Image coding method, image decoding method, image coding apparatus, and image decoding apparatus
An image coding method, comprising: subtracting a prediction signal from the input image signal for each coding unit, thereby generating respective prediction error signals; performing orthogonal transform and quantization on a corresponding one of the prediction error signals for each transform unit, eventually generating quantization coefficients; and coding pieces of management information indicating a structure of the transform units and the quantization coefficients into a tree structure. Each of the transform units corresponds to a corresponding one of leaf nodes in the tree structure. In the coding, for each leaf node, management information and a quantization coefficient are coded, eventually generating a coded signal in which the coded management information and the coded quantization coefficient are arranged in succession for each leaf node.
1. An image coding method, comprising:
splitting an input image signal into a plurality of coding units;
subtracting, for each of the plurality of coding units, a prediction signal from the input image signal, thereby generating prediction error signals for the plurality of coding units, respectively;
splitting a coding unit, from among the plurality of coding units, into a plurality of transform units;
performing, for each of the plurality of transform units obtained by splitting the coding unit, orthogonal transformation and quantization on a corresponding prediction error signal, thereby generating quantization coefficients for the plurality of transform units, respectively;
coding management information and the plurality of transform units into a tree structure, the management information indicating the tree structure,
wherein the plurality of transform units correspond to a plurality of leaf nodes in the tree structure, respectively, and
wherein the coding further includes:
generating, for each of the plurality of leaf nodes, a set including a corresponding piece of the management information and a corresponding one or more of the quantization coefficients; and
recursively coding, into a bitstream, the sets generated for the plurality of leaf nodes, the sets being recursively coded into the bitstream in order,
wherein the plurality of leaf nodes includes a first leaf node and a second leaf node, and
wherein, in the coding, the set generated for the first leaf node including the corresponding piece of the management information and the corresponding one or more of the quantization coefficients for the first leaf node is coded into the bitstream before the set generated for the second leaf node including the corresponding piece of the management information and the corresponding one or more of the quantization coefficients for the second leaf node is coded into the bitstream.
2. The image coding method according to claim 1 ,
wherein the management information includes one or more split flags, each of which indicates whether or not a current node is further split into nodes at a level lower than a current level for the transformation.
3. The image coding method according to claim 2 ,
wherein the management information includes one or more first flags that indicate whether or not a quantization coefficient exists in the transform unit corresponding to the current node.
4. The image coding method according to claim 3 ,
wherein the coding further includes
determining whether or not a value of the first flag corresponding to the current node can be uniquely identified by at least one of (a) the first flag corresponding to an upper node at a level higher than the current level and (b) the first flag of a different node at the current level, and
wherein when it is determined that the value of the first flag of the current node can be uniquely identified, the first flag of the current node is not coded.
5. The image coding method according to claim 3 ,
wherein the coding further includes
coding a difference quantization step for each of the leaf nodes in the coded bitstream,
wherein the difference quantization step indicates a difference between a quantization step that has most recently been used and a quantization step that is used for the corresponding transform unit.
6. The image coding method according to claim 2 ,
wherein the corresponding one or more quantization coefficients includes one or more luminance quantization coefficients and one or more chrominance quantization coefficients,
wherein the management information includes one or more second flags and one or more third flags, each of the one or more second flags indicating whether or not the one or more luminance quantization coefficients exist, and each of the one or more third flags indicating whether or not the chrominance quantization coefficients exist, and
wherein in the coding, for each of the plurality of leaf nodes, each of the one or more second flags is arranged to be subsequent to each of the one or more third flags in the coded bitstream.
7. The image coding method according to claim 2 ,
wherein the corresponding one or more quantization coefficients includes one or more luminance quantization coefficients, one or more chrominance Cb quantization coefficients, and one or more chrominance Cr quantization coefficients,
wherein the management information includes one or more second flags, one or more third flags, one or more fourth flags, each of the one or more second flags indicating whether or not the one or more luminance quantization coefficients exist, each of the one or more third flags indicating whether or not the chrominance Cb quantization coefficients exist, and the one or more fourth flags indicating whether or not the one or more chrominance Cr quantization coefficients exist, and
wherein in the coding, for each of the plurality of leaf nodes, each of the one or more third flags, each of the one or more fourth flags, each of the one or more second flags, the one or more luminance quantization coefficients, the one or more chrominance Cb quantization coefficients, and the one or more chrominance Cr quantization coefficients are coded in order in the coded bitstream.
8. An image coding apparatus, comprising:
a subtraction unit configured to (i) split an input image signal into a plurality of coding units and (ii) subtract, for each of the plurality of coding units, a prediction signal from the input image signal, thereby generating prediction error signals for the plurality of coding units, respectively;
a transform quantization unit configured to (i) split a coding unit, from among the plurality of coding units, into a plurality of transform units and (ii) perform, for each of the plurality of transform units obtained by splitting the coding unit, orthogonal transformation and quantization on a corresponding prediction error signal, thereby generating quantization coefficients for the plurality of transform units, respectively; and
a coding unit configured to code management information and the plurality of transform units into a tree structure, the management information indicating the tree structure,
wherein the plurality of transform units correspond to a plurality of leaf nodes in the tree structure, respectively, and
wherein the coding unit is further configured to (i) generate, for each of the plurality of leaf nodes, a set including a corresponding piece of the management information and a corresponding one or more of the quantization coefficients, and (ii) recursively code, into a bitstream, the sets generated for the plurality of leaf nodes, the sets being recursively coded into the bitstream in order,
wherein the plurality of leaf nodes includes a first leaf node and a second leaf node, and
wherein the set generated for the first leaf node including the corresponding piece of the management information and the corresponding one or more of the quantization coefficients for the first leaf node is coded into the bitstream before the set generated for the second leaf node including the corresponding piece of the management information and the corresponding one or more of the quantization coefficients for the second leaf node is coded into the bitstream.
9. A coding method for coding an image, the coding method comprising:
splitting the image into a plurality of coding units;
subtracting, for each of the plurality of coding units, a prediction signal from the input image signal, thereby generating prediction error signals for the plurality of coding units, respectively;
splitting a coding unit, from among the plurality of coding units, into a plurality of transform units;
performing, for each of the plurality of transform units obtained by splitting the coding unit, orthogonal transformation and quantization on a corresponding prediction error signal, thereby generating quantization coefficients for the plurality of transform units, respectively; and
coding a split flag and the plurality of transform units into a tree structure, each node of the tree structure including the split flag,
wherein, for each node the tree structure, the split flags has one of (i) a first value indicating that the node is not split into lower nodes at a level lower than a current level in the tree structure and (ii) a second value indicating that the node is split into lower nodes at the level lower than the current level in the tree structure,
wherein the plurality of transform units correspond to a plurality of leaf nodes in the tree structure, respectively, and
wherein the coding further includes:
arranging, for each of the plurality of leaf nodes in the tree structure, the split flag having the first value and corresponding coefficients in order, and
recursively coding, for each node in the tree structure including the split flag having the second value, every leaf node subsequent to the node at a level lower than a current level in the tree structure.