Classifications

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  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
  • H04N19/51—Motion estimation or motion compensation
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  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • 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
  • H04N19/119—Adaptive subdivision aspects, e.g. subdivision of a picture into rectangular or non-rectangular coding blocks
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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
  • H04N19/174—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 slice, e.g. a line of blocks or a group of blocks
• • H—ELECTRICITY
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  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • 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
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
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  • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
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  • H04N19/55—Motion estimation with spatial constraints, e.g. at image or region borders
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  • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
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  • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
  • H04N19/625—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using discrete cosine transform [DCT]
• • H—ELECTRICITY
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  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards
• • H—ELECTRICITY
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  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/85—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression
  • H04N19/86—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/85—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression
  • H04N19/86—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness
  • H04N19/865—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using pre-processing or post-processing specially adapted for video compression involving reduction of coding artifacts, e.g. of blockiness with detection of the former encoding block subdivision in decompressed video

Definitions

• the present invention relates generally to the field of image processing and more specifically to the coding and decoding of digital images and digital image sequences.
• 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.
• MVC Motion Picture Codon Coding
• 3D-AVC 3D-AVC
• MV-HEVC 3D-HEVC
• 3D-HEVC 3D-HEVC
• the images and digital image sequences occupy a lot of space in terms of memory, which requires, when transmitting these images, to compress them in order to avoid congestion problems on the communication network used for this transmission. , the flow rate usable on it is generally limited. This compression is also desirable for storing these data.
• Video data compression uses techniques for spatially or temporally prediction of groups of pixel blocks of a current image relative to other groups of blocks of pixels belonging to the same image or to a previous or next image.
• I-images are coded by spatial prediction (intra prediction), and P and B-images are coded by temporal prediction (inter prediction) with respect to other I, P or B-encoded images. decoded using motion compensation.
• the images are cut a first time in blocks of pixels called CTU (abbreviation of "Coded Treeblocks Unit") which are similar to the macroblocks of the H.264 standard. These blocks can then be subdivided into smaller blocks, each of these smaller blocks or each CTU block being coded by intra prediction or between images.
• CTU abbreviation of "Coded Treeblocks Unit”
• a data signal when a CTU block is subdivided into smaller blocks, a data signal, corresponding to each block, is transmitted to the decoder.
• a signal includes:
• coding parameters which are representative of the coding mode used, in particular:
• the decoding is done image by image, and for each image, block CTU per block CTU.
• the elements corresponding stream are read. Inverse quantization and inverse transformation of the coefficients of the smaller blocks are performed. Then, the prediction of each CTU block is calculated and each CTU block is reconstructed by adding the prediction to the decoded prediction residue.
• Intra or inter-competition coding as implemented in the HEVC standard, thus relies on the putting into competition of different coding parameters, such as those mentioned above, in order to select the best mode of coding, which is that is to say, that which will optimize the coding of the block considered according to a predetermined performance criterion, for example the cost rate / distortion well known to those skilled in the art.
• the coding parameters relating to the selected coding mode are contained in the data stream transmitted by the coder to the decoder, in the form of identifiers generally called competition indices.
• the decoder is thus able to identify the coding mode selected to the encoder, then to apply the prediction according to this mode.
• One of the aims of the invention is to overcome disadvantages of the state of the art mentioned above.
• an object of the present invention relates to a method of coding at least one image cut into blocks.
• Such a coding method is remarkable in that it comprises, for a current block to be coded, the steps of:
• Such an arrangement makes it possible, during the coding of an image, to avoid including in the signal to be transmitted to the decoder the indices of the predictor blocks which are used to predict the blocks of the image respectively. This results in a significant decrease in the cost of signaling, insofar as such a provision is reproducible to the decoder.
• the identification of candidate predictor blocks for the prediction of the current block is particularly reliable. It results from the fact that for a current residual block considered, the characteristics of the candidate predictor blocks are very different from each other, which facilitates the final selection of the most suitable candidate predictor block during the determination step according to a predetermined criterion. .
• the blocks of the image preceding the current block being coded in a determined order is a function of the pixels of the previously coded image.
• Such an arrangement thus makes it possible to take account of information of the image which is already available at the time of coding of the current block, thus increasing the performance of the identification of the candidate predictor blocks.
• the previously coded pixels of the image are located along the current block.
• Such an arrangement thus makes it possible to minimize the discontinuities likely to appear along the boundaries of the current block, while corresponding better to the reality of the image.
• the predetermined criterion is the minimization of the bitrate-distortion cost of the image.
• the current block is a block that has previously been obtained as a result of a prediction.
• Such an arrangement is intended to further refine the prediction of the current block so as to obtain optimized coding performance.
• the invention also relates to a device for encoding at least one image cut into blocks, such a device being remarkable in that it comprises, for a current block to be encoded:
• a determination module a set of candidate predictor blocks
• An identification module in the set of candidate predictor blocks, of a candidate predictor block, as a function of the current residual block obtained,
• a determination module among the candidate predictor blocks that may have been selected at the end of the selection step, of a candidate predictor block, using a predetermined criterion
• Such a coding device is able to implement the aforementioned coding method.
• the invention also relates to a method of decoding a data signal representative of at least one image cut into blocks, such a method comprising the steps of:
• the decoding method according to the invention is remarkable in that it comprises, for a current block to be reconstructed, the steps of:
• identification in the aforementioned set, of a candidate predictor block, such identification being a function of said residual current decoded block
• An advantage of such a decoding method lies in the fact that the step of identifying the predictor block capable of reconstructing the current block is reproducible at decoding.
• the data signal received at the decoder advantageously contains no information associated with this identified predictor block, which significantly reduces the cost of signaling this information.
• the fact that the identification of the predictor block is a function of the decoded current residual block allows a reliable reconstruction of the current block.
• the characteristics of the candidate predictor blocks of the determined set being very different from each other, the identification of the predictor block used for the reconstruction of the current block is facilitated. This results in a decoding of the image of better quality.
• the blocks of the image preceding the current block being decoded in a determined order, the identification of a predictor block is a function of the pixels of the previously decoded image.
• the decoding method further comprises a step of determining, in the data signal, information associated with a prediction of the current block, said step of reconstructing the current block being implemented. from such prediction, the identified predictor block and the current residual block determined.
• the invention also relates to a device for decoding a data signal representative of at least one image cut into blocks, such a device comprising:
• Such a decoding device is remarkable in that it comprises, for a current block to be reconstructed:
• an identification module in said set, of a candidate predictor block, said identification being a function of said decoded current residual block
• Such a decoding device is able to implement the aforementioned decoding method.
• the invention also relates to a computer program comprising instructions for implementing one of the coding and decoding methods according to the invention, when it is executed on a computer.
• This program can use any programming language, and be in the form of source code, object code, or intermediate code between source code and object code, such as in a partially compiled form, or in any other desirable form.
• the invention also relates to a computer-readable recording medium on which a computer program is recorded, this program including instructions adapted to the implementation of one of the methods according to the invention, as described herein. -above.
• the invention also relates to a computer-readable recording medium on which a computer program is recorded, this program comprising instructions adapted to the implementation of the coding or decoding method according to the invention, as described. above.
• the recording medium may be any entity or device capable of storing the program.
• the medium may include storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a USB key or a hard disk.
• the recording medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means.
• the program according to the invention can be downloaded in particular on an Internet type network.
• the recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the aforementioned coding or decoding method.
• the decoding method, the coding device, the decoding device, the computer programs and the corresponding recording media mentioned above have at least the same advantages as those conferred by the coding and decoding method according to the present invention. Brief description of the drawings
• FIGS. 1A and 1B show steps of the coding method according to one embodiment of the invention
• FIG. 2 represents an embodiment of a coding device according to the invention able to implement the coding method of FIGS. 1A and 1B,
• FIG. 3 represents an example of partitioning the current image into several blocks of pixels
• FIG. 4 represents an embodiment according to the invention of the step of identifying a candidate predictor block as a function of the current decoded residue block obtained
• FIG. 5 represents steps of the coding method according to another embodiment of the invention.
• FIG. 6 represents an embodiment of a coding device according to the invention able to implement the coding method of FIG. 5;
• FIG. 7 represents steps of the decoding method according to one embodiment of the invention.
• FIG. 8 represents an embodiment of a decoding device according to the invention able to implement the decoding method of FIG. 7,
• FIG. 9 represents steps of the decoding method according to another embodiment of the invention.
• FIG. 10 represents an embodiment of a decoding device according to the invention able to implement the decoding method of FIG. 9.
• the coding method according to the invention is for example implemented in a software or hardware way by modifications of an encoder initially conforming to the HEVC standard.
• the coding method according to the invention is represented in the form of an algorithm comprising steps C1 to C22 as represented in FIGS. 1A and 1B.
• the coding method according to the invention is implemented in a coding device C01 represented in FIG.
• such an encoding device comprises a memory MEM_C01 comprising a buffer memory MT_C01, a processing unit UT_C01 equipped for example with a microprocessor ⁇ and driven by a computer program PG_C01 which implements the method of coding according to the invention.
• the code instructions of the computer program PG_C01 are for example loaded into a RAM memory (not shown) before being executed by the processor of the processing unit UT_C01.
• the coding method shown in FIGS. 1A and 1B applies to any current image of an SQ sequence of images to be encoded.
• a partitioning step is implemented by a partitioning software module MP1 shown in FIG. 2, which module is controlled by the microprocessor ⁇ of the processing unit UT_C01.
• the image ICj thus partitioned is shown in FIG. 3.
• the image ICj is partitioned into four blocks Bi, B 2 , B 3 and B 4 .
• block means coding unit (coding unit).
• coding unit coding unit
• This last terminology is especially used in the HEVC standard, for example in the document "B. Bross, W.-J. Han, J.-R. Ohm, GJ Sullivan, and T. Wiegand, "High efficiency video coding (HEVC) text specification draft 10," JCTVC-L1003 document of JCT-VC, Geneva, CH, 14-23 January 2013.
• such a coding unit groups together sets of pixels of rectangular or square shape, also called blocks, macroblocks, or sets of pixels having other geometrical shapes.
• Said blocks Bi, B 2 , B u , ..., B s are intended to be coded according to a predetermined order of travel, which is for example of the raster scan type. This means that the blocks are coded one after the other, from left to right.
• the coder CO1 selects, as current block, a first block to be encoded B u of the image IC j , such as, for example, the first block B-.
• a set of Q candidate predictor blocks BP1 1 is determined according to the invention ; BP1 2, ..., V BP1, ..., Q BP1 (1 ⁇ v ⁇ Q).
• Such candidate predictor blocks are for example blocks of pixels that have already been coded or not.
• Such blocks are stored beforehand in the MT_CO1 buffer memory of the encoder as represented in FIG. 2. In the example represented, it is in particular a predetermined number of blocks which have been coded just before the current block considered. .
• Such a determination step is implemented by a determination software module DET_CO1 shown in FIG. 2, which module is driven by the microprocessor ⁇ of the processing unit UT_CO1.
• DET_CO1 determination software module
• the candidate predictor block BP1 v is subtracted from the current block B u to produce a residue block Br v .
• the residue block Br v is transformed according to a conventional direct transformation operation such as, for example, a discrete cosine transformation of the DCT type, to produce a transformed Bt block. v .
• the transformed block Bt v is quantized according to a conventional quantization operation, such as, for example, a scalar quantization.
• a conventional quantization operation such as, for example, a scalar quantization.
• a block of quantized coefficients Bq v is then obtained.
• the steps C4 to C6 are implemented by a predictive coding software module PRED_C01 shown in FIG. 2, which module is driven by the microprocessor ⁇ of the processing unit UT_C01.
• the predictive coding module PRED_C01 is able to perform a predictive coding of the current block, according to conventional prediction techniques, such as for example in Intra and / or Inter mode.
• the entropic coding of the quantized coefficient block Bq v is carried out .
• it is a CABAC entropic coding.
• Such a step consists in: a) reading the symbol (s) of the predetermined set of symbols which are associated with said current block,
• Such an entropy coding step is implemented by an entropic coding software module MCE1 shown in FIG. 2, which module is driven by the microprocessor ⁇ of the processing unit UT_C01.
• the entropic coding module MCE1 is for example of the CABAC type. It may also be a Huffman coder known as such.
• step C8 shown in FIG. 1A the block Bq v is dequantized according to a conventional operation of FIG. dequantization, which is the inverse operation of the quantization performed in step C6.
• a block of dequantized coefficients BDq v is then obtained.
• step C9 it is proceeded to the inverse transformation of the dequantized coefficient block BDQ v which is the inverse operation of the direct conversion performed in step C5 above.
• a decoded residue block BDr v is then obtained.
• Steps C8 and C9 are implemented by a PRED "1 _C01 inverse predictive coding software module represented in FIG. 2, which module is driven by the microprocessor ⁇ of the processing unit UT_C01.
• steps C4 to C9 are repeated for each predictor block of the set of predictor blocks BP1 1; BP1 2 , ..., BP1 V , ..., BP1 Q , Q decoded residue blocks BDr 1; BDr 2 ,..., BDr v ,..., BDr Q are obtained at the end of step C9.
• the method according to the invention is used to identify, among all the Q predictor blocks BP1-I, BP1 2 ,..., BP1 V ,. , BP1 Q , at least one predictor block capable of being found at the decoding of the current block B u .
• an identification step is a function of the current decoded residue block BDr v obtained.
• Such an identification step is implemented by a calculation software module CAL1_C01 shown in FIG. 2, which module is controlled by the microprocessor ⁇ of the processing unit UT_C01.
• such an identification consists, for a current decoded residue block BDr v , in building a current decoded block BD V, W by adding to the decoded current block BDr v a candidate predictor block BP1 w (1 ⁇ w ⁇ Q).
• a criterion is applied for minimizing the difference between the decoded pixels of the current image IC j , which are represented by dots in FIG. 4, and the pixels of the decoded block BD V, W along its boundary F.
• This criterion is a mathematical operator denoted SM (BD v , w, IC j ).
• the operator SM (BD V , W , IC j ) is in fact representative of the quadratic error along the boundary F of the decoded residual block BDr v with the image IC j .
• w is the decoded block considered of size NxN pixels
• - BD v , w (n, m) is the value of the pixel of the decoded residue block BD V , W located on the nth row and the mth column of this block,
• IC j (k, l) is the value of the pixel of the image IC j located on the k th line and the I th column of this image, and (lin, col) are the coordinates of the decoded block BD v, w in the image IC j .
• a simplified criterion in which the average of the pixels of the image IC j along the boundary F and the average of the pixels of the decoded block BD V , W - L 'are compared.
• SM operator (BD V , W , ICj) is then written:
• step C10 the decoded block BDv.wmin is determined, which minimizes one of the two aforementioned criteria, such as:
• Kmin argmin K 5 (BD uK, PAC j)
• the block B Dv.wmin is equal to the sum of the candidate predictor block BP1 wmin and the current decoded residue block BDr v .
• the candidate candidate block BP1 wmin is compared with the candidate predictor block BP1 V associated with the decoded residue block BDr v .
• Such a comparison step is implemented by a calculation software module CAL2_C01 shown in FIG. 2, which module is controlled by the microprocessor ⁇ of the processing unit UT_C01.
• the steps C4 to C1 1 are repeated for each predictor block of the set of predictor blocks BP1 i, BP1 2 ,..., BP1 V ,..., BP1 Q determined in FIG. step C3.
• the BPI block wmin is not selected as the identified predictor block.
• a plurality T of identified predictor blocks BP1 i, BP1 2 , BP1 Z , BP1 T is obtained, where 1 ⁇ z ⁇ T ⁇ Q.
• D represents the distortion between the original current block Bi and the reconstructed block Bi
• R represents the bit cost of the coding of the coding parameters used to code the block Bi
• ⁇ represents a Lagrange multiplier whose value is fixed to the coder.
• the predetermined performance criterion only depends on the distortion and is expressed by equation (2) below:
• the criteria J and J ' are calculated conventionally by simulation by a calculation module CAL3_C01 represented in FIG. 2, which module is driven by the microprocessor ⁇ of the processing unit UT_C01.
• the predictive module PRED_C01 of FIG. 2 subtracts the preferential candidate predictor block BP1 op t from the current block B u to produce a residue block Br op t u - Au during a step C15 shown in FIG. 1B, the module
• PRED_C01 of FIG. 2 carries out the transformation of the residue block Br op t u according to a conventional direct transformation operation such as, for example, a discrete cosine transformation of the DCT type, to produce a transformed block Bt op tu- During a step C16 shown in FIG. 1B, the module
• PRED_C01 of FIG. 2 proceeds to the quantization of the transformed block Bt op tu according to a conventional quantization operation, such as, for example, a scalar quantization.
• a block of quantized coefficients Bq op t u is then obtained.
• the entropic coding module MCE1 of FIG. 2 proceeds with the entropic coding of the quantized coefficient block Bq op t u -
• a data flow ⁇ which contains the encoded data of the quantized coefficient block Bq op t u is then delivered at the end of step C17.
• Such a stream is then transmitted by a communication network (not shown) to a remote terminal.
• This comprises the decoder D01 represented in FIG. 7.
• the stream ⁇ furthermore comprises certain information encoded by the coder C01, such as the type of prediction (inter or intra), and, if appropriate, the prediction mode, the partition partitioning type if the block has been partitioned, the reference image index and the displacement vector used in the inter prediction mode.
• the PRED module " 1_C01 of FIG. 2 dequantizes the block Bq op t u according to a conventional dequantization operation, which is the inverse operation of the quantization performed in step C16 A block of dequantized coefficients BDq op tu is then obtained.
• the PRED module " 1_C01 of FIG. 2 carries out the inverse transformation of the block of dequantized coefficients BDq op t u which is the reverse operation of the direct transformation performed in step C15 above.
• a decoded residue block BDr op tu is then obtained.
• the decoded block BD U is constructed by adding to the preferential candidate predictor block BP1 op t the decoded residue block BDr op t u - H is noted that this last block is the same as the decoded block obtained at the end of the image decoding process IC j which will be described later in the description.
• the decoded block BD U is then stored in the buffer memory MT_C01 of FIG. 2, in order to be used by the coder C01 as a candidate predictor block of a next block to be encoded.
• the coder C01 tests whether the current block B u that has just been coded is the last block of the image. If the current block is the last block of the image.
• IC j during a next step C22 shown in Figure 1 B, it ends the coding process.
• This alternative embodiment differs from the previous embodiment in that it implements two types of prediction which will be described below with reference to FIG.
• the coding method according to this other embodiment is represented in the form of an algorithm comprising steps C'1 to C'9 as represented in FIG.
• the coding method according to this other embodiment of the invention is implemented in a coding device C02 shown in FIG. 6.
• such a coding device C02 comprises a memory MEM_C02 comprising a buffer memory MT_C02, a processing unit UT_CO2 equipped for example with a microprocessor ⁇ and driven by a computer program PG_C02 which implements the method coding according to this other embodiment.
• the code instructions of the computer program PG_C02 are for example loaded into a RAM (not shown) before being executed by the processor of the processing unit UT_C02.
• the coding method shown in FIG. 5 applies to any current image of an image SQ sequence to be encoded.
• a current image ICj belonging to the image sequence SQ ld, ICj, ..., I CM (1 ⁇ j ⁇ M) is partitioned. ), in a plurality of blocks Bi, B 2 , B u , ..., B s (1 ⁇ u S S), for example of size 64 ⁇ 64 pixels.
• Such a partitioning step is implemented by a partitioning software module MP2 shown in FIG. 6, which module is controlled by the microprocessor ⁇ of the processing unit UT_C02. Since step C'1 is identical to step C1 of FIG. 1A, it will not be described further.
• said blocks Bi, B 2 , B u ,..., B s are intended to be coded according to a predetermined order of travel, which is for example of the raster scan type. . This means that the blocks are coded one after the other, from left to right.
• the coder C02 selects as the current block a first block to be encoded B u of the image ICj, such as, for example, the first block Bi.
• the current block B u is predicted by conventional intra and / or inter prediction techniques using a predictor block BP1 is i - Such a prediction will be called "primary prediction" in the remainder of the description.
• the aforementioned prediction step makes it possible to construct a residue block Br1 u which is obtained by calculating the difference between the current block B u and the predictor block BP1 se .
• the step C'3 is implemented by a predictive coding software module PRED1_C02 shown in FIG. 6, which module is driven by the microprocessor ⁇ of the processing unit UT_C02.
• a set of Q candidate predictor blocks BP2 1 is determined; BP2 2, ..., V BP2, ..., BP2 Q (1 ⁇ V ⁇ Q). Since such a step is identical to the determination step C3 of FIG. 1A, it will not be described further.
• Such a determination step C'4 is implemented by a determination software module DET_CO2 shown in FIG. 6, which module is controlled by the microprocessor ⁇ of the processing unit UT_CO2.
• a prediction of the residue block Br1 u is carried out by implementing the steps C4 to C13 described above in connection with the figures 1 A and 1 B. Such a prediction will be called “secondary prediction" in the remainder of the description.
• a preferential candidate predictor block BP2 op t is selected.
• step C'5 is implemented using:
• a calculation software module CAL2_C02 which is identical to the module CAL2_C01 of FIG. 2.
• the effectiveness of the preferred candidate predictor block BP2 op t which has been selected is carried out.
• test step C'6 is implemented by a calculation software module CAL4_C02 shown in FIG. 6, which module is driven by the microprocessor ⁇ of the processing unit UT_C02.
• such a test consists in verifying whether the energy of the block Br1 u -BP2 op t is lower than a threshold which corresponds to the value of the energy of the block Br 1 u .
• the test is positive, it means that the preferential candidate predictor block BP2 opt is close to the current original block B u . Therefore, the secondary prediction is applied to the current block B u.
• step C'6 the residue block Br1 u is transformed according to a conventional direct transformation operation.
• a conventional direct transformation operation such as for example a discrete cosine transformation of DCT type, to produce a transformed block Bt1 u .
• the transformed block Bt1 u is quantized according to a conventional quantization operation, such as, for example, scalar quantization.
• a block of quantized coefficients Bq1 u is then obtained.
• the steps C'610 and C'61 1 are implemented by the predictive coding software module PRED1_C02 shown in FIG. 6.
• the entropic coding of the quantized coefficient block Bq1 u is carried out by an entropic coding software module MCE1_CO2 identical to the entropic coding software module MCE_C01 of FIG. furthermore, an indicator Id associated with the preferential candidate predictor block BP2 op t is coded according to a first predetermined value (bit at 0 for example) to indicate that the secondary prediction has not been applied.
• a data flow ⁇ 1 which contains the encoded data of the quantized coefficient block Bq1 i as well as the bit at 0 of the indicator Id, is then output at the end of the step C'612.
• Such a stream is then transmitted by a communication network (not shown) to a remote terminal.
• a communication network (not shown) to a remote terminal.
• This comprises the decoder D02 shown in FIG. 10.
• the stream ⁇ 1 contains information encoded by the coder C02, such as the type of prediction (inter or intra), and if appropriate, the mode prediction, the type of partitioning of a block or macroblock if the latter has been partitioned, the reference image index and the displacement vector used in the inter prediction mode.
• step C'613 the block Bq1 u is dequantized according to a conventional dequantization operation, which is the inverse operation of the quantization performed in step C'61. .
• a block of dequantized coefficients BDq1 u is then obtained.
• step C'614 represented in FIG. 5 the inverse transformation of the dequantized coefficient block BDq1 u is carried out which is the inverse operation of the direct transformation carried out in step C'610 above. .
• a decoded residue block BDr1 u is then obtained.
• steps C'613 and C'614 are implemented by an inverse predictive coding software module PRED1 "1 _C02 shown in FIG. 6, which module is driven by the microprocessor ⁇ of the processing unit UT_C02. is identical to the software module PRED "1 _C01 of Figure 2.
• the coder C02 tests whether the current block B u that has just been coded is the last block of the image ICj.
• the coding method is terminated. If this is not the case, it is proceeded again to the selection step C'2 of the next block to be coded according to the above-mentioned raster scan order, then the steps C'3 to C'6 are reiterated for that next block selected.
• step C'6 If the test performed in step C'6 is positive, during a step C'620 shown in FIG. 5, the module PRED2_C02 of FIG. 6 subtracts the preferential candidate predictor block BP2 opt from the residual block Br1 u to produce a residue block Br2 op t u - During a step C'621 represented in FIG. 5, the module
• PRED2_C02 of FIG. 6 transforms the residue block Br2 op t u according to a conventional direct transformation operation such as, for example, a discrete cosine transformation of the DCT type, to produce a transformed block Bt2 op t u -
• a conventional direct transformation operation such as, for example, a discrete cosine transformation of the DCT type
• PRED2_C02 of FIG. 6 proceeds to the quantization of the transformed block Bt2 op tu according to a conventional quantization operation, such as, for example, a scalar quantization.
• a block of quantized coefficients Bq2 op t u is then obtained.
• the entropic coding module MCE2_CO2 of FIG. 6 proceeds with the entropic coding of the quantized coefficient block Bq2 op t u.
• the indicator Id associated with the predictor block preferential candidate BP2 opt is coded according to a second predetermined value (1-bit, for example) to signal that the secondary prediction has been applied.
• a data stream ⁇ 2 which contains the encoded data of the quantized coefficient block Bq2 op t u and the bit at 1 of the indicator Id, is then output at the end of the step C'623. Such a stream is then transmitted by a communication network (not shown) to the decoder D02 shown in FIG.
• the module PRED2 "1 _C02 of FIG. 6 carries out the dequantization of the block Bq2 op t u according to a conventional operation of dequantization, which is the inverse operation the quantification performed in step C'622.
• a block of dequantized coefficients BDq2 op t u is then obtained.
• the module PRED2 "1 _C02 of FIG. 6 carries out the inverse transformation of the dequantized coefficient block BDq2 op t u which is the inverse operation of the direct transformation carried out in step C'621 above A decoded residue block BDr2 op tu is then obtained.
• the decoded block BD U is constructed by adding to the preferential candidate predictor block BP2 opt the decoded residual block BDr2 op t u.
• the decoded block BD U thus constructed is then stored. in the MT_C02 buffer memory of FIG. 6, for use by the CO 2 coder as a predictor block candidate for a secondary prediction of a next decoded residue block.
• the coder C02 tests whether the current block B u which has just been coded is the last block of the image IC j .
• the coding method is terminated.
• a decoder D01 comprises a memory MEM_D01 comprising a buffer memory MT_D01, a processing unit UT_D01 equipped for example with a microprocessor ⁇ and driven by a computer program PG_D01 which implements the decoding method according to the invention.
• the code instructions of the computer program PG_D01 are for example loaded into a RAM before being executed by the processor of the processing unit UT_D01.
• the decoding method shown in FIG. 8 applies to any current image of an SQ sequence of images to be decoded.
• information representative of the current image IC j to be decoded is identified in the stream ⁇ received at the decoder.
• the first decoding step D1 is the identification in said stream ⁇ of the encoded data Bq ; Bq 2 , ..., Bq u , ... Bq s respectively associated with the residual blocks Bn, Br 2 , Br u , ..., Br s coded previously according to the above-mentioned raster scan path, according to the coding method shown in FIG. Figures 1A and 1B.
• Such an identification step is implemented by an identification module MI_D01 as shown in FIG. 8, said module being driven by the microprocessor ⁇ of the processing unit UT_D01.
• Said blocks Bq ; Bq 2 , Bq u , ..., Bq s are intended to be decoded according to a predetermined order of travel, which is for example of the sequential type, that is to say that they are intended to be decoded one after the other. other in the raster scan order where they were encoded.
• the decoder D01 selects as the current block a first block to be encoded Bq u of the image IC j , such as, for example, the first block Bq-,.
• the entropy decoding of the block Bq u is carried out .
• it is a CABAC entropic decoding.
• Such a step consists of: a) reading the symbol (s) of the predetermined set of symbols which are associated with said current residual block,
• Such an entropy decoding step is implemented by an entropy decoding software module MDE1 shown in FIG. 7, which module is controlled by the microprocessor ⁇ of the processing unit UT_D01.
• the entropy coding module MDE1 is for example of the CABAC type. It can also be a Huffman decoder known as such.
• dequantization of the block BDq u is carried out according to a conventional dequantization operation, which is the inverse operation of the quantization performed in step C16 of FIG. 1B.
• a decoded dequantized block BDt u is then obtained.
• step D5 the inverse transformation of the decoded dequantized block BDt u is carried out which is the inverse operation of the direct transformation performed in step C15 of FIG. decoded residue BDr u is then obtained.
• the steps D4 and D5 are implemented by a PRED "1 _D01 inverse predictive decoding software module represented in FIG. 7, which module is driven by the microprocessor ⁇ of the processing unit UT_D01.
• a set of Q candidate predictor blocks BP1 i, BP1 2 ,..., BP1 V ,..., BP1 is determined according to the invention.
• Q (1 ⁇ V ⁇ Q) Such candidate predictor blocks are, for example, blocks of pixels that have already been decoded or not. Such blocks are stored beforehand in the buffer MT_D01 of the decoder as shown in FIG. 7. In the example shown, it is in particular a predetermined number of blocks that have been decoded just before the current block. decode considered.
• Such a determination step is implemented by a DET_D01 determination software module shown in FIG. 7, which module is driven by the ⁇ microprocessor of the processing unit UT_D01.
• the identification method is carried out according to the invention, among all the Q predictor blocks BP1 ; BP1 2 , ..., BP1 v , ..., BP1 Q, of a preferential candidate predictor block BP1 op t.
• such an identification step is a function of the decoded residue block BDr u obtained.
• Said identification step is implemented by a calculation software module CAL1_D01 shown in FIG. 7, which module is controlled by the microprocessor ⁇ of the processing unit UT_D01.
• such an identification consists, for a current decoded residue block BDr u , of constructing a current decoded block BD U> W by adding to the residual block decoded current BDr u a candidate predictor block BP1 W (1 ⁇ w ⁇ Q).
• This criterion is a mathematical operator noted SM (BD UiW , IC j ).
• the operator SM (BD UiW , IC j ) is in fact representative of the quadratic error along the boundary F of the decoded residual block BDr u with the image IC j .
• W is the decoded block considered of size NxN pixels
• IC j (k, l) is the value of the pixel of the image IC j located on the k th line and the I th column of this image, and (lin, col) are the coordinates of the decoded block BD u> w in the image IC j .
• a simplified criterion can be used, in which the average of the pixels of the image ICj along the border F is compared with the average of the pixels of the decoded block BD U> W.
• the operator SM (BD UiW , ICj) is written then:
• step D7 the decoded block BDv.wmin is identified, which minimizes one of the two aforementioned criteria, such as:
• the block BDv.wmin is equal to the sum of the candidate predictor block BP1 wmin and the current decoded residue block BDr v .
• the candidate predictor block BP1 W min is considered as the preferential candidate predictor block BP1 op t for the inverse prediction of the current decoded residue block BDr u .
• the current block B u is reconstructed by adding to the decoded current residual block BDr u the preferential candidate predictor block BP1 op t identified in step D7.
• Said step D8 is implemented by a calculation software module CAL2_DO1 represented in FIG. 7, which module is driven by the microprocessor ⁇ of the processing unit UT_DO1.
• a decoded block BD U is then obtained and stored in the buffer memory MT_DO1 of FIG. 7, in order to be used by the decoder DO1 as a candidate predictor block of a next block to be decoded.
• step D9 said decoded block BD U is written in a decoded picture I Dj.
• a step is implemented by an image reconstruction software module URI1 as shown in FIG. 7, said module being driven by the microprocessor ⁇ of the processing module UT DO1.
• the decoder D01 tests whether the current block BD U that has just been decoded is the last block contained in the stream ⁇ .
• step D2 it is proceeded, in step D2, to the selection of the next residual block to be decoded according to the above-mentioned raster scan order.
• decoding method is implemented in a software or hardware way by modifying a decoder initially conforming to the HEVC standard.
• the decoding method according to the invention is represented in the form of an algorithm comprising steps D 1 to D 7 as represented in FIG. 9.
• a decoder D02 comprises a memory MEM_D02 comprising a buffer memory MT_D02, a processing unit UT_D02 equipped for example with a microprocessor ⁇ and controlled by a computer program PG_D02 which implements the decoding method according to the invention.
• the code instructions of the computer program PG_D02 are for example loaded into a RAM memory before being executed by the processor of the processing unit UT_D02.
• the decoding method shown in FIG. 9 applies to any current image of an SQ sequence of images to be decoded.
• the first decoding step D'1 is the identification:
• Such an identification step is implemented by an identification module MI_D02 as shown in FIG. 10, said module being controlled by the microprocessor ⁇ of the processing unit UT_D02.
• Said blocks Bq1 1; Bq1 2 , Bq1 u , ..., Bq1 s or Bq2 opt i, Bq2 opt 2,. . . , Bq2 op tu, ... Bq2 op ts are intended to be decoded according to a predetermined order of travel, which is for example sequential, ie the blocks are intended to be decoded one after the other in accordance with to the raster scan order where they were encoded.
• the decoder D 02 selects as a current block a first block to be coded B 1 u or B q 2 op t u of the image IC j , such as for example the first block B q 1 u or Bq2 op t u -
• the index Id associated with the selected block Bq u is read in the stream ⁇ 1 or ⁇ 2.
• Such a reading step is implemented by a reader software module ML_D02 as shown in FIG. 10, said module being driven by the microprocessor ⁇ of the processing unit UT_D02.
• index Id is equal to zero, it means that the current block to be decoded has undergone a primary prediction according to the steps C'610 to C'614 of the encoding method shown in Figure 5. It is therefore the flow ⁇ 1 that the decoder D02 is intended to treat.
• index Id Q
• step D 310 the entropic decoding of the block B q 1 u is carried out .
• step D3 Such a step being identical to the aforementioned step D3, it will not be described further.
• Such an entropy decoding step is implemented by an entropic decoding software module MDE1_D02 shown in FIG. 10, which module is controlled by the microprocessor ⁇ of the processing unit UT_D02.
• the entropy coding module MDE1_D02 is for example of CABAC type. It can also be a Huffman decoder known as such.
• step D 31 1 the dequantization of the block BDq1 u is carried out .
• Such a step being identical to the above-mentioned step D4, it will not be described further.
• a decoded dequantized block BDt1 u is then obtained.
• step D 312 the inverse transformation of the decoded dequantized block BD t 1 u is carried out .
• Such a step being identical to the aforementioned step D5, it will not be described further.
• a decoded residue block BDr1 u is then obtained.
• a predictor block BP1 is i- Such a step consists in adding to the residual decoded current block BDr1 u that the predictor block BP1 is classically selected.
• a decoded block BD U is then obtained following the step D4 and stored in the buffer memory MT_D02 of FIG. 10, in order to be used by the decoder D02 as a candidate predictor block of a next block to be decoded.
• the steps D 31 1 to D 4 are implemented by an inverse predictive decoding software module PRED1 "1 _D02 shown in FIG. 10, which module is driven by the microprocessor ⁇ of the processing unit UT_D02.
• step D shown in FIG. 9 said decoded block BD U is written in a decoded picture ID j .
• Such a step is implemented by an image reconstruction software module URI2 as represented in FIG. 10, said module being controlled by the microprocessor ⁇ of the processing module UT_D02.
• the decoder D02 tests whether the current block BD U that has just been decoded is the last block contained in the stream ⁇ 1.
• step D 2 it is proceeded, in step D 2, to the selection of the residual block according to Bq1 u to be decoded according to the aforementioned sequential order.
• the decoding method described above is then iterated for all the S blocks to be decoded.
• step D'320 the entropy decoding of the block Bq2 op t u is performed.
• Such a step being identical to the aforementioned step D3, it will not be described further.
• a decoded quantized block BDq2 op tu is then obtained at the end of this step.
• Such an entropy decoding step is implemented by an entropic decoding software module MDE2_D02 shown in FIG.
• step D 321 shown in FIG. 9 dequantization of the block BD q 2 op t u is performed. Such a step being identical to the aforementioned step D 4, it will not be described further. A decoded dequantized block BDt2 op t u is then obtained.
• step D 322 shown in FIG. 9 the reverse transformation of the decoded dequantized block BD t 2 op t u is carried out. - Such a step being identical to the aforementioned step D 5, it will not be described any further. .
• a decoded residue block BDr2 op t u is then obtained. Said block The decoded residual BDr2 op t u is then stored in the buffer memory MT_D02 of FIG. 10, in order to be used by the decoder D02 as a candidate predictor block of a next block to be decoded.
• the steps 321 and 322 are D'implemented by a predictive decoding software module inverse Pred2 "1 _D02 shown in Figure 10, which module is controlled by the microprocessor of the ⁇ UT_D02 processing unit.
• a set of Q candidate predictor blocks BP2 1 is determined according to the invention ; BP2 2, ..., V BP2, ..., BP2 Q (1 ⁇ v ⁇ Q). Since such a step is identical to step D6 of FIG. 8, it will not be described further.
• Such a determination step is implemented by a DET_D02 determination software module shown in FIG. 10, which module is driven by the microprocessor ⁇ of the processing unit UT_D02.
• the method according to the invention is used to identify, among the set of Q predictor blocks BP 2 1; BP2 2 ,..., BP2 V ,..., BP2 Q , of a preferential candidate predictor block BP2 op t.
• an identification step is a function of the decoded residue block BDr2 op t z obtained.
• Said identification step is implemented by a calculation software module CAL1_D02 shown in FIG. 10, which module is controlled by the microprocessor ⁇ of the processing unit UT_D02.
• the decoding method uses a criterion for minimizing the difference between the decoded pixels of the current image IC j , which are represented by dots in FIG. 4, and the pixels of decoded block BDr1 u> w located along its border F.
• This criterion is a mathematical operator denoted SM (BDr1 UiW , ICj).
• BDr1 u is the decoded block considered of size NxN pixels
• BDr1 UiW (n, m) is the value of the pixel of the decoded block BDr1 u> w located on the nth row and the mth column of this block,
• ICj is the current image
• ICj (k, l) is the value of the pixel of the image ICj located on the kth row and the ith column of this image, and (lin, col) are the coordinates of the decoded residue block BDr1 u> w in the image ICj.
• a simplified criterion can be used in which the average of the pixels of the image ICj along the boundary F is compared with the average of the pixels of the decoded block BDr1 u> w .
• the operator SM (BDr1 UiW , ICj) is written then:
• the decoded block BDr1 v , wmin is identified which minimizes one of the two aforementioned criteria, such as:
• the block BDr1 v , wmin is equal to the sum of the candidate predictor block BP2 wmin and the current decoded residue block BDr2 op t u -
• the candidate predictor block BP2wmin is considered as the preferential candidate predictor block BP2 opt for the inverse prediction of the current decoded residue block BDr2 op t u -
• the residual current block BD r u is reconstructed by adding to the residual decoded current block BD R 2 op t u the preferential candidate predictor block BP 2 opt identified in step On 324.
• Said step D'325 is implemented by a calculation software module CAL2_D02 shown in FIG. 10, which module is driven by the microprocessor ⁇ of the processing unit UT_D02.
• step D 4 and D 5 are then repeated to deliver a current block BD U.
• step D6 is again implemented to test if the current block BD U is the last block of the image.

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