Classifications

• • 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
  • H04N19/70—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
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/10—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
• • 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
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • 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
  • H04N19/136—Incoming video signal characteristics or properties
• • 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
  • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
  • 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
  • H04N19/167—Position within a video image, e.g. region of interest [ROI]
• • 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
  • H04N19/10—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
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
  • H04N19/46—Embedding additional information in the video signal during the compression process
• • 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
  • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
  • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding

Definitions

• the present invention relates generally to the field of image processing, and more specifically to coding and decoding of digital image parameters, whether these digital images are fixed or part of a digital image sequence.
• the coding / decoding of such image parameters applies in particular to images originating from at least one video sequence comprising:
• the present invention applies similarly to the coding / decoding of 2D or 3D type image parameters.
• 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 image parameters associated with this block are coded in the form of bits using a suitable coding method implemented.
• an encoder such as for example an entropic encoder whose purpose is to encode these parameters without loss.
• the bits obtained after entropy coding are written in a data signal which is intended to be transmitted to the decoder.
• cbf abbreviation for "Coded Block Flag”
• the decoding is done image by image, and for each image, block by block. For each block, the bits representative of the image parameters associated with the block are read and then decoded using a decoding method implemented by a decoder.
• this projection is of the Mercator, equirectangular type, of the CMP (abbreviation of "Cube Map Projection") type, etc.
• CMP abbreviation of "Cube Map Projection”
• the upper and lower areas of this image contain the most deformations that the rest of the image.
• the coding of the parameters associated with the blocks contained in these particular zones is not effective, which furthermore leads to an unnecessary decrease in the gain in flow rate.
• the invention therefore aims at optimizing the signaling cost of the image coding parameters, by implementing a selective coding of these coding parameters which takes into account, at a first level, the characteristic of the image to be coded, and at a second level, the arrangement of the current block to be encoded in this image.
• 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, implementing the following:
• a second syntax element representative of the value of said at least one coding parameter is coded only if the current block belongs to a zone predefined image
• the second syntax element is encoded, whether the current block belongs to the predefined zone or not.
• Such an arrangement makes it possible to avoid coding, then transmitting to the decoder, at least one syntax element representative of a coding parameter of a block, taking into account not only that such a block is located in a block. specific area of the image, for which the coding of this syntax element is not useful in view of the current image coding context, but also of a characteristic of the image to be coded in which the block is located current.
• the coding of the second syntax element representative of the value of said at least one coding parameter is implemented according to a dependent criterion. characteristics of the current block.
• Such an arrangement also makes it possible to implement an adaptive coding of at least one syntax element representative of a coding parameter of a block, according to the value of a criterion depending on the characteristics of the current block, such as by example the size, the value of the residual pixels of this block, the type of transform applied to the residual pixels of this block if the latter has undergone a prediction, etc.
• a criterion depending on the characteristics of the current block, such as by example the size, the value of the residual pixels of this block, the type of transform applied to the residual pixels of this block if the latter has undergone a prediction, etc.
• the characteristic of said at least one image is the type of obtaining said at least one image.
• the current image is a two-dimensional image, it is decided:
• the characteristic of said at least one image is the current encoding context of the image.
• coding level of different quality in the case of image coding applied to medical imaging, it is decided to apply to at least two different areas of the current image a coding level of different quality so as to:
• the invention relates to a device for encoding at least one image cut into blocks, comprising a processing circuit which is arranged for:
• a current block for a current block to be encoded associated with at least one coding parameter, coding the data of the current block.
• the first syntax element is encoded according to a first predefined value representative of the characteristic of the image, coding a second syntax element representative of the value of said at least one coding parameter, only if the current block belongs to a zone predefined image,
• the first syntax element is coded according to a second predefined value representative of the characteristic of the image, coding the second syntax element, whether the current block belongs to the predefined zone or not.
• the invention also relates to a method of decoding a data signal representative of at least one coded picture having been cut into blocks, implementing the following: decoding a first syntax element contained in said data signal, said first syntax element being associated with a characteristic of said at least one image,
• a current block for a current block to be decoded associated with at least one coding parameter, to decode the data of the current block.
• a second syntax element representative of the value of said at least one coding parameter is decoded only if the current block belongs to a predefined zone of the image
• the second syntax element is decoded, whether the current block belongs to the predefined zone or not.
• the decoding of the second syntax element representative of the value of said at least one coding parameter is implemented according to a dependent criterion. characteristics of the current block.
• the characteristic of said at least one image is the type of obtaining said at least one image.
• the characteristic of said at least one image is the current decoding context of the image.
• the invention relates to a device for decoding a data signal representative of at least one coded picture having been cut into blocks, comprising a processing circuit which is arranged for:
• decoding a first syntax element contained in the data signal the first syntax element being associated with a characteristic of said at least one image, for a current block to be decoded associated with at least one coding parameter, to decode the data of the current block.
• Such a decoding device is remarkable in that the processing circuit is arranged for:
• the first syntax element has a first predefined value representative of the characteristic of the image, decoding a second syntax element representative of the value of said at least one coding parameter, only if the current block belongs to a predefined zone of the image,
• the first syntax element has a second predefined value representative of the characteristic of the image, decoding the second syntax element, whether the current block belongs to the predefined zone or not.
• 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.
• Such a 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 another desirable form.
• Still another object of the invention is directed to a computer readable recording medium, and including computer program instructions as mentioned above.
• the recording medium may be any entity or device capable of storing the program.
• the medium may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, a USB key, or a magnetic recording means, for example a hard disk.
• such a 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.
• such a recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute the method in question or to be used in the execution of the latter.
• FIG. 1A represents the steps of the coding method according to one embodiment of the invention
• FIG. 1B represents an alternative of the coding method of FIG. 1A
• FIG. 2 represents a coding device according to one embodiment of the invention
• FIG. 3A represents an image divided into blocks according to a first embodiment
• FIG. 3B represents an image divided into blocks according to a second embodiment
• FIGS. 4A to 4D each represent examples of predefined zones in the current image, in the case of a particular obtaining of the current image,
• FIG. 5A represents a current image in a coding / decoding context where the coder / decoder chooses to apply or not to apply a different level of coding / decoding quality to at least two zones of the current image
• FIG. 5B represents an example of a predefined zone in the current image, in the case where the coder / decoder chooses to apply or not to apply a different quality of coding / decoding level to at least two zones of the current image,
• FIG. 6A represents the steps of the decoding method according to one embodiment of the invention.
• FIG. 6B represents an alternative of the decoding method of FIG. 6A
• FIG. 7 represents a decoding device according to one embodiment of the invention.
• the coding method according to the invention is used to code an image or a sequence of images according to a bit stream close to that obtained by a coding set.
• the coding method according to the invention is used to code an image or a sequence of images according to a bit stream close to that obtained by a coding set.
• the coding method according to the invention is for example implemented in a software or hardware way by modifications of such an encoder.
• the coding method according to the invention is represented in the form of an algorithm comprising operations C1 to C9 as represented in FIG. 1A.
• the coding method according to the invention is implemented in a coding device or coder CO shown in FIG.
• the coder CO comprises a memory MEM_C comprising a buffer memory MT_C, a processor PROC_C controlled by a computer program PG_C which implements the coding method according to the invention.
• the code instructions of the computer program PG_C are for example loaded into a RAM, denoted MR_C, before being executed by the processor PROC_C.
• the encoding method shown in Fig 1 A apply to the entire current image IC j fixed or part of a sequence of L IC-i images, IC j, ..., IC L (1 ⁇ j ⁇ L ) to code.
• the current image IC j comes from at least one video sequence comprising, by way of non-exhaustive examples:
• C1 is, in a manner known per se, the cutting of a current image IC j into a plurality of blocks Bi, B 2 , B u , ..., B s (1 ⁇ u ⁇ S).
• the partitioning is implemented by a partitioning device MP_C shown in FIG. 2, which device is controlled by the processor PROC_C.
• block means coding unit ("coding unit”).
• coding unit means coding unit
• This last terminology is notably used in the standard HEVC "ISO / IEC / 23008-2 Recommendation ITU-T H.265 High Efficiency Video Coding (HEVC)”.
• 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 B ; B 2 , B u , ..., B s are intended to be coded according to a predetermined order of travel, which is for example of the lexicographic type. This means that the blocks are coded one after the other, from left to right.
• the blocks Bi, B 2 , B u , ..., B s have a square shape and all contain K pixels, with K> 1.
• the blocks B ; B 2 , B u , ..., B s are obtained at the end of a single subdivision of the current image IC j into blocks of maximum size.
• the blocks have a size of for example 64 ⁇ 64 pixels.
• the blocks B ; B 2 , B u , ..., B s are obtained at the end of a subdivision of the current image ICj into blocks of size less than or equal to the maximum size mentioned above.
• said blocks are, for example, 64 ⁇ 64 and / or 32 ⁇ 32 and / or 16 ⁇ 6 and / or 8 ⁇ 8 pixels.
• the last blocks on the left and the last blocks on the bottom may not be square.
• the blocks may be for example of rectangular size and / or not aligned with each other.
• the syntax element ESi is a high level syntax element of a video sequence including the current image ICj.
• this element can be coded:
• VCES1 i which is representative of a characteristic of a first type of the current image ICj
• VCES1 2 which is representative of a characteristic of a second type of the current image
• the coding C2 is for example a entropic coding of type CABAC
• the characteristic of the image ICj is the type of obtaining of the latter.
• the characteristic of the image ICj is the type of obtaining of the latter.
• VCES1 1 1
• VCES1 2 0.
• the characteristic of the image IC j is the choice of the encoder to apply or not a coding quality level different to at least two areas of the current image to be encoded.
• the characteristic of the image IC j is the choice of the encoder to apply or not a coding quality level different to at least two areas of the current image to be encoded.
• VCES1 i 1, which indicates that the central zone of the current image is coded according to a level of higher quality than the one applied to the peripheral zone of the current image,
• VCES1 2 0 which indicates that a same level of coding quality is applied to the whole current image .
• the coder CO of FIG. 2 selects as current block a first block to be coded B u of image IC j , such as for example the first block Bi.
• the current block B u is associated with at least one coding parameter.
• a coding parameter is:
• the prediction mode (intra prediction, inter prediction, bi-prediction, prediction by default carrying out a prediction for which no information is transmitted to the decoder (in English "skip");
• DCT 4x4, DCT 8x8 applied to the current block or to the residual pixels of the current block if the latter has undergone a prediction
• a filtering of the current image IC j once coded such as for example that practiced by the technique "Sample Adaptive "Offset” of the HEVC standard (described in Chih-Ming Fu, Alshina, Alshin, Yu-Wen Huang, Ching-Yeh Chen, Chia-Yang Tsai, Chih-Wei Hsu, Shaw-Min Lei; Jeong-Hoon Park, Woo-Jin Han “Sample Adaptive Offset in the HEVC Standard” Published in: IEEE Transactions on Circuits and Systems for Video Technology (Volume: 22, Issue: 12, Dec. 2012);
• the index of the intra prediction mode from a list constructed for the current block
• a filter indicator of the reference pixels that were used to predict the current block
• a second element of syntax ES 2 is representative of the value of said at least one coding parameter.
• the coder CO reads the coded value VCES1 or VCES1 2 of the ES-i syntax element.
• the coded value of the syntax element ESi is VCES1 i and if, in C5, the current block B u belongs to a predefined zone of the current image IC j , it is decided in C6 not to encode the ES 2 syntax element.
• the syntax element ES 2 is set to a predefined value. Such an operation is particularly suitable when the information density of the predefined area of the image is low or very low.
• ES 2 if the element of syntax ES 2 is representative of the prediction mode of the current block B u and that, for example, ES 2 takes:
• ES 2 is representative of the value of the residual pixels of the current block B u and that, for example, ES 2 takes:
• the predefined values VES2 and VES2 2 of the second element of syntax ES 2 are previously stored in an LTSi list which is stored in the buffer memory MT_C of the encoder CO of FIG. 2.
• the coded value of the syntax element ESi is VCES1 i and if, in C5, the current block B u does not belong to the predefined zone of the current image, the predefined value VES2 or VES2 2 taken by the second element of syntax ES 2 is coded in C7. At the end of this coding C7, according to the current coding context, a coded value VCES2i or VCES2 2 of the second syntax element ES 2 is obtained.
• ES 2 if the element of syntax ES 2 is representative of the prediction mode of the current block B u and that, for example, ES 2 takes:
• VES2 a first predefined value indicating an inter prediction of the current block B u
• the syntax element ES 2 is representative of the value of the residual pixels of the current block B u and that, for example, ES 2 takes:
• VES2 or VES2 2 of the element of syntax ES 2 is systematically coded in C7, for example the value , respectively, depending on the current coding context.
• Such coding is, for example, entropic coding of CABAC type ("Context Adaptive Binary Arithmetic Coder" in English) or else an entropy coding of arithmetic type or Huffman type.
• This coding is implemented by an encoding device MC_C represented in FIG. 2.
• the coded value of the syntax element ESi is VCES1 2
• the value VES2 or VES2 2 of the syntax element ES 2 is systematically coded at C7, for example the value , respectively, depending on the current coding context.
• the current image IC j is for example a 2D image obtained by two-dimensional projection of a 180 ° or 330 ° video
• FIG. 4A shows the current image IC j as a 2D image obtained by two-dimensional projection of a 360 ° video.
• a first predefined zone, denoted Z1 of the current image IC j has a height H1 such that 0.2H ⁇ H1 ⁇ 0.8H.
• the blocks contained in the zone Z1 contain the pixels resulting from the projection in the current image IC j of the pixels closest to the equator of the image captured by a 360 ° video capture sphere and thus undergoing little deformation.
• the blocks contained in the zones predefined remaining image, denoted Z2 in Figure 4A contain the pixels resulting from the projection in the image IC j pixels located near the poles of the sphere of 360 ° video capture and thus undergoing maximum deformation.
• FIG. 4B shows the current image IC j as an image
• the predefined zone Z1 of the current image IC j has a height H1 such that 0 ⁇ H1 ⁇ 0.8H.
• the blocks contained in the zone Z1 are the blocks containing the pixels resulting from the projection in the current image IC j of the pixels closest to the equator of the image captured by a half-sphere of video capture 180 ° and undergoing thus little deformation.
• the blocks contained in the predefined zone Z2 of the image are the blocks containing the pixels resulting from the projection in the IC image j of the pixels located near the north pole of the 180 ° video capture sphere and thus undergoing maximum deformation.
• FIG. 4C shows the current image IC j as an image
• a first predefined zone Z1 of the current image IC j has a height H1 such that 0.2H ⁇ H1 ⁇ H.
• the blocks contained in the zone Z1 are the blocks containing the pixels resulting from the projection in the image IC j of the pixels closest to the equator of the image captured by a half-sphere of video capture 180 ° and thus undergoing little deformation.
• the blocks contained in the predefined remaining zone Z2 of the current image IC j are the blocks containing the pixels resulting from the projection in the image IC j of the pixels located near the south pole of the 180 ° video capture sphere and undergoing maximum deformation.
• FIG. 4D shows the current image IC j as an image
• a predefined zone, denoted Z1 of the current image IC j has a height H1 such that 0.2H ⁇ H1 ⁇ 0.8H.
• the blocks contained in the zone Z1 are the blocks containing the pixels resulting from the projection in the current image IC j of the pixels closest to the equator of the image captured by a 360 ° video capture sphere and thus undergoing little deformation.
• Image IC j also contains two other predefined zones Z2 situated on either side of zone Z1.
• a first zone Z2 has a height H2 such that 0.1 H ⁇ H2 ⁇ 0.2H.
• Blocks contained in the zone Z2i of the current image IC j are the blocks containing the pixels resulting from the projection in the image IC j of the pixels located closest to the last line before the south pole of the 360 ° video capture sphere and thus undergoing moderate deformation.
• a second zone Z2 2 has a height H2 2 such that 0.8H ⁇ H2 2 ⁇ 0.9H.
• the blocks contained in the zone Z2 2 of the current image IC j are the blocks containing the pixels resulting from the projection in the image IC j of the pixels situated closest to the first line before the north pole of the capture sphere 360 ° video and thus undergoing moderate deformation.
• Image IC j also contains two other predefined zones situated respectively on either side of zones Z2i and Z2 2 .
• a first zone Z3i has a height H3i such that 0 ⁇ H3i ⁇ 0.1 H.
• the blocks contained in the zone Z3i of the current image IC j are the blocks containing the pixels resulting from the projection in the image IC j of the pixels located closest to the south pole of the 360 ° video capture sphere and thus undergoing maximum deformation.
• a second zone Z3 2 has a height H3 2 such that 0.9H ⁇ H3 2 ⁇ H.
• the blocks contained in the zone Z3 2 of the current image IC j are the blocks containing the pixels resulting from the projection in the image IC j of the pixels located closest to the north pole of the 360 ° video capture sphere and undergoing thus a maximum deformation.
• predefined areas of the current image IC j it is of course possible to define predefined areas of the current image IC j differently.
• the current image IC j is for example a 2D image obtained by CMP projection of a 180 ° or 360 ° video
• one or more specific areas are predefined as a function of the proximity of the pixels relative to each other. at the edges of the cubes used for projection.
• the zones may be defined by the value of a function depending on the coordinates of the block in the current image IC j , or of its processing order among all the blocks of the current image IC j .
• the pixels whose distance from the center of the image is greater than a threshold define a first zone, the other pixels defining a second zone.
• the given pixel PxD belongs to the first zone Z1 if and only if the square root of the value (xc-xp) 2 + (yc-yp) 2 is greater than a threshold T1.
• the given pixel PxD belongs to the first zone Z1 if and only if one of the values
• FIG. 5A represents an example of a current image IC j , for which the characteristic of the image IC j is the choice of the encoder to apply or not a coding quality level different to at least two zones of the current image. .
• VCES1 i 1 to indicate that a first zone of the current image is coded according to a level of NQ1 coding quality less than a NQ2 coding quality level applied to a second zone of the current image
• VCES1 2 0 to indicate that a same level of quality of NQ coding is applied to any zone of the image common.
• FIG. 5B shows an example of predefined zones in the current image IC j .
• the current image CI j includes:
• a first predefined zone Z1 such as for example the peripheral zone of the current image IC j , whose information density is low and for which the quality level of coding NQ1 is applied,
• At least one second predefined zone Z2 such as for example the central zone of the current image IC j , whose information density is higher and for which the quality level of coding NQ2 is applied.
• the given pixel belongs to the first zone Z1 if and only if one of the values
• the data of the current block B u are encoded C8.
• such an encoding C8 implements the application C81 of a transform to the data of the current block B u .
• data means the pixels of the current block B u .
• data are also understood to mean the pixels of a predicted block obtained by means of a prediction of the current block B u with respect to a predictor block that is selected following a call for competition.
• different prediction modes inter, intra or other predetermined, for example by minimizing a distortion rate criterion well known to those skilled in the art.
• Such a transform is for example a DCT (abbreviation of "Discrete Cosine Transform"), DST (abbreviation of "Discrete Sine Transform”) ), type DWT (abbreviation of "Discrete Wavelet Transform”) or type LT (abbreviation of "Lapped Transform”).
• DCT abbreviation of "Discrete Cosine Transform”
• DST abbreviation of "Discrete Sine Transform”
• type DWT abbreviation of "Discrete Wavelet Transform”
• type LT abbreviation of "Lapped Transform”
• Such an operation is performed by a transform calculation device MTR_C, as represented in FIG. 2, which device is controlled by the processor PROC_C.
• the coding C8 further implements a quantization C82 of the data of the transformed block Bt u according to a conventional quantization operation, such as, for example, a scalar or vector quantization.
• a block Bq u of quantized coefficients is then obtained.
• the quantization C82 is implemented by a quantization device MQ_C as represented in FIG. 2, which device is controlled by the processor PROC_C.
• the transform calculation device MTR_C and the quantization device MQ_C are contained in a block coding device MCB_C shown in FIG. 2, which device is controlled by the processor PROC_C.
• the coding C8 also implements a coding C83 of the data of the block Bq u of quantized coefficients.
• the coding C83 is implemented by the coding device MC_C of FIG. 2. At the end of the coding C83 is obtained a coded data set DC U of the current block B u .
• a signal or data stream F which contains:
• the stream construction C9 is implemented by a data signal construction device MCF, as shown in FIG. 2.
• the data signal F is then transmitted by a communication network (not shown) to a remote terminal.
• the data signal F may furthermore comprise certain information encoded by the coder CO, such as, for example:
• decoding (not shown) of the coded DC U data obtained at C8 is then carried out.
• a current decoded block BD U is then reconstructed, such a reconstructed block being 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 thus made available for use by the coder CO of FIG. 2.
• This variant differs from the coding method of FIG. 1A only in that:
• the value VES2i or VES2 2 of the second element of syntax ES 2 can be coded even if the current block B u belongs to the predefined zone of the current image IC j .
• VES2 or VES2 2 of the second element of syntax ES 2 is coded in C7.
• C60 If the criterion is not fulfilled, it is decided in C60 not to encode the value VES2i or VES2 2 of the second element of syntax ES 2 . It is then decided in C60 to assign ES 2 to the first predefined value VES2 or to the second predefined value VES2 2 according to the current coding context. In the case where the current block B u does not belong to the predefined area of the current image IC j , a criterion dependent on the characteristics of the current block is examined at C51.
• VES2 or VES2 2 of the second element of syntax ES 2 is coded in C7.
• C61 If the criterion is not fulfilled, it is decided in C61 not to encode the second element of syntax ES 2 . It is then decided in C61 to assign ES 2 to the first predefined value VES2 or to the second predefined value VES2 2 according to the current coding context.
• VCES1 2 a criterion depending on the characteristics of the current block is examined in C52.
• VES2 or VES2 2 of the second element of syntax ES 2 is coded in C7.
• C62 If the criterion is not fulfilled, it is decided in C62 not to encode the second element of syntax ES 2 . It is then decided in C62 to assign ES 2 to the first predefined value VES2i or to the second predefined value VES2 2 according to the current coding context.
• the value VES2i or VES2 2 of the element of syntax ES 2 is compared with a value of predetermined size VTP.
• the current image IC j is for example a 2D image obtained by projection in two dimensions of a 180 ° or 360 ° video:
• the current block B u does not belong to the predefined zone Z1, in other words belongs to the predefined zone Z2 of the current image ICj, and
• the current image ICj shown in FIG. 4D for which the coded value VCES1 i of the syntax element ES ⁇ indicates for example that the current image ICj is for example a 2D image obtained by projection in two dimensions of a 360 ° video:
• the size of the current block is greater than a predetermined value VTP, for example 32x32, the value VES2-I or VES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is coded in C7,
• C51 it is determined as a criterion that the size of the current block is much greater than a predetermined value VTP, for example 1 6 ⁇ 16, the value VES2-I or VES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is coded in C7, Otherwise, it is decided in C61 not to encode the second element of syntax ES 2 , the latter being assigned to the first predefined value VES2 or to the second predefined value VES2 2 according to the current coding context,
• the size of the current block is greater than a predetermined value VTP, for example 32x32, the value VES2-I or VES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is coded in C7,
• the current block B u does not belong to the predefined zone Z1, in other words belongs to the predefined zone Z2 of the current image ICj, and
• C52 If in C52 (FIG. 1B), it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 8 ⁇ 8, the value VES2 or VES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is coded in C7,
• the decoding method according to the invention is for example implemented in a software or hardware way by modifications of such a decoder.
• the decoding method according to the invention is represented in the form of an algorithm comprising operations D1 to D10 as represented in FIG. 6A.
• the decoding method according to the invention is implemented in a decoding device or decoder DO represented in FIG.
• the decoder DO comprises a memory MEM_D which itself comprises a buffer memory MT_D, a processor PROC_D controlled by a computer program PG_D which implements the method decoding device according to the invention.
• the code instructions of the computer program PG_D are for example loaded into a RAM RAM_D noted, before being executed by the PROC_D processor.
• the decoding method shown in Figure 6A applies to any fixed coded current picture IC j or part of a sequence of L IC-i images, IC j, ..., IC L (1 ⁇ j ⁇ L ) to decode.
• the current image IC j to be decoded originates from at least one video sequence comprising, as non-exhaustive examples:
• the coded value VCES1 i or VCES1 2 is identified in the signal F of a first syntax element ES 1 which is associated with a characteristic of the current image ICj to be decoded.
• the syntax element ES ⁇ is a high-level syntax element of a video sequence comprising the current image ICj to be decoded. For this purpose, depending on the decoding context, this element can be decoded:
• identification D1 is implemented by a PARS_D flow analysis device, as shown in Figure 7, said device being controlled by the PROC_D processor.
• Such a decoding D2 is implemented by a decoding device MD_D shown in FIG. 7, which device is controlled by the processor PROC_D.
• the decoding is for example a CABAC entropic decoding or an arithmetic or Huffman entropy decoding.
• the characteristic of the image ICj is the type of obtaining of the latter.
• the characteristic of the image ICj is the type of obtaining of the latter.
• the image ICj is for example a 2D image which has been obtained by two-dimensional projection of a conventional 360 ° video, it is the coded value VCES1 1 of the syntax element ES ⁇ which is decoded,
• the image ICj is for example a conventional 2D image of fixed type or part of a sequence of images succeeding each other temporally, it is the coded value VCES1 2 of the syntax element ES1 which is decoded.
• the characteristic of the image ICj is the choice of the decoder to apply or not a decoding quality level different to at least two areas of the current image. For this purpose:
• the identification of the coded data Dd, DC 2 ,..., DC U , DCs (1 u u S S) associated with the B blocks is carried out at D3. ; B 2 , B u ,..., B s previously encoded in accordance with the above-mentioned lexicographic order, which were obtained at the end of coding operation C8 of FIG. 1 A. This means that the blocks are decoded one after the other, from left to right.
• Such identification D3 is implemented by the PARS_D flow analysis device of FIG. 7.
• the blocks Bi, B 2, B u, ..., B s have a square shape and contain all pixels K, with K> 1.
• the blocks B ; B 2 , B u , ..., B s are obtained at the end of a single subdivision of the current image ICj into blocks of maximum size.
• the blocks have a size of for example 64 ⁇ 64 pixels.
• the blocks B ; B 2 , B u , ..., B s are obtained at the end of a subdivision of the current image ICj into blocks of size less than or equal to the maximum size mentioned above.
• said blocks are for example of size 64x64, and / or 32x32, and / or 1 6x1 6, and / or 8x8 pixels.
• the last blocks on the left and the last blocks on the bottom may not be square.
• the blocks may be for example of rectangular size and / or not aligned with each other.
• the decoder DO of FIG. 7 selects as current block to be decoded a first set of coded data DC U of the image IC j , such as for example the first set of associated coded data DCi at the first block Bi to be decoded.
• All encoded data DC U B u current block is associated with at least one encoding parameter.
• a coding parameter is:
• the prediction mode (intra prediction, inter prediction, bi-prediction, prediction by default carrying out a prediction for which no information is transmitted to the decoder (in English "skip");
• DCT 4x4, DCT 8x8 applied to the current block or to the residual pixels of the current block if the latter has undergone a prediction
• Offset of the HEVC standard (described in Chih-Ming Fu, Alshina, Alshin, Yu-Wen Huang, Ching-Yeh Chen, Chia-Yang Tsai, Chih-Wei Hsu, Shaw-Min Lei; Jeong-Hoon Park, Woo-Jin Han “Sample Adaptive Offset in the HEVC Standard” Published in: IEEE
• a filter indicator of the reference pixels that were used to predict the current block
• a second element of syntax ES 2 is representative of the value of said at least one coding parameter.
• DO decoder reads in the case of the encoded value VCES1 VCESI or i 2 of the syntax element ES 1 which has been decoded by D2.
• the syntax element ES 2 is set to a predefined value. Such an operation is particularly suitable when the information density of the predefined area of the image is low or very low.
• ES 2 is representative of the prediction mode of the current block B u to be decoded and that, for example, ES 2 takes:
• VES2 a first predefined value indicating an inter prediction of the current block B u
• ES2 2 indicating an intra prediction of the current block B u
• ES 2 is representative of the value of the residual pixels of the current block B u and that, for example, ES 2 takes:
• the predefined values VES2 and VES2 2 of the second syntax element ES 2 are previously stored in an LTS-i list in the buffer MT_D of the decoder DO of FIG. 7.
• ES 2 is representative of the prediction mode of the current block B u and that, for example, ES 2 has been coded:
• VCES2 0 indicating an inter prediction of the current block B u
• VCES2 2 1 indicating an intra prediction of the current block B u
• ES 2 is representative of the value of the remaining pixels of the current block B u and that, for example, ES 2 was coded:
• VCES2 2 1 indicating residual pixels of non-zero value of the current block B u ,
• Such a decoding is for example an entropic decoding of type
• CABAC Context Adaptive Binary Arithmetic Coder
• entropy decoding of arithmetic type or Huffman. This decoding is implemented by the decoding device MD_D shown in FIG. 7.
• the coded value VCES2 or VCES2 2 of the ES 2 syntax element is systematically decoded to D8.
• the data of the current block B u are decoded at D9.
• Such decoding is implemented by a block decoding device MDB_D shown in FIG. 7, which device is controlled by the PROC_D processor.
• the decoding D9 implements, in D91, a decoding of the DC U data associated with the current block B u to be decoded and which have been coded in C8 in FIG. 1 A. At the end of such a decoding, is obtained a set of numerical information associated with the quantized coefficient block Bq u that has been obtained in
• the decoding D91 is implemented by the decoding device
• the decoding D9 further implements a dequantization D92 of the quantized coefficient block Bq u , according to a conventional dequantization operation which is the inverse operation of the quantization C82 of FIG. 1 A.
• a set of current dequantized coefficients BDq u is then obtained.
• Such dequantization is for example of scalar or vector type and is implemented by means of an inverse quantization device MQ "1 _D, as shown in FIG. 7, which device is controlled by the processor PROC_D.
• the decoding D9 further implements the application D93 of a transform to the set of dequantized coefficients BDq u current obtained in D92.
• a transform is an inverse transform from that applied to the C81 coding in FIG. 1A, such as, for example, a DCT, DST, DWT, LT or other transform.
• these transforms are part of a list of LTS transforms 2 "1 which is previously stored in the buffer MT_D of the decoder DO of FIG. 7.
• the type of transform to be applied can be decoded conventionally, by reading, in the data signal F, the index of the transform applied to the coding According to the invention, the type of transform to be applied can be determined by the implementation of the operation D5 of Figure 6A.
• the transformation application D93 is performed by a transform calculation device MTR "1 _D, as shown in FIG. 7, which device is controlled by the processor PROC_D.
• the inverse quantization device MQ "1 _D and the transform calculation device MTR " 1 _D are contained in a block decoding device MDB_D shown in FIG. 7, which device is controlled by the PROC_D processor.
• a current decoded block BD U is obtained.
• data are understood to mean the pixels of the decoded block BD U.
• data are also understood to mean the pixels of a decoded current residue block in the case where a prediction of the block current B u was implemented at the coding and inverse prediction is implemented at decoding.
• the writing D10 is implemented by an image reconstruction URI device as represented in FIG. 7, the URI device being controlled by the PROC_D processor.
• the decoding method which has just been described above is implemented for all the coded data of blocks Dd, DC 2 , DC U ,..., DCs respectively associated with the blocks Bi, B 2 , B u ,. .., B s to decode the current image IC j considered.
• This variant differs from the decoding method of FIG. 6A only in that:
• VCES2i or VCES2 2 of the second element of syntax ES 2 can be decoded even if the current block B u belongs to the predefined zone of the current image IC j .
• VCES2 or VCES2 value 2 of the second ES 2 syntax element is decoded at D8.
• the syntax element ES 2 is set, depending on the context decoding stream, directly to the set value VES2-I or VES2 2 as stored in the list of the decoder LTSI OD of Figure 7.
• the encoded data set DC U is associated with a current block B u which does not belong to the predefined area of the current image IC j .
• a criterion depending on the characteristics of the current block is examined in D61. If the criterion is satisfied, the VCES2i or VCES2 2 value of the second ES 2 syntax element is decoded to D8.
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2i or VES2 2 as stored in the LTSi list of the decoder DO of Figure 7.
• VCES2i or VCES2 2 value of the second ES 2 syntax element is decoded to D8.
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2i or VES2 2 as stored in the LTSi list of the decoder DO of Figure 7.
• the I-value or VES2 VES2 2 of the syntax element ES 2 is compared with a predetermined size value VTP.
• the coded data set DC U is associated with a current block B u which belongs to a predefined zone Z1, and
• the size of the current block is greater than a predetermined value VTP, for example 32x32, the coded value VCES2i or VCES2 2 of the second element of syntax ES 2 representative of the size of the current block
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2i or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7,
• the current block B u does not belong to the predefined zone Z1, in other words belongs to the predefined zone Z2 of the current image IC j , and
• D61 If in D61, it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 16 ⁇ 16, the value VCES 2 1 or VCES 2 2 of the second syntax element ES 2 representative of the size of the current block B u is decoded in D8,
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7.
• D62 If in D62 (FIG. 6B), it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 8x8, the coded value VCES2 or VCES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is decoded in D8, Otherwise, in D72, the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7.
• VTP for example 8x8
• the coded data set DC U is associated with a current block B u which belongs to the predefined zone Z1, and
• D60 If in D60, it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 32x32, the coded value VCES2i or VCES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is decoded in D8,
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTS 1 of the decoder DO of FIG. 7,
• the current block B u belongs to the predefined zone Z2 of the current image IC j .
• D61 If in D61, it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 16 ⁇ 16, the coded value VCES 2 1 or VCES 2 2 of the second syntax element ES 2 representative of the size of the current block B u is decoded in D8,
• the ES 2 syntax element is set, depending on the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the LTSi list of the decoder DO of FIG. 7,
• D62 If in D62, it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 8x8, the value VCES2 1 or VCES2 2 of the second syntax element ES 2 representative of the size of the current block B u is decoded in D8,
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7.
• the coded data set DC U is associated with a current block B u which belongs to a predefined zone Z1, and
• D60 If in D60, it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 32x32, the coded value VCES2i or VCES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is decoded in D8,
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7, if in D6 (FIG. 6B), the current block B u does not belong to the predefined zone Z1, in other words belongs to the predefined zone Z2 of the current image ICj, and
• D61 If in D61, it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 1 6 ⁇ 16, the value VCES 2 1 or VCES 2 2 of the second element of syntax ES 2 representative of the size of the block current B u is decoded in D8,
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7.
• D62 If in D62 (FIG. 6B), it is determined as a criterion that the size of the current block is greater than a predetermined value VTP, for example 8x8, the coded value VCES2i or VCES2 2 of the second element of syntax ES 2 representative of the size of the current block B u is decoded in D8,
• the syntax element ES 2 is set, according to the current decoding context, directly to the predefined value VES2 or VES2 2 as stored in the list LTSi of the decoder DO of FIG. 7.

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