Image encoding method and apparatus, and image decoding method and apparatus
Provided are an image decoding method and an image decoding apparatus for performing the image decoding method, the image decoding method including: determining whether or not to obtain second transform set information; determining the second transform set information based on the determining of whether or not to obtain the second transform set information; selecting any one second transform set applied to a second transform block from among a plurality of second transform set candidates corresponding to a plurality of prediction modes, by using the determined second transform set information; generating a first transform block by inverse-transforming the second transform block based on a plurality of transform matrices included in the selected second transform set; and generating a residual block corresponding to the first transform block by inverse-transforming the first transform block based on a first transform matrix.
1 . An image decoding method supporting a coding unit having a size of 128×128, the image decoding method being performed by an apparatus and comprising:
when a width and a height of a current unit are equal to or less than 64, obtaining, from a bitstream, second transform information for the current unit, wherein the second transform information indicates whether and which one among a plurality of second transform matrices is used,
wherein the second transform information being equal to zero indicates that an inverse second transform is not performed for the current unit,
wherein the second transform information being not equal to zero indicates a second transform matrix among the plurality of second transform matrices, and
wherein, when the width and the height of the current unit are equal to 128, the second transform information for the current unit is not obtained from the bitstream and the inverse second transform is not performed for the current unit;
when the second transform information is not equal to zero, determining the second transform matrix among the plurality of second transform matrices based on the second transform information;
obtaining a first transform coefficient block by performing the inverse second transform based on a second transform coefficient block and the second transform matrix; and
obtaining a residual block for the current unit by performing an inverse first transform based on the first transform coefficient block.
2 . The image decoding method of claim 1 , wherein the second transform information is decoded based on any one of a context-based adaptive binary arithmetic coding (CABAC) method, a fixed length method, and a unary method, and
wherein the CABAC method includes context modeling based on second transform information of a peripheral block of the first transform coefficient block.
3 . The image decoding method of claim 1 , wherein the obtaining of the first transform coefficient block by performing the inverse second transform comprises inverse-rearranging a coefficient of the first transform coefficient block by performing the inverse second transform based on the second transform matrix.
4 . The image decoding method of claim 1 , wherein:
the obtaining of the first transform coefficient block by performing the inverse second transform includes obtaining the first transform coefficient block by performing the inverse second transform based on at least a portion of the second transform coefficient block, and
the second transform coefficient block is a coefficient block having a size of a ratio of 1:N or N:1, wherein the Nis a natural number.
5 . An image encoding method supporting a coding unit having a size of 128×128, the image encoding method being performed by an apparatus and comprising:
obtaining a first transform coefficient block by performing a first transform based on a residual block for a current unit;
determining a second transform matrix among a plurality of second transform matrices;
obtaining a second transform coefficient block by performing a second transform based on the first transform coefficient block and the second transform matrix; and
when a width and a height of the current unit are equal to or less than 64, encoding second transform information for the current unit into a bitstream, wherein the second transform information indicates whether and which one among the plurality of second transform matrices is used,
wherein the second transform information being equal to zero indicates that an inverse second transform is not performed for the current unit,
wherein the second transform information being not equal to zero indicates the second transform matrix among the plurality of second transform matrices, and
wherein, when the width and the height of the current unit are equal to 128, the second transform information for the current unit is not encoded into the bitstream and the second transform is not performed for the current unit.
6 . A non-transitory storage medium storing instructions that, when executed by a processor of an apparatus, cause the apparatus to perform an image encoding method supporting a coding unit having a size of 128×128, the image encoding method comprising:
obtaining a first transform coefficient block by performing a first transform based on a residual block for a current unit;
determining a second transform matrix among a plurality of second transform matrices;
obtaining a second transform coefficient block by performing a second transform based on the first transform coefficient block and the second transform matrix; and
when a width and a height of the current unit are equal to or less than 64, encoding second transform information for the current unit into a bitstream, wherein the second transform information indicates whether and which one among the plurality of second transform matrices is used,
wherein the second transform information being equal to zero indicates that an inverse second transform is not performed for the current unit,
wherein the second transform information being not equal to zero indicates the second transform matrix among the plurality of second transform matrices, and
wherein, when the width and the height of the current unit are equal to 128, the second transform information for the current unit is not encoded into the bitstream and the second transform is not performed for the current unit.