Image decoding method, image coding method, image decoding apparatus, image coding apparatus, and image coding and decoding apparatus

1. An image coding method of coding an image on a per-block basis to generate a bitstream, the image coding method comprising: performing arithmetic coding on a current block to be coded;

determining whether or not the current block is at an end of a slice;

determining whether or not the current block is at an end of a sub-stream when it is determined that the current block is not at the end of the slice, the sub-stream being a structural unit of the image that is different from the slice;

performing arithmetic coding on a sub-last bit indicating the end of the sub-stream and being different from the current block when it is determined that the current block is at the end of the sub-stream;

performing arithmetic coding termination as first termination, which is triggered by the arithmetically coded sub-last bit, when the sub-last bit is arithmetically coded;

performing arithmetic coding termination as second termination, when it is determined that the current block is at the end of the slice; and

performing arithmetic coding on an end-of-slice flag indicating whether or not the current block is at the end of the slice, the end-of-slice flag being different from the sub-last flag,

wherein, when the first termination is performed, same processing as the second termination is performed,

wherein, in the determining of whether or not the current block is at an end of a slice, when it is determined that the current block is at the end of the slice, the end-of-slice flag on which arithmetic coding has been performed indicates a predetermined value of 1, and

wherein a value of 1 is restored by the arithmetic coding performed on the sub-last bit.

2. The image coding method according to claim 1 , further comprising:

writing a bit string into the bitstream after performing the first termination so that a bit length including the sub-stream and the sub-last bit is equal to a multiple of predetermined N bits.

3. The image coding method according to claim 2 ,

wherein, in the performing of arithmetic coding on a sub-last bit, arithmetic coding is performed on a first bit of the bit string, as the sub-last bit.

4. An image coding apparatus which codes an image on a per-block basis to generate a bitstream, the image coding apparatus comprising: processing circuitry; and storage accessible from the processing circuitry, wherein the processing circuitry performs, using the storage, the image coding method according to claim 1 .