Patent ID: 6882751

Claim:
An arithmetic decoding method of decoding arithmetically encoded image data formed of at least one bitplane, by using a single arithmetic operation section and a plurality of memories that can be accessed separately, comprising the steps of: receiving information on a bit depth of the arithmetically encoded image data; storing, when the bit depth of the arithmetically encoded image data is equal to a number of the memories, state variables corresponding to pixels to be decoded, of respective bitplanes of the image data in respective corresponding ones of the memories; storing, when the bit depth of the arithmetically encoded image data is less than the number of the memories, one of the state variables corresponding to pixels to be decoded, of each bitplane of the image data, in at least part of the memories by allocating the one of the state variables thereto; reading ones of the state variables corresponding, respectively, to pixels to be decoded, of each bitplane, from the memories; selecting ones of the state variables read from the memories based on data which have been arithmetically encoded by the arithmetic operation section; and inputting the selected ones of the state variables and values of a more probable symbol which are paired with the selected ones of the state variables, to the arithmetic operation section.