Image decoding method and apparatus
Complexity of coding/decoding of a video is reduced. An image decoding apparatus ( 31 ) includes a CN information decoder ( 10 ) configured to hierarchically split a coding node by at least any of binary tree split and ternary tree split. The CN information decoder refers to a method of splitting an immediately higher node, which is a node one generation higher than a target node, to restrict a method of splitting the target node.
1. An image decoding method for decoding a picture for each of coding tree units, the image decoding method comprising:
decoding a partition tree (PT) split flag in a case that decoding of the PT split flag is required, wherein the PT split flag indicates whether or not the target node is to be split by a binary tree split or a ternary tree split;
decoding a split direction flag in a case that decoding of the split direction flag is required, wherein the split direction flag indicates a split direction;
decoding a split mode selection flag in a case that decoding of the split mode selection flag is required, wherein the split mode selection flag indicates a split method which is the binary tree split or the ternary tree split; and
splitting the target node of the coding tree units by the binary tree split or the ternary tree split based on the split direction flag and the split mode selection flag, wherein
a required condition of decoding of the PT split flag includes that a binary tree (BT) split possibility determination is TRUE or a ternary tree (TT) split possibility determination is TRUE,
a required condition of decoding of the split mode selection flag includes that the BT split possibility determination is TRUE and the TT split possibility determination is TRUE,
the BT split possibility determination is determined based on 1) a height or a width of a target node is greater than or equal to a minimum coding unit (CU) size multiplied by 2, and 2) the width and the height of the target node are less than or equal to a maximum CU size, and 3) a depth of the target node is less than a maximum depth, and based on the additional conditions of, 4-1) the target node is a middle node of three nodes obtained by ternary tree splitting an immediately higher node than the target node, and 4-2) a BT split direction of the target node is a same direction as a TT split direction of the immediately higher node,
the TT split possibility determination is determined based on 1) the height or the width of the target node is greater than or equal to the minimum CU size multiplied by 4, 2) the width and the height of the target node are less than or equal to the maximum CU size 3) the depth of the target node is less than the maximum depth, and
in a case that only one of the BT split possibility determination or the TT split possibility determination is TRUE, not decoding and configuring a value of the split mode selection flag.
2. An image decoding apparatus for decoding a picture for each of coding tree units, the image decoding apparatus comprising:
a coding node (CN) information decoding circuit configured to
decode a partition tree (PT) split flag in a case that decoding of the PT split flag is required, wherein the PT split flag indicates whether or not the target node is to be split by a binary tree split or a ternary tree split,
decode a split direction flag in a case that decoding of the split direction flag is required, wherein the split direction flag indicates a split direction,
decode a split mode selection flag in a case that decoding of the split mode selection flag is required, wherein the split mode selection flag indicates a split method which is the binary tree split or the ternary tree split, and
split the target node of the coding tree units by the binary tree split or the ternary tree split based on the split direction flag and the split mode selection flag, wherein
a required condition of decoding of the PT split flag includes that a binary tree (BT) split possibility determination is TRUE or a ternary tree (TT) split possibility determination is TRUE,
a required condition of decoding of the split mode selection flag includes that the BT split possibility determination is TRUE and the TT split possibility determination is TRUE,
the BT split possibility determination is determined based on 1) a height or a width of a target node is greater than or equal to a minimum coding unit (CU) size multiplied by 2, and 2) the width and the height of the target node are less than or equal to a maximum CU size, and 3) a depth of the target node is less than a maximum depth, and based on the additional conditions of, 4-1) the target node is a middle node of three nodes obtained by ternary tree splitting an immediately higher node than the target node, and 4-2) a BT split direction of the target node is a same direction as a TT split direction of the immediately higher node,
the TT split possibility determination is determined based on 1) the height or the width of the target node is greater than or equal to the minimum CU size multiplied by 4, 2) the width and the height of the target node are less than or equal to the maximum CU size 3) the depth of the target node is less than the maximum depth, and
in a case that only one of the BT split possibility determination or the TT split possibility determination is TRUE, the CN information decoding circuit does not decode and configures a value of the split mode selection flag.