Image decoding method, image coding method, image decoding apparatus, image coding apparatus, program, and integrated circuit

An image coding method for generating a coded stream which includes a plurality of processing units and a header of the processing units, by coding a moving picture using inter prediction, the processing units including at least one processing unit divided into a plurality of sub processing units in a hierarchy which decrease in size from a higher level to a lower level, the hierarchy including:

• a highest hierarchical layer in which a coding unit exists as a largest processing unit;
• and a lower hierarchical layer which is deeper than the highest hierarchical layer and in which a prediction unit exists as a processing unit smaller than the coding unit, the image coding method comprising:
• writing, into the header, hierarchy depth information which is information for identifying a hierarchical layer having a prediction unit in which an adaptive motion vector resolution switch flag necessary for decoding is stored and indicates a hierarchical layer higher than a lowest hierarchical layer in which a smallest prediction unit exists;
• determining a best size of the coding unit;
• writing, into the coding unit, a flag to divide the coding unit into the determined best size;
• determining a hierarchical layer of the coding unit;
• determining whether or not the determined hierarchical layer matches the hierarchical layer identified by the hierarchy depth information;
• writing, into a prediction unit located at a hierarchical layer indicated by the hierarchy depth information or located higher than the indicated hierarchical layer, the adaptive motion vector resolution switch flag to be applied to the prediction unit when the determined hierarchical layer matches the hierarchical layer identified by the hierarchy depth information;
• and
• coding the prediction unit by performing inter prediction using the adaptive motion vector resolution switch flag.