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

An image decoding apparatus that decodes coded image data, said image decoding apparatus comprising:

• a context control unit configured to determine (i) a low-order context which is a context associated with a type of a single quantization coefficient to be decoded of the coded image data and (ii) a high-order context that is common to the low-order context and a context associated with another type;
• a probability information calculation unit configured to calculate decoding probability information to be used in arithmetic decoding of the single quantization coefficient to be decoded, using (i) high-order probability information corresponding to the determined high-order context and (ii) low-order probability information corresponding to the determined low-order context;
• an arithmetic decoding unit configured to perform the arithmetic decoding on each binary symbol of the single quantization coefficient to be decoded, using (i) the high-order probability information corresponding to the determined high-order context and (ii) the low-order probability information corresponding to the determined low-order context, to generate a binary signal;
• and
• a multi-value conversion unit configured to perform multi-value conversion of the binary signal to reconstruct image data,
• wherein said context control unit is further configured to update the high-order probability information and the low-order probability information based on the binary symbol.