Image coding method and image decoding method

1. An image coding method of coding an image having a plurality of blocks, said image coding method comprising

coding the blocks sequentially based on probability information indicating a data occurrence probability,

wherein, in said coding, the probability information is updated depending on data of a first target block to be coded among the blocks, after coding the first target block and before coding a second target block to be coded next among the blocks, and

wherein, in said coding, a third target block in the blocks to be coded among the blocks is coded based on the probability information (i) which is updated depending on the data of the first target block, the first target block being a neighboring block above the third target block and (ii) which is not updated depending on the data of the second target block, and

wherein the third target block (i) is located on a left end of the image, (ii) is different from the second target block, and (iii) is coded after coding the first target block.

2. The image coding method according to claim 1 ,

wherein, in said coding, the blocks are sequentially arithmetic-coded based on the probability information.

3. The image coding method according to claim 1 ,

wherein, in said coding, the blocks are sequentially coded on a line-by-line basis in a horizontal direction from left to right, wherein, after coding a block on far right of a line, a block on far left of a next line immediately below the line is coded.

4. The image coding method according to claim 1 ,

wherein, in said coding, the third target block is coded based on the probability information, the probability information having been updated depending on the data of the first target block immediately above the third target block.

5. The image coding method according to claim 1 ,

wherein, in said coding, sub-blocks included in each of the blocks are sequentially coded based on the probability information,

in said coding, the probability information is further updated depending on data of a first target sub-block to be coded among a first set of sub-blocks included in the first target block, after coding the first target sub-block and before coding a second target sub-block to be coded next among the first set of sub-blocks, and

in said coding, a third target block is coded based on the probability information, the third target block being to be coded first among a second set of sub-blocks included in the third target block, and the probability information having been updated depending on the data of the first target sub-block that is spatially closest to the third target sub-block among the first set of sub-blocks.

6. The image coding method according to claim 1 ,

wherein, in said coding, the probability information is further updated depending on data of a fourth target block on immediately left of the third target block among the blocks, after coding the fourth target block and before coding the third target block,

said image coding method further comprising calculating, from first probability information and second probability information, the probability information used in the coding of the third target block, the first probability information being the probability information updated depending on the data of the first target block in said coding, and the second probability information being the probability information updated depending on the data of the fourth target block in said coding, and

in said coding, the third target block is coded based on the probability information calculated in said calculating.

7. The image coding method according to claim 6 ,

wherein, in said coding, sub-blocks included in each of the blocks are sequentially coded based on the probability information,

in said coding, the probability information is further updated depending on data of a first target sub-block to be coded among a first set of sub-blocks included in the first target block, after coding the first target sub-block and before coding a second target sub-block to be coded next among the first set of sub-blocks,

in said coding, the probability information is further updated depending on data of a third target sub-block to be coded among a second set of sub-blocks included in the fourth target block, after coding the third target sub-block and before coding a fourth target sub-block to be coded next among the second set of sub-blocks,

in said calculating, the probability information is calculated from the first probability information and the second probability information, the probability information being to be used in coding of a fifth target sub-block to be coded first among a third set of sub-blocks included in the third target block, the first probability information being the probability information updated in said coding depending on the data of the first target sub-block that is spatially closest to the fifth target sub-block among the first set of sub-blocks, and the second probability information being the probability information updated in said coding depending on the data of the third target sub-block that is spatially closest to the fifth target sub-block among the second set of sub-blocks, and

in said coding, the fifth target sub-block is coded based on the probability information calculated in said calculating.

8. The image coding method according to claim 7 ,

wherein, in said calculating, the probability information to be used in coding of the fifth target sub-block is calculated by weighting the first probability information and the second probability information according to (a) a spatial distance from the fifth target sub-block to the first target sub-block and (b) a spatial distance from the fifth target sub-block to the third target sub-block.

9. The image coding method according to claim 1 ,

wherein, in said coding, the third target block is coded based on the probability information updated depending on data of the first target block when predetermined condition is satisfied, and the third target block is coded based on the probability information updated depending on data of a target block immediately prior to the third target block when the predetermined condition is not satisfied.

10. An image coding device that codes an image having a plurality of blocks, said image coding device comprising:

a processor; and

a memory having a program stored thereon, the program causing the processor to execute operations including

coding the blocks sequentially based on probability information indicating a data occurrence probability,

wherein, in the coding, the probability information is updated depending on data of a first target block to be coded among the blocks, after coding the first target block and before coding a second target block to be coded next among the blocks, and

wherein, in the coding, a third target block in the blocks to be coded among the blocks is coded based on the probability information (i) which is updated depending on the data of the first target block, the first target block being neighboring block above the third target block and (ii) which is not updated depending on the data of the second target block, and

wherein the third target block (i) is located on a left end of the image, (ii) is different from the second target block, and (iii) is coded after coding the first target block.

11. An integrated circuit that codes an image having a plurality of blocks, said integrated circuit comprising

coding circuitry which, in operation, codes the blocks sequentially based on probability information indicating a data occurrence probability,

wherein said coding circuitry updates the probability information depending on data of a first target block to be coded among the blocks, after coding the first target block and before coding a second target block to be coded next among the blocks, and

wherein said coding circuitry codes a third target block in the blocks to be coded among the blocks based on the probability information (i) which is updated depending on the data of the first target block, the first target block being a neighboring block above the third target block and (ii) which is not updated depending on the data of the second target block, and

wherein the third target block (i) is located on a left end of the image, (ii) is different from the second target block, and (iii) is coded after coding the first target block.