Method of coding and decoding images, coding and decoding device and computer programs corresponding thereto
A method of coding at least one image comprising the steps of splitting the image into a plurality of blocks, of grouping said blocks into a predetermined number of subsets of blocks, of coding each of said subsets of blocks in parallel, the blocks of a subset considered being coded according to a predetermined sequential order of traversal. The coding step comprises, for a current block of a subset considered, the sub-step of predictive coding of said current block with respect to at least one previously coded and decoded block, and the sub-step of entropy coding of said current block on the basis of at least one probability of appearance of a symbol.
1 . An apparatus for decoding an image, the apparatus comprising:
one or more processors that, upon execution of instructions stored in computer-readable media, are configured to perform operations comprising:
receiving a stream representative of at least one coded image;
identifying, from the stream, a plurality of groups of blocks;
processing a first block in a particular group of blocks of the plurality of groups of blocks, wherein processing the first block comprises:
determining that the first block is first in an order of blocks in the particular group of blocks;
in response to determining that the first block is first in the order of blocks in the particular group of blocks, retrieving a first set of probabilities of occurrence of symbols associated with a block that is second in the order of blocks belonging to another group of blocks that is different from the particular group of blocks in the plurality of groups of blocks;
entropy decoding the first block based on the first set of probabilities to obtain a quantized residual block;
generating a prediction of the first block based on at least one previously decoded block;
dequantizing the quantized residual block to obtain a dequantized block;
inverse transforming the dequantized block to obtain a decoded residual block; and
adding the decoded residual block to the prediction of the first block to obtain a decoded block; and
processing a second block in the particular group of blocks, wherein processing the second block comprises:
determining that the second block is not first in the order of blocks in the particular group of blocks;
in response to determining that the second block is not first in the order of blocks in the particular group of blocks, retrieving a second set of probabilities of occurrence of symbols associated with at least one other already decoded block belonging to the particular group of blocks in the plurality of groups of blocks, wherein the second set of probabilities of occurrence of symbols are not associated with blocks that do not belong to the particular group of blocks, and
entropy decoding the second block based on the second set of probabilities to obtain a quantized residual block;
generating a prediction of the second block based on at least one previously decoded block;
dequantizing the quantized residual block to obtain a dequantized block;
inverse transforming the dequantized block to obtain a decoded residual block; and
adding the decoded residual block to the prediction of the second block to obtain a decoded block.
2 . An apparatus for coding at least one image, the apparatus comprising:
one or more processors that, upon execution of instructions stored in computer-readable media, are configured to perform operations comprising:
generating a prediction of a block of an image;
subtracting the prediction from the block of the image to obtain a residual block;
transforming the residual block to obtain a transformed block;
quantizing the transformed block to obtain a block of quantized coefficients; and
entropy coding the block of quantized coefficients, wherein entropy coding the block of quantized coefficients comprises:
determining whether the block of quantized coefficients is first in an order of blocks in a particular group of blocks;
conditioned on determining that the block of quantized coefficients is first in the order of blocks in the particular group of blocks, retrieving a first set of probabilities of occurrence of symbols associated with a second block that is second in the order of blocks belonging to another group of blocks that is different from the particular group of blocks in a plurality of groups of blocks;
entropy coding the block of quantized coefficients based on the first set of probabilities; and
conditioned on determining that the block of quantized coefficients is not first in the order of blocks in the particular group of blocks, retrieving a second set of probabilities of occurrence of symbols associated with at least one other already coded block belonging to the particular group of blocks in the plurality of groups of blocks,
wherein the second set of probabilities of occurrence of symbols are not associated with blocks that do not belong to the particular group of blocks, and
wherein entropy coding the second block is based on the second set of probabilities.
3 . A method of transmitting a bitstream which is encoded by an encoding method, the encoding method comprising:
generating a prediction of a block of an image;
subtracting the prediction from the block of the image to obtain a residual block;
transforming the residual block to obtain a transformed block;
quantizing the transformed block to obtain a block of quantized coefficients; and
entropy coding the block of quantized coefficients, wherein entropy coding the block of quantized coefficients comprises:
determining whether the block of quantized coefficients is first in an order of blocks in a particular group of blocks;
conditioned on determining that the block of quantized coefficients is first in the order of blocks in the particular group of blocks, retrieving a first set of probabilities of occurrence of symbols associated with a second block that is second in the order of blocks belonging to another group of blocks that is different from the particular group of blocks in a plurality of groups of blocks;
entropy coding the block of quantized coefficients based on the first set of probabilities;
conditioned on determining that the block of quantized coefficients is not first in the order of blocks in the particular group of blocks, retrieving a second set of probabilities of occurrence of symbols associated with at least one other already coded block belonging to the particular group of blocks in the plurality of groups of blocks,
wherein the second set of probabilities of occurrence of symbols are not associated with blocks that do not belong to the particular group of blocks, and
wherein entropy coding the second block is based on the second set of probabilities; and
transmitting the bitstream generated based at least in part on the entropy coded block of quantized coefficients.