Method of coding and decoding images, device for coding and decoding computer programs corresponding thereto

A coding device (CO) for at least one image, which coding device is intended to implement a coding method comprising the steps of:

• partitioning (C1, C2) of the image into a plurality of blocks (CTU1, CTU2, . . . , CTUi, . . . , CTUS) that are capable of containing symbols belonging to a predetermined set of symbols,
• entropy coding of a current block on the basis of at least one symbol appearance probability,
• predictive coding of a compression parameter (OP) associated with said current block, said coding method being characterized in that if the current block is the first block to be coded in a considered set (LEm) of consecutive blocks to be coded then the method involves the steps of:
• determination (C40a)), during said step of entropy coding, of symbol appearance probabilities for said first current block, said probabilities being those that are determined at the conclusion of the coding and then the decoding of the last block in another considered set (LEm-1) of blocks, said other set immediately preceding, in the order of coding of the blocks, said considered set,
• assignment (C41a)), during said step of predictive coding of a compression parameter associated with said first current block, of a compression parameter prediction value that is independent of the value of the compression parameter associated with said last block,
• said device comprising:
• means (MP) for partitioning the image into a plurality of blocks (CTU) that are capable of containing symbols belonging to a predetermined set of symbols,
• means (MCE) for entropy coding of a current block on the basis of at least one symbol appearance probability,
• means (MCP) for predictive coding of a compression parameter (QP) associated with said current block,
• said coding device being characterized in that if the current block is the first block to be coded in a considered set of consecutive blocks to be coded then:
• the entropy coding means determine symbol appearance probabilities for said first current block, said probabilities being those that have been determined at the conclusion of the coding and then the decoding of the last block in another considered set of blocks, said other set immediately preceding, in the order of coding of the blocks, said considered set,
• the means for predictive coding of a compression parameter associated with said first current block assign a compression parameter prediction value that is independent of the value of the compression parameter associated with said last block.

A method for decoding a stream (F) that is representative of at least one coded image, comprising the steps of:

• identification (D1), in said stream, of a plurality of coded blocks, said blocks being capable of containing symbols belonging to a predetermined set of symbols,
• entropy decoding of a current coded block on the basis of at least one symbol appearance probability,
• predictive decoding of a compression parameter (QP) associated with said current coded block,
• said decoding method being characterized in that if the current block is the first block to be decoded in a considered set of consecutive blocks to be decoded then the method involves the steps of:
• determination (D30a)), during said step of entropy decoding, of symbol appearance probabilities for said first current block, said probabilities being those that have been determined at the conclusion of the decoding of the last block in another considered set of blocks, said other set immediately preceding, in the order of decoding of the blocks, said considered set,
• assignment (D31a)), during said step of predictive decoding of a compression parameter associated with said first current block, of a compression parameter prediction value that is independent of that of the compression parameter associated with said last block.

A device for decoding a stream (F) that is representative of at least one coded image, which decoding device is intended to implement a decoding method comprising the steps of:

• identification (D1), in said stream, of a plurality of coded blocks, said blocks being capable of containing symbols belonging to a predetermined set of symbols,
• entropy decoding of a current coded block on the basis of at least one symbol appearance probability,
• predictive decoding of a compression parameter (OP) associated with said current coded block,
• said decoding method being characterized in that if the current block is the first block to be decoded in a considered set of consecutive blocks to be decoded then the method involves the steps of:
• determination (D30a)), during said step of entropy decoding, of symbol appearance probabilities for said first current block, said probabilities being those that have been determined at the conclusion of the decoding of the last block in another considered set of blocks, said other set immediately preceding, in the order of decoding of the blocks, said considered set,
• assignment (D31a)), during said step of predictive decoding of a compression parameter associated with said first current block, of a compression parameter prediction value that is independent of that of the compression parameter associated with said last block;
• said device comprising:
• means (EX_DO) for identification, in said stream, of a plurality of coded blocks, said blocks being capable of containing symbols belonging to a predetermined set of symbols,
• means for entropy decoding of a current coded block on the basis of at least one symbol appearance probability,
• means for predictive decoding of a compression parameter (QP) associated with said current coded block,
• said decoding device being characterized in that if the current block is the first block to be decoded in a considered set of consecutive blocks to be decoded then
• the means (MDE) for entropy decoding determine symbol appearance probabilities for said first current block, said probabilities being those that have been determined at the conclusion of the decoding of the last block of another considered set of blocks, said other set immediately preceding, in the order of decoding of the blocks, said considered set,
• the means (MDP) for predictive decoding of a compression parameter associated with said first current block assign a compression parameter prediction value that is independent of that of the compression parameter associated with said last block.