Patent ID: 8755620

Claim:
An image decoding method of reconstructing a coded image including a plurality of processing units having mutually different sizes by decoding the coded image, said image decoding method comprising: obtaining current signals to be decoded of each of the processing units of the coded image; selecting a context of each of the current signals to be decoded from among a plurality of contexts; generating a binary signal by performing arithmetic decoding of the current signal to be decoded by using decoded probability information associated with the context selected in said selecting; reconstructing the coded image by performing multi-value conversion on the binary signal; and updating the decoded probability information associated with the context selected in said selecting, based on the binary signal, wherein a first shared context is set in advance, wherein, in said selecting, the first shared context is selected as the context for the current signal to be decoded in the case where a size of the processing unit which includes the current signal to be decoded is a block size of 16×16, and in the case where the size of the processing unit which includes the current signal to be decoded is a block size of 32×32, and wherein, in said selecting, a dedicated context is selected as the context for the current signal to be decoded in the case where the size of the processing unit which includes the current signal to be decoded is smaller than the block size of 16×16.