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. A method of decoding a current image with a decoding apparatus, comprising:
obtaining coding information for the current image from a bitstream;
dividing a coding block in the current image to obtain one or more sub-blocks based on the coding information,
wherein the coding information includes at least one of a first flag indicating whether to divide the coding block to obtain one or more sub-blocks or a second flag indicating whether to divide the coding block asymmetrically, and
wherein, in case the coding block is divided asymmetrically, a first sub-block having a ¼ size of the coding block is obtained, the first sub-block belonging to the one or more sub-blocks;
obtaining inverse-quantized coefficients of the first sub-block by performing inverse-quantization on the first sub-block;
reconstructing a residual signal of the first sub-block by performing inverse-transform on the inverse-quantized coefficients; and
reconstructing the coding block based on the residual signal, and
wherein obtaining the inverse-quantized coefficients of the first sub-block comprises:
selecting one of a plurality of weight set candidates pre-defined in the decoding apparatus; and
performing the inverse-quantization on the first sub-block based on the selected weight set candidate.
2. The method of claim 1 , wherein each of the weight set candidates includes a plurality of weight components, and
wherein at least one of the weight components belonging to the one of the weight set candidates is different from the weight components belonging to the other of the weight set candidates.
3. The method of claim 1 , wherein a transform type for the inverse-transform of the inverse-quantized coefficients is determined by considering whether or not a size of the first sub-block is greater than a threshold size pre-defined in the decoding apparatus.
4. The method of claim 3 , wherein a number of transform types available for the first sub-block when the size of the first sub-block is greater than the threshold size is different from the number of the transform types available for the first sub-block when the size of the first sub-block is less than or equal to the threshold size.
5. The method of claim 4 , wherein a transform type for the inverse-transform of the quantized coefficients is determined by further considering at least one of the first flag or the second flag.
6. A method of encoding a current image with an encoding apparatus, comprising:
dividing a coding block in the current image to obtain one or more sub-blocks;
obtaining transform coefficients of a first sub-block by performing transform on a residual signal of the first sub-block, the first sub-block belonging to the one or more sub-blocks;
obtaining quantized transform coefficients of the first sub-block by performing quantization on the transform coefficients of the first sub-block; and
generating a bitstream by encoding the quantized transform coefficients of the first sub-block,
wherein coding information for dividing the coding block is encoded into the bitstream,
wherein the coding information includes at least one of a first flag indicating whether to divide the coding block to obtain the one or more sub-blocks or a second flag indicating whether to divide the coding block asymmetrically,
wherein, in case the coding block is divided asymmetrically, the first sub-block having a ¼ size of the coding block is obtained, and
wherein obtaining the quantized transform coefficients of the first sub-block comprises:
selecting one of a plurality of weight set candidates pre-defined in the encoding apparatus; and
performing the quantization on the transform coefficients of the first sub-block based on the selected weight set candidate.
7. A non-transitory computer-readable medium for storing data associated with an image signal, comprising:
a data stream encoded by an encoding method,
wherein the encoding method comprises:
dividing a coding block in the current image to obtain one or more sub-blocks;
obtaining transform coefficients of a first sub-block by performing transform on a residual signal of the first sub-block, the first sub-block belonging to the one or more sub-blocks;
obtaining quantized transform coefficients of the first sub-block by performing quantization on the transform coefficients of the first sub-block; and
generating a bitstream by encoding the quantized transform coefficients of the first sub-block,
wherein coding information for dividing the coding block is encoded into the bitstream,
wherein the coding information includes at least one of a first flag indicating whether to divide the coding block to obtain the one or more sub-blocks or a second flag indicating whether to divide the coding block asymmetrically,
wherein, in case the coding block is divided asymmetrically, the first sub-block having a ¼ size of the coding block is obtained, and
wherein obtaining the quantized transform coefficients of the first sub-block comprises:
selecting one of a plurality of weight set candidates pre-defined in the encoding apparatus; and
performing the quantization on the transform coefficients of the first sub-block based on the selected weight set candidate.
8. A method for transmitting data associated with an image signal, the method comprising:
obtaining a data stream encoded by an encoding method; and
transmitting the data stream,
wherein the encoding method comprises:
dividing a coding block in the current image to obtain one or more sub-blocks;
obtaining transform coefficients of a first sub-block by performing transform on a residual signal of the first sub-block, the first sub-block belonging to the one or more sub-blocks;
obtaining quantized transform coefficients of the first sub-block by performing quantization on the transform coefficients of the first sub-block; and
generating a bitstream by encoding the quantized transform coefficients of the first sub-block,
wherein coding information for dividing the coding block is encoded into the bitstream,
wherein the coding information includes at least one of a first flag indicating whether to divide the coding block to obtain the one or more sub-blocks or a second flag indicating whether to divide the coding block asymmetrically,
wherein, in case the coding block is divided asymmetrically, the first sub-block having a ¼ size of the coding block is obtained, and
wherein obtaining the quantized transform coefficients of the first sub-block comprises:
selecting one of a plurality of weight set candidates pre-defined in the encoding apparatus; and
performing the quantization on the transform coefficients of the first sub-block based on the selected weight set candidate.