Classifications

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  • H04N19/63—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets
  • H04N19/64—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets characterised by ordering of coefficients or of bits for transmission
  • H04N19/647—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets characterised by ordering of coefficients or of bits for transmission using significance based coding, e.g. Embedded Zerotrees of Wavelets [EZW] or Set Partitioning in Hierarchical Trees [SPIHT]
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  • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
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  • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
  • H04N19/13—Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
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  • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
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  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
  • H04N19/176—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a block, e.g. a macroblock
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  • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
  • H04N19/18—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a set of transform coefficients
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  • H04N19/189—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
  • H04N19/192—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding the adaptation method, adaptation tool or adaptation type being iterative or recursive
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  • H04N19/39—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using hierarchical techniques, e.g. scalability involving multiple description coding [MDC], i.e. with separate layers being structured as independently decodable descriptions of input picture data
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  • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding
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  • H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
  • H04N19/91—Entropy coding, e.g. variable length coding [VLC] or arithmetic coding
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  • H04N19/46—Embedding additional information in the video signal during the compression process

Definitions

• the field of the invention is that of signal compression, in particular of a digital image or of a sequence of digital images, in which a prediction of a portion of the signal to be encoded is made from a portion of the already coded signal.
• the encoding / decoding of digital images applies in particular to images from at least one video sequence comprising:
• the present invention applies similarly to the coding / decoding of 2D or 3D type images.
• the invention may especially, but not exclusively, apply to video coding implemented in current AVC and HEVC video encoders and their extensions (MVC, 3D-AVC, MV-HEVC, 3D-HEVC, etc.), and to corresponding decoding.
• the invention can also be applied to audio coding, for example implemented in current audio encoders (EVS, OPUS, MPEG-H, etc.) and their extensions and the corresponding decoding. 2. Presentation of the prior art
• a current block to be coded is predicted from a previously coded decoded block.
• a residual block is obtained by subtracting the original values from the predicted values. It is then transformed using a type of transformation DCT (for "Discrete Cosine Transform" in English) or wavelets.
• DCT Discrete Cosine Transform
• the transformed coefficients are quantized and then their amplitudes are subjected to an entropic coding of the Huffmann type or arithmetic.
• Such coding obtains effective performances because, because of the transformation, the values of the amplitudes to be coded are for the most part zero.
• the signs of the coefficients are coded by a bit 0 or 1.
• An advantage of such a selection is to predict the value of a sign with a correct prediction probability greater than 50%, thus to allow the application of entropic coding to the values of the prediction indicators.
• This entropic coding encodes the sign information with an average bit rate less than one bit per sign, and thus makes it possible to increase the compression ratio.
• a disadvantage of this technique is that by predicting globally all the selected signs, each sign is influenced by the value of others, and the prediction is degraded.
• the invention particularly aims to overcome these disadvantages of the prior art.
• an object of the invention is to propose a solution that more effectively selects the signs to be predicted.
• Another objective of the invention is to propose a solution that is more efficient in compression.
• Yet another object of the invention is to propose a solution that applies to any type of description element of a block of pixels used for coding a digital image.
• a method of coding a digital image said image being divided into a plurality of blocks of pixels processed in a defined order, said method comprising the following steps, implemented for a current block
• the step of encoding the elements of the sequence comprises a traversal of the elements of the sequence and comprises, for a current element, the following sub-steps:
• the invention is based on an entirely new and inventive approach which consists in ordering the elements of description to be predicted according to an associated score and in predicting each element of the sequence based on the best combination of predictions of the values of the elements of the ordered sequence, according to a predetermined cost criterion.
• the current element benefits from an individualized treatment that exploits the knowledge of the real values of the elements already processed, which makes it possible to improve the quality of the prediction of the elements as and when the processing of the sequence and thus increase the compression efficiency.
• the scheduling step produces an initial sequence
• the coding step takes as a current element the first element of a current sequence initialized to the initial sequence and comprises, once the first element processed current, a substep of updating the current sequence by deleting the first element.
• the method comprises a preliminary step of calculating the costs associated with the plurality of combinations of values of the initial sequence, a step of memorizing the majority of combinations and their associated costs, and The selection step selects, for the current element, a combination of values of the initial sequence for which the previously processed elements have their real values.
• the selection step comprises a sub-step for calculating the costs associated with the combinations of possible values of the current sequence as a function of a cost criterion which depends on the real values of the elements previously traveled. .
• An advantage of this solution is that it is economical in memory resources, the calculation of the combinations and their associated costs being implemented on the fly for each current sequence.
• the selection step selects a subset of description elements to be predicted according to predetermined scores, a predetermined score being representative of a level of reliability of the prediction of the element. prediction with which it is associated, and the scheduling step orders the elements to be predicted according to said scores.
• a predetermined score being representative of a level of reliability of the prediction of the element. prediction with which it is associated
• the scheduling step orders the elements to be predicted according to said scores.
• the predetermined cost criterion belongs to a group comprising at least: a criterion for minimizing a distortion along a boundary of the current block with a previously processed block; a proximity criterion with a predetermined value; a criterion for minimizing an energy measurement of a difference between the current block and a prediction of the current block;
• One advantage is that the invention makes it possible to use alternatively several cost criteria and possibly a combination of these criteria.
• a coding device of a digital image said image being divided into a plurality of blocks of pixels processed in a defined order, said device comprising a reprogrammable calculation machine or a dedicated calculating machine adapted and configured for:
• the coding of the elements of the sequence comprises a traversal of the elements of the sequence and, for a current element, is adapted to and configured for:
• the invention also relates to a method of decoding a digital image from a bit stream, said image being divided into a plurality of blocks processed in a defined order, the bit stream comprising coded data representative of elements description of the blocks of the image, said method comprising the following steps, implemented for a block, called current block:
• said method is particular in that the step of decoding the elements of the sequence comprises a path of said elements and comprises, for a current element, the following sub-steps:
• the scheduling step produces an initial sequence
• the decoding step takes as the current element the first element of a current sequence, initialized to the initial sequence and comprises, once the first decoded current element, a substep of updating the current sequence by deleting the first element.
• this embodiment has the advantage of limiting the storage of calculated data and to release the memory as the processing progresses.
• the decoding method comprises a preliminary step of calculating the costs associated with the plurality of combinations of values of the initial sequence, a step of recording the plurality of combinations and their associated costs. and the selecting step selects a combination from the recorded combinations that begin with the decoded values of the previously browsed items in the browse order.
• this embodiment has the advantage of being resource-efficient calculations.
• the combinations and their associated costs are calculated and memorized once and for all.
• the selection step comprises a calculation of the costs associated with the combinations of possible values of the current sequence as a function of a cost criterion which depends on the decoded values of the elements previously traveled.
• the method which has just been described in its different embodiments is advantageously implemented by a device for decoding a digital image from a bit stream comprising coded data representative of said image, said image being divided into a plurality of blocks processed in a defined order, the bitstream comprising coded data representative of elements describing the blocks of the image, said device comprising a reprogrammable calculation machine or a dedicated computing machine, configured for and adapted to , for a block, said current block: Identify a set of description elements of the current block from bitstream data;
• the decoding of the elements of the initial sequence comprises at least two iterations of the following units, configured for and able to be applied to a so-called current sequence, initialized to the initial sequence:
• SEL Cbk Selection of a combination of predicted values of the description elements of the current sequence out of a plurality of possible combinations according to a predetermined cost criterion and from the second element of previously described description values decoded from the initial sequence;
• PRED Prediction of the first element of the sequence by its value in the selected combination
• DEC IP Decoding of an indicator representative of a difference between the decoded value of the current element and the predicted value, from coded data extracted from the bit stream
• the invention also relates to a signal carrying a bit stream comprising coded data representative of pixel block description elements of a digital image, said blocks of pixels being processed in a defined order.
• the signal according to the invention is particular characterized in that said data encoded in the bit stream are obtained according to the coding method according to the invention.
• the invention also relates to a user terminal comprising a device for coding a digital image and a device for decoding a digital image. according to the invention.
• the invention also relates to a computer program comprising instructions for implementing the steps of a method of encoding a digital image as described above, when this program is executed by a processor.
• the invention also relates to a computer program comprising instructions for implementing the steps of a method of decoding a digital image as described above, when this program is executed by a processor.
• These programs can use any programming language. They can be downloaded from a communication network and / or recorded on a computer-readable medium.
• the invention finally relates to recording media, readable by a processor, integrated or not to the coding device of a digital image and to the decoding device of a digital image according to the invention, optionally removable, memorizing respectively a computer program implementing an encoding method and a computer program implementing a decoding method, as described above.
• FIG. 1 schematically illustrates a sequence of digital images to be encoded and the division into blocks of these images according to the prior art
• FIG. 2 schematically shows the steps of a coding method of a digital image according to the invention
• FIG. 3 details the processing step of a block implemented in the coding method according to the invention
• Figure 4 schematically shows a decoded current block of a decoded digital image
• FIG. 5 schematically shows the steps of a method of decoding a digital image according to a first embodiment of the invention
• FIG. 6 shows an example of a simplified structure of a device for coding a digital image and a device for decoding a digital image according to one embodiment of the invention.
• the general principle of the invention is based on an individual and successive processing of description elements of an ordered sequence of description elements to be predicted. For an element of this sequence, the invention selects the best combination of values of the ordered sequence according to a predetermined cost criterion and as a function of the real / decoded values of the elements already processed and on the prediction of the current element of this sequence. by its value in this combination.
• an original video consisting of a sequence of M images II, 12,... IM, with M nonzero integer is considered.
• the images are encoded by an encoder, the encoded data is inserted a bit stream TB transmitted to a decoder via a communication network, or a compressed file FC, intended to be stored on a hard disk for example.
• the decoder extracts the coded data, then received and decoded by a decoder in a predefined order known from the encoder and the decoder, for example in temporal order II, then 12, then IM, this order being able to differ according to the mode of the decoder. production.
• each block C will undergo an encoding or decoding operation consisting of a series of operations, including in a non-exhaustive manner a prediction, a residual calculation of the current block, a transformation of the pixels of the current block into coefficients, a quantization of the coefficients and entropy coding of the quantized coefficients. This sequence of operations will be detailed later.
• the first block to be treated is selected as the current block C.
• this is the first block (in lexicographic order).
• This block has NxN pixels.
• a current block C is processed by implementing an encoding scheme, for example as specified in the HEVC standard, in the document "ISO / IEC 23008-2: 2013 - High efficiency coding and media delivery in heterogeneous environments - Part 2: High efficiency video coding, "International Organization for Standardization, published November 2013.
• This processing step is intended to provide a set of elements E for describing the data to be coded for the current block C.
• These description elements may be of various types. Non-exhaustively, they include: information relating to coding choices of the current block C, for example a coding mode of the current block, such as the INTRA, INTER or SKIP mode, a prediction mode of the current block, among the 35 prediction modes of an INTRA block, a prediction mode of an estimated motion vector for the current block, or the significance of an amplitude of a coefficient, known per se in HEVC; the data values to be encoded, such as the components of a motion vector, the amplitude or the sign of a coefficient; etc.
• a coding mode of the current block such as the INTRA, INTER or SKIP mode
• a prediction mode of the current block among the 35 prediction modes of an INTRA block, a prediction mode of an estimated motion vector for the current block, or the significance of an amplitude of a coefficient, known per se in HEVC
• the decoded current image is designated by ID. Note that in a video encoder, the ID image is (re) constructed in the encoder so that it can be used to predict the other pixels in the image sequence.
• a prediction P of the original block C is determined. It is a prediction block constructed by known means, typically by motion compensation (block from a previously decoded reference image ) in the case of a so-called INTER prediction, or INTRA prediction (block constructed from the decoded pixels immediately adjacent to the current block in the ID image).
• the prediction information related to P is encoded in the bit stream TB or compressed file FC. It is assumed here that there are K prediction modes possible Mi, M2, ..., M K , with K nonzero integer, and that the prediction mode chosen for the block C is the Mk mode.
• the residue R is transformed into a block transformed residue, called
• RT by a DCT transform or transformed into wavelets, both known to those skilled in the art and in particular implemented in the JPEG standards for the DCT and JPEG2000 for the wavelet transform.
• the transformed residue RT is quantized by conventional quantization means, for example scalar or vector, into a quantized residue block RQ.
• This quantized block RQ contains NxN coefficients. As known in the state of the art, these coefficients are scanned in a predetermined order so as to constitute a one-dimensional vector RQ [i], where the index i varies from 0 to N 2 -1. The index i is called the frequency of the coefficient RQ [i].
• these coefficients are scanned in increasing frequency order, for example along a zigzag path, which is known from the JPEG fixed image coding standard.
• the amplitude information of the coefficients of the residual block RQ is encoded by entropy coding, for example according to a Huffman coding or arithmetic coding technique.
• amplitude is meant here the absolute value of the coefficient.
• Amplitude coding means are for example described in the HEVC standard and in the article by Sole et al, entitled “Transform Coefficient Coding in HEVC", published in the journal IEEE Transactions on Circuits and Systems for Video Technology, Volume 22, Issue: 12, pp. 1765 - 1777, December 2012.
• CA amplitudes are obtained.
• step E1 for the current block C, there is thus a set E of data description elements to be encoded, among which are the quantized transformed residual coefficients RQ [i], the signs of these coefficients, the prediction mode Mk etc.
• a subset SE of this set comprising the description elements to be predicted EP for the block C. For example, a predetermined number of elements is selected. to predict according to their amplitude and the size of the current block.
• description elements of a particular type for example signs of transformed and quantized coefficients of the current block RQ, are considered.
• the invention is not limited to this type of element and applies to any other description element of the current block. Other examples will be presented below.
• a first substep E2 we begin by defining an initial subset SEI description elements to predict. For example, these are all the signs of the quantized transformed residual coefficients RQ [i] that are non-zero of the current block.
• a context Cx associated with each coefficient among a plurality J of predetermined contexts with J nonzero integer and j integer between 1 and J.
• Such a context is defined by at least one characteristic of the coefficient or block from which it is derived.
• the size of the quantized residue block RQ is considered: the size of the quantized residue block RQ,
• the prediction of the sign is all the more reliable as the amplitude is high. Similarly, it was found that when the block is larger in size, the frequency of the coefficient lower, the prediction is more reliable. Finally, it has been found that the prediction is more reliable when the current block is associated with intra prediction of a certain type.
• the type of image in which the current block is located for example of the Intra or Inter type, known from the HEVC standard, as a function of the energy of the predictor P, or depending on the total number of non-zero coefficients in the current block.
• Such a score Sj is representative of a reliability level of the prediction of the sign of the coefficient RQ [i].
• the score S takes values in a predetermined set, for example from 0 to 10.
• the score is a simple binary indication, one of which indicates that the sign can be predicted, and the other that the sign can not be predicted.
• the scores S correspond to probabilities known a priori, dependent on the context Cxj associated with the coefficient RQ [i]. We have, in the encoder, a set of probabilities of correct detection of the signs of the coefficients RQ. For example, this set of probabilities is stored in memory.
• the signs to be predicted are selected by thresholding the scores with which they are associated.
• the sign is predicted if and only if Sj > Th, where Th is a predetermined threshold, for example equal to 0.7.
• Th is known from the encoder and the decoder.
• the threshold Th may be chosen during encoding and written in the compressed file or in the bit stream comprising the coded data representative of the digital image Im. For example, if the unit that performs the encoding does not have enough computing resources at a given time, it is possible to increase this threshold Th so as to predict fewer signs, and therefore implement fewer calculations.
• the threshold Th it would also be possible to vary the threshold Th according to the content of the images to be encoded: an image containing a lot of content, such as large variations in brightness or large movements would use a high threshold, and an image with little content such as that low luminosity variations or few movements, would use a lower threshold Th, so as to smooth the complexity or the memory necessary for the coding of each image.
• the signs of the selected coefficients RQ [i] are all associated with a context Cxj and a score Sj greater than the predetermined threshold Th and form a set SE of description EP elements to be predicted.
• the ENP description elements that do not belong to the selected subset SE are conventionally encoded. This step implements coding techniques known to those skilled in the art.
• the description elements EP are ordered. This order can be predefined, and for example correspond to the scan order of the signs as defined in the HEVC standard. Preferably, they are ordered according to their associated score. For example, if the score used is representative of a probability of correct prediction, the elements are ordered by decreasing score.
• this step E5 comprises the following substeps:
• the following steps form an iterative loop that will be repeated several times, depending on the number M of description elements to be predicted selected in the sequence Seq c .
• a description element is likely to take at least two values.
• a sign may be + or -.
• step E52 the various possibilities or hypotheses of combinations of values of the sequence Seq c of elements to be predicted are evaluated using an evaluation function FE or a predetermined cost criterion. .
• K hypotheses or possible combinations with K nonzero integer.
• the hypothesis is ⁇ -, +, -, -, ..., + ⁇ and the resulting cost is 4240.
• the evaluation function must ensure that a minimal cost is generated when the hypothesis of signs is the more likely.
• an evaluation function which consists of measuring the distortion along left borders FG and upper FS of the current block with previously processed blocks.
• a decoded image ID and a virtual decoded block DVs of size NxN pixels of this image are represented with the combination of signs whose cost is to be measured, where DVs (lin, col) is the pixel value of the DVs block located on the lin line and the column col of the block.
• 5M (3, C) ((C (O, a) - 3 (Zin - 1, col + of + ((C (a, O) - 3 (Zin + a, col - 1)) 2 with C ( i, j) the value of the coefficients in the virtual decoded block DVs, with i, j integers between O and N-1.
• FIG. 4 shows the pixels located along the left border FG whose values are from bottom to top yi to y4 and located the pixels situated along the upper boundary FS of the virtual decoded block DVs whose values are from left to right y 4 to y7, as well as the pixels Xi to x 4 and x 4 to X8 respectively located on the other side of the boundaries FG and FS.
• Apply this operator returns to form the sum of (xi-yi) 2+ (x2-y2) 2 + (x3-y3) 2 + (x 4 y 4) 2 + (XS y 4) 2 + (x6-ys ) 2 + (x7-ye) 2 + (xs-y?) 2 .
• the optimal virtual decoded block DVopt is determined which minimizes this measurement:
• DV opt argmin SM DV (lD, DV s ) where ID represents the reconstructed image after decoding.
• ID represents the reconstructed image after decoding.
• the likelihood criterion used is the minimization of the error with the predictor P. This consists in selecting the virtual decoded block which minimizes the error with the predictor P.
• the virtual residue associated with the optimal virtual decoded block is thus identified.
• cost criteria such as, for example, a criterion for minimizing a measurement of distance / proximity to a predetermined value, for example a mean or the minimization of the energy of the residual block.
• each coefficient of the current residual block its real sign (if it is a coefficient whose sign is not predicted), or the sign hypothesis (if it is a coefficient whose sign is to be predicted).
• the virtual decoded block obtained DV is used to calculate the cost CT k associated with the combination CB k evaluated.
• CTo FE ( ⁇ +, +, + ⁇ )
• CTl FE ( ⁇ +, +, - ⁇ )
• CT2 FE ( ⁇ +, -, + ⁇ )
• CT3 FE ( ⁇ +, -, - ⁇ )
• CT4 FE ( ⁇ -, +, + ⁇ )
• CT5 FE ( ⁇ -, +, - ⁇ )
• CT6 FE ( ⁇ -, -, + ⁇ )
• CT7 FE ( ⁇ -, -, - ⁇ )
• the first element of the current sequence Seqc is predicted by the value it takes in the combination Ck 2 . In this example, this value is +.
• the corresponding IP prediction indicator is calculated. To do this, we compare the predicted value of sO with its real value.
• the IP indicator indicates whether the predicted sign is equal to or different from the real sign. For example, it is 0 if the predicted and real signs are equal, 1 otherwise. In this case, the predicted value is a +, the real value a -, so the IP indicator of the first sign EDO is set to 1.
• the IP indicator obtained is coded.
• a known entropy coding technique is used, such as for example a Huffman coding, arithmetic coding or CABAC coding used in the HEVC standard.
• a coded value of the prediction indicator is obtained.
• the prediction indicator since only the description elements which are associated with a representative score of a sufficient level of reliability are predicted, the prediction indicator more often takes the value 1 than the value 0. This is set to profit by entropic coding to reduce the size of the compressed signal.
• the entropy coding takes into account the score S associated with the predicted sign to code the IP indicator.
• the score has a value between 0 (low reliability of the prediction) and 10 (high reliability of the prediction)
• the entropic coding of the indicators is parameterized taking into account the score, so as to exploit the more or less uniform distribution of the indicators.
• CABAC-type entrapic coding known from the HEVC standard, is used by initializing the probabilities used in CABAC based on the predetermined scores.
• step E5 we test if the first sign EDo is the last of the sequence. If this is the case, the processing of step E5 is finite because the sequence comprises only one element. Otherwise, we update the current sequence Seq c E5 7 , removing the first EDo element that has just been processed. The second element EDi of the initial sequence thus becomes prime and the first iteration has been completed.
• step E52 two embodiments of step E52 are envisaged:
• the combinations calculated for the initial sequence, already exploited for the first iteration, are reused. It is assumed that they have been saved in a memory.
• K combinations of the first iteration we eliminate those for which So does not have its real value.
• CT4 to CT7 we keep only the 4 combinations CT4 to CT7 for which So is - and their associated costs:
• CT 4 FE ( ⁇ -, +, + ⁇ )
• CT 5 FE ( ⁇ -, +, - ⁇ )
• CT 5 FE ( ⁇ -, -, + ⁇ )
• CT 7 FE ( ⁇ -, -, - ⁇ )
• the costs associated with the combinations of the new current sequence are recalculated.
• K 2 2 possible combinations.
• the four possible combinations are evaluated using an evaluation function that may be different from that implemented at the first iteration. For example, a measurement of the energy of the coefficients of the decoded virtual residue block DVs is used and the combination which minimizes this measurement is chosen. This evaluation function is more precise, but also more complex to calculate and therefore better adapted to shorter sequences.
• the new current sequence only includes the sign S 2 .
• the third and last iteration is performed in a similar manner.
• the corresponding IP prediction indicator is calculated. Since the real value of S 2 is equal to +, the IP indicator indicates a correct prediction and is equal to 0.
• the iterations of the step E5 apply to the first element of the sequence, which is updated by deleting the first element once treated.
• This embodiment has the advantage of reducing at each iteration the length of the current sequence to be processed.
• the invention is not limited to this choice of implementation.
• the initial sequence can be preserved and the index of the current element can be progressed with each new iteration of step E5.
• the option of previously calculating the costs associated with all combinations of possible values of the initial sequence and to memorize them, is the most suitable.
• the decoded block is constructed by applying to the quantized residue RQ the dequantization and inverse transform steps (known per se).
• a decoded residue block RD is obtained.
• the predictor block P is added to RD to obtain the decoded block BD.
• the decoded block BD is also added to the reconstructed image ID. This makes it possible to have in the encoder a decoded version of the current image. This decoded version is used in particular during the step of constructing a prediction of the signs selected to be predicted.
• description elements are selected to predict a type other than the signs.
• the description element M indicative of the INTRA / INTER prediction mode is considered (in the HEVC standard, such a description element is called “pred_mode_flag")
• the description element A indicative of the amplitude of the first quantized residual coefficient for the current block in the HEVC standard, such a description element is called “coeff_abs_level_remaining”
• the description element T indicates the use or not of an inverse transform (in the HEVC standard, such a description element is called "transform_skip_flag”).
• an element M can take a value between 0 and 34.
• An element A can take values between 0 and 2 15 -1.
• the starting set consists of the description elements ⁇ M, A, T ⁇ .
• the score of T is less than the necessary threshold Th, while M and A have a higher score.
• the subset SE is therefore ⁇ M, A ⁇ .
• the TB bitstream is intended to be presented at the input of a decoder, local or remote.
• a signal carrying the bit stream is transmitted to the decoder via a communication network.
• the current block C is processed by implementing the decoding scheme, corresponding to the coding scheme used by the encoder, for example as specified in the HEVC standard.
• a set of ED elements for describing the data to be decoded for the current block C is identified.
• a prediction P 'of the block to be decoded C. is carried out.
• the prediction information related to P' is read in the bit stream or compressed file and decoded.
• the prediction mode information is decoded.
• the amplitude information of the residue to be decoded RQ ' is also decoded into the bit stream or compressed file and decoded. We now know the amplitudes of RQ '[i], but not yet the signs.
• the decoding method according to the invention implements the step of selecting the description elements to be predicted from the determined description elements. This step has already been described in detail for the coding method in relation to FIGS. 2 and 3.
• the description elements to be predicted are advantageously selected according to predetermined scores.
• An SE set is obtained.
• the method reads in the bitstream TB the coded data relating to the description elements of the unpredicted current block and decodes them.
• Step D 4 it orders the elements of the set SE obtained in an initial sequence Seq ,, by decreasing scores, as already described for the coding method according to the invention.
• Step D5 of decoding the description elements to be predicted will now be detailed in a particular embodiment. It will be noted that it is very similar to step E 5 implemented by the coding method according to the invention which has just been described.
• steps (D52 to D56) form an iterative loop which will be repeated several times, depending on the number M of description elements to be predicted selected in the sequence Seq c .
• D5 2 the best combination is selected in the sense of an evaluation function FE, the same as that used by the coding method which produced the bitstream to be decoded, among the possible value combinations of the current Seq sequence. c .
• evaluation function FE the same as that used by the coding method which produced the bitstream to be decoded
• the first description element of the sequence Seq c is decoded. In the following, it is assumed that the elements of description are signs.
• CTo FE ( ⁇ +, +, + ⁇ )
• CT ! FE ( ⁇ +, +, - ⁇ )
• CT 2 FE ( ⁇ +, -, + ⁇ )
• CT 3 FE ( ⁇ +, -, - ⁇ )
• CT 4 FE ( ⁇ -, +, + ⁇ )
• CT 5 FE ( ⁇ -, +, - ⁇ )
• CT 5 FE ( ⁇ -, -, + ⁇ )
• CT 7 FE ( ⁇ -, -, - ⁇ )
• the value of the first sign sO is predicted by its value in the combination Cb2. This is a +.
• the IP prediction indicator corresponding to this first sign sO is decoded from coded data extracted from the bit stream or compressed file. This indicator indicates whether the predicted sign has been correctly predicted or not. For example, assume that the decoded value is a 1 and is associated with an incorrect prediction. In D55, we deduce that the decoded value of the sign sO is a -.
• CT 4 FE ( ⁇ -, +, + ⁇ )
• CT 5 FE ( ⁇ -, +, - ⁇ )
• CT 5 FE ( ⁇ -, -, + ⁇ )
• CT 7 FE ( ⁇ -, -, - ⁇ )
• CT 6 is identified as the minimum cost
• the IP indicator corresponding to D2 is decoded from the coded data extracted from the bit stream or compressed file, an indicator is decoded, which indicates whether the predicted sign is equal or different from the actual sign. In our example, suppose that the decoded value of IP is 0, which means that the prediction of this sign is correct.
• the last sign S2 is decoded.
• CT 5 FE ( ⁇ -, -, + ⁇ )
• CT 7 FE ( ⁇ -, -, - ⁇ )
• CT6 is identified as the minimum cost.
• the last sign S2 in the predefined order is predicted, in D5 3 , by its value in the combination Cb6: it is a +.
• an IP indicator associated with the sign S2 is decoded at D5 4 . It indicates whether the sign S2 has been correctly predicted or not. In our example, suppose that the decoded value is 0, which corresponds to a correct prediction.
• step D6 reconstruction of the current block C from the decoded description elements, EP predicted (D 5 ) and non-predicted NPs ( ⁇ 3), amplitude information of the coefficients of the residual block RQ 'and of the prediction P 'obtained in Di.
• step D6 we first dequantize the RQ 'block to obtain a dequantized block. This is done by means adapted to the quantization used during the coding (scalar dequantization, vector dequantization ...), known to those skilled in the art.
• the dequantized residue is then subjected to a reverse transform from that used in the coding.
• the decoded residue is then obtained.
• the decoded block BD ' is reconstructed by adding the decoded residue to the prediction P'.
• This block is integrated with the image being decoded.
• step D7 it comes to test whether the current block is the last block to be processed, given the order of travel of the blocks, defined above. If yes, the decoding is complete. If not, the next step is the step C of selecting the next block and the steps of the decoding process are repeated.
• step D2 since all the elements of the initial sequence selected according to the predetermined scores are predicted, it is therefore known as soon as the outcome of step D2 how many IP prediction indicators are to be extracted from the bitstream or the compressed file.
• this makes it possible to implement an implementation of the invention which decorrelates the reading and analysis operations of the coded data contained in the bit stream or compressed file (for "parsing", in English) of the processing operations. of the current block according to the encoding / decoding scheme implemented. For example, one could organize the decoding by using a specific component for the analysis / reading of the coded data in the bitstream and another for the reconstruction operations of the decoded blocks. An advantage of this parsing independence is to allow a parallelization of the decoding operations.
• module and “unit”, used in this document, can correspond either to a software component, or to a hardware component, or to a set of hardware and / or software components, able to implement perform the function (s) described for the module or unit concerned.
• FIG. 6 an example of a simplified structure of a device 100 for encoding a digital image and a device 200 for decoding a bit stream according to the invention is now presented.
• the device 100 implements the coding method according to the invention which has just been described in connection with Figure 2. Only the main elements relating to the implementation of the technique according to the invention are illustrated.
• the device 100 comprises a processing unit 110, equipped with a processor ⁇ , and driven by a computer program Pgi 120, stored in a memory 130 and implementing the method according to the invention.
• the code instructions of the computer program Pgi 120 are for example loaded into a RAM memory before being executed by the processor of the processing unit 110.
• the processor of the processing unit 110 sets implement the steps of the method described above, according to the instructions of the computer program 120.
• the processor 110 is adapted to and configured to: process (PROC) a current block and obtain a set description elements of this block;
• ORDER ordering the description elements of the subset in a sequence, said initial sequence, according to said scores
• the device 100 is furthermore configured to encode the non-predicted elements (ENC ENP) and to reconstruct the decoded block BD and the decoded image (RECONST).
• ENC ENP non-predicted elements
• RECONST decoded image
• the encoding of the elements of the initial sequence comprises at least two iterations of the following units, configured for and able to be applied to a so-called current sequence, initialized to the initial sequence: selection (SEL Cbk) of a combination of values of the description elements of the current sequence out of a plurality of possible combinations according to a predetermined cost criterion and, from the second element, of previously described description element values of the initial sequence; prediction (PRED) of the first element of the sequence by its value in the selected combination; coding (COD IP) of an indicator representative of a difference between the value of the current element and the predicted value, and
• the device 100 furthermore comprises a unit Mi for storing the coding contexts of the coefficients, predetermined scores associated with each of these contexts, predicted values for the selected description elements, and the plurality of combinations of values of the selected sequence of description elements to be predicted.
• These units are driven by the ⁇ processor of the processing unit 110.
• such a device 100 can be integrated in a user terminal equipment TU, such as an encoder, a personal computer, a tablet, a digital camera, a smart mobile phone (for "smartphone") etc.
• the device 100 is then arranged to cooperate at least with the following module of the terminal TU: a data transmission / reception module E / R, through which the bit stream TB or the compressed file FC is transmitted in a network telecommunications, for example a wired, radio or wireless network.
• a network telecommunications for example a wired, radio or wireless network.
• the decoding device 200 implements the decoding method according to the invention which has just been described in relation to FIG. 5.
• the device 200 comprises a processing unit 210, equipped with a processor ⁇ 2, and driven by a computer program Pg2 220, stored in a memory 230 and implementing the method according to the invention.
• the code instructions of the computer program Pg2 220 are for example loaded into a RAM before being executed by the processor of the processing unit 210.
• the processor of the processing unit 210 sets implement the steps of the method described above, according to the instructions of the computer program 220.
• the device 200 is adapted to and configured to:
• DEC Decode
• the decoding of the elements of the initial sequence comprises at least two iterations of the following units, configured for and able to be applied to a so-called current sequence, initialized to the initial sequence:
• PRED Prediction of the first element of the sequence by its value in the selected combination
• DEC IP Decoding of an indicator representative of a difference between the decoded value of the current element and the predicted value, from coded data extracted from the bit stream
• the device 200 is further configured to decode the unpredicted elements (DEC ENP) and to reconstruct the decoded block BD and the decoded picture (RECONST).
• DEC ENP unpredicted elements
• RECONST decoded picture
• the device 200 furthermore comprises a unit M 2 for storing the coding contexts of the coefficients, predetermined scores associated with each of these contexts, predicted values for the description elements selected for a block C and combinations Cbk of values of the elements. description of the sequence to be predicted.
• such a device 200 can be integrated in a user terminal TU, for example a decoder, a TV connection box (for "Set-Top-Box", in English), a digital television, a computer, a tablet, a smart mobile phone, etc.
• the device 200 is then arranged to cooperate at least with the following module of the terminal TU: a data transmission / reception module E / R, through which the bit stream
• TB or compressed FC file is received from the telecommunications network.
• a DISP module for displaying decoded digital images.
• the invention which has just been presented can find many applications, in particular in the context of video signal compression, audio (speech, sound), still images, images acquired by an imaging module medical. It applies for example to two-dimensional (2D), three-dimensional (3D) contents including a depth map, or multispectral images (whose color intensities are different from the three red green blue bands) or finally to full images.

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