Image coding method, image decoding method, image coding apparatus, image decoding apparatus, and image coding and decoding apparatus
An image coding method comprising: obtaining current signals to be coded of each of the processing units of the image; generating a binary signal by performing binarization on each of the current signals to be coded; selecting a context for each of the current signals to be coded from among a plurality of contexts; performing arithmetic coding of the binary signal by using coded probability information associated with the context selected in the selecting; and updating the coded probability information based on the binary signal, wherein, in the selecting, the context for the current signal to be coded is selected, as a shared context, for a signal which is included in one of a plurality of processing units and has a size different from a size of the processing unit including the current signal to be coded.
1. An image coding method of compression-coding an image including a plurality of processing units having mutually different sizes, said image coding method comprising:
obtaining current signals to be coded of each of the processing units of the image;
generating a binary signal by performing binarization on each of the current signals to be coded;
selecting a context for each of the current signals to be coded from among a plurality of contexts;
performing arithmetic coding of the binary signal by using coded probability information associated with the context selected in said selecting; and
updating the coded probability information associated with the context selected in said selecting, based on the binary signal generated in said generating,
wherein a first shared context is set in advance,
wherein, in said selecting, the first shared context is selected as the context for the current signal to be coded in the case where a size of the processing unit which includes the current signal to be coded is a block size of 16×16, and in the case where the size of the processing unit which includes the current signal to be coded is a block size of 32×32, and
wherein, in said selecting, a dedicated context is selected as the context for the current signal to be coded in the case where the size of the processing unit which includes the current signal to be coded is smaller than the block size of 16×16.
2. The image coding method according to claim 1 , further comprising
performing frequency transform on the image to generate transform coefficients of frequency components and to generate the current signals to be coded which respectively indicate the transform coefficients of the frequency components,
wherein in said selecting, a dedicated context is selected as the context for the current signal to be coded in the case where the frequency component corresponding to the current signal to be coded is lower than a predetermined frequency.
3. The image coding method according to claim 1 , further comprising
performing frequency transform on the image to generate transform coefficients of frequency components and to generate the current signals to be coded which respectively indicate the transform coefficients of the frequency components,
wherein a second shared context is set in advance, and
wherein in said selecting, the second shared context is selected as the context for the current signal to be coded in the case where the frequency component corresponding to the current signal to be coded is higher than a predetermined frequency.
4. The image coding method according to claim 1 , further comprising
segmenting the image into a plurality of sub blocks each having the same sub processing unit size,
wherein in said generating, the binary signal is generated by performing binarization on the current signals to be coded of each of the sub blocks, and
in said selecting, the context which is set for each of the sub blocks having the sub processing unit size in advance is selected.
5. An image coding apparatus which compression-codes an image including a plurality of processing units having mutually different sizes, said image coding apparatus comprising:
a storage unit configured to store a plurality of contexts;
a binarization unit configured to obtain current signals to be coded included in the plurality of processing units of the image and generate a binary signal by performing binarization on each of the current signals to be coded;
a context selection control unit configured to select a context for each of the current signals to be coded from among a plurality of contexts;
a context control unit configured to execute a coded probability information identification process for identifying coded probability information associated with the context selected by said context selection control unit and an update process for updating, based on the binary signal, the coded probability information associated with the context selected by said context selection control unit; and
an arithmetic coding unit configured to perform arithmetic coding of the binary signal by using the coded probability information identified by said context control unit,
wherein a shared context is set in advance,
wherein said context selection control unit is configured to select the shared context as the context for the current signal to be coded in the case where a size of the processing unit which includes the current signal to be coded is a block size of 16×16, and in the case where the size of the processing unit which includes the current signal to be coded is a block size of 32×32, and
wherein said context selection control unit is configured to select a dedicated context as the context for the current signal to be coded in the case where the size of the processing unit which includes the current signal to be coded is smaller than the block size of 16×16.