Image decoding method, image coding method, image decoding apparatus, image coding apparatus and integrated circuit for generating a code stream with a hierarchical code structure
An image decoding method decodes a coded stream which includes processing units and a header of the processing units, and which is generated by coding a moving picture using inter prediction. The processing units includes at least one processing unit divided in a hierarchy, the hierarchy including a highest hierarchical layer in which a coding unit exists as a largest processing unit and a lower hierarchical layer in which a prediction unit exists. The method includes identifying, by parsing hierarchy depth information stored in the header and indicating a hierarchical layer higher than a lowest hierarchical layer in which a smallest prediction unit exits, a hierarchical layer which is indicated by the hierarchy depth information or a hierarchical layer higher than the indicated hierarchical layer. The hierarchical layer includes a prediction unit in which a reference index is stored. The prediction unit is decoded using the reference index.
1. An image decoding method for decoding a coded stream, the image decoding method comprising:
receiving a coded stream which includes a plurality of processing units and a header of the processing units, the coded stream having been generated by coding an image using inter prediction,
wherein the processing units including at least one processing unit divided into a plurality of sub-processing units in a multiple-level hierarchy in which the size of a sub-processing unit at one level is larger than the size of a sub-processing unit at a lower level,
wherein the hierarchy including a prediction unit that is a sub-processing unit at a level lower than the highest level,
wherein a reference index necessary for decoding said prediction unit is stored in either said processing unit that is divided or a sub-processing unit at a level higher than said prediction unit, and
wherein said header including hierarchy depth information indicating the unit where the reference index is stored;
parsing said header to obtain said hierarchy depth information;
using said hierarchy depth information to obtain said reference index; and
decoding said prediction unit using said reference index.
2. An image decoding apparatus for decoding a coded stream the image decoding apparatus comprising:
a hardware processor; and
a non-transitory, computer-readable memory device coupled to said hardware processor, said hardware processor, using said memory device, perform the following steps:
receiving a coded stream which includes a plurality of processing units and a header of the processing units, the coded stream having been generated by coding an image using inter prediction,
wherein the processing units including at least one processing unit divided into a plurality of sub-processing units in a multiple-level hierarchy in which the size of a sub-processing unit at one level is larger than the size of a sub-processing unit at a lower level,
wherein the hierarchy including a prediction unit that is a sub-processing unit at a level lower than the highest level,
wherein a reference index necessary for decoding said prediction unit is stored in either said processing unit that is divided or a sub-processing unit at a level higher than said prediction unit, and
wherein said header including hierarchy depth information indicating the unit where the reference index is stored;
parsing said header to obtain said hierarchy depth information;
using said hierarchy depth information to obtain said reference index; and
decoding said prediction unit using said reference index.
3. An image decoding apparatus for decoding a coded stream, the image decoding apparatus comprising:
a receiver that receives a coded stream which includes a plurality of processing units and a header of the processing units, the coded stream having been generated by coding an image using inter prediction,
wherein the processing units including at least one processing unit divided into a plurality of sub-processing units in a multiple-level hierarchy in which the size of a sub-processing unit at one level is larger than the size of a sub-processing unit at a lower level,
wherein the hierarchy including a prediction unit that is a sub-processing unit at a level lower than the highest level,
wherein a reference index necessary for decoding said prediction unit is stored in either said processing unit that is divided or a sub-processing unit at a level higher than said prediction unit, and
wherein said header including hierarchy depth information indicating the unit where the reference index is stored;
an identifier that parses said header to obtain said hierarchy depth information and uses said hierarchy depth information to obtain said reference index; and
a decoder that decodes said prediction unit using said reference index.