IMAGE CODING METHOD, IMAGE DECODING METHOD, IMAGE CODING APPARATUS, AND IMAGE DECODING APPARATUS

An image coding method for performing compression-coding on image data includes: binarizing a signal to be coded of the image data, to generate a binary signal; determining a low-order context which is a context associated with a type of the signal to be coded, and a high-order context that is common to the low-order context and a context associated with another type; calculating coding probability information to be used in arithmetic coding of the binary signal, 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; performing the arithmetic coding on the binary signal using the coding probability information; and updating the high-order probability information and the low-order probability information based on the binary signal.