EP4725192A1 - Encoding and decoding methods using offset-based filtering and corresponding apparatuses - Google Patents

Abstract

A decoding method is disclosed. Video data is decoded (S800) to obtain reconstructed samples of a picture region. A distribution of reconstructed sample values in the picture region is obtained. A plurality of bands are determined (S804) responsive to said distribution, a band being a subrange of a sample range. To each reconstructed sample is added an offset value obtained (S805) for the band said reconstructed sample belongs to.

Description

ENCODING AND DECODING METHODS USING OFFSET-BASED FILTERING AND CORRESPONDING APPARATUSES CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of European Application No. 23305896.5, filed on June 6, 2023 which is incorporated herein by reference in its entirety. TECHNICAL FIELD At least one of the present embodiments generally relates to a method and an apparatus for decoding (encoding respectively) a picture region using offset-based filtering. BACKGROUND To achieve high compression efficiency, image and video coding schemes usually employ prediction and transform to leverage spatial and temporal redundancy in the video content. Generally, intra or inter prediction is used to exploit the intra or inter picture correlation, then the differences between the original block and the predicted block, often denoted as prediction errors or prediction residuals, are transformed, quantized, and entropy coded. To reconstruct the video, the compressed data are decoded by inverse processes corresponding to the entropy coding, quantization, transform, and prediction. SUMMARY In one implementation, a distribution of reconstructed sample values in a picture region is obtained. In an example, the distribution may be a distribution obtained for one component. In another example, the distribution may be a joint distribution obtained for at least two components. From the obtained distribution, bands are determined, a band being a subrange of a sample range. Reconstructed sample values in the picture region may then be filtered by adding an offset value associated with the band the reconstructed sample belongs to. In an example, bands are determined by dividing the sample range into a plurality of bands so that at least one band located around a sample value of highest frequency is narrower than at least another band. In another example, bands are determined by dividing the sample range into a plurality of bands so that each band comprises approximately a same number of samples. A flag may be encoded for each region of a picture to indicate whether bands are determined for that region responsive to its distribution or whether bands are determined to be of equal size. Such a flag may be encoded for each component separately. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 illustrates a block diagram of a system within which aspects of the present embodiments may be implemented; FIG.2 illustrates a block diagram of an embodiment of a video encoder; FIG.3 illustrates a block diagram of an embodiment of a video decoder; FIG.4 illustrates the determination of reconstructed sample category in case of Sample Adaptive Offset (SAO) Edge Offset (EO) mode; FIG.5 illustrates Band Offset (BO) mode with an associated starting band position and offsets of four consecutive bands; FIG. 6 depicts a block diagram of a decoding workflow in case of Cross Component Sample Adaptive Offset (CCSAO) ; FIG.7 illustrates candidate positions used for a CCSAO Band Offset classifier; FIG.8 depicts a flowchart of a decoding method according to a specific embodiment; FIG.9 depicts an histogram of an image region and further illustrates the division of the sample ranges into bands of unequal sizes according to a specific embodiment; and FIG.10 depicts a flowchart of an encoding method according to a specific embodiment. DETAILED DESCRIPTION This application describes a variety of aspects, including tools, features, embodiments, models, approaches, etc. Many of these aspects are described with specificity and, at least to show the individual characteristics, are often described in a manner that may sound limiting. However, this is for purposes of clarity in description, and does not limit the application or scope of those aspects. Indeed, all of the different aspects can be combined and interchanged to provide further aspects. Moreover, the aspects can be combined and interchanged with aspects described in earlier filings as well. The aspects described and contemplated in this application can be implemented in many different forms. FIGs. 1, 2 and 3 below provide some embodiments, but other embodiments are contemplated and the discussion of FIGs. 1, 2 and 3 does not limit the breadth of the implementations. At least one of the aspects generally relates to video encoding and decoding, and at least one other aspect generally relates to transmitting a bitstream generated or encoded. These and other aspects can be implemented as a method, an apparatus, a computer readable storage medium having stored thereon instructions for encoding or decoding video data according to any of the methods described, and/or a computer readable storage medium having stored thereon a bitstream generated according to any of the methods described. In the present application, the terms “reconstructed” and “decoded” may be used interchangeably, the terms “encoded” or “coded” may be used interchangeably, the terms “pixel” and “sample” may be used interchangeably and the terms “image,” “picture” and “frame” may be used interchangeably. Usually, but not necessarily, the term “reconstructed” is used at the encoder side while “decoded” is used at the decoder side. Various methods are described herein, and each of the methods comprises one or more steps or actions for achieving the described method. Unless a specific order of steps or actions is required for proper operation of the method, the order and/or use of specific steps and/or actions may be modified or combined. Additionally, terms such as “first”, “second”, etc. may be used in various embodiments to modify an element, component, step, operation, etc., such as, for example, a “first decoding” and a “second decoding”. Use of such terms does not imply an ordering to the modified operations unless specifically required. So, in this example, the first decoding need not be performed before the second decoding, and may occur, for example, before, during, or in an overlapping time period with the second decoding. For the sake of clarity, satisfying, failing to satisfy a condition and configuring condition parameter(s) are described throughout embodiments described herein as relative to a threshold (e.g., greater, or lower than), a (e.g., threshold) value, configuring the (e.g., threshold) value, etc.). For example, satisfying a condition may be described as being above a (e.g., threshold) value, and failing to satisfy a condition (e.g., performance criteria) may be described as being below a (e.g., threshold) value. Embodiments described herein are not limited to threshold- based conditions. Any kind of other condition and parameter(s) (such as e.g., belonging or not belonging to a range of values) may be applicable to embodiments described herein. The present aspects are not limited to VVC or HEVC, and can be applied, for example, to other standards and recommendations, whether pre-existing or future-developed, and extensions of any such standards and recommendations (including VVC and HEVC). Unless indicated otherwise, or technically precluded, the aspects described in this application can be used individually or in combination. FIG. 1 illustrates a block diagram of an example of a system in which various aspects and embodiments can be implemented. System 100 may be embodied as a device including the various components described below and is configured to perform one or more of the aspects described in this application. Examples of such devices, include, but are not limited to, various electronic devices such as personal computers, laptop computers, smartphones, tablet computers, digital multimedia set top boxes, digital television receivers, personal video recording systems, connected home appliances, and servers. Elements of system 100, singly or in combination, may be embodied in a single integrated circuit, multiple ICs, and/or discrete components. For example, in at least one embodiment, the processing and encoder/decoder elements of system 100 are distributed across multiple ICs and/or discrete components. In various embodiments, the system 100 is communicatively coupled to other systems, or to other electronic devices, via, for example, a communications bus or through dedicated input and/or output ports. In various embodiments, the system 100 is configured to implement one or more of the aspects described in this application. The system 100 includes at least one processor 110 configured to execute instructions loaded therein for implementing, for example, the various aspects described in this application. Processor 110 may include embedded memory, input output interface, and various other circuitries as known in the art. The system 100 includes at least one memory 120 (e.g., a volatile memory device, and/or a non-volatile memory device). System 100 includes a storage device 140, which may include non-volatile memory and/or volatile memory, including, but not limited to, EEPROM, ROM, PROM, RAM, DRAM, SRAM, flash, magnetic disk drive, and/or optical disk drive. The storage device 140 may include an internal storage device, an attached storage device, and/or a network accessible storage device, as non-limiting examples. System 100 includes an encoder/decoder module 130 configured, for example, to process data to provide an encoded video or decoded video, and the encoder/decoder module 130 may include its own processor and memory. The encoder/decoder module 130 represents module(s) that may be included in a device to perform the encoding and/or decoding functions. As is known, a device may include one or both of the encoding and decoding modules. Additionally, encoder/decoder module 130 may be implemented as a separate element of system 100 or may be incorporated within processor 110 as a combination of hardware and software as known to those skilled in the art. Program code to be loaded onto processor 110 or encoder/decoder 130 to perform the various aspects described in this application may be stored in storage device 140 and subsequently loaded onto memory 120 for execution by processor 110. In accordance with various embodiments, one or more of processor 110, memory 120, storage device 140, and encoder/decoder module 130 may store one or more of various items during the performance of the processes described in this application. Such stored items may include, but are not limited to, the input video, the decoded video or portions of the decoded video, the bitstream, matrices, variables, and intermediate or final results from the processing of equations, formulas, operations, and operational logic. In some embodiments, memory inside of the processor 110 and/or the encoder/decoder module 130 is used to store instructions and to provide working memory for processing that is needed during encoding or decoding. In other embodiments, however, a memory external to the processing device (for example, the processing device may be either the processor 110 or the encoder/decoder module 130) is used for one or more of these functions. The external memory may be the memory 120 and/or the storage device 140, for example, a dynamic volatile memory and/or a non-volatile flash memory. In several embodiments, an external non-volatile flash memory is used to store the operating system of a television. In at least one embodiment, a fast external dynamic volatile memory such as a RAM is used as working memory for video coding and decoding operations, such as for MPEG-2, (MPEG refers to the Moving Picture Experts Group, MPEG-2 is also referred to as ISO/IEC 13818, and 13818-1 is also known as H.222, and 13818-2 is also known as H.262), HEVC (HEVC refers to High Efficiency Video Coding, also known as H.265 and MPEG-H Part 2), or VVC (Versatile Video Coding, a new standard being developed by JVET, the Joint Video Experts Team). The input to the elements of system 100 may be provided through various input devices as indicated in block 105. Such input devices include, but are not limited to, (i) a radio frequency (RF) portion that receives an RF signal transmitted, for example, over the air by a broadcaster, (ii) a Component (COMP) input terminal (or a set of COMP input terminals), (iii) a Universal Serial Bus (USB) input terminal, and/or (iv) a High Definition Multimedia Interface (HDMI) input terminal. Other examples, not shown in FIG.1, include composite video. In various embodiments, the input devices of block 105 have associated respective input processing elements as known in the art. For example, the RF portion may be associated with elements suitable for (i) selecting a desired frequency (also referred to as selecting a signal, or band-limiting a signal to a band of frequencies), (ii) down converting the selected signal, (iii) band-limiting again to a narrower band of frequencies to select (for example) a signal frequency band which may be referred to as a channel in certain embodiments, (iv) demodulating the down converted and band-limited signal, (v) performing error correction, and (vi) demultiplexing to select the desired stream of data packets. The RF portion of various embodiments includes one or more elements to perform these functions, for example, frequency selectors, signal selectors, band-limiters, channel selectors, filters, downconverters, demodulators, error correctors, and demultiplexers. The RF portion may include a tuner that performs various of these functions, including, for example, down converting the received signal to a lower frequency (for example, an intermediate frequency or a near-baseband frequency) or to baseband. In one set-top box embodiment, the RF portion and its associated input processing element receives an RF signal transmitted over a wired (for example, cable) medium, and performs frequency selection by filtering, down converting, and filtering again to a desired frequency band. Various embodiments rearrange the order of the above-described (and other) elements, remove some of these elements, and/or add other elements performing similar or different functions. Adding elements may include inserting elements in between existing elements, for example, inserting amplifiers and an analog-to-digital converter. In various embodiments, the RF portion includes an antenna. Additionally, the USB and/or HDMI terminals may include respective interface processors for connecting system 100 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, may be implemented, for example, within a separate input processing IC or within processor 110 as necessary. Similarly, aspects of USB or HDMI interface processing may be implemented within separate interface ICs or within processor 110 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor 110, and encoder/decoder 130 operating in combination with the memory and storage elements to process the datastream as necessary for presentation on an output device. Various elements of system 100 may be provided within an integrated housing, Within the integrated housing, the various elements may be interconnected and transmit data therebetween using suitable connection arrangement 115, for example, an internal bus as known in the art, including the I2C bus, wiring, and printed circuit boards. The system 100 includes communication interface 150 that enables communication with other devices via communication channel 190. The communication interface 150 may include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel 190. The communication interface 150 may include, but is not limited to, a modem or network card and the communication channel 190 may be implemented, for example, within a wired and/or a wireless medium. Data is streamed to the system 100, in various embodiments, using a Wi-Fi network such as 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 channel 190 and the communications interface 150 which are adapted for Wi-Fi communications. The communications channel 190 of these embodiments is typically connected to an access point or router that provides access to outside networks including the Internet for allowing streaming applications and other over-the-top communications. Other embodiments provide streamed data to the system 100 using a set-top box that delivers the data over the HDMI connection of the input block 105. Still other embodiments provide streamed data to the system 100 using the RF connection of the input block 105. 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 100 may provide an output signal to various output devices, including a display 165, speakers 175, and other peripheral devices 185. The display 165 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 165 can be for a television, a tablet, a laptop, a cell phone (mobile phone), or other device. The display 165 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 other peripheral devices 185 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 185 that provide a function based on the output of the system 100. For example, a disk player performs the function of playing the output of the system 100. In various embodiments, control signals are communicated between the system 100 and the display 165, speakers 175, or other peripheral devices 185 using signaling such as AV. Link, CEC, or other communications protocols that enable device-to-device control with or without user intervention. The output devices may be communicatively coupled to system 100 via dedicated connections through respective interfaces 160, 170, and 180. Alternatively, the output devices may be connected to system 100 using the communications channel 190 via the communications interface 150. The display 165 and speakers 175 may be integrated in a single unit with the other components of system 100 in an electronic device, for example, a television. In various embodiments, the display interface 160 includes a display driver, for example, a timing controller (T Con) chip. The display 165 and speaker 175 may alternatively be separate from one or more of the other components, for example, if the RF portion of input 105 is part of a separate set-top box. In various embodiments in which the display 165 and speakers 175 are external components, the output signal may be provided via dedicated output connections, including, for example, HDMI ports, USB ports, or COMP outputs. The embodiments can be carried out by computer software implemented by the processor 110 or by hardware, or by a combination of hardware and software. As a non-limiting example, the embodiments can be implemented by one or more integrated circuits. The memory 120 can be of any type appropriate to the technical environment and can be implemented using any appropriate data storage technology, such as optical memory devices, magnetic memory devices, semiconductor-based memory devices, fixed memory, and removable memory, as non-limiting examples. The processor 110 can be of any type appropriate to the technical environment, and can encompass one or more of microprocessors, general purpose computers, special purpose computers, and processors based on a multi-core architecture, as non-limiting examples. FIG. 2 illustrates an example video encoder 200, such as a VVC (Versatile Video Coding) encoder. FIG. 2 may also illustrate an encoder in which improvements are made to the VVC standard or an encoder employing technologies similar to VVC. Before being encoded, the video sequence may go through pre-encoding processing (201), for example, applying a color transform to the input color picture (e.g., conversion from RGB 4:4:4 to YCbCr 4:2:0), or performing a remapping of the input picture components in order to get a signal distribution more resilient to compression (for instance using a histogram equalization of one of the color components). Metadata can be associated with the pre- processing and attached to the bitstream. In the encoder 200, a picture is encoded by the encoder elements as described below. The picture to be encoded is partitioned (202) and processed in units of, for example, CUs (Coding Units). Each unit is encoded using, for example, either an intra or inter mode. When a unit is encoded in an intra mode, it performs intra prediction (260), e.g. using an intra-prediction tool such as Decoder Side Intra Mode Derivation (DIMD). In an inter mode, motion estimation (275) and compensation (270) are performed. The encoder decides (205) which one of the intra mode or inter mode to use for encoding the unit, and indicates the intra/inter decision by, for example, a prediction mode flag. Prediction residuals are calculated, for example, by subtracting (210) the predicted block (a.k.a. prediction block) from the original image block. The prediction residuals are then transformed (225) into transform coefficients c (a.k.a prediction residual transform coefficients) which are quantized (230) into quantization indexes ^^_^ (a.k.a transform coefficient levels or quantized transform coefficients on the encoder side). The quantization levels (a.k.a quantization indexes) ^^_^ , as well as motion vectors and other syntax elements such as the picture partitioning information, are entropy coded (245) to output a bitstream. The encoder can skip the transform and apply quantization directly to the non-transformed residual signal. The encoder can bypass both transform and quantization, i.e., the residual is coded directly without the application of the transform or quantization processes. The encoder decodes an encoded block to provide a reference for further predictions. The quantized transform coefficients are de-quantized (240) (a.k.a. scaled) and inverse transformed (250) to decode prediction residuals. Combining (255) the decoded prediction residuals and the predicted block, an image block is reconstructed. In-loop filters (265) are applied to the reconstructed picture to perform, for example, deblocking/SAO (Sample Adaptive Offset)/ALF (Adaptive Loop Filter) filtering to reduce encoding artifacts. The filtered image is stored in a reference picture buffer (280). In-loop filters (265) are thus used to enhance reconstructed images before storing them in the reference picture buffer (280). In- loop filters form a whole family. Among them, deblocking filters (DBF) aim at reducing blocking artifacts occurring along block boundaries. Deblocking filters are usually designed to improve subjective quality, that is, the noticeability of such coding errors by the human psychovisual system. In usual video coding standards such as HEVC and VVC, deblocking filters are predetermined based on coding information (such as prediction modes, motion vectors, transform coefficients) and on local variations across block boundaries. On the other hand, adaptive loop filters (ALF) are learnt at encoder side in order to minimize a mean squared error with respect to source images, then the learned filter weights are encoded into the bitstream. Adaptive loop filters are usually applied at CTU-level (CTU stands for “Coding Tree Unit”), while deblocking filters are applied along block borders. FIG. 3 illustrates a block diagram of an example video decoder 300. In the decoder 300, a bitstream is decoded by the decoder elements as described below. Video decoder 300 generally performs a decoding pass reciprocal to the encoding pass as described in FIG. 2. The encoder 200 also generally performs video decoding as part of encoding video data. In particular, the input of the decoder includes a video bitstream, which can be generated by video encoder 200. The bitstream is first entropy decoded (330) to obtain quantization levels ^^_^ (a.k.a. transform coefficient levels or quantization levels on the decoder side), prediction modes, motion vectors, and other coded information. The picture partition information indicates how the picture is partitioned. The decoder may therefore divide (335) the picture according to the decoded picture partitioning information. The quantization levels ^^_^ are de- quantized (340) into reconstructed transform coefficients ^^_^ . De-quantization is also named scaling. The reconstructed transform coefficients ^^_^ are inverse transformed (350) to obtain the prediction residuals. Combining (355) the prediction residuals and the predicted block (a.k.a. prediction block), an image block is reconstructed. The predicted block can be obtained (370) from intra prediction (360) or motion-compensated prediction (i.e., inter prediction) (375). In- loop filters (365) are applied to the reconstructed picture to perform, for example, deblocking/SAO (Sample Adaptive Offset)/ALF (Adaptive Loop Filter) filtering to reduce encoding artifacts. The filtered image is stored at a reference picture buffer (380). Note that, for a given picture, the contents of the reference picture buffer 380 on the decoder 300 side is identical to the contents of the reference picture buffer 280 on the encoder 200 side for the same picture. The decoded picture can further go through post-decoding processing (385), for example, an inverse color transform (e.g., conversion from YCbCr 4:2:0 to RGB 4:4:4) or an inverse remapping performing the inverse of the remapping process performed in the pre-encoding processing (201). The post-decoding processing can use metadata derived in the pre-encoding processing and signaled in the bitstream. The Sample Adaptive Offset (SAO) allows adding offsets to some categories of reconstructed samples to reduce coding artefacts. To this aim, reconstructed samples are classified into categories. In HEVC and VVC, SAO filtering may be activated or de-activated at video level, slice level and CTU level. A CTU can be coded with three SAO modes: inactive (OFF), edge offset (EO), band offset (BO). For a given CTU, the SAO mode is specified by an index, e.g. SaoTypeIndex. For EO, the sample classification is based on local directional structures in the picture to be filtered. For BO, the sample classification is based on sample values. For EO or BO, one set of parameters (e.g. the offsets, the SAO mode, the class in case of EO and the band position in case of BO) per channel (e.g. Y, U, V) is either explicitly encoded or derived from neighboring CTUs (merge case). SAO can be applied to the luma and chroma components, where the SAO mode is the same for chroma components. In the following the chroma components may be interchangeably referred to as Cb and Cr or U and V. In the case where SAO filtering is activated for a CTU, the samples are categorized into NC categories (e.g. defined by syntax element sao_eo_class) , e.g. NC=5 for EO and NC=32 for BO in HEVC. For sample s in category c(s), the sample can be adjusted to s = s + off(c(s)), where off(n) is the offset value of category n. In HEVC, the offsets values of only M categories, M< NC, are decoded from the bitstream, the other offset values being set to 0. In HEVC, M=4. For BO, absolute offset values and signs are decoded. For EO, only absolute offset values are decoded, the signs being inferred from the category (positive sign for categories 1 and 2, and negative sign for categories 3 and 4) as indicated on FIG.4. Edge Offset FIG.4 illustrates the determination of reconstructed sample category in case of edge offset mode. EO uses four 1-D directional patterns for sample classification. Therefore, four EO classes are specified based on the directions, and each EO class corresponds to one direction: horizontal, vertical, 135° diagonal, and 45° diagonal, as shown in FIG.4 where the label “p” represents a current sample and the labels “n0” and “n1” represent two neighboring samples. The encoder may decide the best 1-D directional pattern (EO class) using a rate-distortion optimization (RDO) and signal this additional information in the encoded data as side information.. TABLE 1 For a given EO class, each sample is classified into one of five (NC = 5) categories based on local gradients and identified by an index EdgeIdx in Table 1. Specifically, the current sample value, labeled as “p_c,” is compared with its two neighbors n₀ and n₁ along the selected 1-D direction. The categorization rules for a sample are summarized in Table 1. Categories 1 and 4 are associated with a local valley and a local peak along the selected 1-D pattern, respectively, categories 2 and 3 are associated with concave and convex corners along the selected 1-D pattern, respectively. Positive offsets are used for categories 1 and 2, and negative offsets are used for categories 3 and 4. If the current sample value does not belong to categories 1- 4 (i.e., the current sample value is the same as its two neighbors, or if n₀ < p_c < n₁ or n₀ > p_c > n₁), then it is in category 0 and SAO is not applied (i.e., offset is 0). M offset values are encoded with M=(NC-1). More precisely, the absolute values of M offsets are signaled by the encoder, one absolute value for each category. The signs of the offsets are not encoded but implicitly derived from the corresponding EO categories. Band Offset For BO, the range of sample values (for example, [0 ; 255] in 8-bit) for a component ‘c’ is uniformly split into N(c)=32 bands. A band is thus a subrange (a.k.a. subdivision) of the range of sample values. In HEVC, only signed offset values of M, e.g. M=4, consecutive bands and the starting band position are signaled to the decoder as illustrated on FIG.5. On this figure, the starting band is the eighteenth band and the encoded offset values are {0, 0, 2, 3}. The starting band position (i.e. an index) indicates the position of the first band with an encoded offset within the 32 bands. One offset is coded for each of the M bands and the remaining bands have an offset equal to zero. When the starting band position is close to the last band position, the offset values may correspond to non-consecutive bands since the bands are managed as a circular buffer. Note for BO, those four signaled bands can be considered as four categories, and the remaining bands can be considered as another category. In the present application, we use the terms “band” and “category” interchangeably. In case of EO or BO, the SAO mode and offsets are possibly not coded but copied from the neighboring above or left CTU (Merge mode). Once classified, the reconstructed samples may be filtered by adding the offset of the category they belong to. This may be implemented through a look-up table (LUT) denoted lutSAO[c] containing for each band and for each component ‘c’ an associated offset. It contains zero except for the M consecutive categories that contain offsets to be added to the reconstructed samples: recSAO[x] = rec[x] + lutSAO[c][ rec[x] >> s ] (1) where rec[x] is the reconstructed samples at position ‘x’ for the current component ‘c’, before applying SAO, rec_SAO[x] is the reconstructed samples at position ‘x’ for the current component ‘c’, after applying SAO, s is equal to (BD(c) – 5) and lutSAO[c] contains the offsets for the component ‘c’, BD(c) is the bit-depth of the component ‘c’, and “>>” is arithmetic right shift. Cross-Component Sample Adaptive Offset (CCSAO) Similarly to SAO, the CCSAO classifies the reconstructed samples into different categories, properly derives one offset for each category and adds the offset to the reconstructed samples in that category. However, different from SAO which only uses one single luma/chroma component of current sample as input, the CCSAO may use all three components to classify the current sample into different categories. To facilitate the parallel processing, the output samples from the de-blocking filter are used as the input of the CCSAO for the classification stage only. FIG. 6 depicts a block diagram of the decoding workflow when the CCSAO is applied. As in SAO, there is two modes for classifying the reconstructed samples, EO and BO. In EO mode, similar to the edge classifier of SAO in VVC, the edge-based (EO) classifier of CCSAO also uses the four 1-D directional patterns for sample classification: horizontal, vertical, 135° diagonal and 45° diagonal, as shown in FIG.4. For every 1-D pattern, each sample is classified based on the sample difference between the luma sample value labeled as “c” and its two neighbor luma samples labeled as “n₀” and “n₁” along the selected 1-D pattern. Similar to SAO, the encoder may decide the best 1-D directional pattern using a rate-distortion optimization (RDO) and signal this additional information in each classifier/set. Both the sample differences “n₀-p” and “n₁-p” are compared against a pre-defined threshold value (Th) to derive a final information, namely an index identifying a particular category denoted “class_idx”. The encoder selects the best “Th” value from an array of pre-defined threshold values based on RDO and the index into the “Th” array is signaled. Furthermore, an additional difference between CCSAO edge-based classifier and the SAO edge-based classifier in VVC is that, in the former, Chroma samples use the co-located Luma samples for deriving the edge information (samples “n0”, “p” and “n1” are the co-located luma samples) whereas, in the later Chroma samples use its own neighboring samples for deriving the edge information. The Edge-based classifier process is formulated as follows: Ea=( n₀-p<0)? (n₀-p<(-Th)? 0:1) : (n₀-p<(Th)? 2:3) (2) Eb=( n1-p<0)? (n1-p<(-Th)? 0:1) : (n1-p<(Th)? 2:3) (3) ^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^ = ^^_^ * 16 + Ea * 4 + Eb (4) ^^′_^^^ ൌ ^^ ^^ ^^ ^^1^ ^^_^^^ ^ ^^_^^ௌ^ை^ ^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^^^ (5) Where ^^_^^ௌ^ை^ ^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^^ is the value of CCSAO offset that is applied to the category identified by ^^ ^^ ^^ ^^ ^^_ ^^ ^^ ^^ ; ^^_^^^ is a reconstructed sample to be processed, i.e. before applying CCSAO ; ^^′_^^^ is the reconstructed sample once processed, i.e. after applying CCSAO ; Clip1() is a clipping operator ensuring that the reconstructed sample value is inside the sample range. ^^_^ is a variable (a.k.a. band information) derived as follows : ^^{^^ ൌ ^cur ∙ ^^^௨^^ ≫ ^^ ^^ (or)} ^_{^^ ൌ ^ ^^ ^^ ^^1 ∙ ^^^^^^^ ≫ ^^ ^^ (or) (6) ^^^ ൌ ^ ^^ ^^ ^^2 ∙ ^^^^^ଶ^ ≫ ^^ ^^} where BD is the internal coding bit-depth In the above equations (6), the sample “cur” is the current sample being processed, ^^ ^^ ^^1 and ^^ ^^ ^^2 are the co-located samples. When Luma samples are processed, ^^ ^^ ^^1 and ^^ ^^ ^^2 are the co-located ^^_^ and ^^_^ samples respectively. When Chroma( ^^_^^ samples are processed, ^^ ^^ ^^1 and ^^ ^^ ^^2 are the co-located ^^ and ^^_^ samples respectively. Similarly When Chroma( ^^_^^ samples are processed, ^^ ^^ ^^1 and ^^ ^^ ^^2 are the co-located ^^ and ^^_^ samples respectively. {N_cur, N_col1, N_col2} are the numbers of equally divided bands applied to { cur, col1, col2 } full range respectively. Based on RDO, encoder signals one sample among the samples “cur”, “col1", "col2" used in deriving the band information, namely ^^_^ . Consequently, the decoder is informed which equation among the above three equations (6) to use in order to derive the band information ^^_^. In BO mode, for a given luma/chroma sample, three candidate samples are selected to classify the given sample into different categories: one collocated Y sample, one collocated U sample, and one collocated V sample. The sample values of these three selected samples are then classified into three different bands { bandY, bandU, bandV }, and a joint index “i" is used to indicate the category of the given sample. One offset is signaled and added to the reconstructed samples that fall into that category, which can be formulated as: ^^ ^^ ^^ ^^ _^^ ൌ ^ ^^ _{^^ ^^ ^^} ∙ ^^ _^^^ ≫ ^^ ^^ ^_{^ ^^ ^^ ^^ ^^ ൌ} ^ _{^^ ^^ ^^ ^^ ∙ ^^ ^^}^ _{≫ ^^ ^^} (7) ^^ ^^ ^^ ^^ _^^ ൌ ^ ^^ _{^^ ^^ ^^} ∙ ^^ _^^^ ≫ ^^ ^^ ^_{^ ൌ ^^ ^^ ^^ ^^ ^^ ∙} ^ _{^^ ^^ ∙ ^^ ^^}^ _{^ ^^ ^^ ^^ ^^ ^^ ∙ ^^ ^^ ^ ^^ ^^ ^^ ^^ ^^ ^^′ ൌ ^^ ^^ ^^ ^^1^ ^^ ^ ^^ ^^^^} ⁽⁸⁾ In equations (7), { Y_col, that are used to classify the current sample; {NY, NU, NV} are the numbers of equally divided bands applied to { Y_col, U_col, V_col } full range respectively; BD is the internal coding bit-depth. In the current design, the collocated luma sample can be chosen from 9 candidate positions, while the collocated chroma sample positions are fixed, as depicted in FIG.7. In equations (8), C_rec and C’_rec are the reconstructed samples before and after the CCSAO is applied and σCCSAO[i] is the value of CCSAO offset that is applied to the i-th BO category. Both SAO and CCSAO uses band classification of the reconstructed samples before applying offsets correction. However, depending on the picture characteristics, the number of samples in some bands may be low compared to other bands. This may jeopardize the coding efficiency of SAO or CCSAO since some overhead signaling can be spent to code the position of the significant band values. In addition, the adequation of the offset with corresponding range values may be imprecise. In contrast, a decoding method (an encoding method respectively) is disclosed below whereby the band offset classification of the reconstructed samples is adapted by using non-equally based band classification. This makes it possible to improve coding efficiency of SAO or CCSAO (e.g. if the number of samples in this band is empty or small, or by tailoring the band width to the amount of samples in the band). FIG.8 depicts a flowchart of a decoding method according to a specific embodiment. At S800, video data are decoded to obtain reconstructed samples of a picture region. At S802, a distribution of said reconstructed sample values is obtained in the picture region. The distribution associates a frequency of occurrence with each value of a sample range, e.g. [0;255] for an 8-bit picture, the frequency of occurrence of one value being the number of reconstructed samples in the picture region having this value. This distribution may be represented in the form of a LUT or an histogram. Such an histogram is represented on top of FIG.9. However, the present principles are not limited to these representations. On the histogram the values min and max are respectively the lowest and highest reconstructed sample values of the picture region and B1 and B2 are the bins with highest values (i.e. highest number of samples). At S804, a plurality of bands, i.e. subranges of sample range, are determined responsive to the distribution. In an example, N bands are determined N being a positive integer, e.g. N=32. In other examples, N=16 or N=4. In another example, N>3. In an example, bands are determined so that at least one band around the sample value of highest frequency is narrower than at least another band as illustrated on bottom of FIG. 9. In an example, the narrowest band comprises the sample value of highest frequency, e.g. B1 on FIG.9. In another example, bands are determined so that each band comprises approximately a same number of samples. In a practical implementation, an average number of samples is computed as Th=NbSampleRegion/ N(c), where NbSampleRegion is the number of samples in the considered region and N(c) is the number of bands, e.g. N(c)=32. The bands are for example determined by applying the following algorithm for a given component c: x=0 sum = 0 for (k=0 to k=N(c)-1) { While ( sum < ((k+1)*NbSampleRegion) / N(c) ) { sum= sum+Lutinit[x] Lut_HISTO[c] [x] = k x=x+1 } k=k+1 } While ( x < xMax ) { LutHISTO[c] [x] = N(c)-1; x = x + 1 } where Lutinit[x] is an initial look-up table storing the frequency of occurrence of each value of the sample range and thus corresponds to the distribution obtained at S802; and LutHISTO[c] [x] is a look-up table storing the index of the band corresponding to the sample value ‘x’. The obtained bands have approximately a same number of samples that is close to NbSampleRegion/ N(c). However, this number of samples per band may be slightly different from one band to another. Consequently, the bands may have unequal sizes (a.k.a band width) as opposed to regular SAO filtering wherein bands have equal size as illustrated on FIG. 5. On FIG. 9, the bands are narrower around the sample values associated with the two highest bins B1 and B2. Also, in the example depicted in FIG. 9, most of the sample values fall into two bins B1 and B2, then one may have better precision in the selection of the offset values associated to these 2 bins if the band width is narrowed. At S805, an offset value is obtained for each band. The offsets values are for example decoded from encoded data, e.g. from a bitstream. Offsets are possibly not decoded but copied from neighboring CTU (Merge mode) or inferred to zero. For example, the offset values associated with band/category that do not contain any sample are inferred to zero. In another example, the offset values associated with K band/category that contain the fewer number of samples are inferred to zero. In another example, the offset values associated with K band/category that contain the fewer relative number of samples compared to B1 are inferred to zero. At S806, an offset value is added to each reconstructed sample, said offset value being associated with the band the reconstructed sample belongs to. In case of SAO filtering, equation (1) becomes recSAO[x] = rec[x] + lutSAO[c][ lutHISTO[c][ rec[x] ] ], where lutHISTO[c] is the LUT that contains the index ‘lutHISTO[c][x]’ of the band corresponding to the sample value ‘x’. In case of SAO, the values of lut_HISTO[c][x] are included in [0,…N(c)-1], e.g. [0, 31] in case of 32 bands. In case of CCSAO EO, ‘lutHISTO[c]’ is the LUT that contains the index ‘iB’ of the band corresponding to the sample value ‘x’ of the component ‘c’, the CC-SAO equations (6) are modified as follows : ^^_^ ൌ lutHISTO^c^ ^cur^ (or) ^^_^ ൌ lut_HISTO^c^ ^col1^ (or) ^^_^ ൌ lut_HISTO^c^ ^col2^ Equations (2) to (5) then apply to obtain the filtered reconstructed sample ^^′_^^^. In case of CCSAO BO, equations (7) are modified as follows : ^^ ^^ ^^ ^^_^ ൌൌ lutHISTO^ ^^ ൌ ^^^^ ^^_^^^^ (or) ^^ ^^ ^^ ^^_^ ൌ lut_HISTO^ ^^ ൌ ^^^^ ^^_^^^^ (or) ^^ ^^ ^^ ^^_^ ൌ lut_HISTO^ ^^ ൌ ^^^^ ^^_^^^^ Then equations (8) apply to obtain the filtered reconstructed sample ^^′_^^^. In case of CC-SAO, the values of lutHISTO[c][x] are included in [0,…NY-1], [0,…NU-1] or [0,…N_V-1] for ‘c’ equal to Y, U or V respectively. In a variant, both types of classification may be used, namely the regular classification with bands of equal width and the newly disclosed classification with bands of unequal width. In this case, a flag may be decoded that indicates whether the regular classification with bands of equal width or the newly disclosed classification with bands of unequal width is used. The flag may be decoded per picture or slice (all the CTU of the picture/slice use regular band classification or newly disclosed classification) or per CTU for example. Said otherwise, different CTUs of a same picture may use different types of classification, e.g. one CTU using the regular classification with bands of equal width and another CTU using the newly disclosed classification with bands of unequal width. In another variant, a separate flag may be decoded for each component (e.g., Y, U or V) or for each type of component (e.g., luma or chroma) that indicates whether the regular classification with bands of equal width or the newly disclosed classification with bands of unequal width is used for that component. In another variant, in case of CCSAO, the unequal (or regular) band classification may apply for CCSAO BO only (or for CCSAO EO only). This may be signaled by decoding a flag indicating, for example, whether the newly disclosed classification with bands of unequal width applies to CCSAO BO only. In another example, this may be signaled by decoding a flag indicating, for example, whether the newly disclosed classification with bands of unequal width applies to CCSAO EO only. In an example, one distribution (e.g., the histogram) is obtained per region. The region may be a group of CTUs or one CTU for example. The size of the region may be decoded. In another example, the distribution (e.g., the histogram) is obtained for several components jointly. For example, if a joint distribution is obtained for U and V, then lutHISTO[UorV][x] contains the band index of samples U and samples V with value equal to ‘x’. In this case Nu=Nv. FIG.10 depicts a flowchart of an encoding method according to a specific embodiment. At S900, video data are encoded and reconstructed. Indeed, an encoder comprises a so-called decoding loop to reconstruct samples that may be further used for prediction of other video data. The encoding method comprises steps S902, S904 and S906 that are respectively identical to steps S802, S804 and S806 of the decoding method. At S905, an offset value is obtained for each band/category. On the encoder side, the offset values are obtained for example using RDO and possibly encoded into a bitstream. Offsets are possibly not encoded but copied from neighboring CTU (Merge mode) or inferred to zero. For example, the offset values associated with band/category that do not contain any sample are inferred to zero. In another example, the offset values associated with K band/category that contain the fewer number of samples are inferred to zero. In another example, the offset values associated with K band/category that contain the fewer relative number of samples compared to B1 are inferred to zero. In an example, both types of classification are used, namely the regular classification with bands of equal width and the newly disclosed classification with bands of unequal width. In this case, a flag may be encoded per picture region to indicate whether the regular classification with bands of equal width or the newly disclosed classification with bands of unequal width is used. The flag may be coded per picture region, e.g. per picture or slice (all the CTU of the picture/slice use regular band classification or newly disclosed classification) or per CTU for example. In another variant, one code a separate flag for each component (e.g., Y, U or V) or for each type of component (e.g., luma or chroma) that indicates whether the regular classification with bands of equal width or the newly disclosed classification with bands of unequal width is used for that component. In another variant, in case of CCSAO, the unequal (or regular) band classification may apply for CCSAO BO only (or for CCSAO EO only). This may be signaled by encoding a flag indicating, for example, whether the newly disclosed classification with bands of unequal width apply to CCSAO BO only. This may be signaled by encoding a flag indicating, for example, whether the newly disclosed classification with bands of unequal width apply to CCSAO EO only. In an example, one distribution (e.g., the histogram) is obtained per region. The region may be a group of CTUs or one CTU for example. The size of the region may be signaled in the encoded data. In another example, the distribution (e.g., the histogram) is obtained for several components jointly. For example, if a joint distribution is obtained for U and V, then lut_HISTO[UorV][x] contains the band index of samples U and samples V with value equal to ‘x’. Moreover, the present aspects are not limited to ECM, VVC or HEVC, and can be applied, for example, to other standards and recommendations, and extensions of any such standards and recommendations. Unless indicated otherwise, or technically precluded, the aspects described in this application can be used individually or in combination. Various numeric values are used in the present application. The specific values are for example purposes and the aspects described are not limited to these specific values. Various implementations involve decoding. “Decoding”, as used in this application, can encompass all or part of the processes performed, for example, on a received encoded sequence in order to produce a final output suitable for display. In various embodiments, such processes include one or more of the processes typically performed by a decoder, for example, entropy decoding, inverse quantization, inverse transformation, and differential decoding. In various embodiments, such processes also, or alternatively, include processes performed by a decoder of various implementations described in this application, for example, decode re-sampling filter coefficients, re-sampling a decoded picture. As further examples, in one embodiment “decoding” refers only to entropy decoding, in another embodiment “decoding” refers only to differential decoding, and in another embodiment “decoding” refers to a combination of entropy decoding and differential decoding, and in another embodiment “decoding” refers to the whole reconstructing picture process including entropy decoding. Whether the phrase “decoding process” is intended to refer specifically to a subset of operations or generally to the broader decoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art. Various implementations involve encoding. In an analogous way to the above discussion about “decoding”, “encoding” as used in this application can encompass all or part of the processes performed, for example, on an input video sequence in order to produce an encoded bitstream. In various embodiments, such processes include one or more of the processes typically performed by an encoder, for example, partitioning, differential encoding, transformation, quantization, and entropy encoding. In various embodiments, such processes also, or alternatively, include processes performed by an encoder of various implementations described in this application, for example, determining re-sampling filter coefficients, re-sampling a decoded picture. As further examples, in one embodiment “encoding” refers only to entropy encoding, in another embodiment “encoding” refers only to differential encoding, and in another embodiment “encoding” refers to a combination of differential encoding and entropy encoding. Whether the phrase “encoding process” is intended to refer specifically to a subset of operations or generally to the broader encoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art. This disclosure has described various pieces of information, such as for example syntax, that can be transmitted or stored, for example. This information can be packaged or arranged in a variety of manners, including for example manners common in video standards such as putting the information into an SPS, a PPS, a NAL unit, a header (for example, a NAL unit header, or a slice header), or an SEI message. Other manners are also available, including for example manners common for system level or application level standards such as putting the information into one or more of the following: a. SDP (session description protocol), a format for describing multimedia communication sessions for the purposes of session announcement and session invitation, for example as described in RFCs and used in conjunction with RTP (Real-time Transport Protocol) transmission. b. DASH MPD (Media Presentation Description) Descriptors, for example as used in DASH and transmitted over HTTP, a Descriptor is associated with a Representation or collection of Representations to provide additional characteristic to the content Representation. c. RTP header extensions, for example as used during RTP streaming. d. ISO Base Media File Format, for example as used in OMAF and using boxes which are object-oriented building blocks defined by a unique type identifier and length also known as 'atoms' in some specifications. e. HLS (HTTP live Streaming) manifest transmitted over HTTP. A manifest can be associated, for example, to a version or collection of versions of a content to provide characteristics of the version or collection of versions. 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. Some embodiments refer to rate distortion optimization. In particular, during the encoding process, the balance or trade-off between the rate and distortion is usually considered, often given the constraints of computational complexity. The rate distortion optimization is usually formulated as minimizing a rate distortion function, which is a weighted sum of the rate and of the distortion. There are different approaches to solve the rate distortion optimization problem. For example, the approaches may be based on an extensive testing of all encoding options, including all considered modes or coding parameters values, with a complete evaluation of their coding cost and related distortion of the reconstructed signal after coding and decoding. Faster approaches may also be used, to save encoding complexity, in particular with computation of an approximated distortion based on the prediction or the prediction residual signal, not the reconstructed one. Mix of these two approaches can also be used, such as by using an approximated distortion for only some of the possible encoding options, and a complete distortion for other encoding options. Other approaches only evaluate a subset of the possible encoding options. More generally, many approaches employ any of a variety of techniques to perform the optimization, but the optimization is not necessarily a complete evaluation of both the coding cost and related distortion. 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 in, 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, for example, computers, cell phones, portable/personal digital assistants ("PDAs"), 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 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, or retrieving the information from memory. 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”, for example, in the cases of “A/B”, “A and/or B” and “at one 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”, 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 (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. Also, as used herein, the word “signal” refers to, among other things, indicating something to a corresponding decoder. For example, in certain embodiments the encoder signals a particular flag, EO orientation, SAO mode, etc. In this way, in an embodiment the same parameter is used at both the encoder side and the decoder side. Thus, for example, an encoder can transmit (explicit signaling) a particular parameter to the decoder so that the decoder can use the same particular parameter. Conversely, if the decoder already has the particular parameter as well as others, then signaling can be used without transmitting (implicit signaling) to simply allow the decoder to know and select the particular parameter. By avoiding transmission of any actual functions, a bit savings is realized in various embodiments. It is to be appreciated that signaling can be accomplished in a variety of ways. For example, one or more syntax elements, flags, and so forth are used to signal information to a corresponding decoder in various embodiments. While the preceding relates to the verb form of the word “signal”, the word “signal” can also be used herein as a noun. As will be evident to one of ordinary skill in the art, implementations 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. For example, a signal can be formatted to carry the bitstream 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 data stream and modulating a carrier with the encoded data 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. A number of embodiments has been described above. Features of these embodiments can be provided alone or in any combination, across various claim categories and types. A decoding method is disclosed that comprises: decoding video data to obtain reconstructed samples of a picture region; obtaining a distribution of reconstructed sample values in the picture region; determining a plurality of bands responsive to said distribution, a band being a subrange of a sample range; and adding to each reconstructed sample an offset value obtained for the band said reconstructed sample belongs to. In an example, determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that at least one band located around a sample value of highest frequency is narrower than at least another band. In an example, determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that each band comprises approximately a same number of samples. In an example, decoding a flag for said picture region indicating that bands determined responsive to the distribution of reconstructed sample values are used. In an example, decoding one flag per component of the picture region indicating for the component whether bands determined responsive to a distribution of reconstructed sample values are used or whether bands of equal size are used. In an example, decoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to band offset filtering only. In an example, decoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to edge offset filtering only. In an example, a joint distribution is obtained for one component, e.g. Y, U or V. In an example, a joint distribution is obtained for at least two components. An encoding method is also disclosed that comprises: encoding and reconstructing video data to obtain reconstructed samples of a picture region; obtaining a distribution of reconstructed sample values in the picture region; determining a plurality of bands responsive to said distribution, a band being a subrange of a sample range; and adding to each reconstructed sample an offset value obtained for the band said reconstructed sample belongs to. In an example, determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that at least one band located around a sample value of highest frequency is narrower than other bands. In an example, determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that each band comprises approximately a same number of samples. In an example, encoding a flag for said picture region indicating that bands determined responsive to the distribution of reconstructed sample values are used. In an example, encoding one flag per component of the picture region indicating for the component whether bands determined responsive to a distribution of reconstructed sample values are used or whether bands of equal size are used. In an example, encoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to band offset filtering only. In an example, encoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to edge offset filtering only. In an example, a joint distribution is obtained for at least two components. A decoding apparatus comprising one or more processors and at least one memory coupled to said one or more processors, wherein said one or more processors are configured to perform the decoding method. An encoding apparatus comprising one or more processors and at least one memory coupled to said one or more processors, wherein said one or more processors are configured to perform the encoding method. A computer program is disclosed that comprises program code instructions for implementing the decoding method (encoding method respectively). A computer readable storage medium is disclosed that has stored thereon instructions for implementing the decoding method (encoding method respectively).

Claims

CLAIMS 1. A decoding method comprising: decoding (S800) video data to obtain reconstructed samples of a picture region; obtaining (S802) a distribution of reconstructed sample values in the picture region; determining (S804) a plurality of bands responsive to said distribution, a band being a subrange of a sample range; and adding (S806) to each reconstructed sample an offset value obtained (S805) for the band said reconstructed sample belongs to.

2. The method of claim 1, wherein determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that at least one band located around a sample value of highest frequency is narrower than at least another band.

3. The method of claim 1, wherein determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that each band comprises approximately a same number of samples.

4. The method of any one of claims 1 to 3, comprising decoding a flag for said picture region indicating that bands determined responsive to the distribution of reconstructed sample values are used.

5. The method of any one of claims 1 to 3, comprising decoding one flag per component of the picture region indicating for the component whether bands determined responsive to a distribution of reconstructed sample values are used or whether bands of equal size are used.

6. The method of any one of claims 1 to 5, comprising decoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to band offset filtering only.

7. The method of any one of claims 1 to 5, comprising decoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to edge offset filtering only.

8. The method of any one of claims 1 to 7, wherein a joint distribution is obtained for at least two components.

9. An encoding method comprising: encoding and reconstructing video data to obtain reconstructed samples of a picture region; obtaining a distribution of reconstructed sample values in the picture region; determining a plurality of bands responsive to said distribution, a band being a subrange of a sample range; and adding to each reconstructed sample an offset value obtained for the band said reconstructed sample belongs to.

10. The method of claim 9, wherein determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that at least one band located around a sample value of highest frequency is narrower than other bands.

11. The method of claim 9, wherein determining a plurality of bands responsive to said distribution comprises dividing the sample range into a plurality of bands so that each band comprises approximately a same number of samples.

12. The method of any one of claims 9 to 11, comprising encoding a flag for said picture region indicating that bands determined responsive to the distribution of reconstructed sample values are used.

13. The method of any one of claims 9 to 11, comprising encoding one flag per component of the picture region indicating for the component whether bands determined responsive to a distribution of reconstructed sample values are used or whether bands of equal size are used.

14. The method of any one of claims 9 to 13, comprising encoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to band offset filtering only.

15. The method of any one of claims 9 to 13, comprising encoding one flag in case of cross component sample adaptive offset indicating whether bands determined responsive to said distribution apply to edge offset filtering only.

16. The method of any one of claims 9 to 15, wherein a joint distribution is obtained for at least two components.

17. A decoding apparatus comprising one or more processors and at least one memory coupled to said one or more processors, wherein said one or more processors are configured to perform the method of any one of claims 1-9.

18. An encoding apparatus comprising one or more processors and at least one memory coupled to said one or more processors, wherein said one or more processors are configured to perform the method of any one of claims 9-16.

19. A computer program comprising program code instructions for implementing the method according to any one of claims 1-9 when executed by a processor.

20. A computer readable storage medium having stored thereon instructions for implementing the method of any one of claims 1-9.

21. A computer program comprising program code instructions for implementing the method according to any one of claims 9-16 when executed by a processor.

22. A computer readable storage medium having stored thereon instructions for implementing the method of any one of claims 9-16.