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. A method of coding at least one image, the method comprising:
dividing an image into a plurality of blocks;
grouping the plurality of blocks into a number of subsets of blocks; and
coding in parallel the subsets of blocks, the blocks of a subset coded according to a predetermined sequential order of traversal, wherein the coding for a subset of blocks comprises:
predictive coding a current block of the subset of blocks with respect to at least one previously coded and decoded block to obtain a predicted block;
subtracting the predicted block from the current block to obtain a residual block;
obtaining a block of quantized coefficients based on the residual block; and
entropy coding of the block of quantized coefficients based at least on probabilities of symbol occurrence, wherein the entropy coding comprises:
determining whether the current block is first in an order of blocks in the subset of blocks;
conditioned on determining that the current block is the first in the order of blocks in the subset of blocks, entropy coding the block of quantized coefficients using a first set of probabilities of symbol occurrence, the first set of probabilities associated with a predetermined block of at least one other subset; and
conditioned on determining that the current block is not the first block in the order of blocks in the subset of blocks, entropy coding the block of quantized coefficients using a second set of probabilities of symbol occurrence, the second set of probabilities associated with at least one other coded block belonging to the same subset,
wherein the predetermined block of the at least one other subset is entropy coded using the second set of probabilities.
2. The method of claim 1 , wherein obtaining the block of quantized coefficients based on the residual block comprises:
transforming the residual block to obtain a transformed block; and
quantizing the transformed block to obtain the block of quantized coefficients.
3. The method of claim 1 , wherein the predetermined block of the at least one other subset is second in an order of blocks of the at least one other subset.
4. The method of claim 1 , wherein the second set of probabilities is not associated with blocks that do not belong to the same subset.
5. 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:
dividing an image into a plurality of blocks;
grouping the plurality of blocks into a number of subsets of blocks; and
coding in parallel the subsets of blocks, the blocks of a subset coded according to a predetermined sequential order of traversal, wherein the coding for a subset of blocks comprises:
predictive coding a current block of the subset of blocks with respect to at least one previously coded and decoded block to obtain a predicted block;
subtracting the predicted block from the current block to obtain a residual block;
obtaining a block of quantized coefficients based on the residual block; and
entropy coding of the block of quantized coefficients based at least on probabilities of symbol occurrence, wherein the entropy coding comprises:
determining whether the current block is first in an order of blocks in the subset of blocks;
conditioned on determining that the current block is the first in the order of blocks in the subset of blocks, entropy coding the block of quantized coefficients using a first set of probabilities of symbol occurrence, the first set of probabilities associated with a predetermined block of at least one other subset; and
conditioned on determining that the current block is not the first block in the order of blocks in the subset of blocks, entropy coding the block of quantized coefficients using a second set of probabilities of symbol occurrence, the second set of probabilities associated with at least one other coded block belonging to the same subset,
wherein the predetermined block of the at least one other subset is entropy coded using the second set of probabilities.
6. The apparatus of claim 5 , wherein obtaining the block of quantized coefficients based on the residual block comprises:
transforming the residual block to obtain a transformed block; and
quantizing the transformed block to obtain the block of quantized coefficients.
7. The apparatus of claim 5 , wherein the predetermined block of the at least one other subset is second in an order of blocks of the at least one other subset.
8. The apparatus of claim 5 , wherein the second set of probabilities is not associated with blocks that do not belong to the same subset.
9. 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 that includes at least one coded image;
identifying, from the stream, a number of subsets of blocks corresponding to the coded image;
processing the number of subsets of blocks, comprising, for a particular subset of blocks of the number of subsets of blocks:
processing a first block of the particular subset of blocks, comprising:
determining that the first block is first in an order of blocks in the particular subset of blocks;
in response to determining that the first block is first in the order of blocks in the particular subset of blocks, obtaining a first set of probabilities of symbol occurrence associated with a predetermined block of at least one other subset of blocks of the number of subsets of blocks;
entropy decoding the first block based on the first set of probabilities to obtain a quantized residual block;
dequantizing the quantized residual block to obtain a dequantized block;
inverse transforming the dequantized block to obtain a decoded residual block; and
constructing a decoded block by adding a predicted block to the decoded residual block; and
processing a second block in the particular subset of blocks, comprising:
determining that the second block is not first in the order of blocks in the particular subset of blocks;
in response to determining that the second block is not first in the order of blocks in the particular subset of blocks, obtaining a second set of probabilities of symbol occurrence associated with at least one other already decoded block belonging to the particular subset of blocks;
entropy decoding the second block based on the second set of probabilities to obtain a quantized residual block;
dequantizing the quantized residual block to obtain a dequantized block;
inverse transforming the dequantized block to obtain a decoded residual block; and
constructing a decoded block by adding a predicted block to the decoded residual block.
10. The apparatus of claim 9 , wherein the predetermined block of the at least one other subset is second in an order of blocks of the at least one other subset.
11. The apparatus of claim 9 , wherein the second set of probabilities is not associated with blocks that do not belong to the particular subset of blocks.