in each partial luminance range based on the global attenuation value and the attenuation value associated to said partial luminance range; for each frontier between two consecutive luminance ranges, computing a minimum factor representing a minimum of the factors computed for these two consecutive partial luminance ranges; computing a final correction factor for each frontier between two consecutives partial luminance ranges based on the minimum factor corresponding to said frontier and the global attenuation value; and modifying a second coordinate of at least one of the initial tuples using the final correction factors to obtain new tuples, the new tuples being the parameters defining the first color correction function. 2023PF00945 In an embodiment, the parameters defining the second color correction function are also obtained from the parameters defining a first color correction function. In an embodiment, a level of use of the parameters defining the first color correction function for computing the parameters of the tone mapping function and the parameters of the second color correction function depends on a single value. In a third aspect, one or more of the present embodiments provide a non- transitory information storage medium storing program code instructions for implementing the method according to the first aspect. In a fourth aspect, one or more of the present embodiments provide computer program comprising program code instructions for implementing the method according to the first aspect. In a fifth aspect, one or more of the present embodiments provide a signal generated by the method of the first aspect or by the device of the second aspect. 4. BRIEF SUMMARY OF THE DRAWINGS Fig.1 illustrates an example of SL-HDR1 system; Fig. 2 illustrates schematically a detail of a pre-processing module of a SL-HDR1 system; Fig. 3 illustrates schematically a detail of a post-processing module of a SL-HDR1 system; Fig. 4 illustrates schematically an example of hardware architecture of a processing module able to implement various aspects and embodiments; Fig. 5 illustrates a block diagram of an example of a first system in which various aspects and embodiments are implemented; Fig. 6 illustrates a block diagram of an example of a second system in which various aspects and embodiments are implemented; Fig.7 illustrates schematically an example of pre-processing process; 2023PF00945 Fig.8 illustrates schematically an example of post-processing process; Fig.9 illustrates schematically a first embodiment of a chroma clipping limiter process; Fig. 10 illustrates schematically a detail of the first embodiment of a chroma clipping limiter process; Fig. 11 illustrates schematically a second embodiment of a chroma clipping limiter process; Fig. 12 illustrates a detail of the second embodiment of the chroma clipping limiter process; and, Fig. 13 illustrates a second detail of the second embodiment of the chroma clipping limiter process. 5. DETAILED DESCRIPTION Various aspects and embodiments are described in the following in the context of a SL-HDR1 system. Fig.1 illustrates an example of SL-HDR1 system. The SL-HDR1 system of Fig. 1 comprises a server 1 and a client system 3 communicating via a communication network 2. The client system 3 is connected to a first display device 5, called HDR display device, capable of displaying a HDR content using a communication link 4 and to a second display device 7, called SDR display device, capable of displaying a SDR content, using a communication link 6. The server 1 obtains an original HDR content and generates a SDR encoded signal and metadata. The client system 3 receives the SDR encoded signal and the metadata and generates a decoded SDR content and reconstructs a HDR content from the decoded SDR content and the metadata. The server 1 comprises a pre-processing module detailed in relation to Fig. 2, an encoding module 12 and a transmission module 14. The pre-processing module 10 generates a SDR content and metadata from the original HDR content applying a process described in the following in relation to Fig. 7, 9, 10, 11, 12 and 13. The encoding module 12 encodes said SDR content and the metadata. The encoding module 12, for example, generates an encoded video stream compliant with 2023PF00945 video compression standards HEVC (ISO / IEC 23008-2 – MPEG-H Part 2, High Efficiency Video Coding / ITU-T H.265), AVC (ISO / IEC 14496-10 - MPEG-4 Part 10, Advanced Video Coding) or VVC (ISO / IEC 23090-3 – MPEG-I: Versatile Video Coding (VVC) / ITU-T H.266). The metadata are for example carried out by SEI messages such as the SL-HDR Information through a user data registered SEI message (as detailed in annex A of SL-HDR1 standard ETSI TS 103433-1 V1.4.1), and / or Mastering Display Colour Volume (MDCV) SEI messages. When encoded, the encoded video stream is transmitted by the transmission module 14 to the client system 3 via the communication network 2. The client system 3 comprises a reception module 30, a decoding module 32, and a post-processing module 34 detailed in relation to Fig.3. The reception module 30 receives the encoded video stream comprising the encoded SDR content and the metadata. The decoding module 32 decodes the encoded video stream to reconstruct the SDR content and the metadata. No further processing is applied on the SDR content that is transmitted directly to the SDR display device 7. The post-processing module 34 reconstructs the HDR content from the decoded SDR content and the metadata applying a process described in relation to Fig.8. Fig.2 illustrates schematically a detail of the pre-processing module 10. The pre-processing module 10 comprises a conversion module 10A and a HDR- to-SDR signal decomposition module 10C. The HDR-to-SDR signal decomposition module 10C requires linear-light RGB signal at its input. The conversion module 10A enables format adaptation to the input required by the HDR-to-SDR signal decomposition module 10C, i.e. it converts the input HDR video that can have any format (OETF, YUV, …) into a linear-light RGB signal, if needed. The HDR-to-SDR signal decomposition module 10C generates a SDR backward compatible version of the original HDR signal, using an invertible process described in relation to steps 701 to 708 of Fig. 7 that guarantees a high quality reconstructed HDR signal. In an embodiment, the pre-processing module 10 comprises an optional gamut mapping module 10B. The gamut mapping module 10B may be used when the original 2023PF00945 HDR signal and the SDR signal are represented with different color gamut or color spaces. Fig.3 illustrates schematically a detail of the post-processing module 34. The post-processing module 34 comprises a SDR-to-HDR reconstruction module 34C and a conversion module 34A. The SDR-to-HDR reconstruction module 34C receives the decoded SDR signal and the metadata and inverts the process of the HDR-to-SDR signal decomposition module 10C to reconstruct a HDR signal as described in relation to steps 801 to 807 of Fig.8. The conversion module 34A enables format adaptation of the reconstructed HDR signal to a targeted system (e.g. a Set Top Box (STB), a connected TV, etc.) connected with the client system 3. The conversion module 34A applies a process described by step 808 of Fig.8. In the embodiment wherein the pre-processing module 10 comprise a gamut mapping module 10B, the post-processing module 34 comprises an optional inverse gamut mapping module 34B inverting the process of the gamut mapping module 10B. Fig. 4 illustrates schematically an example of hardware architecture of a processing module 100 comprised in the server 1, in the pre-processing module 10, the encoding module 12 or the transmission module 14 or in the client system 3, in the reception module 30, the decoding module 32 or the post-processing module 34 and able to implement different aspects and embodiments. The processing module 100 comprises, connected by a communication bus 1005: a processor or CPU (central processing unit) 1000 encompassing one or more microprocessors, general purpose computers, special purpose computers, and processors based on a multi-core architecture, as non-limiting examples; a random access memory (RAM) 1001; a read only memory (ROM) 1002; a storage unit 1003, which can include non-volatile memory and / or volatile memory, including, but not limited to, Electrically Erasable Programmable Read-Only Memory (EEPROM), Read-Only Memory (ROM), Programmable Read-Only Memory (PROM), Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), flash, magnetic disk drive, and / or optical disk drive, or a storage medium reader, such as a SD (secure digital) card reader and / or a hard disc drive (HDD) and / or a network accessible storage device; at least one communication interface 1004 for 2023PF00945 exchanging data with other modules, devices, systems or equipment. The communication interface 1004 can include, but is not limited to, a transceiver configured to transmit and to receive data over the communication network 2. The communication interface 1004 can include, but is not limited to, a modem or a network card. For example, the communication interface 1004 enables for instance the processing module 100: to receive the original HDR content and to output the encoded video stream comprising the encoded SDR content and metadata when the processing module 100 is comprised in the server 1; to receive the original HDR content and to output the SDR content with metadata when the processing module 100 is comprised in the pre-processing module 10; to receive a SDR content and metadata and to output an encoded video stream representative of said SDR content and of the metadata when the processing module 100 is comprised in the encoding module 12; to receive the encoded video stream and to transmit the encoded video stream to the client system 3 when the processing module is comprised in the transmission module 14; to receive the encoded video stream from the server 1 and output a corresponding SDR and / or HDR content when the processing module 100 is comprised in the client system 3; to receive the encoded video stream from the server 1 and forward said encoded video stream to the decoding module 32 when the processing module 100 is comprised in the reception module 30; to receive the encoded video stream from the reception module 30 and to output a reconstructed SDR content and metadata when the processing module 100 is comprised in the decoding module 32; to receive the reconstructed SDR content and metadata and to output a reconstructed HDR content when the processing module 100 is comprised in the post-processing module 34. The processor 1000 is capable of executing instructions loaded into the RAM 1001 from the ROM 1002, from an external memory (not shown), from a storage medium, or from a communication network. When the processing module 100 is powered up, the processor 1000 is capable of reading instructions from the RAM 1001 and executing them. These instructions form a computer program causing, for example, the implementation by the processor 1000 of a pre-processing process described in relation to Figs.7, 9, 11, 12 and 13 or of a post-processing process described in relation to Fig.8 or both. 2023PF00945 All or some of the algorithms and steps of said processes may be implemented in software form by the execution of a set of instructions by a programmable machine such as a DSP (digital signal processor) or a microcontroller, or be implemented in hardware form by a machine or a dedicated component such as a FPGA (field- programmable gate array) or an ASIC (application-specific integrated circuit). DSP , microcontrollers, FPGA, ASIC, processors are all examples of electrical circuitries. Fig. 5 illustrates a block diagram of an example of system A adapted to implement the server 1, the pre-processing module 10, the encoding module 12 and / or a transmission module 14 and in which various aspects and embodiments are implemented. System A can be embodied as a device including the various components or modules described above and is configured to perform one or more of the aspects and embodiments described in this document. Examples of such system include, but are not limited to, various electronic systems such as personal computers, laptop computers, smartphones, tablet computers, connected home appliances, servers and a camera. Components of system A, singly or in combination, can be embodied in a single integrated circuit (IC), multiple ICs, and / or discrete components. For example, in at least one embodiment, the system A comprises one processing module 100 that implement either the pre-processing module 10, the encoding module 12 or the transmission module 14 or any combination of these modules. In various embodiments, the system A is communicatively coupled to one or more other systems, or other electronic devices, via, for example, a communications bus or through dedicated input and / or output ports. The input to the processing module 100 can be provided through various input modules as indicated in block 60. Such input modules include, but are not limited to, (i) a radio frequency (RF) module that receives an RF signal transmitted, for example, over the air by a broadcaster, (ii) a component (COMP) input module (or a set of COMP input modules), (iii) a Universal Serial Bus (USB) input module, and / or (iv) a High Definition Multimedia Interface (HDMI) input module. Other examples, not shown in FIG.5, include composite video. In various embodiments, the input modules of block 60 have associated respective input processing elements as known in the art. For example, the RF module can be associated with elements suitable for (i) selecting a desired frequency (also 2023PF00945 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 module 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. 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 module includes an antenna. Additionally, the USB and / or HDMI modules can include respective interface processors for connecting system A 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 the processing module 100 as necessary. Similarly, aspects of USB or HDMI interface processing can be implemented within separate interface ICs or within the processing module 100 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to the processing module 100. Various elements of system A can be provided within an integrated housing. Within the integrated housing, the various elements can be interconnected and transmit data therebetween using suitable connection arrangements, for example, an internal bus as known in the art, including the Inter-IC (I2C) bus, wiring, and printed circuit boards. For example, in the system A, the processing module 100 is interconnected to other elements of said system A by the bus 1005. 2023PF00945 The communication interface 1004 of the processing module 100 allows the system A to communicate on the communication network 2. The communication network 2 can be implemented, for example, within a wired and / or a wireless medium. Data is streamed, or otherwise provided, to the system A, in various embodiments, using a wireless network such as a Wi-Fi network, for example IEEE 802.11 (IEEE refers to the Institute of Electrical and Electronics Engineers). The Wi- Fi signal of these embodiments is received over the communications network 2 and the communications interface 1004 which are adapted for Wi-Fi communications. The communications network 2 of these embodiments is typically connected to an access point or router that provides access to external networks including the Internet for allowing streaming applications and other over-the-top communications. Still other embodiments provide streamed data to the system A using the RF connection of the input block 60. As indicated above, various embodiments provide data in a non- streaming manner, for example, when the system A is a camera, a smartphone or a tablet. Additionally, various embodiments use wireless networks other than Wi-Fi, for example a cellular network or a Bluetooth network. The system A can provide an output signal to various output devices using the communication network 2 or the bus 1005. For example, when implementing the pre- processing module 10, the system A provides the output signal to the encoding module 12 using the bus 1005 or the communication network 2. When implementing the server 1, the system A provides the SDR signal and the metadata to the client system 3 using the communication network 2. Various implementations involve applying a pre-processing process and or an encoding process. The pre-processing process or the encoding process, as used in this application, can encompass all or part of the processes performed, for example, on a received HDR image or video stream in order to produce a SDR content or an encoded SDR content with metadata. In various embodiments related to the encoding process, such process includes one or more of the processes typically performed by a video encoder, for example, an AVC encoder, an HEVC encoder, a VVC encoder, an AV1 encoder or a VP9 encoder. Fig. 6 illustrates a block diagram of an example of the system B adapted to implement a client system 3, a reception module 30, a decoding module 32 and / or a 2023PF00945 post-processing module 34 and in which various aspects and embodiments are implemented. System B can be embodied as a device including the various components and modules described above and is configured to perform one or more of the aspects and embodiments described in this document. 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, and a connected home appliances. Elements or modules of system B, singly or in combination, can be embodied in a single integrated circuit (IC), multiple ICs, and / or discrete components. For example, in at least one embodiment, the system B comprises one processing module 100 that implement either the reception module 30, the decoding module 32, and the post-processing module 34, or any combinations of these modules. In various embodiments, the system B is communicatively coupled to one or more other systems, or other electronic devices, via, for example, a communications bus or through dedicated input and / or output ports. The input to the processing module 100 can be provided through various input modules as indicated in block 60 already described in relation to Fig.5. Various elements of system B can be provided within an integrated housing. Within the integrated housing, the various elements can be interconnected and transmit data therebetween using suitable connection arrangements, for example, an internal bus as known in the art, including the Inter-IC (I2C) bus, wiring, and printed circuit boards. For example, in the system B, the processing module 100 is interconnected to other elements of said system B by the bus 1005. The communication interface 1004 of the processing module 100 allows the system B to communicate on the communication network 2. The communication network 2 can be implemented, for example, within a wired and / or a wireless medium. Data is streamed, or otherwise provided, to the system B, in various embodiments, using a wireless network such as a Wi-Fi network, for example IEEE 802.11 (IEEE refers to the Institute of Electrical and Electronics Engineers). The Wi- Fi signal of these embodiments is received over the communications network 2 and the communications interface 1004 which are adapted for Wi-Fi communications. The communications network 2 of these embodiments is typically connected to an access 2023PF00945 point or router that provides access to external networks including the Internet for allowing streaming applications and other over-the-top communications. Still other embodiments provide streamed data to the system B using the RF connection of the input block 60. As indicated above, various embodiments provide data in a non- streaming manner. Additionally, various embodiments use wireless networks other than Wi-Fi, for example a cellular network or a Bluetooth network. The system B can provide an output signal to various output devices, including the display 64 (corresponding to the display devices 5 or 7 in Fig.1), speakers 65, and other peripheral devices 66. The display 64 of various embodiments includes one or more of, for example, a touchscreen display, an organic light-emitting diode (OLED) display, a curved display, and / or a foldable display. The display 64 can be for a television, a tablet, a laptop, a cell phone (mobile phone), or other devices. The display 64 can also be integrated with other components (for example, as in a smart phone), or separate (for example, an external monitor for a laptop). The display 64 is SDR or HDR content compatible. The other peripheral devices 66 include, in various examples of embodiments, one or more of a stand-alone digital video disc (or digital versatile disc) (DVR, for both terms), a disk player, a stereo system, and / or a lighting system. Various embodiments use one or more peripheral devices 66 that provide a function based on the output of the system B. For example, a disk player performs the function of playing the output of the system B. In various embodiments, control signals are communicated between the system B and the display 64, speakers 65, or other peripheral devices 66 using signaling such as AV.Link, Consumer Electronics Control (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 B via dedicated connections through respective interfaces 61, 62, and 63. Alternatively, the output devices can be connected to system B using the communication network 2 via the communication interface 1004. The display 64 and speakers 65 can be integrated in a single unit with the other components of system B in an electronic device such as, for example, a television. In various embodiments, the display interface 61 includes a display driver, such as, for example, a timing controller (T Con) chip. The display 64 and speakers 65 can alternatively be separate from one or more of the other components, for example, if the RF module of input 60 is part of a separate 2023PF00945 set-top box. In various embodiments in which the display 64 and speakers 65 are external components, the output signal can be provided via dedicated output connections, including, for example, HDMI ports, USB ports, or COMP outputs. Various implementations involve applying a post-processing process and a decoding process. The decoding process, as used in this application, can encompass all or part of the processes performed, for example, on a received encoded video stream in order to produce a SDR signal. In various embodiments, such decoding process include one or more of the processes typically performed by an image or a video decoder, for example, an H.264 / AVC decoder, H.265 / HEVC decoder, an H.266 / VVC decoder, and AV1 decoder or a VP9 decoder. The post-processing process encompasses all process required to reconstruct an HDR content from a reconstructed SDR content and metadata. When a figure is presented as a flow diagram, it should be understood that it also provides a block diagram of a corresponding apparatus. Similarly, when a figure is presented as a block diagram, it should be understood that it also provides a flow diagram of a corresponding method / process. The implementations and aspects described herein can be implemented in, for example, a method or a process, an apparatus, a software program, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method), the implementation of features discussed can also be implemented in other forms (for example, an apparatus or program). An apparatus can be implemented in, for example, appropriate hardware, software, and firmware. The methods can be implemented, for example, in 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, for example, computers, cell phones, portable / personal digital assistants ("PDAs"), smartphones, tablets and other devices that facilitate communication of information between end-users. Reference to “one embodiment” or “an embodiment” or “one implementation” or “an implementation”, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” or “in one implementation” or “in an 2023PF00945 implementation”, as well any other variations, appearing in various places throughout this application are not necessarily all referring to the same embodiment. Additionally, this application may refer to “determining” various pieces of information. Determining the information can include one or more of, for example, estimating the information, calculating the information, predicting the information, retrieving the information from memory or obtaining the information for example from another device, module or from user. Further, this application may refer to “accessing” various pieces of information. Accessing the information can include one or more of, for example, receiving the information, retrieving the information (for example, from memory), storing the information, moving the information, copying the information, calculating the information, determining the information, predicting the information, or estimating the information. Additionally, this application may refer to “receiving” various pieces of information. Receiving is, as with “accessing”, intended to be a broad term. Receiving the information can include one or more of, for example, accessing the information, or retrieving the information (for example, from memory). Further, “receiving” is typically involved, in one way or another, during operations such as, for example, storing the information, processing the information, transmitting the information, moving the information, copying the information, erasing the information, calculating the information, determining the information, predicting the information, or estimating the information. It is to be appreciated that the use of any of the following “ / ”, “and / or”, and “at least one of”, “one or more of” for example, in the cases of “A and / or B” and “at least one of A and B”, “one or more of A and B” is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of “A, B, and / or C” and “at least one of A, B, and C”, “one or more of A, B and C” such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options 2023PF00945 (A and B and C). This may be extended, as is clear to one of ordinary skill in this and related arts, for as many items as are listed. As will be evident to one of ordinary skill in the art, implementations or embodiments can produce a variety of signals formatted to carry information that can be, for example, stored or transmitted. The information can include, for example, instructions for performing a method, or data produced by one of the described implementations or embodiments. For example, a signal can be formatted to carry a SDR image or video sequence and metadata of a described embodiment. Such a signal can be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal. The formatting can include, for example, encoding a SDR image or video sequence with metadata in an encoded stream and modulating a carrier with the encoded stream. The information that the signal carries can be, for example, analog or digital information. The signal can be transmitted over a variety of different wired or wireless links, as is known. The signal can be stored on a processor-readable medium. Fig.7 illustrates schematically an example of pre-processing process. The example of pre-processing process of Fig. 7 is adapted to a SL-HDR1 system in NCL (Non-Constant Luminance) mode. In this example, the pre-processing module 10 obtains an original HDR content and generates a SDR content and metadata. The pre-processing process is executed by the processing module 100 comprised in the server 1, on each pixel of each image of the original HDR content. In the example of Fig. 7, a pixel comprises three color components corresponding to the primary colors Red (R), Green (G) and Blue (B), i.e. a pixel is a RGB signal. In a step 701, the processing module 100 obtains an image of an original HDR content and derives a tone mapping curve represented by tone mapping parameters from said image. As described for example in the standard SL-HDR1 section 7.2.3.1, the tone mapping parameters comprise tmInputSignalBlackLevelOffset, tmInputSignalWhiteLevelOffset, shadowGain, highlightGain, midToneWidthAdjFactor, tmOutputFineTuningNumVal, tmOutputFineTuningX[i] and tmOutputFineTuningY[i] with i between zero and tmOutputFineTuningNumVal-1. Said tone mapping parameters are transmitted as metadata to the client system 3 in the form of a SL-HDR information SEI message 2023PF00945 defined in Annex A of SL-HDR1. Once the mapping parameters have been derived, a luminance tone mapping function ^^ ^^ ^^்ெis obtained from the metadata. In a step 702, the processing module 100 applies a gamma conversion to the linear-light RGB signal as follows: భ ^^ௌé^^ംù ^^భ equal to “2.4”. In a step 703, the processing module 100 derives a luminance (luma) component ^^′^ௗ^_^^^from the gammatized RSGSBS signal of the image as follows: ^^ௌ^^^ ^ In a step 704, the processing module 100 applies a tone mapping to the luma component ^^′^ௗ^_^^^to obtain a tone mapped value ^^′^ௗ^_^^^as follows: ^^′^ௗ^_^^^ൌ ^^ ^^ ^^்ெ^ ^^′^ௗ^_^^^^ (eq.3) ∈ ^0; 1023^). In a step 705, the processing module 100 derives chrominance (chroma) components from the gammatized RGB signal as follows: ^^′^ௗ^_^^^ ^^ ^^ௌ^ଶ^^′ ^ ^ ^ൈ 1024 (eq.4) conversion matrix. A=^ ^^^^^ଶ^^ ^்is for example a ଷcanonical 3x3 RGB-to-YUV conversion matrix (e.g. as specified in ITU-R Rec. BT.2020 or ITU-R Rec. BT.709 depending on the color space). In a step 706, the processing module 100 applies a joint normalization and color correction to the chroma components ^^′^ௗ^_^^^and ^^′^ௗ^_^^^to obtain normalized corrected chroma components ^^′^ௗ^_^^^and ^^′^ௗ^_୮୰^as follows: భ ^ ം ^^^é^ 2023PF00945 ^^′^ௗ^_^^^and ^^′^ௗ^_^^^being clipped between two clipping values [CLIP_MIN;CLIP_MAX] (for example being clipped in [CLIP_MIN=-512; CLIP_MAX=511]). ^ ఉబ൫௬ᇱೞ^^_^^^൯corresponds to a color correction function and is called ColorCorrection(y) in the following. In the SL-HDR1 case, the color correction function ColorCorrection(y) is defined later in this document. In particular, the color correction function ColorCorrection(y) is constructed using parameters defined in section 6.3.6 of SL-HDR1, defined by a number of n=saturationGainNumVal Saturation Gain Function Curve Points, the number saturationGainNumVal being between “0” and “6” and a Saturation Gain Function Curve Point being a 8-bits tuple (sgf_x[i], sgf_y[i]) in the following (i.e., saturationGainX[i] and saturationGainY[i] in SL-HDR1), hence ranging from “0” to “255”. The tuples (saturationGainX[i], saturationGainY[i]) and the number saturationGainNumVal are transmitted as metadata to the client system 3 in the form of a SL-HDR information SEI message defined in Annex A of SL-HDR1. In a step 707, the processing module 100 applies a chroma injection to the tone mapped luma value ^^′^ௗ^_^^^to obtain a corrected tone mapped luma value ^^′^ௗ^_^^^_^௨௧as follows: ൌ ^^′^ௗ^_^^^െ max ^0, ^^. ^^′^ௗ^ ^^. ^^′ ^ (eq.6) ^_^^^ ^ௗ^_^^^In a step 708, the processing module 40 converts the luma and chroma values ^^′^ௗ^_^^^_^௨௧, ^^′^ௗ^_^^^and ^^′^ௗ^_^^^in a given output format. Step 708 comprises a for example equal to “512” to the chroma components ^^′^ௗ^_^^^and ^^′^ௗ^_^^^, optionally a sub-step of down-sampling the chroma components that compresses the signal by reducing the number of chroma samples, and optionally a sub-step of converting from full range values (YUV components range from “0” to “1023” when encoded in 10 bits) to limited range values (Y component ranges from “64” to “940”, and UV components range from “64” to “960”) to obtain the luma and chroma components ^^^ௗ^_^^^_^௨௧, ^^^ௗ^_^^^_^௨௧, ^^^ௗ^_^^^_^௨௧representative of a pixel of a SDR signal. The objective of step 708 is for example to convert a full range YUV 444 signal in a limited range YUV 420 signal. The SDR image resulting from step 708 is provided to the encoding module 12 which signals this SDR image in 2023PF00945 video data along with the metadata, the video data being transmitted to the client system 3 by the transmission module 14. Sometimes, for some specific HDR RGB values, the SDR chroma components ^^′^ௗ^_^^^and ^^′^ௗ^_^^^generated in step 706 are higher than CLIP_MAX or are lower and thus are clipped to their maximum possible value (i.e. CLIP_MAX) or to their minimum possible value (i.e. CLIP_MIN). This clipping produces reconstruction errors in the HDR reconstructed signal at the client system side. To get rid of the SDR chroma components clipping, ^^′^ௗ^_^^^and ^^′^ௗ^_^^^can be lowered either by decreasing ^^^ଶ^^ଷ൨ coefficient matrix or by decreasing the color correction function ColorCorrection(y) (i.e.^ఉబ൫௬ᇱೞ^^_^^^൯). The method proposed in the following in relation to Fig. 9 uses the color correction function ColorCorrection(y) to get rid of the clipping of ^^′^ௗ^_^^^and ^^′^ௗ^_^^^while maintaining saturation and hue consistency in the UV color space (i.e.,UV domain). The method proposed in the following in relation to Figs.11, 12 and 13 propose to correct the tone mapping function (and the inverse tone mapping function) or to correct the tone mapping function (and the inverse tone mapping function) and the color correction function to get rid of the clipping of ^^′^ௗ^_^^^and ^^′^ௗ^_^^^while maintaining saturation and hue consistency in the xy color space (i.e., xy domain). Fig. 8 illustrates schematically an example of post-processing process. The process of Fig.8 is executed by the processing module 100 when the processing module 100 implements the post-processing module 34 and more particularly the SDR-to-HDR reconstruction module 34C. The reconstruction process is applied to each pixel of the decoded SDR content generated by the decoding module 32. The reconstruction process of Fig.8 follows for example the pre-processing processes of Fig.7. Hence, the signal outputted by the pre-processing process is the input signal of the reconstruction process. In a step 801, the processing module 100 converts the received YUV 420 signal to a full range YUV444 signal ^^′^ௗ^_^^^௧_^^, ^^′^ௗ^_^^^௧, ^^′^ௗ^_^^^௧(inverse process of step 708). 2023PF00945 After conversion, the processing module 100 centers the chroma components ^^′^ௗ^_^^^௧and ^^′^ௗ^_^^^௧to obtain centered chroma components ^^′^ௗ^_^^^௧_^^and ^^′^ௗ^_^^^௧_^^. The centering is performed as follows: ^^^′^ௗ^_^^^௧_^^ ൌ ^^′^ௗ^_^^^௧ െ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^where One can note that ^^′^ௗ^_^^^௧_^^ൌ ^^ᇱ^ௗ^_^^^and ^^′^ௗ^_^^^௧_^^ൌ^ௗ^_^^^. a chroma injection correction to the luma component as follows: ^^′^ௗ^_^^^௧ൌ ^^^ௗ^_^^^௧_^^^ max ^0; ^^ ൈ ^^′^ௗ^_^^^௧_^^^ ^^ ൈ ^^′^ௗ^_^^^௧_^^^ (eq.7) where the parameters a and b are defined as mu0and mu1in section 7.2.4 of document SL-HDR1 and max (x,y) takes the maximum of x and y. One can note that ^^′^ௗ^_^^^௧ൌ ^^ᇱ^ௗ^_^^^. The luma component ^^′^ௗ^_^^^௧is then clipped in [0; 1023]. In a step 803, the processing module 100 derives the luma component ^^′^ௗ^_^^^௧by applying an inverse tone mapping to the luma component ^^′^ௗ^_^^^௧: ^^′^ௗ^_^^^௧ൌ ^^ ^^ ^^ ^^ ^^ ^^்ெ^ ^^′^ௗ^_^^^௧൧ (eq.8) Where ^^ ^^ ^^ ^^ ^^ which is the inverse of the luminance tone mapping function ^^ ^^ ^^்ெ. As indicated above, the parameters of the tone mapping function ^^ ^^ ^^்ெare provided by the pre-processing module 10 to the post-processing module 34 thanks to the SL-HDR1 metadata. One can note that ^^′^ௗ^_^^^௧ൌ ^^′^ௗ^_^^^module 100 applies an inverse color correction to the centered chroma components ^^′^ௗ^_^^^௧_^^and ^^′^ௗ^_^^^௧_^^as follows: ^^^′^ௗ^_^^^௧ ^^′′^^ ^ൌ ^^൫^ௗ^_^^^௧_^^^^ ୮^^′^ௗ^_^^^௧൯.^^^′ ^(eq. 9)One can The inverse color correction function ^^^൫ ^^′^ௗ^_^^^௧൯ (called lutCC[] in section 7.2.3.2 of SL-HDR1) is specified in the SL-HDR SEI message and depends on ^^ ^^ ^^்ெ(and therefore depends also on ^^ ^^ ^^ ^^ ^^ ^^்ெ). The color correction function applied at the 2023PF00945 pre-processing module 10 (ColorCorrection(y) = 1 / ^^^^ ^^ᇱ^ௗ^_^^^^) is therefore defined by ColorCorrection(y) =^ ^ఉ౦൫௬ᇱೞ^^_^^^൯.௬ᇱ^^^_^^^=ఉ౦൫௬ᇱೞ^^_^^^൯.^^௩^^்^ಾ^௬ᇱೞ^^_^^^൧ processing module 10 side is compensated correction (based on1 / ^^^൫ ^^′^ௗ^_^^^௧൯) applied at the post-processing module 34 side. As indicated above,the parameters of the color correction function^ఉబ൫௬ᇱೞ^^_^^^൯are provided by the pre- processing module 10 to the post-processing module 34 thanks to the SL-HDR1 metadata. Therefore : ^^ఉబ൫௬ᇱೞ^^_^^^൯^൫ ^^′^ௗ^_^^^൯ ൌ^ᇱ^^^_^^^ൌ In a step 805, the processing module 100 computes an intermediate HDR RGB signal as follows: 1 ^^^ 1 é ^^′ℎ ^^ ^^_ ^^ ^^ ^^ù ) In a step HDR RGB ^^^signal ^^^^൩ to retrieve gamma RGB values: ^^^భ ^^ଶ ^^^ ^^1 ^^′^ௗ^_^^^é^^ംù^^ௌ^^^ ^ ^^ ^^′ ^ ^^ ^ ^^భ ^^^11) 2023PF00945 ^^ଶభ ^^^ଶ൩ being then clip to ^ ^^ ^^ ^^ ^^ ^^ ^^ ^^^ംwhere peakLum is a predefined peak ^^ଶluminance value. In a step 807, the processing module 100 regenerates a linear light signal from the scaled RGB signal: ^^ ^^ଶఊ^ ^^൩ൌ^^^ଶఊ^^^ ^^ଶఊIn a step 808, the processing module 100 converts the linear light signal to a desired output format. Fig.9 illustrates schematically a first embodiment of a chroma clipping limiter process. The main intends of the method of Fig.9 are twofold: 1. Avoiding SDR chroma component clipping while preserving hue: If one or both of the U (i.e. ^^′^ௗ^_^^^) or V (i.e. ^^′^ௗ^_^^^) components needs to be lowered by an attenuation value UDivMax for U and / or by an attenuation value VDivMax for V in order to avoid clipping, both the U and V components should be lowered by a same attenuation value UVDivMax, i.e. the highest attenuation value: UVDivMax = MAX(UDivMax, VDivMax). This ensures that the hue of the original HDR content is preserved in the UV domain. As the color correction function ColorCorrection(y) is applied to both ^^′^ௗ^_^^^and ^^′^ௗ^_^^^components at the same time, the attenuation value UVDivMax is applied on the color correction function ColorCorrection(y) when computing ^^′^ௗ^_^^^and ^^′^ௗ^_^^^(in step 706). color correction function ColorCorrection(y) (i.e. ఉబ൫௬ᇱೞ^^_^^^൯) needs to be compensated by the same amount of correction in the appropriate color correction function ^^^൫ ^^′^ௗ^_^^^௧൯ in step 804 to ensure a correct HDR reconstruction. that describe the color correction function ColorCorrection(y) (i.e.ఉబ൫௬ᇱೞ^^_^^^൯^ shape are sent to the post-processing module 34 in the metadata that are transmitted by the server 1 to the client system 3. 2023PF00945 2. Maintaining as much as possible SDR saturation: If the highest attenuation value (i.e. the highest amount of color correction UVDivMax) is applied to all points of the ColorCorrection(y) function, it risks to desaturate unnecessarily the chroma components for all the luminance range, even if the correction is needed only on a small portion of the luminance range. To avoid unnecessary desaturations, the luminance range of the color correction function ColorCorrection(y) in segmented in a finite number of partial luminance ranges n. When dealing with a “10” bits SDR content, the maximum number of partial luminance ranges “n” is “1024”, i.e. each value of y can have a specific color correction function ColorCorrection(y) value. In each partial luminance range i (i = [0;n-1]), attenuation values UDivMax[i], VDivMax[i] and UVDivMax[i] are computed. The highest attenuation value (i.e. the highest amount of color correction) UVDivMax is the maximum value of all the attenuation values UVDivMax[i]. A resaturation factor over the highest amount of color correction UVDivMax may be applied in each partial luminance range by computing a resaturation factor Resaturation[i] = UVDivMax / UVDivMax[i] with i = [0;n- 1]. This potentially allows resaturation for each partial luminance range, still avoiding UV components clipping in this partial luminance range. Each frontier of two consecutive partial luminance ranges is assigned to one of the n-1=saturationGainNumVal initial tuples (sgf_x[i], sgf_y[i]) representing the color correction function ColorCorrection(y). A resaturation factor ResaturationFrontier[j] with j = [0..n-2] that can be applied at this frontier is the minimum value of the resaturation factors Resaturation[i] of the two consecutive ranges that surround this frontier. Then a color correction factor that can be applied at each frontier is computed as ColorCorrectionFrontier[j]=UVDivMax / ResaturationFrontier[j]. Finally the color correction factors at the frontiers ColorCorrectionFrontier[j] are used to modify the color correction function ColorCorrection(y). This above process, detailed below in relation to Fig.9, insures that for each of the partial luminance range: 2023PF00945 ^ U and V clipping is avoided while preserving hue; ^ saturation is maintained as much as possible. The method of Fig.9 is executed on a current image of an original HDR content by the processing module 100 of the server 1 in step 701 of the pre-processing of Fig. 7. In a step 900, the processing module 100 applies steps 701 to 706 of the pre- processing method of Fig.7 to each pixel of the current image. In step 706, no clipping is applied to ^^′^ௗ^_^^^and ^^′^ௗ^_^^^. Step 900 results in an image of pixels wherein each pixel is associated to three component values ( ^^′^ௗ^_^^^, ^^′^ௗ^_^^^, ^^′^ௗ^_^^^^. In a step 901, the processing module 100 segments the full range of luminance values (i.e. [0 .. 1023] for example) in n partial luminance ranges with (n- 1)=saturationGainNumVal. Each frontier between two consecutive partial luminance ranges corresponds to a given sgf_x[i] coordinate of one of the initial tuples (sgf_x[i],sgf_y[i]) representing the color correction function ColorCorrection(), with i = [0..n-2]. In a step 902, the processing module 100 estimates an attenuation value for the chroma components in each partial luminance range, said attenuation value allowing lowering the chroma components to avoid a clipping of said component. In other words, the processing module 100 estimates the attenuation values UDivMax[j] for the component U and VDivMax[j] for the component V and the highest attenuation value: UVDivMax[j] for j=0 to n-1. Fig.10 represents schematically a process for determining an attenuation value for chroma components in each partial luminance range. The process of Fig.10 is an embodiment of step 902. In a step 9020, the processing module 100 initializes the attenuation values UDivMax[j] and VDivMax[j] to “1” for each possible value of the n number of partial luminance ranges j from “0” to n-1, intermediate attenuation values UDivCur and VDivCur to “1” and a variable i to “0”. In step 9021, the processing module 100 determines if i is equal to a value NbPixels, wherein NbPixels represents a number of pixels minus 1 in the current image. In step 9021, the processing module 100 obtains the values of the component of a ^^^௧pixel of the current image ( ^^′^ௗ^_^^^, ^^′^ௗ^_^^^, ^^′^ௗ^_^^^). If i<NbPixels, step 9021 is 9022. 2023PF00945 In step 9022, the processing module 100 determines the partial luminance range (identified by the identifier j) to which belong the current pixel. In an embodiment, the partial luminance range identifier j is determined as follows: j = INT( ^^′^ௗ^_^^^ / (FullRangeMaxValue / (n)) +0.5) wherein INT(x) takes the integer value of x, FullRangeMaxValue is the maximum value of the full range of luminance values. In the current example, FullRangeMaxValue=1023. In a step 9023, the processing module 100 compares the value ^^′^ௗ^_^^^of the component U to a maximum clipping value CLIP_MAX. In the current example of embodiment, CLIP_MAX=511. If ^^′^ௗ^_^^^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^, step 9023 is followed by step 9024. Otherwise step 9023 is followed by step 9026. In step 9024, the processing module 100 computes an intermediate attenuation value UDivCur for component U as follows: ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^^′^ௗ^^⁄ ^^ ^^ ^^ ^^_ ^^ ^^ ^^ In a step 9025, the processing module 100 computes an attenuation value UDivMax[j] for component U for the partial luminance range j identified in step 9022 as follows: UDivMax[j] = max(UDivCur, UDivMax[j]) Step 9025 is followed by step 9026. In the step 9026, the processing module 100 compares the value ^^′^ௗ^_^^^of the component U to the minimum clipping value CLIP_MIN. In the current example of embodiment, CLIP_MIN=-512. If ^^′^ௗ^^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^, step 9026 is followed by step 9027. Otherwise step 9026 is followed by step 9029. In step 9027, the processing module 100 computes an intermediate attenuation value UDivCur for the component U as follows: ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^^′^ௗ^_^^^⁄^^ ^^ ^^ ^^_ ^^ ^^ ^^In a step 9028, the processing module 100 computes an attenuation value UDivMax[j] for the component U for the partial luminance range j identified in step 9022 as follows: UDivMax[j] = max(UDivCur, UDivMax[j]) 2023PF00945 In step 9029, the processing module 100 compares the value ^^′^ௗ^_^^^of the V component to the maximum clipping value CLIP_MAX. If ^^′^ௗ^_^^^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^, step 9029 is followed by step 9030. Otherwise step 9029 is followed by a step 9032. In step 9030, the processing module 100 computes an intermediate attenuation value VDivCur for component V as follows: ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^^′^ௗ^_^^^⁄ ^^ ^^ ^^ ^^_ ^^ ^^ ^^ In a step 9031, the processing module 100 computes an attenuation value VDivMax[j] for component V for the partial luminance range j identified in step 9022 as follows: VDivMax[j] = max(VDivCur, VDivMax[j]) In a step 9032, the processing module 100 compares the value ^^′^ௗ^_^^^of the component V to the minimum clipping value CLIP_MIN. In the current example of embodiment, CLIP_MIN=-512. If ^^′^ௗ^_^^^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^, step 9032 is followed by step 9033. Otherwise step 9032 is followed by step 9035. In step 9033, the processing module 100 computes an intermediate attenuation value VDivCur for the component V as follows: ^^ ^^ ^^ ^^ ^^ ^^ ^^ ൌ ^^′^ௗ^_^^^⁄ ^^ ^^ ^^ ^^_ ^^ ^^ ^^ In a step 9034, the processing module 100 computes an attenuation value VDivMax[j] for the component V for the partial luminance range j identified in step 9022 as follows: VDivMax[j] = max(VDivCur, VDivMax[j]) In step 9035, the variable i is incremented of one unit. If i=NbPixels, an attenuation value for chroma components U and V is determined in each partial luminance range in a step 9036. In each partial luminance range, the attenuation value for chroma components U and V is determined as follows: UVDivMax[j] = MAX(UDivMax[j],VDivMax[j]) In a first variant of the process of Fig. 10, a filtering is applied for computing the intermediate attenuation values UDivCur and VDivCur of the ^^^௧pixel by computing a weighted average with the intermediate attenuation values UDivCur and VDivCur computed for at least one pixel neighboring the ^^^௧pixel. In a second variant of the process of Fig.10, a histogram of all different values of UDivCur and VDivCur is computed. This allows to detect some high UDivCur and VDivCur values that may appear erratically due to noise present in the current image. 2023PF00945 In that case, there is no need to apply the high intermediate attenuation values UDivCur and VDivCur corresponding to said noise on all the pixels. Thus, consistent intermediate attenuation values UDivCur and VDivCur can be estimated by forcing a fixed predetermined minimum count of intermediate attenuation values UDivCur and VDivCur by counting the number of bins present in the histogram, starting from the highest bins. Back to Fig. 9, in a step 903, the processing module 100 determines a global attenuation value for the chroma components (i.e., a highest amount of color correction) UVDivMax from the attenuation values for the chroma components U and V UVDivMax[j] determined for each partial luminance range: UVDivMax = MAX(UVDivMaxPartial[j]) with j = [0;n-1] In a step 904, the processing module 100 computes a resaturation factor Resaturation[j] for each partial luminance range as follows: Resaturation[j] = UVDivMax / UVDivMax[j] with j = [0;n-1] The resaturation factor allows maintaining a saturation in (i.e., allows resaturing) each partial luminance range, still avoiding a clipping of chroma components U and V in this partial luminance range. In a step 905, the processing module 100 computes, for each frontier between two consecutive partial luminance ranges, a value ResaturationFrontier[k] (k = [0;n-2] representing a minimum of the resaturation factors computed for these two consecutive partial luminance ranges. As an example, if n=7: ResaturationFrontier [0] = MIN(Resaturation [0], Resaturation [1]); ResaturationFrontier [1] = MIN(Resaturation [1], Resaturation [2]); ResaturationFrontier [2] = MIN(Resaturation [2], Resaturation [3]); ResaturationFrontier [3] = MIN(Resaturation [3], Resaturation [4]); ResaturationFrontier [4] = MIN(Resaturation [4], Resaturation [5]); ResaturationFrontier [5] = MIN(Resaturation [5], Resaturation [6]). In a step 906, the processing module 100 computes a final correction factor ColorCorrectionFrontier[k] for each frontier between two consecutives partial luminance ranges as follows: ColorCorrectionFrontier[k] = ResaturationFrontier[k] / UVDivMax, with k in [0;n-2]. 2023PF00945 In a step 907, the processing module 100 multiplies each coordinate sgf_y[k] of the initial tuples (sgf_x[k], sgf_y[k]) representing the color correction function ColorCorrection(y) by a corresponding final correction factor ColorCorrectionFrontier[]: ColorCorrectionToApply[k] = y[k] × ColorCorrectionFrontier[k], with k in [0;n-2] Step 907 allows obtaining new tuples (sgf_x[k], ColorCorrectionToApply[k]) preventing the clipping of SDR chroma components while maintaining saturation and preserving hue of the derived SDR signal. During step 907, the coordinate sgf_y[k] of at least one tuple (sgf_x[k], sgf_y[k]) is modified. The n-1 new tuples (sgf_x[k], ColorCorrectionToApply[k]), where k is an integer value in [0;n-2], are used in step 706 and transmitted in the metadata to the client system 3 in place of the initial tuples (sgf_x[k], sgf_y[k]). The post-processing process remains identical to the process described in relation to Fig. 8 except in that the new tuples (sgf_x[k], ColorCorrectionToApply[k]) are used instead of the initial tuples (sgf_x[k], sgf_y[k]) to derive the function ^^^^^. In the following, a second embodiment of a chroma clipping limiter process is proposed. The second embodiment comprises applying the chroma clipping limiter process of Fig.9. However, the new tuples (sgf_x[i], ColorCorrectionToApply[k]) are not transmitted in the metadata but used for modifying at least the tone mapping function ^^ ^^ ^^்ெ. This second embodiment is based on the following properties of the color correction function ^^^^ ^^ᇱ^ௗ^^^^^ and of the inverse color correction function ^^^^ ^^ᇱ^ௗ^^^^^ : ^^^൫ ^^′^ௗ^_^^^൯ ൌ ^^^൫ ^^′^ௗ^_^^^൯. ^^′^ௗ^_^^^In a first variant, the second embodiment applies the correction, determined by the chroma clipping limiter process of Fig.9, by modifying the tone mapping function ^^ ^^ ^^்ெonly. In a second variant the second embodiment applies the correction, 2023PF00945 determined by the chroma clipping limiter process of Fig. 9, by modifying the tone mapping function ^^ ^^ ^^்ெand the the color correction function ColorCorrection(y) (i.e. ^ ఉబ൫௬ᇱೞ^^_^^^൯^ via the tuples (sgf_x[k], sgf_y[k]). Fig. 11 illustrates schematically a second embodiment of a chroma clipping limiter process. The chroma clipping limiter process of the second embodiment is applied by the processing module 100 of the server 1 in step 701 of the pre-processing process of Fig.7. In the first variant of the second embodiment, for a given RGB linear-light input pixel, leading to a ^^′^ௗ^_^^^value via equation (eq.2) and leading to a ^^′^ௗ^_^^^value ^^′via equation (eq.3), if the values^^ௗ^_^^^^^′ ^need to be corrected by a correction factor in order to not exceed ^^ ^^ ^^ ^^_ ^^ lower than CLIP_MIN) , then the correction factor corr needs to be applied so that ^^^′ ᇱ^ௗ^_^^^_^^^^^ ൌ ^^ ^^ ^^ ^^. ^^^ ^ௗ^_^^^^^ᇱ ^ On the server 1 side, the first variant of the second embodiment comprises replacing the tone mapping function ^^ ^^ ^^்ெby a corrected tone mapping function ^^ ^^ ^^்ெ_^^^^in step 704 so that: ^^′^ௗ^_^^^_^^^^ൌ ^^ ^^ ^^்ெ_^^^^^ ^^′^ௗ^_^^^^ with ^^′ In that case, in step 706 : ^^′^ 1 ^^′^ ௗ^_^^^_^^^^ ^ௗ^_^^^′ൌ^^. ^^^ ^^^′^^ 2023PF00945 ^^′^ ^ௗ^_^^^_^^^^ ௬ᇱೞ^^_^^^ ^^′^ௗ^_^^^ ௬ᇱ ^^′^ௗ^_^^^^^′ ^ ൌ _^^^^ . ^^^′ ^ = ^^ ^^ ^^ ^^ . ೞ^^_^^^ . ^^^′ ^ ൌ ensures that the components ^^′^ௗ^_^^^_^^^^and ^^′^ௗ^_^^^_^^^^are not clipping anymore. The corrected tone mapping function ^^ ^^ ^^்ெ_^^^^is obtained by modifying the original tone mapping function ^^ ^^ ^^்ெ. In SL-HDR1, as described in section C.2.2, the obtaining of the tone mapping function ^^ ^^ ^^்ெcomprises a step of obtaining a tone mapping curve (section C.2.2.4) followed by a step of obtaining an adjustment curve (section C.2.2.5) resulting from an application of a fine-tuning curve to the tone mapping curve. The tone mapping curve is defined by the five parameters shadowGain, highlightGain, midToneWidthAdjFactor, and tmInputSignalBlackLevelOffset, tmInputSignalWhiteLevelOffset. The fine-tuning curve is defined by the parameter tmOutputFineTuningNumVal, and the two arrays of size tmOutputFineTuningNumVal tmOutputFineTuningX[i] and tmOutputFineTuningY[i] defining a fine-tuning function. The parameter tmOutputFineTuningNumVal provide a value between “0” and “10”. As already mentioned above, the parameters specifying the tone mapping curve and the fine-tuning curve are signaled in the metadata that are transmitted by the server 1 to the client system 3. For instance, the arrays tmOutputFineTuningX[i] and tmOutputFineTuningY[i] are signaled in the metadata by syntax elements tone_mapping_output_fine_tuning_x[i] and tone_mapping_output_fine_tuning_y[i], the metadata being signaled in the form of a SL-HDR information SEI message defined in Annex A of SL-HDR1. In the first variant of the second embodiment, the modification of the tone mapping function ^^ ^^ ^^்ெallowing obtaining the corrected tone mapping function ^^ ^^ ^^்ெ_^^^^is obtained by modifying the parameters tmOutputFineTuningX[i] and tmOutputFineTuningY[i] of the fine-tuning curve. The modified parameters tmOutputFineTuningX[i] and tmOutputFineTuningY[i] are then signaled in the metadata by the syntax elements tone_mapping_output_fine_tuning_x[i] and tone_mapping_output_fine_tuning_y[i]. 2023PF00945 Then, on the client system 3 side, in the SDR to HDR reconstruction module 34C implemented by the post-processing module (34), as the corrected tone mapping function ^^ ^^ ^^்ெ_^^^^is transmitted thanks to the syntax element tmOutputFineTuningNumVal and the arrays tone_mapping_output_fine_tuning_x[i] and tone_mapping_output_fine_tuning_y[i], equation (eq.8) becomes: ^^′^ௗ^_^^^௧ ൌ ^^ ^^ ^^ ^^ ^^ ^^்ெ_^^^^^ ^^′^ௗ^_^^^௧_^^^^^ ൌ ^^ ^^ ^^ ^^ ^^ ^^்ெ_^^^^^ ^^′^ௗ^_^^^_^^^^^ ൌ with ^^ ^^ ^^ ^^ ^^ ^^்ெ_^^^^being the inverse of ^^ ^^ ^^்ெ_^^^^. Therefore, the correct ^^′^ௗ^_^^^௧value is recovered. Equation (eq.9) becomes: ^^^′ ᇱ^ௗ^_^^^௧_^^^^^^′ ^ ൌ ^^^^ ^ௗ^_^^^௧_^^൫ ^^′^ௗ^_^^^௧_^^^^൯. ^^^^^^ᇱ ^ ൌ decomposition module 10C is compensated by the SDR-to-HDR reconstruction module 34C, so that the reconstruction process is preserved. In the following, the syntax elements tone_mapping_output_fine_tuning_x[i] and tone_mapping_output_fine_tuning_y[i] signaling the fine-tuning function are called respectively ftf_x[i] and ftf_y[i] and tmOutputFineTuningNumVal is called NumFTF. In a step 1101, the processing module 100 obtains new tuples (sgf_x[i], ColorCorrectionToApply[i]). For example, the process of Fig.9 is applied to determine 2023PF00945 the new tuples (sgf_x[i], ColorCorrectionToApply[i]). In step 1101, the processing module 100 obtains therefore parameters defining a color correction function preventing clipping of color components of a SDR picture resulting from a tone mapping of an initial HDR picture. In a step 1102, the processing module 100 signals new values of the parameters ftf_x[i] and ftf_y[i] in the metadata, the new values being derived from the new tuples (sgf_x[i], ColorCorrectionToApply[i]). In other words, the processing module 100 signals parameters defining the tone mapping function in metadata, the parameters of the tone mapping functions being derived from the parameters defining the color correction function. In a first variant of step 1102, it is supposed that the definition of the tone mapping curve doesn’t use the fine-tuning function. In that case, the new tuples (sgf_x[i], ColorCorrectionToApply[i]) are directly mapped into values sub_ftf_x[i] and sub_ftf_y[i] that are then stored in the syntax elements ftf_x[i] and ftf_y[i] after a conversion. Fig.12 describes schematically the first variant of step 1102. In a step 11021, the processing module 100 initialize a variable i to zero. In a step 11022, the processing module 100 determines if the variable i is equal to NumFTF. If yes, the processing module 100 steps the process of Fig. 12 in a step 11023. Otherwise, the processing module 100 applies a step 11024. During step 11024, the processing module 100 converts the values sub_ftf_x[i] and sub_ftf_y[i] which are gamma signal values respectively into perceptual uniform signal values CC_ftf_PU_orig[i] and CC_ftf_PU_mod[i] applying the method described in section 7.2.3.1.3 of the standard SL-HDR1 (ETSI TS 103433-1 V1.4.1). In a step 11025, the processing module 100 signals the ithcomponent of the NumFTF values CC_ftf_PU_orig[i] and CC_ftf_PU_mod[i] in the syntax elements ftf_x[i] and ftf_y[i]: ftf_x[i] = CC_ftf_PU_orig[i] ftf_y[i] = CC_ftf_PU_mod[i] 2023PF00945 In a step 11026 the processing module 100 increments the variable i of one unit. Step 11026 is followed by step 11022. In a second variant of step 1102, it is supposed that the definition of the tone mapping curve use the fine-tuning function. Therefore, the values sub_ftf_x[i] and sub_ftf_y[i] need to be interpolated to match and correct the values of the syntax elements ftf_x[i] and ftf_y[i]. This is done using the following method: Fig.13 describes schematically the second variant of step 1102. In a step 11030, the processing module 100 initialize a variable i to zero. In a step 11031, the processing module 100 determines if the variable i is equal to NumFTF. If yes, the processing module 100 steps the process of Fig. 13 in a step 11032. Otherwise, the processing module 100 applies a step 11033. In step 11033, the processing module 100 converts the value of the syntax element ftf_x[i], which is a perceptual uniform signal in a gamma signal by first applying a perceptual uniform to linear signal conversion as described in section C.2.2.7 of SL-HDR1 and then by applying a gamma function g(y) = y(1 / 2.4) to the obtained linear signal. This leads to a value of a gamma signal sgf_x_from_ftf[i]. In a step 11034, the processing module 100 interpolate the saturation gain function to find the correction needed for a gamma signal sgf_x_from_ftf[i]. This is done first by finding the corresponding segment of the saturation gain function, i.e., finding between which successive sgf_x[i] values the current sgf_x_from_ftf [i] is located, and determining a function representing the saturation gain function straight line (the piece of the piece wise saturation gain function) of that segment and second, computing a value of a gamma signal sgf_y_from_ftf[i] based on sgf_x_from_ftf[i] and on the determined function representing the piece of the piece wise saturation gain function. The following pseudo code could be applied to determine the value of a gamma signal sgf_y_from_ftf[i]: x1, x2, y1, y2 are floating point variables. sgfSegmentFound is an integer value initialized to zero. sfg_x_incr is an integer value initialized to zero. while (sgfSegmentFound=0) 2023PF00945 { if ( ( sfg_x_incr == 0 ) and ( sgf_x_from_ftf[i] < (sub_ftf_x[0] / 255) ) ) { x1 = 0; y1 =0.5; x2 = sub_ftf_x[0] / 255; y2 = sub_ftf_y[0] / 255; sgfSegmentFound = 1; } else if ( sfg_x_incr = ( sgf_x.size() - 1 ) ) { x1 = 1; y1 = 0.5; x2 = sub_ftf_x[sfg_x_incr] / 255; y2 = sub_ftf_y[sfg_x_incr] / 255; sgfSegmentFound = 1; } else if ( ( sgf_x_from_ftf[i] > sub_ftf_x[sfg_x_incr] / 255 ) and ( sgf_x_from_ftf[i] <= sub_ftf_x[sfg_x_incr + 1] / 255) ) { x1 = sub_ftf_x[sfg_x_incr] / 255; y1 = sub_ftf_y[sfg_x_incr] / 255; x2 = sub_ftf_x[sfg_x_incr + 1] / 255; y2 = sub_ftf_y[sfg_x_incr + 1] / 255; sgfSegmentFound = 1; } else sfg_x_incr= sfg_x_incr +1; } sgf_y_from_ftf[i] = ( ( y2 - y1 ) × sgf_x_from_ftf[i] + x2 × y1 - x1 × y2 ) / ( x2 - x1 ) × 255; An example of C code implementation is the following: 2023PF00945 float x1, x2, y1, y2; bool sgfSegmentFound = false; int sfg_x_incr = 0; while ( !sgfSegmentFound ) { if ( ( sfg_x_incr == 0 ) && ( sgf_x_from_ftf[i] < ( (float)sub_ftf_x[0] / 255.f ) ) ) / / first sgf point is not (0 - 0) { x1 = 0.f; y1 = .5f; x2 = (float)sub_ftf_x[0] / 255.f; y2 = (float)sub_ftf_y[0] / 255.f; sgfSegmentFound = true; } else if ( sfg_x_incr == ( sgf_x.size() - 1 ) ) / / last sgf point is not (1 - 1) { x1 = 1.f; y1 = .5f; x2 = (float)sub_ftf_x[sfg_x_incr] / 255.f; y2 = (float)sub_ftf_y[sfg_x_incr] / 255.f; sgfSegmentFound = true; } else if ( ( sgf_x_from_ftf[i] > (float)sub_ftf_x[sfg_x_incr] / 255.f ) && ( sgf_x_from_ftf[i] <= (float)sub_ftf_x[sfg_x_incr + 1] / 255.f ) ) { x1 = (float)sub_ftf_x[sfg_x_incr] / 255.f; y1 = (float)sub_ftf_y[sfg_x_incr] / 255.f; x2 = (float)sub_ftf_x[sfg_x_incr + 1] / 255.f; y2 = (float)sub_ftf_y[sfg_x_incr + 1] / 255.f; sgfSegmentFound = true; } else sfg_x_incr++; 2023PF00945 } sgf_y_from_ftf[i] = ( ( y2 - y1 ) * sgf_x_from_ftf[i] + x2 * y1 - x1 * y2 ) / ( x2 - x1 ) * 255.f; Step 11034 is followed by step 11035 during which the processing module 100 computes a correction correction_sgf_y that has been applied to the gamma signal sgf_y_from_ftf[i] compared to default value def_sgf_y: correction_sgf_y = sgf_y_from_ftf[i] / def_sgf_y In a step 11036, the processing module 100 converts the perceptual uniform signal ftf_y[i] into gamma signal by first applying a perceptual uniform to linear signal conversion as described in section C.2.2.7 of SL-HDR1 and then, by applying a gamma function g(y) = y(1 / 2.4) to the converted signal. This leads to a value original_sgf_y_from_ftf[i]. In a step 11037, the processing module 100 corrects the value original_sgf_y_from_ftf[i] with the computed correction correction_sgf_y as follows: corrected_sgf_y_from_ftf[i] = original_sgf_y_from_ftf[i] × correction_sgf_y In a step 11038, the processing module 100 converts the gamma signal corrected_sgf_y_from_ftf[i] into a perceptual uniform signal corrected_ftf_y[i], as described in section 7.2.3.1.3 of SL-HDR1. In a step 11039, the processing module 100 signals the perceptual uniform signal corrected_ftf_y[i] into the syntax element ftf_y[i] only if corrected_ftf_y[i] is lower than the original value of ftf_y[i]. Indeed, the correction can only lower the fine- tuning curve, as only decreased luminance can decrease the risk of clipping. Step 11039 is followed by step 11040 during which the variable i is incremented of one unit. Step 11040 is followed by step 11031. Back to Fig.11, step 1102 is followed by a step 1103. In step 1103, the processing module 100 signals values representative of the saturation gain function. The coordinates sgf_x[i] of the saturation gain function is 2023PF00945 mapped to the frontiers values of two consecutive partial luminance ranges as in the method of Fig. 9. The coordinates sgf_y[i] values are filled with their default values sgf_y_default[i]. In a step 1104, the processing module 100 determines the tone mapping function and the inverse tone mapping function based on the new values of the syntax elements ftf_x[i] and ftf_y[i]. In a step 1105, the processing module 100 determines the color correction function^ఉబ൫௬ᇱೞ^^_^^^൯=^ఉ౦൫௬ᇱೞ^^_^^^൯.௬ᇱ^^^_^^^=^ఉ౦൫௬ᇱೞ^^_^^^൯.^^௩^^்^ಾ^௬ᇱೞ^^_^^^൧. As ^^ ^^ ^^ ^^ ^^ to be computed before further processing. In the second variant of the second embodiment, in addition to modifying the tone mapping function, the color correction function is also modified. In that case, the new tuples (sgf_x[i], ColorCorrectionToApply[i]) are divided partly into parameters (sgf_x[i], sub_sgf_y[i]) that are then mapped into parameters (sgf_x[i], sgf_y[i]) of the saturation gain function and partly into parameters (sub_ftf_x[i], sub_ftf_y[i]) that are then converted into parameters (ftf_x[i], ftf_y[i]) of the fine-tuning function. A ratio of the correction to be applied to the saturation gain function and to the fine-tuning function is controlled via a parameter ratioSgf. If ratioSgf = 1, the correction is done on the saturation gain function only and not on the fine-tuning function. This is equivalent to applying the method of the first embodiment (Fig.9) only. If ratioSgf = 0 the correction is done on the fine-tuning function only and not on the saturation gain function. This case corresponds to the first variant of the second embodiment. When 0 < ratioSgf < 1, a trade-off between the first embodiment and the first variant of the second embodiment is obtained. In the second variant of the second embodiment, the level of use of the new tuples (sgf_x[i], ColorCorrectionToApply[i]) for computing the parameters of the saturation gain function and the parameters of the fine-tuning function is controlled by the ratio ratioSgf. 2023PF00945 The process of Fig. 11 is applied with the following modifications. Again, the chroma clipping limiter process of the second embodiment is applied by the processing module 100 of the server 1 in step 701 of the pre-processing process of Fig.7. In step 1101, based on the ratio ratioSgf, the tuples (sub_ftf_x[i], sub_ftf_y[i]) and values sub_sgf_y[i] are computed as follow: For each value of i from i=0 to i=(saturationGainNumVal-1): sub_sgf_y[i] = sgf_y_default – ((sgf_y_default - ColorCorrectionToApply [i] ) × ratioSgf + 0.5)); sub_ftf_y[i] = sgf_y_default - sub_sgf_y[i] + ColorCorrectionToApply [i]; sub_ftf_x[i] = sgf_x[i]; Step 1102 remains unchanged. In step 1103, the processing module 100 signals values representative of the saturation gain function. The coordinates sgf_x[i] of the saturation gain function is mapped to the frontiers values of two consecutive partial luminance ranges as in the method of Fig.9. The coordinates sgf_y[i] are filled with the values sub_sgf_y[i]. Steps 1104 and 1105 remains unchanged. As a result of the second variant of the second embodiment, it can be noted that the closer to zero is ratioSgf, the better is the color consistency (i.e. the color is close to the original color) and the lower is the luminance. The closer to “1” is ratioSgf, the worse is the color consistency and the higher is the luminance. We described above a number of embodiments. Features of these embodiments can be provided alone or in any combination. Further, embodiments can include one or more of the following features, devices, or aspects, alone or in any combination, across various claim categories and types: ^ A bitstream or signal that includes one or more of the described image data or video data, or variations thereof. ^ Creating and / or transmitting and / or receiving and / or decoding a bitstream or signal that includes one or more of the described image data or metadata, or variations thereof. 2023PF00945 ^ A server, camera, TV, set-top box, cell phone, tablet, personal computer or other electronic device that performs at least one of the embodiments described. ^ A TV, set-top box, cell phone, tablet, , personal computer or other electronic device that performs at least one of the embodiments described, and that displays (e.g. using a monitor, screen, or other type of display) a resulting image. ^ A TV, set-top box, cell phone, tablet, personal computer or other electronic device that tunes (e.g. using a tuner) a channel to receive a signal including encoded images and metadata, and performs at least one of the embodiments described. ^ A TV, set-top box, cell phone, tablet, or other electronic device that receives (e.g. using an antenna) a signal over the air that includes an encoded images and metadata, and performs at least one of the embodiments described. ^ A server, camera, cell phone, tablet, personal computer or other electronic device that tunes (e.g. using a tuner) a channel to transmit a signal including encoded images and metadata, and performs at least one of the embodiments described. ^ A server, camera, cell phone, tablet, personal computer or other electronic device that transmits (e.g. using an antenna) a signal over the air that includes encoded images and metadata, and performs at least one of the embodiments described.

Claims

2023PF00945 Claims 1. A method comprising: obtaining (701) a first picture in a first dynamic range; obtaining (1101) parameters defining a first color correction function preventing clipping of color components of a second picture resulting from a tone mapping of the first picture in a second dynamic range; signaling (1102) parameters defining a tone mapping function in metadata, the parameters of the tone mapping function being derived from the parameters defining the first color correction function; signaling (1103) parameters defining a second color correction function in the metadata, the parameters defining the second color correction function being obtained from default values; and signaling a third picture in the second dynamic range obtained (1104, 1105) using the signaled parameters of the tone mapping function and the signaled parameters of the second color correction function in video data along with the metadata.

2. The method of claim 1 wherein the parameters defining the tone mapping function define a fine-tuning function and the obtaining of the parameters defining the tone mapping function comprises a conversion of the parameters defining the first color correction function from a gamma signal to a perceptual uniform signal.

3. The method of claim 1 or 2 wherein the parameters defining the first color correction function are points defining a piece wise saturation gain function and the obtaining of the parameters defining the tone mapping function comprises an interpolation of the piece wise saturation gain function from the points.

4. The method of claim 1, 2 or 3 wherein the obtaining of the parameters defining a first color correction function comprises: segmenting (901) a range of luminance values of an initial luma component of the first picture data in partial luminance ranges, each frontier between two consecutive partial luminance ranges depending on a first coordinate of one of initial tuples defining an initial color correction function;2023PF00945 estimating (902) an attenuation value for initial chroma components of the first picture data in at least one partial luminance range, each attenuation value allowing lowering the initial chroma components to avoid a clipping of said initial chroma component; determining (903) a global attenuation value for the initial chroma components using the estimated attenuation values; computing (904) a factor for each partial luminance range allowing maintaining a saturation in each partial luminance range based on the global attenuation value and the attenuation value associated to said partial luminance range; for each frontier between two consecutive luminance ranges, computing (905) a minimum factor representing a minimum of the factors computed for these two consecutive partial luminance ranges; computing (906) a final correction factor for each frontier between two consecutives partial luminance ranges based on the minimum factor corresponding to said frontier and the global attenuation value; and modifying (907) a second coordinate of at least one of the initial tuples using the final correction factors to obtain new tuples, the new tuples being the parameters defining the first color correction function.

5. The method according to any previous claim wherein the parameters defining the second color correction function are also obtained from the parameters defining the first color correction function.

6. The method of claim 5 wherein a level of use of the parameters defining the first color correction function for computing the parameters of the tone mapping function and the parameters of the second color correction function depends on a single value.

7. A device comprising electronic circuitry configured for: obtaining (701) a first picture in a first dynamic range; obtaining (1101) parameters defining a first color correction function preventing clipping of color components of a second picture resulting from a tone mapping of the first picture in a second dynamic range;2023PF00945 signaling (1102) parameters defining a tone mapping function in metadata, the parameters of the tone mapping function being derived from the parameters defining the first color correction function; signaling (1103) parameters defining a second color correction function in the metadata, the parameters defining the second color correction function being obtained from default values; and signaling a third picture in the second dynamic range obtained (1104, 1105) using the signaled parameters of the tone mapping function and the signaled parameters of the second color correction function in video data along with the metadata.

8. The device of claim 7 wherein the parameters defining the tone mapping function define a fine-tuning function and the obtaining of the parameters defining the tone mapping function comprises a conversion of the parameters defining the first color correction function from a gamma signal to a perceptual uniform signal.

9. The device of claim 7 or 8 wherein the parameters defining the first color correction function are points defining a piece wise saturation gain function and the obtaining of the parameters defining the tone mapping function comprises an interpolation of the piece wise saturation gain function from the points.

10. The device of claim 7, 8 or 9 wherein the obtaining of the parameters defining a first color correction function comprises: segmenting (901) a range of luminance values of an initial luma component of the first picture data in partial luminance ranges, each frontier between two consecutive partial luminance ranges depending on a first coordinate of one of initial tuples defining an initial color correction function; estimating (902) an attenuation value for initial chroma components of the first picture data in at least one partial luminance range, each attenuation value allowing lowering the initial chroma components to avoid a clipping of said initial chroma component; determining (903) a global attenuation value for the initial chroma components using the estimated attenuation values;2023PF00945 computing (904) a factor for each partial luminance range allowing maintaining a saturation in each partial luminance range based on the global attenuation value and the attenuation value associated to said partial luminance range; for each frontier between two consecutive luminance ranges, computing (905) a minimum factor representing a minimum of the factors computed for these two consecutive partial luminance ranges; computing (906) a final correction factor for each frontier between two consecutives partial luminance ranges based on the minimum factor corresponding to said frontier and the global attenuation value; and, modifying (907) a second coordinate of at least one of the initial tuples using the final correction factors to obtain new tuples, the new tuples being the parameters defining the first color correction function.

11. The device according to any previous claim from claim 7 to 10 wherein the parameters defining the second color correction function are also obtained from the parameters defining a first color correction function.

12. The device of claim 11 wherein a level of use of the parameters defining the first color correction function for computing the parameters of the tone mapping function and the parameters of the second color correction function depends on a single value.

13. Non-transitory information storage medium storing program code instructions for implementing the method according to any previous claim from claim 1 to 6.

14. A computer program comprising program code instructions for implementing the method according to any previous claim from claim 1 to 6.

15. A signal generated by the method of any previous claim from claim 1 to 6 or by the device of any previous claim from claim 7 to 12.

Images