Image data encoding/decoding method and apparatus
A method for decoding a 360-degree image includes: receiving a bitstream obtained by encoding a 360-degree image; generating a prediction image by making reference to syntax information obtained from the received bitstream; combining the generated prediction image with a residual image obtained by dequantizing and inverse-transforming the bitstream, so as to obtain a decoded image; and reconstructing the decoded image into a 360-degree image according to a projection format. Here, generating the prediction image includes: checking, from the syntax information, prediction mode accuracy for a current block to be decoded; determining whether the checked prediction mode accuracy corresponds to most probable mode (MPM) information obtained from the syntax information; and when the checked prediction mode accuracy does not correspond to the MPM information, reconfiguring the MPM information according to the prediction mode accuracy for the current block.
1. An image decoding method performed by an image decoding apparatus, the image decoding method comprising:
receiving a bitstream in which an image is encoded;
obtaining index information for specifying a block division type of a current block in the image from the bitstream;
determining the block division type of the current block from a candidate group pre-defined in the image decoding apparatus based on the index information;
dividing the current block into a plurality of sub-blocks based on the determined block division type; and
decoding each of the sub-blocks to reconstruct the current block,
wherein the candidate group includes at least one of a non-division, a first quad-division, a second quad-division, a binary-division or a triple-division, and
wherein the first quad-division divides one coding block into four coding blocks based one horizontal line and one vertical line, the second quad-division divides one coding block into four coding blocks based on three horizontal lines or three vertical lines, the binary-division divides one coding block into two coding blocks, and the triple-division divides one coding block into three coding blocks.
2. The method of claim 1 ,
wherein the current block is a largest coding block or a block resulting from dividing the largest coding block,
wherein a size of the largest coding block is variably determined based on information on the largest coding block,
wherein the information on the largest coding block is signaled from the bitstream.
3. The method of claim 2 ,
wherein the size of the largest coding block is set equal to 128×128 or 64×64 according to the information on the largest coding block.
4. The method of claim 1 ,
wherein a number of the candidate division types available for the current block is different dependent on at least one of a size of the current block or a shape of the current block.
5. The method of claim 4 ,
wherein when the size of the current block is equal to or greater than a pre-determined threshold, the candidate group for the current block includes the non-division, the first quad-division, the second quad-division, the binary-division, and the triple-division, and
when the size of the current block is less than the pre-determined threshold, the candidate group for the current block does not include at least one of the second quad-division or the triple-division.
6. The method of claim 5 ,
wherein the pre-determined threshold is representative of 16.
7. An image encoding method performed by an image encoding apparatus, the image encoding method comprising:
determining a block division type of a current block in an image from a candidate group pre-defined in the image encoding apparatus, index information for specifying the determined block division type of the current block being encoded into a bitstream;
dividing the current block into a plurality of sub-blocks based on the determined block division type; and
encoding each of the sub-blocks to encode the current block,
wherein the candidate group includes at least one of a non-division, a first quad-division, a second quad-division, a binary-division or a triple-division, and
wherein the first quad-division divides one coding block into four coding blocks based one horizontal line and one vertical line, the second quad-division divides one coding block into four coding blocks based on three horizontal lines or three vertical lines, the binary-division divides one coding block into two coding blocks, and the triple-division divides one coding block into three coding blocks.
8. A non-transitory computer-readable recording medium storing a bitstream that is generated by an image encoding method performed by an image encoding apparatus, the image encoding method comprising:
determining a block division type of a current block in an image from a candidate group pre-defined in the image encoding apparatus, index information for specifying the determined block division type of the current block being encoded into a bitstream;
dividing the current block into a plurality of sub-blocks based on the determined block division type; and
encoding each of the sub-blocks to encode the current block,
wherein the candidate group includes at least one of a non-division, a first quad-division, a second quad-division, a binary-division or a triple-division, and
wherein the first quad-division divides one coding block into four coding blocks based one horizontal line and one vertical line, the second quad-division divides one coding block into four coding blocks based on three horizontal lines or three vertical lines, the binary-division divides one coding block into two coding blocks, and the triple-division divides one coding block into three coding blocks.
9. A method of transmitting a bitstream that is generated by an image encoding method performed by an image encoding apparatus, the image encoding method comprising:
determining a block division type of a current block in an image from a candidate group pre-defined in the image encoding apparatus, index information for specifying the determined block division type of the current block being encoded into a bitstream;
dividing the current block into a plurality of sub-blocks based on the determined block division type; and
encoding each of the sub-blocks to encode the current block,
wherein the candidate group includes at least one of a non-division, a first quad-division, a second quad-division, a binary-division or a triple-division, and
wherein the first quad-division divides one coding block into four coding blocks based one horizontal line and one vertical line, the second quad-division divides one coding block into four coding blocks based on three horizontal lines or three vertical lines, the binary-division divides one coding block into two coding blocks, and the triple-division divides one coding block into three coding blocks.