BR112018016440B1 - DECODER, METHOD FOR DECODING BLOCK COEFFICIENTS, ENCODER FOR ENCODING BLOCK COEFFICIENTS, AND NON-TRAINER COMPUTER READABLE STORAGE MEDIA - Google Patents

Abstract

The invention proposes a decoder for decoding block coefficients of a video sequence from a bit stream. The decoder comprises a decoding module configured to decode one or more coefficient vectors of each block from the bit stream. The decoder comprises a scanning module configured to reconstruct, for at least one block, hidden information from one or more coefficients of that block, the hidden information that constitutes or is part of the scan order information associated with that block. The decoder comprises a scan order selector configured to select a scan order for each block from a set of scan orders, preferably from a set of pre-defined and generated scan orders, based on the order information. associated with that block. The decoder comprises a deserializer configured to reverse scan, for each block, one or more coefficient vectors of that block in accordance with the scan order selected for that block, so as to obtain a coefficient matrix.

Description

TECHNICAL FIELD

[001] The present invention relates more generally to the field of video processing and to a method and equipment for scanning order selection, in particular content-adaptive scanning order selection, and specifically relates to a decoder for decoding block coefficients of a video sequence and an encoder for encoding block coefficients of a video sequence.

FUNDAMENTALS

[002] Digital video communication and storage applications are implemented by a wide range of digital devices, such as digital cameras, cellular radiotelephones, portable computers, broadcast systems, and video teleconferencing systems. One of the most important and challenging tasks of these applications is video compression. The task of video compression is complex and is constrained by two contradictory parameters: compression efficiency and computational complexity. Video coding standards, such as ITU-T H.264/AVC or ITU-T H.265/HEVC High Efficiency Video Coding (HEVC) standard, provide a good trade-off between these parameters. For that reason, support for video coding standards is a mandatory requirement for almost all video compression applications.

[003] State of the art video coding standards are based on partitioning a source image into blocks. The processing of these blocks depends on their dimensions, spatial position and a coding mode specified by an encoder. Coding modes can be classified into two groups according to the type of prediction: intra-prediction and inter-prediction modes. Intraprediction modes use pixels from the same image to generate reference samples to calculate prediction values for the pixels in the block being reconstructed. Intraprediction can also be called spatial prediction. Interprediction modes are designed for temporal prediction and use reference samples from previous or next images to predict pixels from blocks in the current image. After a prediction stage, transformation coding is performed for a prediction error that is the difference between an original signal and its prediction. Then, the transformation coefficients and collateral information are encoded using a type entropy encoder, for example, Context Adaptive Binary Arithmetic Coding (CABAC) for AVC/H.264 and HEVC/H.265.

[004] Evidently, prediction errors have different statistics for different prediction modes and strongly depend on the content to be predicted. Therefore, different transformations are cost-effective from the perspective of compression performance for different cases. To increase the coding efficiency of the transformation coding stage, multiple transformations can be used that have different energy compressions for different specific cases.

[005] The ITU-T H.265/HEVC standard known, for example, from ISO/IEC 23008-2:2013, “Information technology - High-efficiency coding and media delivery in heterogeneous environments - Part 2: High Efficiency Video Coding”, November 2013, presents a set of prior art video encoding tools that provide a reasonable trade-off between encoding efficiency and computational complexity. An overview of the ITU-T H.265/HEVC standard is given in the article by Gary J. Sullivan, “High Efficiency Video Coding (HEVC) Standard Overview,” in IEEE Transactions on Circuits and Systems for Video Technology, Vol. 22, No. 12, December 2012, the entire contents of which are incorporated herein by reference.

[006] Similar to the ITU-T H.264/AVC video coding standard, the HEVC/H.265 video coding standard provides for dividing the source image into blocks, for example, coding units (CUs) . Each of the CUs can further be divided into both smaller CUs and prediction units (PUs). A PU can be intrapredicted or interpredicted according to the type of processing applied to the PU pixels. In the case of interprediction, a PU represents an area of pixels that is processed by motion compensation using a motion vector specified for a PU. For intraprediction, the PU specifies the prediction mode for a set of transformation units (TUs). A TU can have different dimensions (for example, 4x4, 8x8, 16x16 and 32x32 pixels) and can be processed in different ways. For a TU transformation encoding is being performed, that is, the prediction error is being transformed with a discrete cosine transform or a discrete sine transform - in the HEVC/H.265 standard, it is applied to intracoded blocks - and quantized. Therefore, reconstructed pixels contain quantization noise and blocking artifacts that can influence prediction accuracy.

[007] In all previous video coding standards except HEVC/H.265, only one transformation was used to keep the design simple. The HEVC/H.265 standard specifies two transformations for intracoding: DST for 4x4 blocks, because this transformation provides better power compression for small intrapredicted blocks, and DCT for other blocks.

[008] Furthermore, a mode-dependent coefficient digitization technique (MDCS) is adopted for the HEVC/H.265 standard. The basic idea behind this is to select a scanning order subject to a selected mode of intraprediction. For intracoded blocks, the digitization order of a 4x4 transform block (TB) and an 8x8 TB luma block is determined by the intraprediction mode, see Joel Sole, Rajan Joshi, Nguyen Nguyen, Tianying Ji, Marta Karczewicz, Gordon Clare, Felix Henry and Alberto Duenas. “Transformation Coefficient Coding in HEVC”, IEEE Transactions on Circuits and Systems for Video Technology, Vol. 22, No. 12, December 2012, pp. 1765-1777. Each of the 35 intraprediction modes uses one of three possible scan orders: diagonal, horizontal, or vertical. A lookup table maps the intraprediction mode to one of the scans.

[009] This tool explores the horizontal or vertical correlation of the residual depending on the intraprediction mode. For example, for a horizontal prediction mode the energy of transformation coefficients is grouped into the first few columns, so that a vertical scan results in fewer bins being entropy coded. Similarly to a vertical prediction, a horizontal scan is beneficial. Experiments have shown that including horizontal and vertical scans for large TBs offers little compression efficiency, so the application of these scans is limited to the two smallest TBs.

[0010] Techniques similar to MDCS are considered in the document Yung-Lyul Lee, Ki-Hun Han, Dong-Gyu Sim and Jeongil Seo. “Adaptive Scanning for H.264/AVC Intracoding”, ETRI Journal, Volume 28, Number 5, October 2006, pp. 668-671, in the document Byeong-Doo Choi, Jin-Hyung Kim and Sung-Jea Ko. “Adaptive Digitization of Coefficients Based on Intraprediction Mode”, ETRI Journal, Volume 29, Number 5, October 2007, pp. 694-696, and in the document Md. Salah Uddin Yusuf and Mohiuddin Ahmad. “A New Scanning Scheme for Spatial Directional Prediction of AVS Intracoding”, International Journal of Advanced Research in Electrical Electronics and Instrumentation Engineering, Vol. 2, Issue 8, August 2013, pp. 41204126. Scan orders differ from those used in the HEVC/H.265 standard. It is also proposed to map intraprediction modes to scan orders.

[0011] Furthermore, the partition mode - as known from Bae Keun Lee, Jae Cheol Kwom and Joo Young Kim. “Method and Equipment for Digitizing Coefficients Based on Prediction Unit Partition Mode”, United States Patent Application Publication, US 2014/0314143 A1, PCT/KR2012/009373, November 8, 2012 -, and quantization parameters (QP) - as known from Thai-Ha Nguyen, Yoichi Yagasaki and Ali Tabatabai. “Digitization and Applications of Adaptive Digitization of QP Coefficients”, United States Patent Application Publication, US 2011/0249726 A1, April 1, 2011 - can be used as resources for selecting a digitization order not only for intracoding, but also for intercoding.

[0012] Therefore, there is a wide variety of scanning orders, which can be efficient for the same TU modes and dimensions. This is the main reason why a procedure based on RDO (Rate-Distortion Optimization) or similar - for example, based on distortion or activity analysis - can be used to make a final decision about which of the potential scan orders should be selected. .

[0013] An example of how it is possible to select a scanning order in an RDO-based procedure is known, for example, from Muhammed Zeyd Coban and Marta Karczewicz. “Adaptive Digitization of Transformation Coefficients for Video Coding”, United States Patent Application Publication, US 2012/0099646 A1, October 17, 2011. In this case, the digitization order that provides the lowest RD cost is selected. Therefore, the main advantage of this technique is that a selected scan order provides the highest coding gain. Therefore, the coding efficiency of this technique is higher than that for other methods if signaling overhead is not taken into account.

[0014] This prior art proposes two algorithms for selecting the scanning order that provides the greatest coding gain. The main distinguishing feature between these two algorithms is that different mechanisms are used to detect such TBs where this adaptive scan order selection technique is inapplicable, i.e., a standard scan order is used. In a first algorithm, the number of significant transformation coefficients is compared with a threshold number. In a second algorithm, the position of the last significant transformation coefficients is compared with a threshold position. In contrast to previously described techniques, a selected digitization order must be assigned for both of these cases, so that a decoder can apply a correct digitization order to the received transformation coefficients. Therefore, the main disadvantage of techniques that use an RDO-based decision-making procedure is signaling overhead.

[0015] Another way to improve compression efficiency when compared to MDCS is to adapt a scan order according to statistics collected for blocks that have similar values of parameters such as intraprediction mode, partition mode, block size, etc. instead of using previously defined scanning orders. Consequently, initial scan orders are defined to use in cases where one statistic is not sufficient. When the amount of blocks used to collect statistics exceeds a threshold, the scanning order can be adapted based on the collected statistics, see Yan Ye and Marta Karczewicz. “Adaptive Coefficient Digitization for Video Coding”, United States Patent, US 8,488,668 B2, June 4, 2008. A similar technique is known from Sridhar Srinivasan. “Coefficient adaptive digitization order”, European Patent Specification, EP 1679903 B1, 30 November 2005.

[0016] However, such an adaptive scan order based on statistics collected from previously encoded or decoded blocks does not always provide a coding efficiency that is greater than predefined scan orders such as zigzag, diagonal, vertical, horizontal, clockwise and helical scans. counterclockwise, etc.

SUMMARY

[0017] Having recognized the above-mentioned problems and disadvantages, the present invention aims to improve the state of the art. In particular, the object of the present invention is to provide a video decoder, a decoding method, a video encoder and a coding method for improved coding efficiency.

[0018] The present invention aims in particular to improve coding efficiency by means of an improved scanning order to digitize a matrix of coefficients into one or more vectors of coefficients or to inversely digitize one or more vectors of coefficients into a matrix of coefficients .

[0019] Furthermore, the present invention aims to improve coding efficiency by reducing signaling overhead.

[0020] The aforementioned objective of the present invention is achieved by the solution provided in the attached independent claims. Advantageous implementations of the present invention are further defined in the respective dependent claims.

[0021] A first aspect of the present invention provides a decoder for decoding block coefficients of a video sequence from a bit stream. The decoder comprises a scan configuration list module configured to provide one or more predefined scan orders. A scanning order is also known in the art as a scanning pattern. The decoder comprises a scan order generator configured to generate one or more scan orders. The decoder comprises a scan order selector configured to select a scan order for each block from predefined scan orders generated based on scan order information contained in the bit stream. The decoder comprises a decoding module configured to decode one or more coefficient vectors of each block from the bit stream. The decoder comprises a deserializer configured to inversely scan, for each block, the one or more coefficient vectors of that block in accordance with the scan order selected for that block so as to obtain a matrix of coefficients. The scan order generator is configured to generate one or more scan orders that depend on the one or more coefficient matrices previously obtained from blocks of the video sequence.

[0022] Therefore, the present invention is advantageous in that it provides both predefined scanning orders and generated scanning orders adaptable to content. By extending the set of available digitization orders, the rate-distortion efficiency of quantization can be consequently improved.

[0023] In one form of implementation of the decoder according to the first aspect of the invention, the scan pattern list module is configured to provide one or more predefined scan orders for each of a plurality of coding parameter sets. The scan order generator is configured to generate a scan order for each of the sets of coding parameters that depend on the one or more previously obtained coefficient matrices associated with that set of coding parameters. The scan order selector is configured to select a scan order for each block by determining a set of coding parameters for that block, and select the scan order for the coefficient matrix obtained for that block from the scan orders predefined and generated for the given set of encoding parameters.

[0024] In this way, both predefined scan orders and content-adaptive generated scan orders can be provided for each set of encoding parameters. Therefore, different scan orders can be generated for different sets of coding parameters, so that the set of available scan orders can be increased and adapted for each set of coding parameters. Therefore, the selected scanning order can further improve the rate-distortion efficiency.

[0025] In particular, each set of coding parameters may correspond, for example, to a combination of one or more prediction modes, a partition mode, one or more transformation parameters, and one or more quantization parameters. .

[0026] In one form of implementation of the decoder according to the first aspect of the invention, the decoder comprises a coefficient distribution estimator configured to provide, for each of the sets of coding parameters, a distribution statistic of one or more previously obtained coefficient matrices associated with that set of coding parameters. The scan order generator is configured to generate the scan order for each of the sets of coding parameters that depend on the distribution statistics for that set of coding parameters.

[0027] In this way, the generated scan orders can reflect a distribution statistic of previous coefficient matrices. The generated scan orders can therefore provide good coding efficiency for subsequent coefficient matrices if the distribution statistics of the subsequent matrices are similar to those of the previous coefficient matrices.

[0028] In one form of decoder implementation according to the first aspect of the invention, if the selected scanning order for a given block is predefined, the coefficient distribution estimator is configured not to update or is configured to reset the statistics distribution for the set of coding parameters of the given block.

[0029] Thus, if the scan order selected for a given block is a predefined scan order, this means that, for the given block's set of coding parameters, the generated scan order can provide a coding efficiency that is worse than that of the predefined scan orders. Therefore, the given block presents a distribution statistic that does not correspond to that of the previous coefficient matrices, so the given block's distribution statistic is preferably not used to update the distribution statistic provided by the coefficient distribution estimator. Alternatively, it may be preferable to restart the distribution statistic provided by the coefficient distribution estimator, since the statistic of previous coefficient matrices may no longer match the statistic of the current coefficient matrices.

[0030] In one form of implementation of the decoder according to the first aspect of the invention, the decoding module is configured to analyze, for each block, coding parameter information from the bit stream. The scan order selector is configured to determine the set of encoding parameters of a given block according to the parsed encoding parameter information for that given block.

[0031] In this way, the decoder can obtain information regarding the set of coding parameters and use the predefined and generated scanning orders that correspond to this set of coding parameters, so as to improve the coding efficiency.

[0032] In one form of implementation of the decoder according to the first aspect of the invention, the decoding module is configured to analyze scan order information that identifies the scan order selected from the bit stream.

[0033] In this way, the decoder is able to identify the selected digitization order from the bit stream and, depending on whether this selected digitization order is predefined or generated, the decoder can correctly inversely digitize the coefficient vectors and can, for example, whether or not to correctly update the distribution statistic provided by the coefficient distribution estimator.

[0034] The functions of the decoder according to the first aspect of the invention and any functions of any of its implementation forms can be performed by a processor or a computer, and any of its means can be implemented as software and/or hardware on such processor or computer.

[0035] A second aspect of the present invention provides a method for decoding block coefficients of a video sequence from a bit stream. The method comprises providing one or more predefined scanning orders. The method comprises generating one or more scanning orders. The method comprises selecting a scan order for each block from predefined scan orders generated based on scan order information contained in the bit stream. The method comprises decoding one or more coefficient vectors of each block from the bit stream. The method comprises inversely digitizing, for each block, the one or more coefficient vectors of that block in accordance with the digitization order selected for that block in order to obtain a matrix of coefficients. Generating one or more digitization orders comprises generating one or more digitization orders that depend on one or more coefficient matrices previously obtained from blocks of the video sequence.

[0036] Additional features or implementations of the method according to the second aspect of the invention can perform the functionality of the decoder according to the first aspect of the invention and its different forms of implementation.

[0037] The method according to the second aspect of the invention or any of its implementation forms can be executed by a processor or a computer.

[0038] A third aspect of the present invention provides an encoder for encoding block coefficients of a video sequence into a bit stream, the coefficients of each block being contained in a respective coefficient matrix. The encoder comprises a scan pattern list module configured to provide one or more predefined scan orders. The encoder comprises a scan order generator configured to generate one or more scan orders. The encoder comprises a scan order selector configured to select a scan order for each block from the predefined and generated scan orders. The encoder comprises a serializer configured to digitize, for each block, the coefficient matrix of that block in accordance with the digitization order selected for that block so as to obtain one or more coefficient vectors. The encoder comprises an encoding module configured to encode the coefficient vectors into a bit stream. The digitization order generator is configured to generate one or more digitization orders that depend on the one or more previously digitized coefficient matrices of blocks of the video sequence.

[0039] Therefore, the present invention is advantageous in that it provides both predefined scanning orders and generated scanning orders adaptable to content. By extending the set of available digitization orders, the rate-distortion efficiency of quantization can be consequently improved.

[0040] In one form of encoder implementation according to the third aspect of the invention, the scanning pattern list module is configured to provide one or more predefined scanning orders for each of a plurality of coding parameter sets. The scan order generator is configured to generate a scan order for each of the coding parameter sets that depend on the one or more previously digitized coefficient matrices associated with that coding parameter set. The scan order selector is configured to select a scan order for each block by determining a set of coding parameters for that block, and select the scan order for that block's coefficient matrix from the predefined scan orders and generated for the given set of encoding parameters.

[0041] In this way, both predefined scan orders and content-adaptive generated scan orders can be provided for each set of encoding parameters. Therefore, different scan orders can be generated for different sets of coding parameters, so that the set of available scan orders can be increased and adapted for each set of coding parameters. Therefore, the selected scanning order can further improve the rate-distortion efficiency.

[0042] In particular, each set of coding parameters may correspond to a combination of one or more prediction mode, a partition mode, one or more transformation parameters, and one or more quantization parameters.

[0043] In one form of implementing the encoder in accordance with the third aspect of the invention, the encoder comprises a coefficient distribution estimator configured to provide, for each of the sets of encoding parameters, a distribution statistic of one or more matrices of previously digitized coefficients associated with that set of coding parameters. The scan order generator is configured to generate the scan order for each of the coding parameter sets that depends on the distribution statistics for that coding parameter set.

[0044] In this way, the generated scan orders can reflect a distribution statistic of previous coefficient matrices, so that these generated scan orders can provide good coding efficiency for subsequent coefficient matrices in case the distribution statistic of the subsequent matrices be similar to that of the previous coefficient matrices.

[0045] In one form of encoder implementation according to the third aspect of the invention, if the selected scanning order for a given coefficient matrix is predefined, the coefficient distribution estimator is configured not to update or is configured to reset the distribution statistics for the set of encoding parameters of the given block.

[0046] Thus, if the scan order selected for a given block is a predefined scan order, this means that, for the given block's set of coding parameters, the generated scan order can provide a coding efficiency that is worse than that of the predefined scan orders. Therefore, the given block presents a distribution statistic that does not correspond to that of the previous coefficient matrices, so the given block's distribution statistic is preferably not used to update the distribution statistic provided by the coefficient distribution estimator. Alternatively, it may be preferable to restart the distribution statistic provided by the coefficient distribution estimator, since the statistic of previous coefficient matrices may no longer match the statistic of the current coefficient matrices.

[0047] In one form of implementing the encoder in accordance with the third aspect of the invention, the encoder comprises a signaling module configured to add scan order information that identifies the scan order selected from the bit stream.

[0048] Therefore, it is advantageous that the decoder is able to identify the selected digitization order from the bit stream and, depending on whether this selected digitization order is predefined or generated, the decoder can correctly inversely digitize the coefficient vectors. and may, for example, correctly update or not the distribution statistic provided by the coefficient distribution estimator.

[0049] In one form of encoder implementation according to the third aspect of the invention, the scan order selector is configured to select the scan order from predefined scan orders generated based on a cost function.

[0050] In this way, a procedure based on the cost function can be used to accurately select a scanning order between the generated scanning orders and the predefined scanning orders. Consequently, even if scan orders generated based on statistics collected from previously encoded or decoded blocks do not provide better coding efficiency than predefined scan orders, the selection of scan orders can improve coding efficiency. In particular, the cost function may, for example, be a Rate-Distortion Optimization (RDO) function.

[0051] The functions of the encoder according to the third aspect of the invention and any functions of any of its implementation forms can be performed by a processor or a computer, and any of its means can be implemented as software and/or hardware on such processor or computer.

[0052] A fourth aspect of the present invention provides a method for encoding block coefficients of a video sequence into a bit stream, the coefficients of each block being contained in a respective coefficient matrix. The method comprises providing one or more predefined scanning orders. The method comprises generating one or more scanning orders. The method comprises selecting a scan order for each block from the predefined and generated scan orders. The method comprises digitizing, for each block, the coefficients of that block according to the digitization order selected for that block in order to obtain one or more vectors of coefficients. The method comprises encoding the coefficient vectors in the bit stream. Generating one or more digitization orders comprises generating one or more digitization orders that depend on the one or more previously digitized coefficient matrices of blocks of the video sequence.

[0053] Additional features or implementations of the method according to the fourth aspect of the invention can perform the functionality of the encoder according to the third aspect of the invention and its different forms of implementation.

[0054] The method according to the fourth aspect of the invention or any of its implementation forms can be executed by a processor or a computer.

[0055] A fifth aspect of the present invention provides a decoder, preferably in accordance with the first aspect, for decoding block coefficients of a video sequence from a bit stream. The decoder comprises a decoding module configured to decode one or more coefficient vectors of each block from the bit stream. The decoder comprises a scanning module configured to reconstruct, for at least one block, hidden information from one or more coefficients of that block, the hidden information constituting or forming part of scan order information associated with that block. The decoder comprises a scan order selector configured to select a scan order for each block from a set of scan orders, preferably from a set of predefined and generated scan orders based on scan order information. associated with that block. The decoder comprises a deserializer configured to inversely scan, for each block, the one or more coefficient vectors of that block in accordance with the scan order selected for that block so as to obtain a matrix of coefficients.

[0056] In this way, coding efficiency is advantageously improved by the fact that signaling overhead is reduced.

[0057] In one form of implementation of the decoder according to the fifth aspect of the invention, the verification module is configured to reconstruct, for at least one block, the hidden information from at least one coefficient hiding vector chosen from between the one or more vectors of coefficients obtained for that block. In particular, the one or more coefficient vectors may correspond to a respective coefficient group (CG), the coefficient hiding vector then corresponding to the coefficient group on which data hiding is performed. In this way, the reconstruction of hidden information from several vectors of hidden coefficients, for example preferably from several groups of coefficients, is advantageous in that more bits can be hidden and a higher index for the digitization order information can be be rebuilt.

[0058] In one form of implementation of the decoder according to the fifth aspect of the invention, the verification module is configured to reconstruct, for at least one block, the hidden information from the coefficient hiding vector that depends on a condition hiding, the hiding condition comprising a comparison of a parameter that depends on the coefficient hiding vector with a threshold. This makes concealment easier.

[0059] In one form of implementation of the decoder according to the fifth aspect of the invention, the parameter is: - a number of significant coefficients within the coefficient hiding vector, or - a distance between first and last significant coefficients within the vector of coefficient hiding, or - a ratio of an absolute maximum value to a non-zero absolute minimum value of the coefficients within the coefficient hiding vector. The hiding condition is true if the parameter is above the threshold, and false if the parameter is below the threshold. In this way, the concealment condition is advantageously provided.

[0060] In one form of decoder implementation according to the fifth aspect of the invention, the verification module is configured to check the hiding condition, and to reconstruct the hidden information from the coefficient hiding vector if the hiding condition concealment is true. In this way, the scanning order can be selected without additional side information coming from the bit stream.

[0061] In one form of implementation of the decoder according to the fifth aspect of the invention, if the concealment condition is false, the scan order selector is configured to select a predefined default scan order. In this way, a scanning order can be selected even if hiding is not possible on the encoder side.

[0062] In one form of implementation of the decoder according to the fifth aspect of the invention, the verification module is configured to reconstruct the hidden information from the coefficient hiding vector by applying a verification function to the coefficient hiding vector , a result of the verification function being the information hidden. In this way, the scanning order can be advantageously obtained from the coefficients.

[0063] In one form of implementation of the decoder according to the fifth aspect of the invention, the result of the verification function depends on the coordinates (x, y), within the coefficient matrix, of the last significant coefficient of the coefficient hiding vector. The verification function can, for example, be the following function: mod(x + y + R,2) x and y being the coordinates and R being an integer value. In this way, the result of the verification function can be obtained directly from the coefficient coordinates.

[0064] In one form of implementation of the decoder according to the fifth aspect of the invention, the verification module is configured to reconstruct, for a first block, hidden information from one or more coefficients of the first block, the hidden information constituting or forming part of scan order information associated with the first block, and the scan order selector is configured to select, for the first and at least one second block, a scan order based on the scan order information associated with the first block. Thus, this form of implementation provides a “blend mode” decoding, in which the selected scan order value for the second block is reconstructed/predicted using the coefficient values of the first block without hiding anything within the coefficients of the first block. second block. For example, the first and second blocks are spatially adjacent.

[0065] In particular, the scan order selector may be configured to select, for a group of blocks, a scan order based on scan order information associated with the first block, where the group of blocks may comprise the first block and a plurality of second blocks. The block group may include multiple blocks within a block group that have at least one non-standard scanning index hidden within their coefficients. Alternatively, the group of blocks may include several sequentially coded blocks such that said coded blocks have the same scanning index. Alternatively, the group of blocks may include several blocks and/or several blocks sequentially encoded with coefficients for which the concealment condition is false.

[0066] In particular, in blending mode, several options are available for the decoder to know that no scanning order information is hidden in the coefficients of at least one second block. First, side information can be encoded into the bitstream, for example, a flag for a group of blocks that enables or disables the use of merge mode for those. Secondly, without collateral information, it is proposed to apply the merge rule to the second block depending on the hiding condition and set of encoding parameters of the first block and/or the second block. In other words, a merge is applied to the second block if the hiding condition is not satisfied for the second block, that is, the scan order for the second block is selected based on the scan order information associated with the first block. Thirdly, a combination of the two alternatives is proposed, said combination comprising collateral information in the bit stream and applying a merge dependent on the hiding condition.

[0067] The functions of the decoder according to the fifth aspect of the invention and any functions of any of its implementation forms can be performed by a processor or a computer, and any of its means can be implemented as software and/or hardware on such processor or computer.

[0068] A sixth aspect of the present invention provides a method, preferably in accordance with the second aspect, for decoding block coefficients of a video sequence from a bit stream. The method comprises decoding one or more coefficient vectors of each block from the bit stream. The method comprises reconstructing, for at least one block, hidden information from one or more coefficients of that block, the hidden information constituting or forming part of scanning order information associated with that block. The method comprises selecting a scan order for each block from a set of scan orders, preferably from a set of predefined and generated scan orders, based on scan order information associated with that block. The method comprises inversely digitizing, for each block, the one or more coefficient vectors of that block according to the digitization order selected for that block, thereby obtaining a matrix of coefficients.

[0069] Additional features or implementations of the method according to the sixth aspect of the invention can perform the functionality of the decoder according to the fifth aspect of the invention and its different forms of implementation.

[0070] The method according to the sixth aspect of the invention or any of its implementation forms can be executed by a processor or a computer.

[0071] A seventh aspect of the present invention provides an encoder, preferably according to the third aspect, for encoding block coefficients of a video sequence into a bit stream, the coefficients of each block being contained in a respective coefficient matrix . The encoder comprises a scan order selector configured to select a scan order for each block from a set of scan orders, preferably from a set of predefined and generated scan orders. The encoder comprises a serializer configured to digitize, for each block, the coefficient matrix of that block in accordance with the digitization order selected for that block so as to obtain one or more coefficient vectors. The encoder comprises a hiding module configured to hide, for at least one block, scan order information that identifies the selected scan order for that block at least partially in one or more coefficients of that block (i.e., configured to hide those scanning order information or part thereof in those one or more coefficients). The encoder comprises a coding module configured to encode the coefficient vectors in the bit stream. In this way, coding efficiency can be improved by reducing signaling overhead.

[0072] In one form of encoder implementation according to the seventh aspect of the invention, the hiding module is configured to hide, for at least one block, the scanning order information in at least one chosen coefficient hiding vector. between the one or more vectors of coefficients obtained for that block.

[0073] In one form of encoder implementation according to the seventh aspect of the invention, the hiding module is configured to hide, for at least one block, the scanning order information in the coefficient hiding vector that depends on a hiding condition, the hiding condition comprising a comparison of a parameter that depends on the coefficient hiding vector with a threshold.

[0074] In one form of encoder implementation according to the seventh aspect of the invention, the parameter is: - a number of significant coefficients within the coefficient hiding vector, or - a distance between first and last significant coefficients within the vector of coefficient hiding, or - a ratio of an absolute maximum value to a non-zero absolute minimum value of the coefficients within the coefficient hiding vector, where the hiding condition is true if the parameter is above the threshold, and false if the parameter is below the limit.

[0075] In one form of encoder implementation according to the seventh aspect of the invention, the hiding module is configured to check the hiding condition, and to hide the scan order information in the coefficient hiding vector if the condition concealment is true.

[0076] In one form of encoder implementation according to the seventh aspect of the invention, if the hiding condition is false, the scan order selector is configured to recursively select another scan order from the set of scan orders until the hiding condition for that other selected scan order is true. Therefore, the selection of other scanning orders is advantageous in that it is possible to perform data hiding even if the first selected scanning order would imply a false hiding condition.

[0077] In one form of encoder implementation according to the seventh aspect of the invention, if the hiding condition is false and the selected scanning order is a predefined standard scanning order, the hiding module is configured to not hide the Scan order information in the coefficient hiding vector.

[0078] In one form of encoder implementation according to the seventh aspect of the invention, the hiding module is configured to hide, for at least one block, the scanning order information in the coefficient hiding vector by means of: - apply a check function to the coefficient hiding vector in order to obtain a result of the check function, - determine whether the result of the check function matches the scan order information, - if not, modify the coefficient hiding vector so that the result of the verification function matches the scan order information.

[0079] In one form of encoder implementation according to the seventh aspect of the invention, the result of the verification function depends on the coordinates (x, y), within the coefficient matrix, of the last significant coefficient of the coefficient hiding vector. The verification function can, for example, be the following function: mod(x + y + R,2) x and y being the coordinates and R being an integer value.

[0080] In one form of encoder implementation according to the seventh aspect of the invention, if an identical scan order is selected by the scan order selector for a first and at least a second block, the hiding module is configured to hide scan order information that identifies the identical scan order in one or more coefficients of the first block only. In this way, coding according to a “blending mode” is possible. In such a mode, preferably scan order information identifying the identical scan order is not hidden in coefficients of the second block. In other words, the scan order value selected for the second block is reconstructed/predicted on the decoder side using the scan order information hidden in coefficients of the first block. The first and second blocks are, for example, spatially adjacent or, for example, successive blocks in the bit stream. Therefore, the second block's scan order information can be transmitted to the decoder without hiding anything within the second block's coefficients.

[0081] In particular, a group of blocks comprising the first block and one or more second blocks may be a group of blocks that have at least one non-standard scanning index hidden within their coefficients. Alternatively, the group of blocks may include several sequentially coded blocks such that said coded blocks have the same scanning index. Alternatively, the group of blocks may include several blocks and/or several blocks sequentially encoded with coefficients for which the concealment condition is false.

[0082] In particular, in the blending mode, several options are available for the decoder to know that no scanning order information is hidden in the coefficients of at least one second block. First, the encoder adds side information to the bitstream, for example, a flag that enables or disables the use of blending mode for one or more blocks, for example, for the one or more second blocks. Secondly, without collateral information, it is proposed to apply the merge rule to the second block depending on the hiding condition and set of encoding parameters of the first block and/or the second block. In other words, a merge is applied to the second block if the hiding condition is not satisfied for the second block, that is, the scan order for the second block is selected based on the scan order information associated with the first block. Thirdly, a combination of the two alternatives is proposed, said combination comprising collateral information in the bit stream and applying a merge dependent on the hiding condition.

[0083] The functions of the encoder according to the seventh aspect of the invention and any functions of any of its implementation forms can be performed by a processor or a computer, and any of its means can be implemented as software and/or hardware on such processor or computer.

[0084] An eighth aspect of the present invention provides a method, preferably in accordance with the fourth aspect of the invention, for encoding block coefficients of a video sequence into a bit stream, the coefficients of each block being contained in a respective matrix of coefficients. The method comprises selecting a scan order for each block from a set of scan orders, preferably from a set of predefined and generated scan orders. The method comprises digitizing, for each block, the coefficient matrix of that block in accordance with the digitization order selected for that block in order to obtain one or more coefficient vectors. The method comprises hiding, for at least one block, scanning order information that identifies the selected scanning order for that block at least partially in one or more coefficients of that block. The method comprises encoding the coefficient vectors in the bit stream.

[0085] Additional features or implementations of the method according to the eighth aspect of the invention can perform the functionality of the encoder according to the seventh aspect of the invention and its different forms of implementation.

[0086] The method according to the eighth aspect of the invention or any of its implementation forms can be executed by a processor or a computer.

[0087] A ninth aspect of the present invention provides a computer program comprising program code for performing the method according to the second, fourth, sixth or eighth aspect of the invention, when the computer program is executed on a device. computing.

[0088] It should be noted that all devices, elements, units and means described in the present patent application can be implemented in software or hardware elements or any type of combination thereof. All steps that are performed by the various entities described in the present patent application, as well as the functionalities described to be performed by the various entities, are intended to mean that the respective entity is adapted or configured to execute the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific modality or step is to be wholly formed by eternal entities not reflected in the detailed description of a specific element of that entity performing that specific step or functionality, it should be clear to a person skilled in the art of technique that these methods and functionalities can be implemented in respective software or hardware elements, or any type of combination thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] The above aspects and forms of implementation of the present invention will be explained in the following description of specific embodiments in relation to the attached drawings, in which:

[0090] Fig. 1 shows a video encoder according to an embodiment of the present invention;

[0091] Fig. 2 shows a video decoder according to an embodiment of the present invention;

[0092] Fig. 3 shows a flowchart for estimating coefficient distribution in the video decoder according to an embodiment of the present invention;

[0093] Fig. 4 shows a flowchart for estimating coefficient distribution in the video encoder according to an embodiment of the present invention;

[0094] Fig. 5 shows a flowchart of an initialization of a list of scanning orders in accordance with an embodiment of the present invention;

[0095] Fig. 6 shows a flowchart of implicit and explicit signaling of selected scanning orders in accordance with an embodiment of the present invention;

[0096] Figs. 7 and 8 show a concealment condition in accordance with an embodiment of the present invention;

[0097] Fig. 9 shows a decoding of coefficient entropy according to the state of the art;

[0098] Fig. 10 shows an embodiment of the present invention for improving coding efficiency by reducing signaling overhead in the bit stream;

[0099] Fig. 11 shows a coefficient reorderer according to the present invention; It is

[00100] Fig. 12 shows an example of occultation conditions defined for scanning orders.

DETAILED DESCRIPTION OF MODALITIES

[00101] Fig. 1 shows a video encoder in accordance with an embodiment of the present invention, and shows in particular an encoder 100 for encoding block coefficients of a video sequence in a data stream 107, the coefficients of each block being contained in a respective matrix of coefficients.

[00102] The encoder comprises a scan pattern list module 110 configured to provide one or more predefined scan orders.

[00103] The encoder comprises a scan order generator 111 configured to generate one or more scan orders.

[00104] The encoder comprises a scan order selector 109 configured to select a scan order for each block from the predefined and generated scan orders.

[00105] The encoder comprises a serializer 104 configured to digitize, for each block, the coefficient matrix of that block in accordance with the digitization order selected for that block so as to obtain one or more coefficient vectors.

[00106] The encoder comprises a coding module 106 configured to encode the coefficient vectors into a bit stream 107.

[00107] Scan order generator 111 is configured to generate one or more scan orders that depend on one or more previously scanned coefficient matrices of blocks of the video sequence.

[00108] Fig. 2 shows a video decoder in accordance with an embodiment of the present invention, and shows in particular a decoder 200 for decoding block coefficients of a video sequence from a data stream 207.

[00109] The decoder comprises a scan pattern list module 210 configured to provide one or more predefined scan orders.

[00110] The decoder comprises a scan order generator 211 configured to generate one or more scan orders.

[00111] The decoder comprises a scan order selector 209 configured to select a scan order for each block from predefined scan orders generated based on SCAN_IDX scan order information contained in the bit stream.

[00112] The decoder comprises a decoding module 206 configured to decode one or more coefficient vectors of each block from the bit stream 207.

[00113] The decoder comprises a deserializer 204 configured to inversely digitize, for each block, the one or more coefficient vectors of that block in accordance with the digitization order selected for that block in order to obtain a matrix of coefficients.

[00114] Scan order generator 211 is configured to generate one or more scan orders that depend on one or more coefficient matrices previously obtained from blocks of the video sequence.

[00115] In particular, Fig. 1 shows an example of an encoder-side coding residual part with content-adaptive scanning order sections. In the example, encoder 100 is configured to apply interprediction or intraprediction to each block of each image in the video sequence. An intraprediction mode uses pixels from the same image to generate reference samples to calculate prediction values for the pixels in the block being reconstructed. An interprediction mode is designed for temporal prediction and uses reference samples from previous or next images to predict pixels of the current image block. The result of the prediction stage may be a residual signal 101 which is the difference between an original signal of a block and its prediction signal obtained through interprediction or intraprediction.

[00116] A prediction mode for obtaining the residual signal 101 may correspondingly refer to both intraprediction and interprediction mode. Further, the prediction mode may correspond to any of a plurality of available prediction modes or directions. For example, the plurality of available prediction modes may comprise up to 35 intra-prediction modes, which may include 33 directional modes and 2 non-directional modes, such as a direct current (DC) prediction mode and a DC prediction mode. to soar. The 33 directional modes can cover an angular range of p radians or 180 degrees. If the direction of a vertical mode is considered to be zero degrees, the 33 directional modes can be symmetric about the geometric axis at -45 degrees. Regarding the prediction mode, the encoder can be configured to determine, for a given block, one of the plurality of available prediction modes based on a Rate-Distortion Optimization (RDO).

[00117] A Coding Tree Unit (CTU) is the root of a video sequence coding structure of a predefined dimension, which contains a portion of an image (e.g., 64x64 pixels). A CTU can be partitioned into Coding Units (CUs). A CU is a basic video sequence encoding structure of a predefined dimension, which contains a part of an image that belongs to a CTU. A CU can be partitioned into other CUs. A Prediction Unit (PU) is a coding structure that is the result of partitioning a CU. A PU can be partitioned into several Transformation Units (TUs) or coincide with a single TU. A TU can be intrapredicted or interpredicted according to the type of processing applied to the PU pixels. In the case of interprediction, a PU represents an area of pixels that is processed by motion compensation using a motion vector specified for a PU.

[00118] In this regard, a partition mode may depend on the PU, and in particular on the size and/or orientation of the PU. The partition mode may correspond to any of a plurality of available partition modes. The encoder may be configured to determine, for a block or PU, one of the plurality of available partition modes based on an RDO method. For example, the partition mode can correspond to a horizontally oriented shape, in which a CU can be partitioned into 2NxN PUs or blocks. Also, the partition mode can correspond to a vertically oriented shape, in which a CU can be partitioned into Nx2N PUs or blocks, or a square shape in which a CU can be partitioned into 2Nx2N PUs or blocks.

[00119] The residual signal 101 can be provided to a transformation module 102 to transform encode the residual signal 101 to obtain transformation coefficients. In particular, for intraprediction a PU can specify a prediction mode for a set of TUs. A TU can have different dimensions - for example, 4x4, 8x8, 16x16 and 32x32 pixels - and can be processed in different ways. Examples of transforms that can be applied to a residual signal include, for example, Discrete Cosine Transform (DCT) and Discrete Sine Transform (DST).

[00120] In this regard, a transformation parameter can have the size or shape of the TU, or both size and shape. An additional transformation parameter can be the transform being applied, for example, DCT or DST among others.

[00121] The residual signal 101 calculated for a block of the source image is transformed by the transformation module 102 and then quantized by a quantization module 103. The quantization module 103 processes the transformation coefficients in order to obtain quantized transformation coefficients (QTCs) in the form of a coefficient matrix.

[00122] In this regard, a quantization parameter may correspond to the number of significant coefficients of the coefficient matrix, that is, the number of coefficients of the coefficient matrix that have a non-zero value.

[00123] The coefficient matrix is serialized via the serializer 104 by scanning in an order determined by the scan order selector 109. The scan order can be selected either from the predefined scan orders provided by the scan default list 110 as from the generated scan orders provided by the scan order generator 111. The scan orders provided by the standard scan list 110 are predefined on the side of both the encoder 100 and the decoder 200 and therefore a scan order selected from from the scan pattern list 110 is static, that is, it is not modified during the entire encoding or decoding process. The scan orders provided by the scan order generator 111 are dynamic, that is, they are generated depending on one or more coefficient matrices previously obtained from blocks of the video sequence. In particular, the generated scanning orders can be generated according to the distribution statistics of coefficient matrices during the encoding or decoding process.

[00124] The one or more vectors of coefficients obtained by the serializer 104 from a matrix of coefficients are stored in a quantized coefficient buffer 105. The encoding module 106 may be in the form of an entropy encoding module for encoding by entropy of the coefficient vectors in the bit stream 107. The scan order that is selected by the scan order selector 109 can be identified through scan index information or SCAN_IDX scan orders.

[00125] This scan index information can be explicitly added to bitstream 107, that is, the value of SCAN_IDX scan order information can be stored in bitstream 107 via a dedicated parameter or variable. Alternatively, a hiding module 112 can be configured to at least partially hide SCAN_IDX scan order information in the coefficient vectors, i.e., in the values of the coefficient matrix after serialization. For example, the hiding module 112 may correspondingly perform adjustments of the coefficients stored in the quantized coefficient buffer 105 so that a corresponding verification module located in a verification module 212 of the decoder 200 may obtain the SCAN_IDX scan order information by the application. of a verification function to those. The resulting adjusted coefficients or coefficient vectors stored in the quantized coefficient buffer 105 may then be entropy encoded and transmitted to the decoder 200 in the bit stream 107.

[00126] The coefficients of one or more coefficient vectors stored in the quantized coefficient buffer 105 may then be adjusted or not, depending on whether SCAN_IDX scan order information is transmitted explicitly or implicitly in the bit stream 107, i.e., depending whether scan order information is hidden or not.

[00127] In particular, the scan pattern list module 110 is configured to provide one or more predefined scan orders for each of a plurality of coding parameter sets. Scan order generator 111 is configured to generate a scan order for each of the sets of coding parameters that depend on one or more previously scanned coefficient matrices associated with that set of coding parameters. The scan order selector 109 is configured to select a scan order for each block by: - determining a set of coding parameters for that block, and - selecting the scan order for the coefficient matrix for that block from the orders predefined and generated scan numbers for the given set of encoding parameters.

[00128] In this regard, a set of coding parameters corresponds to a specific combination of at least one or more of: - a prediction mode, - a partition mode, - one or more transformation parameters, and - one or more quantization parameters.

[00129] The prediction mode, partition mode, transformation parameters and quantization parameters are generally referred to by reference 108 in Fig. 1. For example, a set of coding parameters can correspond to only one mode prediction mode (e.g., a specific directional intraprediction mode), to just one partition mode (e.g., a specific PU orientation), to just one or more transformation parameters (e.g., a specific dimension and/or shape of TU), or to just one or more quantization parameters (e.g., a specific number of significant coefficients from the coefficient matrix). Also, the set of encoding parameters may correspond to a specific combination of prediction mode, partition mode, transformation parameters and/or quantization parameters.

[00130] Encoder 100 may comprise a coefficient distribution estimator 113 configured to provide, for each of the sets of coding parameters, a distribution statistic of one or more previously digitized coefficient matrices associated with that set of coding parameters. The scan order generator 111 is configured to generate the scan order for each of the sets of coding parameters that depend on the distribution statistics for that set of coding parameters.

[00131] In particular, the coefficients stored in the quantized coefficient buffer 105 are also a source for the estimation of coefficient distribution statistics that is used by the scan order generator 111. However, prior to estimating the coefficient distribution, the Stored coefficients are deserialized back from the coefficient vector to a coefficient array via a deserializer 114.

[00132] The distribution statistic of a coefficient matrix preferably comprises, as defined in US 2008/0310504, an indication of the probability that a coefficient value at a position of the two-dimensional coefficient matrix is zero or non-zero and may, for example, understanding a count, probability, or other statistical metric associated with each of the positions of the two-dimensional coefficient matrix. A generated scan order that depends on such a distribution statistic may correspondingly be a scan order that is configured to scan with higher priority those coefficient positions that are more likely to have non-zero coefficients.

[00133] In particular, if the selected scan order for a given block is a generated scan order, the coefficient distribution estimator 113 can be configured to update the distribution statistic for the given block's set of encoding parameters. according to the distribution statistics of the coefficient matrix of the given block. The distribution statistics of the coefficient matrix of the given block may reflect whether the coefficient at a position in the coefficient matrix of the given block is zero or non-zero. The distribution statistic provided by the coefficient distribution estimator 113 may then, for example, be updated depending on said distribution statistic of the coefficient matrix of the given block.

[00134] In particular, if the selected scanning order for a given coefficient matrix is predefined, the coefficient distribution estimator 113 may be configured not to update or may be configured to reset the distribution statistic for the set of scanning parameters. coding of the given block. Resetting the distribution statistic may, for example, consist of resetting said count, probability, or other statistical metric.

[00135] This update, non-update, or reset of the distribution statistic performed by the coefficient distribution estimator 113 that depends on the scan order selector 109 having selected a generated or predefined scan order is reflected in Fig. 1 by a dashed arrow from scan order selector 109 to coefficient distribution estimator 113.

[00136] The decoder of the proposed modality is shown in Fig. 14. The processing stages are similar to those of the encoder (see Fig. 13) and are applied in reverse order. The most important difference is that the quantized coefficient buffer stores QTCs after they are deserialized, that is, as an array of QTCs but not QTCs as one or more vectors.

[00137] In particular, Fig. 2 shows an example of a residual decoding part with selection of content-adaptive scanning orders. In the example, decoder 200 is configured to obtain a residual signal 201 from bit stream 207. After generating, by decoding module 206 (e.g., an entropy decoding module) and deserializer 204, the coefficient matrix comprising quantized transformation coefficients, a quantized coefficient buffer 205 stores said coefficient matrix. The stored coefficient matrix is then processed by an inverse quantization module 203 and an inverse transformation module 202 to obtain the residual signal 201 corresponding to the residual signal 101 in the encoder 100. Using the residual signal 201, the encoded video sequence can be reconstructed according to known techniques.

[00138] The coefficient distribution estimator 213 of the decoder 200 may be similar or identical in function to the coefficient distribution estimator 113 of the encoder 100. In the example, they differ in that the coefficient distribution estimator 213 receives as input the matrix of coefficients stored in the quantized coefficient buffer 205 while the coefficient distribution estimator 113 receives as input the coefficient matrix obtained from the deserializer 114.

[00139] The present invention proposes the combined use of predefined scanning orders and scanning orders generated on the side of both the encoder 100 and the decoder 200 depending on the previously digitized coefficient matrices, respectively obtained, from blocks of the video sequence. In particular, the generated digitization orders are generated by analyzing a distribution statistic of the coefficients within the coefficient matrix, that is, by analyzing a distribution of the quantized transformation coefficients.

[00140] A specific feature of the proposed invention is that distribution statistics for quantized transformation coefficients (QTCs) are estimated with greater accuracy when taking into account the selected scanning order, as shown, for example, in Figs. 1 and 2 by the arrow between the scan order selector 109, 209 and the coefficient distribution estimator 113, 213. This more accurate estimate may consist of, for example, updating, not updating, or resetting the distribution statistic as shown above.

[00141] The distribution of coefficients can be estimated with greater precision by dividing the source data into 4 stationary periods and estimating the distribution of coefficients only within these stationary periods. A stationary period is a number of blocks that have a similar distribution of QTCs and are spatially close to each other.

[00142] In the present invention, it is particularly proposed to detect a stationary period by introducing a limit on the number of processed blocks that are marked to have adaptively generated scanning order. When the scan order is selected from predefined scan orders by the scan default list module, there is no need to update the distribution statistics, as for this case the fact that the scan order is a predefined order indicates that the currently processed block belongs to a different stationary period.

[00143] Fig. 3 shows a flowchart for estimating distribution statistics in the video decoder according to an embodiment of the present invention.

[00144] In the video decoder, the estimation 301 of the distribution statistics by the coefficient distribution estimator 213 comprises several steps.

[00145] In a step 302, the prediction mode, partition mode, transformation parameters and/or quantization parameters 208 for a block are analyzed from the bit stream 207. Preferably, this analysis is performed by the decoding module 206. According to the analyzed information, the scanning order selector 209 preferably determines the encoding mode of that block.

[00146] In a step 303, the SCAN_IDX scan order information that identifies the selected scan order for that block is analyzed from the bit stream 207. This analysis is preferably done by the decoding module 206.

[00147] In a step 304, the scan order selector 209 selects the scan order for that block from the predefined scan orders generated based on the analyzed SCAN_IDX scan order information.

[00148] In a step 305, it is determined whether the selected scan order is a predefined scan order provided by the scan pattern list module 210 or a generated scan order provided by the scan order generator 211.

[00149] If the scan order selected for that block is a generated order (e.g., provided by scan order generator 211), the coefficient distribution estimator 213 updates, in a step 306, the current distribution statistic. This current distribution statistic is preferably obtained from previous blocks. The current distribution statistic is updated according to a coefficient matrix distribution statistic obtained for that block.

[00150] If, however, the scan order selected for that block is a predefined order (e.g., provided by the scan pattern list module 210), the coefficient distribution estimator 213 processes, in one step 306, the statistics of that block separately from the current distribution statistic. For example, the coefficient distribution estimator 213 may not update or may reset the current distribution statistic.

[00151] After step 306 or 307, estimation 301 of the distribution statistic ends (at step 308).

[00152] Fig. 4 shows a flowchart of estimating distribution statistics in the video encoder according to an embodiment of the present invention.

[00153] In the video encoder, the estimation 401 of the distribution statistics by the coefficient distribution estimator 113 comprises several steps.

[00154] In a step 402, an RDO procedure is performed by the scan order selector 109 for the purpose of selecting from among the predefined scan orders provided by the scan pattern list module 110 and the generated scan orders provided by the scan order generator 111, the scan order that provides the minimum rate-distortion (RD) cost. In this step, the SCAN_IDX scan order information of the selected scan order is obtained.

[00155] In a step 403, the scan order corresponding to the selected SCAN_IDX scan order information is obtained.

[00156] Additional steps 404 to 407 correspond to steps 305 to 308 of Fig. 3.

[00157] As shown in Figs. 3 and 4, on both the encoder and decoder sides a list of digitization orders is initialized. This includes elements from the scan pattern list module and scan orders generated by the scan order generator. Depending on whether the scan order selected by the scan order selector is generated or predefined, a decision is made regarding the distribution statistic. This decision may consist of whether or not to update the current distribution statistic, or restarting the current distribution statistic.

[00158] One of the possible ways to initialize the scan order list is shown in Fig. 5. Fig. 5 correspondingly shows a flowchart 500 of an initialization 501 of a scan order list in accordance with an embodiment of the present invention .

[00159] Its initialization depends on the prediction mode, partition mode, transformation parameters and quantization parameters specified for a block being processed.

[00160] In a step 502, it is determined whether the prediction mode of that block is a planar intraprediction mode. If this is true, a standard scan list of predefined scan orders is defined 508 to comprise predefined diagonal scan orders and predefined Z order. If this is false, step 503 is performed.

[00161] In step 503, it is determined whether the prediction mode of that block is a DC intraprediction mode. If this is true, a standard scan list of predefined scan orders is defined 508 to comprise predefined diagonal and Z-order scan orders. If this is false, step 504 is performed.

[00162] In step 504, it is determined whether the prediction mode of that block is an angular intraprediction mode close to the horizontal. If this is true, a standard scan list of predefined scan orders is defined 509 to comprise vertical, vertical-diagonal and helical scan orders. If this is false, step 505 is performed.

[00163] In step 505, it is determined whether the prediction mode of that block is an angular intraprediction mode close to vertical. If this is true, a standard scan list of predefined scan orders is defined 510 to comprise horizontal, horizontal-diagonal and helical scan orders. If this is false, step 506 is performed.

[00164] In step 506, it is determined whether the prediction mode of that block is an angular intraprediction mode close to the diagonal. If this is true, a standard scan list of predefined scan orders is defined 511 to comprise diagonal, Z-order and helical scan orders. If this is false, step 507 is performed. In step 507, a standard scan list of predefined scan orders is defined to comprise a diagonal scan order.

[00165] After defining the scan order list of predefined scan orders for that block, the scan order list is adjusted 512 using the partition mode, transformation parameters, and quantization parameters of that block.

[00166] In a step 513, the one or more generated scan orders provided by the scan order generator are added to the predefined scan orders so that, for example, the encoder scan order selector 109 can select the From the predefined and generated scan orders, the scan order that provides the minimum RD cost.

[00167] As shown in Fig. 5, the predefined scanning orders may depend on the prediction mode and/or the partition mode and/or the transformation parameters and/or the quantization parameters. For example, the most likely scan orders for the planar or DC intramode cases are the Z order and the diagonal scan order. For angular modes, the directionality of the residual signal can be taken into account so that predefined scan orders can be selected to be orthogonal to the intramode directionality.

[00168] Then this list of predefined scan orders can be updated according to other coding parameters, such as partition mode, transformation parameters and quantization parameters. In particular, this list can be updated according to partition and transformation dimensions.

[00169] For example, in interprediction mode, non-square prediction modes can also indicate the directional nature of the residual signal and the list of predefined scan orders can be appropriately updated: if a partition rectangle is oriented vertically, then orders horizontal and horizontal-diagonal scans are added to the scan list. The list of predefined scan orders is updated accordingly for horizontally oriented partition: in such a case, vertical and vertical-diagonal scan orders are added to the list of predefined scan orders.

[00170] For example, this list of predefined scan orders can be updated according to the transformation dimensions. Smaller TU dimensions introduce restrictions on some scanning patterns. So, for example, helical scans may be excluded from the list of predefined scan orders if the TU dimension is less than 8x8 pixels.

[00171] Quantization parameters (QP) can affect both the list of predefined scan orders and the signaling method. For high QP values, the number of scanning patterns can be reduced. For example, helical scans can be ignored for all TU dimensions, since QTCs are more aligned to the left, top, and upper left corner of the QTC array.

[00172] An example of the dependence of the signaling scheme on the QP is shown in Fig. 6. Fig. 6 shows in particular a flowchart 600 of implicit and explicit signaling of selected scan order in accordance with an embodiment of the present invention.

[00173] In a step 601, a QP value is obtained. If that QP value is less than or equal 602 to a QP value for high bit rates QPHBR, then the SCAN_IDX scan order information must be entropy 603 encoded in the bit stream.

[00174] If the QP value is above the QPHBR value and below another QP value for low bitrates QPLBR, then the SCAN_IDX scan order information must be partially entropy encoded 606 and partially hidden within the scan coefficients. transformation quantized by the hiding module 112.

[00175] If the QP value is above the QPHBR value and above or equal to that other QP value for low bit rates QPLBR, then the SCAN_IDX scan order information must be hidden 605 within the transformation coefficients quantized by the scanning module. concealment 112.

[00176] Consequently, hiding becomes more expensive with increasing bitrate and is completely turned off for high bitrates. On the contrary, for low bitrates, hiding becomes more preferable. On the other hand, that is, for intermediate bitrates, both signaling mechanisms are being used. The signaling mechanism selection is performed for each block or TU depending on whether obfuscation can be performed for that one.

[00177] In accordance with the present invention, a decoder 200 is proposed for decoding block coefficients of a video sequence from a bit stream 207. The decoder comprises: - a decoding module 206 configured to decode one or more vectors of coefficients of each block from the bit stream 207, - a verification module 212 configured to reconstruct, for at least one block, hidden information from one or more coefficients of that block, the hidden information constituting or forming part of SCAN_IDX scan order information associated with that block, - a scan order selector 209 configured to select a scan order for each block from a set of scan orders, preferably from a set of predefined scan orders and generated, based on the SCAN_IDX scan order information associated with that block, - a deserializer 204 configured to inversely scan, for each block, the one or more coefficient vectors of that block in accordance with the scan order selected for that mode block to obtain a matrix of coefficients.

[00178] According to the present invention, a corresponding encoder 100 is proposed to encode block coefficients of a video sequence in a bit stream 107, the coefficients of each block being contained in a respective coefficient matrix. The encoder comprises: - a scan order selector 109 configured to select a scan order for each block from a set of scan orders, preferably from a set of predefined and generated scan orders, - a serializer 104 configured to scan, for each block, the coefficient matrix of that block in accordance with the scanning order selected for that block so as to obtain one or more coefficient vectors, - a hiding module 112 configured to hide, for at least one block, SCAN_IDX scan order information that identifies the selected scan order for that block at least partially in one or more coefficients of that block, - a coding module 106 configured to encode the coefficient vectors in the bit stream 107.

[00179] Coding efficiency can then be improved because the signaling overhead in the bit stream 107, 207 generated by the encoder and received by the decoder can be reduced.

[00180] Preferably, the verification module 212 is configured to reconstruct, for at least one block, the hidden information from at least one coefficient hiding vector chosen from the one or more coefficient vectors obtained for that block. Also, the hiding module 112 is configured to hide, for at least one block, the SCAN_IDX scan order information in at least one coefficient hiding vector chosen from the one or more coefficient vectors obtained for that block.

[00181] Reconstruction and concealment may depend on a concealment condition. Such a hiding condition comprises a comparison of a parameter that depends on the coefficient hiding vector with a threshold.

[00182] The parameter may be: - a number of significant coefficients, i.e. non-zeros, within the coefficient hiding vector, or - a distance between first and last significant coefficients within the coefficient hiding vector, or - a ratio of an absolute maximum value to a non-zero absolute minimum value of the coefficients within the coefficient hiding vector, where the hiding condition is true if the parameter is above the threshold, and false if the parameter is below the threshold.

[00183] Figs. 7 and 8 show a concealment condition in accordance with an embodiment of the present invention. In particular, Fig. 7 shows a block or TU that is subdivided into coefficient groups (CGs), each coefficient vector corresponding to a coefficient group. Fig. 8 shows an example of a vector of coefficients that illustrates the case in which the parameter consists of the distance N between the first and last significant coefficients, that is, non-zeros, within the vector of coefficients. If the value of N is above a TSIG threshold, then the hiding condition is true and scan order information can be hidden in that coefficient vector.

[00184] In particular, the verification module 212 may be configured to reconstruct the hidden information from the coefficient hiding vector by applying a verification function to the coefficient hiding vector, a result of the verification function being the hidden information. Also, the hiding module 112 is configured to hide, for at least one block, the SCAN_IDX scan order information in the coefficient hiding vector by: - applying a check function to the coefficient hiding vector in order to obtain a result of the check function, - determine whether the result of the check function matches the SCAN_IDX scan order information, - if not, modify the coefficient hiding vector so that the result of the check function matches the SCAN_IDX scan order information .

[00185] It is proposed that the result of the verification function depends on the coordinates (x, y), within the coefficient matrix, of the last significant coefficient of the coefficient hiding vector. The verification function can, for example, be the following function: mod(x + y + R,2) x and y being the coordinates and R being an integer value.

[00186] For example, the check function may also be one of the following functions or other known check functions: - a parity check function applied to the least significant bits of some coefficient selected from the coefficient matrix using a binary pattern, and - a parity check function applied to a position index of the last or first non-zero coefficients or to a linear combination of the position index of the last and first non-zero coefficients.

[00187] In this regard, Fig. 9 shows an entropy decoding 901 of coefficients in accordance with the state of the art, and particularly in accordance with the H.265 video coding standard. Entropy decoding 901 comprises decoding 902 the X and Y coordinates of the last significant, i.e. non-zero, QTC. Then, a mask of significance values of QTCs (significance mask) is assigned 903 according to a scanning order, starting from the last significant QTC. Values and signals are analyzed 904, 905 from the bit stream only for significant coefficient values.

[00188] Therefore, an extension of the 1D significance mask can be obtained from the scan order and coordinates of the last significant QTC. Obviously, it is not enough to just apply known data hiding methods to embed scan order indication data into QTCs, since QTCs are analyzed from the bit stream using scan order information.

[00189] Fig. 10 shows an embodiment of the present invention, and in particular an embodiment for improving coding efficiency by reducing signaling overhead in the bit stream 107, 207 generated by the encoder and received by the decoder.

[00190] In the embodiment of Fig. 10, it is possible to hide scanning orders within QTCs. During the encoding process, several different scanning orders - indexed by SCAN_IDX - are applied during the quantization 1001 and hiding 1002 stages. The quantization procedure 1001 may use digitization information to estimate the number of bits (i.e., rate of bits) to encode QTC values and to perform rate-distortion optimization by adjusting these QTC values relative to the estimated bit rate.

[00191] If the hiding was unsuccessful 1003, i.e., for example, if the hiding condition is false, then another SCAN_IDX scan order is selected 1004. Preferably another scanning order is selected until the hiding is successful . If the selected scan is a standard scan order, for example, obfuscation is not performed.

[00192] If the hiding is successful or the selected scan order is the default, then it is possible to reorder 1005 the QTCs according to the default scan order. The following steps comprise signaling 1006 the QTCs and entropy coding 1007. Said steps 1006 and 1007 may correspond to blocks 104 and 106 of Fig. 1. Serialization 1006 may also be inserted between 1001 and 1002 as in the case of Fig. 1 .

[00193] Concealment 1002 comprises checking the concealment condition, and also modifying QTCs so that the concealment condition is satisfied. This modification may include: changing QTC values, setting QTC values to zero, and making insignificant (zero-valued) QTCs significant (non-zero). Of course, it is always possible to adjust QTCs so that the hiding condition is satisfied. However, the adjustments of QTCs on the encoder side are restricted by the distortion caused by these adjustments, and reasonable adjustment restrictions are applied. For example, due to the quantization procedure, a reasonable adjustment of coefficients is plus or minus one. This restriction makes it possible that the hiding operation cannot be performed, that is, there were no possible adjustments of QTCs to satisfy the hiding condition (1003 evaluates to “no” case for non-standard scans).

[00194] On the decoder side, after entropy decoding 1011, the hidden information is recovered 1012 from serialized data and therefore the hiding stage needs information about scan orders that will be used on the decoder side so that it can be inlined relative to the selected scanning order. The data hiding procedure can also be performed in conjunction with quantization, as is done, for example, for Signal Bit Hiding. However, hiding may fail for some of the QTCs since the hiding condition is not satisfied. For example, TU has a significant number of QTCs that are less than a threshold. In this case, additional processing depends on whether the scanning order is the standard one. If standard scanning is used, the decoder can obtain it 1015 by applying the same obfuscation condition to QTCs analyzed during the entropy decoding stage. Otherwise, the scan order is ignored and the next scan order is checked, if available.

[00195] If the default scan order is in effect, the QTCs reordering stage can be skipped, because the source and target scans are the same. For non-standard scanning orders it is proposed to perform coefficient reordering, so that the entropy encoding and entropy decoding stages can be performed without changes. A specific implementation may use remapping operation to avoid unnecessary copy-to-reorder operation, that is, by resetting a correspondence between 2D QTC matrix coordinates and 1D position within a selected scan. At the serialization/deserialization stage this remapping can provide CABAC context indices and less significant QTC coordinates for the given 1D scan position as if the QTCs were reordered.

[00196] Fig. 11 shows a coefficient reorderer according to the present invention and, in particular, shows an example of a QTC reorderer for a 4x4 block: diagonal to horizontal scan reordering.

[00197] In this regard, refer to the document “Coding of Transformation Coefficients in HEVC” by Joel Sole et al., IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 22, NO. 12, December 2012, pages 1765-1777. In Section V.B of this document, it is mentioned that a meaningful flag is encoded using a context model for each coefficient between the last one in the scan order (which is deleted) and the DC coefficient. For a 4x4 TB transformation block, i.e. matrix of QTCs, the context depends on the position of the coefficient within the TB, as in H.264/AVC. Despite the fact that entropy coding is performed for serialized and binarized data, the context model for encoding a significance bit of a QTC is selected depending on the position of this QTC within an array of QTCs, and the significance of adjacent QTCs. spatially (right and lower). The prior art decoder parses significance bit from the bit stream using context model, which is selected according to the QTC position for which this bit is being parsed and the positions of previously decoded significant QTCs. If the scanning order is unavailable to the decoder, the spatial position of QTC is undefined and therefore the context model cannot be obtained.

[00198] The proposed reordering stage, as shown, for example, in Fig. 11, before the entropy encoder, guarantees that the decoder and decoder will use the same scanning order and the same context models for the encoded QTCs/ decoded.

[00199] Fig. 11 describes in particular a case in which, after quantization, a matrix of QTCs was obtained (bottom left thereof) with the least significant coefficient (for diagonal scanning) located at (x=1, y= two). In case of diagonal scanning, 8 coefficient significance bits must be encoded.

[00200] For the purpose of selecting another scanning order (e.g., by selector 109), e.g., horizontal rather than diagonal scanning, it may be beneficial to encode the first two QTC bit rows plus two QTC bit rows from the third row (10 QTCs in total). However, if these coefficients are reordered from the diagonal to a horizontal scan (as shown at the top of Fig. 11), the position of the last of the same 8 QTC bits must be encoded.

[00201] For the entropy coding module 106, two scans are available: - a standard one, which should be used by the entropy coding module 206 to analyze the bit stream, - the scan selected by the scan order selector 109 .

[00202] When the entropy coding module selects a context model according to the position of QTCs, it not only uses X, Y defined by the scan order selector 109, but recalculates X, Y for the corresponding position of QTC after being reordered.

[00203] For example, in the example of Fig. 11, it is proposed to consider a case in which the scan order selector 109 selected diagonal scanning and the default scanning is horizontal. The entropy coding module 106 will encode the coefficient placed at position (x=1, y=1) (marked as “E” for diagonal scanning) using the reordered position context module (x0, y=2) (also marked as “E” for horizontal scanning), as well as adjacent coefficients will be defined not as “I” and “H”, but as “F” and “I”.

[00204] This reordering operation can be implemented as a remapping of the X and Y coordinates from a selected scan to the standard one, that is, to implement this reordering it is not necessary to perform memory copy/swap operations for QTCs, but just provide a lookup table for the x and y coordinates for each of the pairs (select scan, default scan).

[00205] Data hiding can use known methods to embed scan order in QTCs. However, in the present case of scanning order hiding, another possibility is that a scanning order can be specified by a condition applied to coordinates of the last significant QTC value (x, y), for example: mod(x + y,2) = scan_idx (C1)

[00206] In this case the encoder can modify the position of the last significant QTC for the purpose of indicating a digitization that should be used by the decoder. The hiding condition for the described hiding method is a set of coordinates specified for a scanning order. In this regard, FIG. 12 shows an example of occultation conditions defined for scan orders.

[00207] In Fig. 12, “X” marks indicate positions that are checked using condition (C1). It is also possible to combine this technique with data hiding within QTC values. For example, the value retrieved from the last significant QTC position can be used as a part of the hiding condition for hiding within QTC values.

[00208] It is known that concealment is more efficient if host and target signals have a universal distribution. Another embodiment of this invention is the possibility of making the distribution of (C1) closer to universal by randomization. Specifically, an additional source of random noise R can be added:

[00209] The value of R should be as unrelated to the scanning order as possible. For example, it may be a number of adjacent TUs, a parity value of a sum of reference sample values, or a total number of encoded bits.

[00210] Therefore, the invention proposes, to reduce signaling overhead, to obtain a digitization order before deserialization of QTCs, during entropy decoding. When hiding TU-related data (such as intraprediction mode, filter flag, etc.) the information being hidden is used after the deserialization and dequantification stages. The invention therefore proposes a possibility of using hidden data in QTCs before these coefficients are deserialized.

[00211] The present invention describes a quantization procedure that is applicable to residues obtained after prediction and transformation processes used, for example, for coding mobile images. The objective of the present invention is to improve the quantization rate-distortion efficiency by extending the set of available scan orders using different coding resources (e.g., intraprediction mode, block size, partition mode) at the TU level. A specific implementation of this invention is presented as a technique that simultaneously uses mode-dependent and RDO-based scan selection mechanisms.

[00212] The present invention solves problems related to RDO-based selection of scan orders. In particular, it solves the problem where adaptive scan orders based on statistics collected from previously encoded or decoded blocks do not always provide better coding efficiency over known predefined scan patterns. Therefore, an RDO-based procedure to select only one scan among the generated scan orders adaptive to the content and predefined scan patterns is proposed as a solution.

[00213] In particular, the present invention solves the above-mentioned problem of increasing the coding efficiency of selecting scan orders by the fact that both predefined scan patterns and adaptively generated scan orders are available.

[00214] The present invention in its multimedia coding modalities further provides the advantage that it can be used in many potential applications in hybrid video coding structures that are compatible with the Joint Exploration Model (JEM) which is the foundation for a standard next generation video encoding. An additional advantage is the reduced BD rate (Bj0ntegaard Delta Rate) and subjective quality improvements compared to JEM1. An additional advantage is that a computationally complex Adaptive Multiple Transformation (AMT) also known as Enhanced Multiple Transformation (EMT) can be replaced by a simpler adaptive scan order selection procedure.

[00215] One aspect of the present invention is the combination of predefined scan patterns or orders with adaptively generated scan orders. Furthermore, the addition of a signaling mechanism to a scan order selection procedure allows to significantly improve the adaptive scan order generation process to improve its coding efficiency.

[00216] The present invention has been described together with several embodiments as examples as well as implementations. However, other variations can be understood and carried out by those skilled in the art and carrying out the claimed invention, from studies of the drawings, this disclosure and the independent claims. In the claims, as well as in the description, the word “comprising” does not exclude other elements or steps and the indefinite article “one” does not exclude a plurality. A single element or other unit may satisfy the functions of several entities or items mentioned in the claims. The mere fact that some measures are mentioned in the different mutual dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims (37)

1. Decoder, characterized by comprising: a non-transitory computer-readable medium carrying a computer program comprising a program code; and one or more processors configured to execute program code for: decoding one or more coefficient vectors of a bit stream representing a sequence of video frames, wherein each video frame is associated with one or more blocks, and in that each coefficient vector of the one or more coefficient vectors corresponds to a block associated with a video frame of the sequence of video frames, reconstruct, for at least one block, hidden information from the coefficient vector corresponding to the at least one block, wherein the hidden information comprises a portion of scan order information associated with the at least one block, selecting, for each block, a scan order for the block from a set of scan orders based on the order information of scans associated with the at least block, and reversely scanning, for each block, the one or more coefficient vectors in accordance with the scan order selected for the block so as to obtain a matrix of coefficients for the block. 2. Decoder, according to claim 1, characterized by the fact that reconstructing, for the at least one block, the hidden information comprises: reconstructing, for the at least one block, the hidden information from a hidden information vector coefficients chosen from one or more vectors of coefficients obtained for at least one block. 3. Decoder, according to claim 1, characterized by the fact that reconstructing, for the at least one block, the hidden information comprises: reconstructing, for the at least one block, the hidden information from a hidden information vector coefficients that depends on a hiding condition, wherein the hiding condition is based on a comparison of a parameter that depends on the coefficients hiding vector with a threshold. 4. Decoder according to claim 3, characterized in that the parameter is: - a number of significant coefficients within the coefficient hiding vector, or - a distance between first and last significant coefficients within the coefficient hiding vector , or - a ratio of an absolute maximum value to a non-zero absolute minimum value of the coefficients within the coefficient hiding vector, where the hiding condition is true if the parameter is above the threshold, and false if the parameter is below of the limit. 5. Decoder according to claim 3 or 4, characterized in that the one or more processors are further configured to execute program code to check the hiding condition, and to reconstruct the hidden information from the hiding vector of coefficients if the hiding condition is true. 6. The decoder of claim 3, wherein, if the concealment condition is false, selecting, for each block, the scan order comprises selecting a predefined default scan order. 7. Decoder according to claim 2, characterized by the fact that reconstructing, for the at least one block, the hidden information comprises: reconstructing, for the at least one block, the hidden information from the coefficient hiding vector by applying a verification function to the coefficient hiding vector, wherein a result of applying the verification function comprises the hidden information. 8. Decoder, according to claim 7, characterized by the fact that the result of applying the verification function depends on the coordinates (x, y), within the coefficient matrix, of a last significant coefficient of the coefficient hiding vector, where the verification function comprises the following function: mod(x + y + R,2) where x and y are the coordinates of the coefficient matrix and R is an integer value. 9. The decoder of claim 1, wherein the one or more processors are further configured to execute program code to: reconstruct, for a first block, hidden information from the coefficient vector corresponding to the first block, wherein the hidden information comprises a portion of scan order information associated with the first block, and selecting, for the first and at least one second block, a scan order that is based on the scan order information associated with the first block . 10. Method for decoding block coefficients, characterized by comprising: decoding one or more coefficient vectors of a bit stream representing a sequence of video frames, wherein each video frame is associated with one or more blocks, and wherein each coefficient vector of the one or more coefficient vectors corresponds to a block associated with a video frame of the sequence of video frames, reconstruct, for at least one block, hidden information from the one or more coefficient vectors of the at least block, wherein the hidden information comprises a portion of scan order information associated with the at least one block, selecting, for each block, a scan order for the block from a set of scan orders based on the order information of scans associated with at least one block, and obtain a coefficient matrix by inverse scanning, for each block, of the one or more coefficient vectors according to the scan order selected for the block. 11. Encoder for encoding block coefficients, characterized by comprising: a non-transitory computer readable medium carrying a computer program comprising a program code; and one or more processors configured to execute program code to: select, for each block, a scan order for the block from a set of scan orders, wherein each block corresponds to a respective coefficient matrix, scan , for each block, the matrix of coefficients corresponding to the block according to the scan order selected for the block to obtain a coefficient vector corresponding to the block, hide, for at least one block, scan order information identifying the order of selected scanning for the at least one block at least partially in the coefficient vector corresponding to the at least one block, encode, for each block, the coefficient vector corresponding to the blocks in a bit stream representing a sequence of video frames, in that each video frame is associated with one or more blocks, and wherein each coefficient vector of the one or more coefficient vectors corresponds to a block associated with a video frame of the video frame sequence. 12. Encoder according to claim 11, characterized by the fact that hiding, for the at least one block, the scan order information comprises: hiding, for the at least one block, the scan order information in a coefficient hiding vector chosen from the coefficient vectors corresponding to at least one block. 13. Encoder according to claim 12, characterized by the fact that hiding, for the at least one block, the scan order information in the coefficient hiding vector is based on a hiding condition, wherein the condition of Hiding is based on a comparison of a parameter that depends on the coefficient hiding vector with a threshold. 14. Encoder according to claim 13, characterized in that the parameter is: - a number of significant coefficients within the coefficient hiding vector, or - a distance between first and last significant coefficients within the coefficient hiding vector , or - a ratio of an absolute maximum value to a non-zero absolute minimum value of the coefficients within the coefficient hiding vector, where the hiding condition is true if the parameter is above the threshold, and false if the parameter is below of the limit. 15. Encoder according to claim 13, characterized by the fact that the one or more processors are further configured to execute program code to: check the hiding condition, and hide scan order information in the hiding vector of coefficients if the hiding condition is true. 16. The encoder of claim 13, wherein, if the hiding condition is false, the one or more processors are further configured to execute program code to recursively select another scan order from the set of scan orders until the occultation condition for that other selected scan order is true. 17. Encoder according to claim 13, characterized in that, if the hiding condition is false, selecting, for each block, the scan order comprises selecting a predefined default scan order. 18. Encoder according to claim 12, characterized in that hiding, for the at least one block, the scan order information in the coefficient hiding vector comprises: applying a check function to the coefficient hiding vector to obtain a result of applying the check function, and determine whether the result of applying the check function matches the scan order information, and, if not, modify the coefficient hiding vector so that the result of applying the check function matches to scan order information. 19. Encoder, according to claim 18, characterized in that the result of applying the verification function depends on the coordinates (x, y), within the coefficient matrix, of a last significant coefficient of the coefficient hiding vector, in which the verification function comprises the following function: mod(x + y + R,2) x and y being the coordinates of the coefficient matrix and R being an integer value. 20. The encoder of claim 11, wherein, if an identical scan order is selected for a first and at least a second block, the one or more processors are further configured to execute program code for : hide scan order information that identifies identical scan order in one or more coefficients of the first block. 21. The decoder of claim 1, wherein the one or more processors are further configured to execute program code to: obtain one or more predefined scan orders, generate one or more scan orders generated, and select, for each block, the scan order for the block from the one or more predefined scan orders and the one or more scan orders generated based on the scan order information for the block contained in the bit stream, in which generating the one or more scan orders generated depends on one or more coefficient matrices previously obtained from blocks. 22. The decoder of claim 21, wherein the one or more predefined scan orders are obtained for each of a plurality of coding parameter sets, wherein the one or more processors are further configured to execute the program code to: generate, for each set of coding parameters, a scan order for the set of coding parameters depending on one or more previously obtained coefficient matrices associated with the set of coding parameters, which to select, to each block, the scan order for the block comprises: determining a set of coding parameters for the block, and selecting the scan order for the coefficient matrix obtained for the block from the one or more predefined scan orders and the one or more scan orders generated for the block's given set of scan parameters. 23. The decoder of claim 22, wherein the one or more processors are further configured to execute program code to: obtain, for each of the plurality of coding parameter sets, distribution statistics of one or more previously obtained coefficient matrices associated with the set of coding parameters, and generate, for each set of coding parameters, the scan order for the set of coding parameters that depend on the distribution statistics for the set of coding parameters. codification. 24. The decoder of claim 23, wherein if the scan order selected for a given block is a predefined scan order, then the one or more processors are further configured to execute program code to not update or reset the distribution statistics for the given block's set of encoding parameters. 25. The decoder of claim 23, wherein the one or more processors are further configured to execute program code to: analyze, for each block, coding parameter information from the bit stream, and determining the set of encoding parameters of a given block according to the analyzed encoding parameter information for the given block. 26. The decoder of claim 21, wherein the one or more processors are further configured to execute program code to: analyze scan order information that identifies the scan order selected from the stream of bits. 27. The method of claim 10, further comprising: obtaining one or more predefined scan orders, generating one or more generated scan orders, and selecting, for each block, the scan order for the block from the one or more predefined scan orders and the one or more scan orders generated based on the scan order information for the block contained in the bitstream in which to generate the one or more scan orders generated depends on one or more coefficient matrices previously obtained from blocks. 28. The encoder of claim 11, wherein the one or more processors are further configured to execute program code to: obtain one or more predefined scan orders, generate one or more scan orders generated, and select, for each block, the scan order for the block from the one or more predefined scan orders and the one or more generated scan orders, where generating the one or more generated scan orders depends of one or more coefficient matrices previously obtained from blocks. 29. The encoder of claim 28, wherein the one or more predefined scan orders are obtained for each of a plurality of encoding parameter sets, wherein the one or more processors are additionally configured to execute program code to: generate, for each coding parameter set, a scan order for the coding parameter set depending on one or more previously obtained coefficient matrices associated with the coding parameter set, wherein Selecting, for each block, the scan order for the block comprises: determining a set of block coding parameters, and selecting the scan order for the coefficient matrix obtained for the block from the one or more pre-scan orders. -defined and the one or more scan orders generated for the given set of coding parameters of the block. 30. The encoder of claim 29, wherein the one or more processors are further configured to execute program code to: obtain, for each of the plurality of encoding parameter sets, distribution statistics of a or more previously obtained coefficient matrices associated with the coding parameter set, and generating, for each coding parameter set, the scan order for the coding parameter set depending on the distribution statistics for the coding parameter set. 31. The encoder of claim 30, wherein if the scan order selected for a given block is a predefined scan order, then the one or more processors are further configured to execute the code of program to not update or reset the distribution statistics for the given block's set of coding parameters. 32. The encoder of claim 28, wherein the one or more processors are further configured to execute program code to add scan order information identifying the selected scan order in the bit stream. 33. Encoder according to claim 28, characterized in that selecting, for each block, the scan order from the one or more predefined scan orders and the one or more generated scan orders is based on a cost function. 34. Non-transitory computer-readable storage medium comprising instructions for execution on a processor, wherein the instructions, when executed by the processor, cause the processor to perform the method as defined in claim 10. 35. Decoder according to claim 1, characterized in that the set of scan orders comprises a set of predefined scan orders and generated scan orders. 36. Encoder according to claim 11, characterized in that the set of scan orders comprises a set of predefined scan orders and generated scan orders. 37. Method according to claim 10, characterized by the fact that the set of scan orders comprises a set of predefined scan orders and generated scan orders.