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

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.

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.