Implicit LMCS codewords

Abstract

Methods and apparatus are provided for calculation of codewords to implement a mapping function in video encoders and decoders. In one embodiment, the mapping is used in a Luma Mapping Chroma Scaling function. In another embodiment, the codeword calculation is done before in-loop filter. In another embodiment, the codeword calculation is done after in-loop filtering. In another embodiment, codeword information is explicitly signaled from an encoder to a decoder.

Description

IMPLICIT LMCS CODEWORDSCROSS REFERENCE TO RELATED APPLICATIONThis application claims the benefit of European Serial No. 23306643.0 filed September 29, 2023, which is incorporated by reference herein in its entirety.TECHNICAL FIELDAt least one of the present embodiments generally relates to a method or an apparatus for video encoding or decoding, compression or decompression.BACKGROUNDTo achieve high compression efficiency, image and video coding schemes usually employ prediction, including motion vector 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 frame correlation, then the differences between the original image and the predicted image, 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.SUMMARYAt least one of the present embodiments generally relates to a method or an apparatus for video encoding or decoding, and more particularly, to a method or an apparatus for calculation of codewords to generate mapping functions in an encoding and decoding process.According to a first aspect, there is provided a method. The method comprises steps for performing a calculation using codewords to determine tables for a mapping function; implementing the mapping function on a video block; and, encoding the video block using the mapped portion of the video block.According to a second aspect, there is provided another method. The method comprises steps for performing a calculation using codewords to determine tables for a mapping function; implementing the mapping function on a video block; and, decoding the video block using the mapped portion of the video block.According to another aspect, there is provided an apparatus. The apparatus comprises a processor and a memory. The processor can be configured to operate on digital video data according to the aforementioned methods.According to another aspect, there is provided an apparatus. The apparatus comprises a processor and a memory. The processor can be configured to encode a block of a video or decode video data by executing any of the aforementioned methods.According to another general aspect of at least one embodiment, there is provided a device comprising an apparatus according to any of the decoding embodiments; and at least one of (i) an antenna configured to receive a signal, the signal including the video block, (ii) a band limiter configured to limit the received signal to a band of frequencies that includes the video block, or (iii) a display configured to display an output representative of the video block.According to another general aspect of at least one embodiment, there is provided a non-transitory computer readable medium containing data content generated according to any of the described encoding embodiments or variants.According to another general aspect of at least one embodiment, there is provided a signal comprising video data generated according to any of the described encoding embodiments or variants.According to another general aspect of at least one embodiment, video data or a bitstream is formatted to include data content generated according to any of the described encoding embodiments or variants.According to another general aspect of at least one embodiment, there is provided a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the described decoding embodiments or variants.These and other aspects, features and advantages of the general aspects will become apparent from the following detailed description of exemplary embodiments, which is to be read in connection with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSFigure 1 illustrates a block diagram of an example of a system in which various aspects and embodiments are implemented.Figure 2 illustrates an example of a block-based hybrid video encoder.Figure 3 illustrates a block diagram of an example video decoder.Figure 4 illustrates an encoder with a new LMCS CW calculation block placed before the in-loop filters in one embodiment under the present aspects.Figure 5 illustrates the position of a new LMCS CW calculation block in a decoder loop in one embodiment under the present aspects.Figure 6 illustrates a new position of the LMCS CW calculation block in an encoder in a second embodiment under the present aspects.Figure 7 illustrates a new position of the LMCS CW calculation block in a decoder in a second embodiment under the present aspects.Figure 8 illustrates one embodiment of a first method under the described aspects.Figure 9 illustrates one embodiment of a second method under the described aspects.Figure 10 illustrates one embodiment of an apparatus under the described aspects.Figure 11 illustrates a standard, generic, video compression scheme.Figure 12 illustrates a standard, generic, video decompression scheme.Figure 13 illustrates a processor-based system for encoding / decoding under the general described aspects.DETAILED DESCRIPTION The embodiments described here are in the field of video compression and generally relate to video compression and video encoding and decoding more specifically to a method or an apparatus for calculation of codewords to generate mapping functions in an encoding and decoding process.To achieve high compression efficiency, image and video coding schemes usually employ block-based prediction, including motion vector 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 frame 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 inverseprocesses corresponding to the entropy coding, quantization, transform, and prediction.In the HEVC (High Efficiency Video Coding) video compression standard, motion compensated temporal prediction is employed to exploit the redundancy that exists between successive pictures of a video.To do so, a motion vector is associated to each prediction unit (PU). Each CTU (Coding Tree Unit) is represented by a Coding Tree in the compressed domain. This is a quad-tree division of the CTU, where each leaf is called a Coding Unit (CU).Each CU is then given some Intra or Inter prediction parameters (Prediction Info). To do so, it is spatially partitioned into one or more Prediction Units (PUs), each PU being assigned some prediction information. The Intra or Inter coding mode is assigned on the CU level.Figure 1 illustrates a block diagram of an example of a system in which various aspects and embodiments are implemented. Figure 2 illustrates an example of a block-based hybrid video encoder 200. 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 is first analyzed to determine when a luma mapping chroma scaling (LMCS) is applied and the Code Words (CW) to be applied (295). 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). In an inter mode, motion estimation (275) and compensation (270) are performed. When LMCS is applied a forward mapping of the motion compensated prediction is applied (285). 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 from the original image block.The prediction residuals are then transformed (225) and quantized (230). Thequantized transform coefficients, 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) and inverse transformed (250) to decode prediction residuals. Combining (255) the decoded prediction residuals and the predicted block, an image block is reconstructed. When LMCS is applied an inverse mapping is performed on the reconstructed picture (290). 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).Figure 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 Figure 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 transform coefficients, 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 transform coefficients are de-quantized (340) and inverse transformed (350) to decode the prediction residuals. Combining (355) the decoded prediction residuals and the predicted block, an image block is reconstructed. When LMCS is applied an inverse mapping is performed on the reconstructed picture (390). The predicted block can be obtained (370) from intra prediction (360) or motion- compensated prediction (i.e., inter prediction) (375). When LMCS is applied a forward mapping of the motion compensated prediction is applied (325). In-loop filters (365) are applied to the reconstructed image. The filtered image is stored at a reference picture buffer (380). Note that, for a given picture, the contents of the reference picturebuffer 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 described embodiments are in the context of video compression. The embodiments specifically focus on defining the luma mapping Code words of the LMCS (Luma Mapping Chroma Scaling) function at the decoder side based on the decoded information in order to avoid the transmission of such information.The goal is to improve the compression efficiency, that is, to reduce the bitrate while maintaining the quality, or equivalently to improve the quality while maintaining the bitrate.In most of the sequences especially for captured content one’s, data range of the luminance is not corresponding to 1024 levels as expected for a 10-bit signal, but it corresponds to the limited range of 64-940 (also named standard range). In ECM- 8.0, the LMCS function allows modification of the luminance of the content to better exploit the 10-bit capabilities. A mapping function is applied to luminance thanks to a pre-calculated look-up table (LUT), computed at the encoder side. Values of the LUT are defined by the encoder based on specific characteristic of the content. For this purpose, the 10-bit representation (1024 levels) is split into 16 pieces (intervals) of 64 levels. The current version of LMCS mapping function derivation in ECM-8.0 encoder includes the following steps in the Random-Access mode.For a given video or video chunk, some parameters are extracted, typically on l-frames such as the histogram and the local variance of the frame per pieces. The result of the histogram is given with 16 values (corresponding to the 16 pieces), each corresponding to 1 / 16 of the range of values between 0 and 1023 for a 10 bits signal. H ist[O] corresponds to the occurrence of samples having a luminance between 0 and 63 on the whole picture, Hist

[0001] corresponds to the occurrence of sample having a luminance between 64 and 127 and so on. Hist[i] for i=0 to 15 are normalized so that Hist[0] + ... + Hist

[0015] = 1.0.The variance of the sample P having the value of luminance P(x,y) is calculated as the sum of square values of pixels on a 5x5 window divided by the size of thewindow minus the square of the average value on this window. This variance is summed with variances of the same piece, the piece is determined by the luma value of the current sample.If Hist[0] and Hist

[0015] are both below a threshold (e.g., 0.001), the LCMS function is activated meaning that the Code Words from 0-63 and 960-1023 are not currently used for coding this sequence.There are 896 codes used to code values between 64 and 959. The new Number of Code Words (NbCW) can be between 896 and 1022 to encode these 896 values between 64 and 959. At this stage NbCW is always a multiple of 14. NbCW is determined based on different thresholds calculated from histogram and variance values.At the previous step, the number of codewords per piece is the same (NbCW is a multiple of 14). The refinement process will use the histogram and the variance value of each piece to slightly modify the number of CW per piece around the initial value calculated at the previous step. This corresponds to the following pseudo-code: for (int i = 0; i < 16; i++) { if (Histfi] > 0.001) { hist = Histfi] > 0.4 ? 0.4 : Hist fi] ; deltal = (uintl6 t) (10.0 * hist + 0.5) ; delta2 = (uintl6 t) (20.0 * hist + 0.5) ; if (normVarfi] < 0.8) { m binCWfi] = m binCWfi] + delta2;} else if (normVarfi] < 0.9) { m binCWfi] = m binCWfi] + deltal;} if (normVarfi] > 1.2) { m binCWfi] = m binCWfi] - delta2;} else if (normVarfi] > 1.1) { m binCWfi] = m binCWfi] - deltal;}}A correction step is applied to ensure the sum of number of CW per piece is notabove 1023.A specific processing is applied for QP<=22 with threshold again to determine whether the NbCW is modified or not. If it is modified, the value is set to 924.The LUT corresponding to the number of CW per piece is generated. It is called the Forward_Mapping LUT and it will be used each time a conversion from the nonmapped to the mapped domain is required. In parallel the lnverse_Mapping LUT is also generated based on the same number of CW per pieces. It will be used each time a conversion from the mapped to the non-mapped domain is required. The Forward_Mapping and lnverse_Mapping are applied to the video for any other frames than l-frames.The LMCS parameters are signaled by the encoder in the Adaptation Parameter Set (APS).Table 1. LMCS syntax table.At decoder side, the decoder decodes this information, rebuilds the forward and inverse mapping functions, and uses these functions during the decoding process (forward mapping is applied to inter prediction samples, and inverse mapping is applied after the reconstruction process and before the in-loop filtering).The LMCS function as it is derived in the ECM8.0 encoder requires a large amount of processing on the l-frame to extract video parameters (histogram, variance) and to calculate the number of code words per piece based on histogram and local variance. Moreover, since the number of CW per piece depends on the content, thesevalues are calculated at the encoder side and the number of CW per piece is transmitted in the bit stream every I frame. It means that there is an extra cost to transmit this data. In the described embodiments a solution is proposed to avoid transmitting the number of CW per piece to avoid or limit this extra cost.The main point of the embodiments is to avoid transmitting Code Word information, for example every l-frame, by calculating at the decoder side the same information that are used to generate the LUTs of the LMCS function (Forward and Inverse mapping of the video) based on decoded frames statistics. Therefore, an implicit mode is used, where the LMCS function is therefore inferred from the decoded picture. To do this, a corresponding position is defined in both decoder and encoder loops to apply the calculation of video parameters that are used to generate the number of CW. The implicit mode is optional, so information is transmitted indicating whether the CW or number of codewords is implicitly defined at the decoder or explicitly signaled in the bitstream and in which APS the new data is stored.In a second embodiment a simplified version of the LMCS algorithm is proposed to reduce the amount of calculation required at the decoder side.In a third embodiment, the number of CW each frame has the possibility to be redefined.In a fourth embodiment another position in both decoder and encoder loop is proposed to apply the calculation of video parameters that are used to generate the number of CW.Embodiment 1 : implicit calculation of the LUT at the decoder sideA first principle is to calculate the LUTs for forward and inverse mapping the same way at the encoder and the decoder side when the implicit mode is activated. The usual way to generate the LUTs at the encoder side is to extract video parameters (as described earlier) and to calculate the LUTs based on the calculated number of CW per piece. One method for the calculation is to determine when a luma mapping is applied (LMCS) and code words (CW) to be applied, as depicted in Figure 2 (295). Since the calculation needs to be the same at encoder and decoder side, the calculation must be done exactly at the same place in the decoding loop. Figure 4 depicts the encoder with the new LMCS CW calculation block (495) placed before the in-loop filters. Figure 5 depicts the position of the same new LMCS CW calculation block (595) in the decoder loop. The calculation itself may be the one described in anearlier section. It corresponds to the extraction of video parameters (histogram and variance) and to the definition of the number of CW per piece.Signaling at picture header level In WC, in addition to the signaling of the LMCS parameters in APSs, the APS to be used by each picture is indicated in the PPS using an APS id (ph_lmcs_aps_id). An excerpt of the picture header is given below:In an embodiment, when LMCS is enabled for the picture (ph_lmcs_enabled_flag is true), a flag ph_lmcs_update_flag is inserted in the picture header to indicate whether the LMCS parameters of the APS of id ph_lmcs_aps_id must be recomputed from the decoded picture once the decoding of the picture is done (Figure 4, steps 495, 595). This is illustrated in the syntax table below.The process is as follows:If LMCS is enabled for the picture (ph_lmcs_enabled_flag is true) Decode the picture using the LMCS parameters from APS of id ph_lmcs_aps_idIf ph_lmcs_update_flag is true,Compute the LMCS parameters from the decoded picture Update the APS of id ph_lmcs_aps_idOtherwise Decode the picture without LMCSIn a variant, the APS to update may be different from the APS used for the current picture (ph_lmcs_aps_id), so the id of the other APS to update is signaled (ph_lmcs_new_aps_id). The LMCS parameters derived from the current decoded picture apply to the APS with id ph_lmcs_new_aps_id.The process is as follows:If LMCS is enabled for the picture (ph_lmcs_enabled_flag is true)Decode the picture using the LMCS parameters from APS of id ph_lmcs_aps_idIf ph_lmcs_update_flag is true,Compute the LMCS parameters from the decoded picture Update the APS of id ph_lmcs_new_aps_idOtherwise Decode the picture without LMCSIn another embodiment, when LMCS is disabled for the picture (ph_lmcs_enabled_flag is false), a flag ph_lmcs_compute_flag is inserted in the picture header to indicate whether LMCS parameters of the APS of id ph_lmcs_new_aps_id must be computed from the decoded picture once the decoding of the picture is done (steps 495, 595). If the flag is true, it is required to signal the id of the APS for which the LMCS parameters must be computed (ph_lmcs_new_aps_id). This is illustrated in the syntax table below.The process is as follows:- If LMCS is enabled for the picture (ph_lmcs_enabled_flag is true)Decode the picture using the LMCS parameters from APS of id ph_lmcs_aps_id- OtherwiseDecode the picture without LMCSIf ph_lmcs_compute _flag is true,Compute the LMCS parameters from the decoded picture Update the APS of id ph_lmcs_new_aps_idIn a variant, the possibility to compute LMCS parameters is enabled whatever the value of ph_lmcs_enabled_flag. Once the picture is decoded, it is always possible to compute the LMCS parameters from the decoded picture and to assign them to an APS (with id ph_lmcs_new_aps_id). This is illustrated in the syntax table below.The process is as follows:- If LMCS is enabled for the picture (ph_lmcs_enabled_flag is true)Decode the picture using the LMCS parameters from APS of id ph_lmcs_aps_id- OtherwiseDecode the picture without LMCS- If ph_lmcs_compute_flag is true,Compute the LMCS parameters from the decoded picture Update the APS of id ph_lmcs_new_aps_idVariant: signal a new flag in the APS SyntaxIn another variant, when the lmcs_data is always executed for each frame (whether LMCS is applied to the frame or not), a new flag is added in the LMCS data: lmcs_cw_implicit_at_decoder_flag to control whether the implicit LMCS mode at decoder is used. When LMCS implicit at decoder is true (the flag lmcs_cw_implicit_at_decoder_flag is true), the calculation of the Code Words is performed and parameters are stored in the current APS ID.For example, when a picture refers to an APS with a given APS ID, once the picture is fully decoded, the LMCS parameters are recomputed from the decoded picture, and the LMCS parameters of this APS are updated.The process is as follows:- If LMCS is enabled for the picture (ph_lmcs_enabled_flag is true)Execute lmcs_dataDecode the picture using the LMCS parameters from APS of id ph_lmcs_aps_idIf implicit calculation is enable (lmcs_cw_implicit_at_decoder_flag is true)Recompute LMCS parameters from APS id- OtherwiseExecute lmcs_dataDecode the picture without applying LMCSIf implicit calculation is enable (lmcs_cw_implicit_at_decoder_flag is true)Recompute LMCS parameters from APS idEmbodiment 2: Recompute LMCS parameters from APS idSimplification of the LMCS functionIn order to simplify the calculation of the CW per piece, the following modifications of the LMCS functions are proposed based on a previous section.Step 1 : only the histogram is calculated giving the same 16 values (1 per piece) as previouslyStep 2: remains the sameStep 3: The NbCW is always set to a predefined value (for example 1022)Step 4: the refinement is done using the following pseudo-code: for (int i = 0; i < 16; i++) { if (Histfi] > 0.001) { hist = Histfi] > 0.4 ? 0.4 : Histfi] ; deltal = (uintl6 t) (10.0 * hist + 0.5) ; m binCWfi] = m binCWfi] + deltal;}}The values used in this pseudo-code are examples; they can be signaled in the bitstream as control parameters of the LMCS derivation process.For practical implementation, an integer-implementation may be preferred. Let’s consider that the histogram values Hist[i] are normalized so that Hist[0] + ... + Hist

[0015] = 2AK, K being a predefined integer value corresponding to the precision used to represent H ist[i] . The process may be descried as follows: for (int i = 0; i < 16; i++) { if (Hist [i] > ThO) { hist = Histfi] > Thl ? Thl : Histfi] ; deltal = ( A * hist + 2 (K-1) ) » K; m binCWfi] = m binCWfi] + deltal;}} where ThO, Th1, A are parameters either fixed, or signaled, for example in the SPS, PPS or APS. For instance, by default, K = 10, ThO = 1 , Th1 = 410, A = 10.A correction step is applied to ensure that the sum of number of CW per piece is not above 1023.Step 5: no specific treatment for QP<=22Step 6: the LUTs are generate the same way using the CW generatedIn this embodiment, the new algorithm requires only the calculation of the histogram per piece. This simplification reduces the complexity required at the decoderwhen lmcs_cw_implicit_at_decoder_flag is equal to 1. It applies to bloc 495 and 595 respectively in Figure 4 and Figure 5, respectively.Embodiment 3: LMCS function with variable number of piecesIn a variant, since it is possible to not transmit data relative to LMCS parameters, the number of pieces can be increased without extra cost. The LMCS function described earlier in its simplified version isStep 1 : only the histogram is calculated giving the same N values (1 per piece) where N can be more or less than 16 (e.g.32, 64 or 8 or not a power of 2)Step 2: remains the sameStep 3: The NbCW is always set to a predefined value (for example 1022)Step 4: the refinement is done using the following pseudo-code: for ( int i = 0 ; i < N; i++) { if (Histfi] > 0.001) { hist = Histfi] > 0.4 ? 0.4 : Histfi] ; deltal = (uintl6 t) (10.0 * hist + 0.5) ; m binCWfi] = m binCWfi] + deltal; } }The values used in this pseudo-code are examples, they can be signaled in the bitstream as control parameters of the LMCS derivation process.For practical implementation, an integer-implementation may be preferred. Let’s consider that the histogram values Hist[i] are normalized so that Hist[0] + ... + Hist[N-1 ] = 2AK, K being a predefined integer value corresponding to the precision used to represent Hist[i] . The algorithm may be descried as follows: for (int i = 0; i < N; i++) { if (Hist [i] > ThO) { hist = Histfi] > Thl ? Thl : Histfi] ; deltal = ( A * hist + 2 (K-1) ) » K; m binCWfi] = m binCWfi] + deltal;where ThO, Th1 , A are parameters either fixed, or signaled for example in the SPS, PPS or APS. For instance, by default, K = 10, ThO = 1 , Th1 = 410, A = 10.Embodiment 4: New position in the processing loop to calculate CW for LMCSIn this embodiment, the LMCS CW calculation block is placed after the in-loop filters block. Figure 6 depicts the new position of the LMCS CW calculation block (695) in the encoder. Figure 7 depicts the new position of the LMCS CW calculation block (795) in the decoder.One embodiment of a method 800 under the general aspects described here is shown in Figure 8. The method commences at start block 801 and control proceeds to block 810 for performing a calculation using codewords to determine tables for a mapping function. Control proceeds from block 810 to block 820 for implementing the mapping function on a video block. Control proceeds from block 820 to block 830 for encoding the video block using the mapped portion of the video block.One embodiment of a method 900 under the general aspects described here is shown in Figure 9. The method commences at start block 901 and control proceeds to block 910 for performing a calculation using codewords to determine tables for a mapping function. Control proceeds from block 810 to block 820 for implementing the mapping function on a video block. Control proceeds from block 820 to block 830 for encoding the video block using the mapped portion of the video block.Figure 10 shows one embodiment of an apparatus 1000 for encoding, decoding, compressing or decompressing, or filtering of video data using the aforementioned methods. The apparatus comprises Processor 1010 and can be interconnected to a memory 1020 through at least one port. Both Processor 1010 and memory 1020 can also have one or more additional interconnections to external connections.Processor 1010 is also configured to either insert or receive information in a bitstream and, either compressing, encoding, or decoding using any of the described aspects.The embodiments described here include 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 clarityin 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. Figures 11 , 12, and 13 provide some embodiments, but other embodiments are contemplated and the discussion of Figures 11 , 12, and 13 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 “pixel” and “sample” may be used interchangeably, 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.Various methods and other aspects described in this application can be used to modify modules, for example, the intra prediction, entropy coding, and / or decoding modules (160, 260, 145, 230), of a video encoder 100 and decoder 200 as shown in Figure 11 and Figure 12. Moreover, the present aspects are not limited to WC 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 WC and HEVC). 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.Figure 11 illustrates an encoder 100. Variations of this encoder 100 are contemplated, but the encoder 100 is described below for purposes of clarity without describing all expected variations.Before being encoded, the video sequence may go through pre-encoding processing (101), 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 100, a picture is encoded by the encoder elements as described below. The picture to be encoded is partitioned (102) and processed in units of, for example, CUs. 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 (160). In an inter mode, motion estimation (175) and compensation (170) are performed. The encoder decides (105) 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 (110) the predicted block from the original image block.The prediction residuals are then transformed (125) and quantized (130). The quantized transform coefficients, as well as motion vectors and other syntax elements, are entropy coded (145) 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 (140) and inverse transformed (150) to decode prediction residuals. Combining (155) the decoded prediction residuals and the predicted block, an image block is reconstructed. In-loop filters (165) are applied to the reconstructed picture to perform, for example, deblocking / SAO (Sample Adaptive Offset) filtering to reduce encoding artifacts. Thefiltered image is stored at a reference picture buffer (180).Figure 12 illustrates a block diagram of a video decoder 200. In the decoder 200, a bitstream is decoded by the decoder elements as described below. Video decoder 200 generally performs a decoding pass reciprocal to the encoding pass as described in Figure 11. The encoder 100 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 100. The bitstream is first entropy decoded (230) to obtain transform coefficients, motion vectors, and other coded information. The picture partition information indicates how the picture is partitioned. The decoder may therefore divide (235) the picture according to the decoded picture partitioning information. The transform coefficients are de-quantized (240) and inverse transformed (250) to decode the prediction residuals. Combining (255) the decoded prediction residuals and the predicted block, an image block is reconstructed. The predicted block can be obtained (270) from intra prediction (260) or motion- compensated prediction (i.e. , inter prediction) (275). In-loop filters (265) are applied to the reconstructed image. The filtered image is stored at a reference picture buffer (280).The decoded picture can further go through post-decoding processing (285), 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 (101). The post-decoding processing can use metadata derived in the pre-encoding processing and signaled in the bitstream.Figure 13 illustrates a block diagram of an example of a system in which various aspects and embodiments are implemented. System 1000 can be embodied as a device including the various components described below and is configured to perform one or more of the aspects described in this 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, connected home appliances, and servers. Elements of system 1000, 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 processing and encoder / decoder elements of system 1000 are distributed across multiple ICs and / or discretecomponents. In various embodiments, the system 1000 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. In various embodiments, the system 1000 is configured to implement one or more of the aspects described in this document.The system 1000 includes at least one processor 1010 configured to execute instructions loaded therein for implementing, for example, the various aspects described in this document. Processor 1010 can include embedded memory, input output interface, and various other circuitries as known in the art. The system 1000 includes at least one memory 1020 (e.g., a volatile memory device, and / or a nonvolatile memory device). System 1000 includes a storage device 1040, 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. The storage device 1040 can include an internal storage device, an attached storage device (including detachable and non-detachable storage devices), and / or a network accessible storage device, as non-limiting examples.System 1000 includes an encoder / decoder module 1030 configured, for example, to process data to provide an encoded video or decoded video, and the encoder / decoder module 1030 can include its own processor and memory. The encoder / decoder module 1030 represents module(s) that can be included in a device to perform the encoding and / or decoding functions. As is known, a device can include one or both of the encoding and decoding modules. Additionally, encoder / decoder module 1030 can be implemented as a separate element of system 1000 or can be incorporated within processor 1010 as a combination of hardware and software as known to those skilled in the art.Program code to be loaded onto processor 1010 or encoder / decoder 1030 to perform the various aspects described in this document can be stored in storage device 1040 and subsequently loaded onto memory 1020 for execution by processor 1010. In accordance with various embodiments, one or more of processor 1010, memory 1020, storage device 1040, and encoder / decoder module 1030 can store one or more of various items during the performance of the processes described in thisdocument. Such stored items can 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 1010 and / or the encoder / decoder module 1030 is used to store instructions and to provide working memory for processing that is needed during encoding or decoding. In other embodiments, however, a memory external to the processing device (for example, the processing device can be either the processor 1010 or the encoder / decoder module 1030) is used for one or more of these functions. The external memory can be the memory 1020 and / or the storage device 1040, 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, for example, 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 1000 can be provided through various input devices as indicated in block 1130. 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 Figure 13, include composite video.In various embodiments, the input devices of block 1130 have associated respective input processing elements as known in the art. For example, the RF portion can 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) downconverting 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 downconverted and band-limited signal, (v) performing error correction, and (vi) demultiplexing to select the desired stream of data packets. The RF portion of various embodiments includes one or more elements to perform these functions, for example, frequency selectors, signal selectors, band-limiters, channel selectors, filters, downconverters, demodulators, error correctors, and demultiplexers. The RF portion can include a tuner that performs various of these functions, including, for example, downconverting 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, downconverting, and filtering again to a desired frequency band. Various embodiments rearrange the order of the above-described (and other) elements, remove some of these elements, and / or add other elements performing similar or different functions. Adding elements can include inserting elements in between existing elements, such as, for example, inserting amplifiers and an analog-to-digital converter. In various embodiments, the RF portion includes an antenna.Additionally, the USB and / or HDMI terminals can include respective interface processors for connecting system 1000 to other electronic devices across USB and / or HDMI connections. It is to be understood that various aspects of input processing, for example, Reed-Solomon error correction, can be implemented, for example, within a separate input processing IC or within processor 1010 as necessary. Similarly, aspects of USB or HDMI interface processing can be implemented within separate interface les or within processor 1010 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor 1010, and encoder / decoder 1030 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 1000 can be provided within an integrated housing, Within the integrated housing, the various elements can be interconnected and transmit data therebetween using suitable connection arrangement, for example, an internal bus as known in the art, including the Inter-IC (I2C) bus, wiring, and printed circuit boards.The system 1000 includes communication interface 1050 that enables communication with other devices via communication channel 1060. Thecommunication interface 1050 can include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel 1060. The communication interface 1050 can include, but is not limited to, a modem or network card and the communication channel 1060 can be implemented, for example, within a wired and / or a wireless medium.Data is streamed, or otherwise provided, to the system 1000, 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 WiFi signal of these embodiments is received over the communications channel 1060 and the communications interface 1050 which are adapted for Wi-Fi communications. The communications channel 1060 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. Other embodiments provide streamed data to the system 1000 using a set-top box that delivers the data over the HDMI connection of the input block 1130. Still other embodiments provide streamed data to the system 1000 using the RF connection of the input block 1130. As indicated above, various embodiments provide data in a nonstreaming manner. Additionally, various embodiments use wireless networks other than Wi-Fi, for example a cellular network or a Bluetooth network.The system 1000 can provide an output signal to various output devices, including a display 1100, speakers 1110, and other peripheral devices 1120. The display 1100 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 1100 can be for a television, a tablet, a laptop, a cell phone (mobile phone), or another device. The display 1100 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 1120 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 1120 that provide a function based on the output of the system 1000. For example, a disk player performs the function of playing the output of the system 1000.In various embodiments, control signals are communicated between the system 1000 and the display 1100, speakers 1110, or other peripheral devices 1120using 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 1000 via dedicated connections through respective interfaces 1070, 1080, and 1090. Alternatively, the output devices can be connected to system 1000 using the communications channel 1060 via the communications interface 1050. The display 1100 and speakers 1110 can be integrated in a single unit with the other components of system 1000 in an electronic device such as, for example, a television. In various embodiments, the display interface 1070 includes a display driver, such as, for example, a timing controller (T Con) chip.The display 1100 and speaker 1110 can alternatively be separate from one or more of the other components, for example, if the RF portion of input 1130 is part of a separate set-top box. In various embodiments in which the display 1100 and speakers 1110 are external components, the output signal can 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 1010 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 1020 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 1010 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 nonlimiting examples.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 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.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. 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 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.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.Note that the syntax elements as used herein are descriptive terms. As such, they do not preclude the use of other syntax element names.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.Various embodiments may refer to parametric models or 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. It can be measured through a Rate Distortion Optimization (RDO) metric, or through Least Mean Square (LMS), Mean of Absolute Errors (MAE), or other such measurements. Rate distortion optimization is usually formulated asminimizing 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 ofinformation. 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 least 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 one of a plurality of transforms, coding modes or flags. In this way, in an embodiment the same transform, parameter, or mode is used at boththe 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.The preceding sections describe a number of embodiments, across various claim categories and types. 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:At least one embodiment comprises implementing a mapping operation by performing a calculation on codewords at corresponding points in an encoding and decoder process.At least one embodiment comprises encoding or decoding according to the above embodiments to implement a luma mapping chroma scaling function.At least one embodiment comprises any of the above embodiments with the codeword calculation performed before in-loop filteringAt least one embodiment comprises any of the above embodiments with the codeword calculation performed after in-loop filteringAt least one embodiment further comprises any of the above embodiments wherein the codeword calculation is performed implicitly.At least one embodiment further comprises any of the above embodiments wherein a fixed number of codewords is used for implementing the mapping function.At least one embodiment comprises any of the above embodiments wherein at least one flag is used to indicate whether implicit mode is used to calculate codewords.At least one embodiment comprises any of the above embodiments wherein the above flags are in the adaptation parameter set.At least one embodiment comprises any encoding or decoding operation based on the above operations.At least one embodiment comprises performing encoding or decoding with the aforementioned methods on a sub-block.At least one embodiment comprises a bitstream or signal that includes one or more of the described syntax elements, or variations thereof.At least one embodiment comprises a bitstream or signal that includes syntax conveying information generated according to any of the embodiments described.At least one embodiment comprises creating and / or transmitting and / or receiving and / or decoding according to any of the embodiments described.At least one embodiment comprises a method, process, apparatus, medium storing instructions, medium storing data, or signal according to any of the embodiments described.At least one embodiment comprises inserting in the signaling syntax elements that enable the decoder to determine decoding information in a manner corresponding to that used by an encoder.At least one embodiment comprises creating and / or transmitting and / or receiving and / or decoding a bitstream or signal that includes one or more of the described syntax elements, or variations thereof.At least one embodiment comprises a TV, set-top box, cell phone, tablet, or other electronic device that performs transform method(s) according to any of the embodiments described.At least one embodiment comprises a TV, set-top box, cell phone, tablet, or other electronic device that performs transform method(s) determination according to any of the embodiments described, and that displays (e.g., using a monitor, screen, or other type of display) a resulting image.At least one embodiment comprises a TV, set-top box, cell phone, tablet, or other electronic device that selects, bandlimits, or tunes (e.g., using a tuner) a channel to receive a signal including an encoded image, and performs transform method(s) according to any of the embodiments described.At least one embodiment comprises 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 image, and performs transform method(s).

Claims

CLAIMS1. A method, comprising: performing a calculation using codewords to determine tables for a mapping function; implementing the mapping function on a video block; and, encoding the video block using the mapped video block.

2. An apparatus, comprising: a memory, and a processor, configured to: perform a calculation using codewords to determine tables for a mapping function; implement the mapping function on a video block; and, encode the video block using the mapped video block.

3. A method, comprising: performing a calculation using codewords to determine tables for a mapping function; implementing the mapping function on a video block; and, decoding the video block using the mapped video block.

4. An apparatus, comprising: a memory, and a processor, configured to: perform a calculation using codewords to determine tables for a mapping function; implement the mapping function on a video block; and, decode the video block using the mapped video block.

5. The method of Claim 1 or 3, or the apparatus of Claim 2 or 4, wherein said calculation using codewords is performed before an in-loop filter.

6. The method of Claim 1 or 3, or the apparatus of Claim 2 or 4, wherein said calculation using codewords is performed after an in-loop filter.

7. The method of any one of Claims 1 , 3, 5, or 6, or the apparatus of any one of Claims 2, 4, 5, or 6, wherein an inverse mapping function is applied to the video block prior to storage in a reference picture buffer.

8. The method of any one of Claims 1 , 3, 5 - 7, or the apparatus of any one of Claims 2, 4, or 5-7, wherein an inverse mapping function is applied to the video block from a reference picture buffer.

9. The method of any one of Claims 1 , 3, 5 - 8, or the apparatus of any one of Claims 2, 4, or 5-8, wherein a flag in a picture header is indicative of whether Luma Mapping Chroma Scaling parameters are recomputed.

10. The method of any one of Claims 1 , 3, 5- 9, or the apparatus of any one of Claims 2, 4, or 5-9, wherein a flag is indicative of whether an implicit Luma Mapping Chroma Scaling mode is used.11 . The method of any one of Claims 1 , 3, 5- 10, or the apparatus of any one of Claims 2, 4, or 5-10, wherein codeword information is explicitly signaled in a bitstream and indicates which adaptation parameter set said codeword information is stored.

12. A device comprising: an apparatus according to Claim 2; and at least one of (i) an antenna configured to receive a signal, the signal including the video block, (ii) a band limiter configured to limit the received signal to a band of frequencies that includes the video block, and (iii) a display configured to display an output representative of the video block.

13. A non-transitory computer readable medium containing data content generated according to the method of any one of claims 1 , or 3 through 11 , or by the apparatus of any one of claims 2, or 3 through 11 , for playback using a processor.

14. A signal comprising video data generated according to the method of any one of claims 1 , or 3 through 11 , or by the apparatus of any one of claims 2, or 3 through 11 , for playback using a processor.

15. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of claims 1 , or 3 through 11 .

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