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

An image coding method, comprising:

• performing Sample Adaptive Offset (SAO) processing on a luminance signal, a chrominance Cb signal, and a chrominance Cr signal which are included in a target block to be coded;
• performing arithmetic coding on a first flag indicating whether or not an SAO parameter for the target block is identical to an SAO parameter for a left neighboring block immediately left of the target block, the SAO parameter for the target block indicating details of the SAO processing;
• performing arithmetic coding on the SAO parameter for the target block, when the SAO parameter for the target block is different from the SAO parameter for the left neighboring block;
• and
• performing arithmetic coding on a second flag indicating whether or not the SAO parameter for the target block is identical to an SAO parameter for an upper neighboring block immediately above the target block,
• wherein, in the performing of the arithmetic coding on the first flag, the arithmetic coding is performed on the first flag for the luminance signal, the chrominance Cb signal, and the chrominance Cr signal by using only a single first context,
• in the performing of the arithmetic coding on the first flag and the performing of the arithmetic coding on the second flag, a same context determination method is used to determine both:
• the single first context to be used in the arithmetic coding on the first flag;
• and a single second context to be used in the arithmetic coding on the second flag,
• the same context determination method is used to determine each of the single first context and the single second context to be shared for luminance signals, chrominance Cb signals, and chrominance Cr signals which are included in a same picture,
• the single first context is used in common for coding a plurality of the first flag in a same picture,
• the single second context is used in common for coding a plurality of the second flag in a same picture, and
• in the performing of the SAO processing,
• each of pixels included in the target block is classified to one of categories,
• the each of the pixels is added with an offset value corresponding to the classified one of the categories, and
• the SAO parameter includes:
• information indicating a method of classifying to the categories;
• and information indicating the offset value.