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US 11,902,530 B2Granted
Image coding method based on transform and apparatus therefor
AssigneeLG Electronics Inc.
InventorsMoonmo Koo, Hyeongmoon Jang, Seunghwan Kim, Jaehyun Lim
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Abstract
An image decoding method according to the present document may comprise the steps of: deriving an intra prediction mode of a chroma block as a cross-component linear model (CCLM) mode on the basis of intra prediction mode information; updating the intra prediction mode of the chroma block on the basis of an intra prediction mode of a luma block corresponding to the chroma block; when the chroma block is not square, remapping the updated intra prediction mode to a wide-angle intra prediction mode; and determining an LFNST set including LFNST matrices on the basis of the remapped intra prediction mode.
Claims12
An image decoding method performed by a decoding apparatus, the method comprising:
- obtaining intra prediction mode information and an LFNST index from a bitstream;
- deriving an intra prediction mode for a chroma block as a cross-component linear model (CCLM) mode based on the intra prediction mode information;
- derives prediction samples for the chroma block based on the CCLM mode;
- performing an LFNST to derive transform coefficients;
- and
- deriving residual samples for the chroma block based on the transform coefficients,
- wherein the performing of the LFNST comprising:
- updating the intra prediction mode for the chroma block based on an intra prediction mode for a luma block corresponding to the chroma block;
- modifying the updated intra prediction mode to a wide angle intra prediction mode based on a width of the chroma block not being equal to a height of the chroma block;
- determining an LFNST set comprising LFNST matrices based on a modified intra prediction mode by the wide angle intra prediction mode mapping process;
- and
- performing a matrix operation based on an LFNST matrix derived from the LFNST index and the LFNST set;
- wherein the updated intra prediction mode is derived as an intra prediction mode corresponding to a specific position in the luma block,
- wherein the specific position is set to ((xTbY+(nTbW*SubWidthC)/2), (yTbY+(nTbH*SubHeightC)/2)),
- wherein xTbY and yTbY denote top-left coordinates of the luma block,
- wherein nTbW and nTbH denote the width and the height of the chroma block, and
- wherein SubWidthC and SubHeightC denote variables corresponding to a color format.
14 more elements
An image encoding method performed by an encoding apparatus, the method comprising:
- deriving an intra prediction mode for a chroma block as a cross-component linear model (CCLM) mode;
- deriving prediction samples for the chroma block based on the CCLM mode;
- deriving residual samples for the chroma block based on the prediction samples;
- and
- performing an LFNST to derive transform coefficients;
- wherein the performing of the LFNST comprising:
- updating the intra prediction mode for the chroma block based on an intra prediction mode for a luma block corresponding to the chroma block;
- modifying the updated intra prediction mode to a wide angle intra prediction mode based on a width of the chroma block not being equal to a height of the chroma block;
- determining an LFNST set comprising LFNST matrices based on a modified intra prediction mode by the wide angle intra prediction mode mapping process;
- and
- performing a matrix operation based on one LFNST matrix,
- wherein the updated intra prediction mode is derived as an intra prediction mode corresponding to a specific position in the luma block,
- wherein the specific position is set to ((xTbY+(nTbW*SubWidthC)/2), (yTbY+(nTbH *SubHeightC)/2)),
- wherein xTbY and yTbY denote top-left coordinates of the luma block,
- wherein nTbW and nTbH denote the width and the height of the chroma block, and
- wherein SubWidthC and SubHeightC denote variables corresponding to a color format.
13 more elements
A transmitting method of data for an image, the method comprising:
- obtaining a bitstream for the image, wherein the bitstream is generated based on deriving an intra prediction mode for a chroma block as a cross-component linear model (CCLM) mode;
- deriving prediction samples for the chroma block based on the CCLM mode;
- deriving residual samples for the chroma block based on the prediction samples;
- performing an LFNST to derive transform coefficients;
- and encoding image information related to the transform coefficients;
- and
- transmitting the data comprising the bitstream,
- wherein the performing of the LFNST comprising:
- updating the intra prediction mode for the chroma block based on an intra prediction mode for a luma block corresponding to the chroma block;
- modifying the updated intra prediction mode to a wide angle intra prediction mode based on a width of the chroma block not being equal to a height of the chroma block;
- determining an LFNST set comprising LFNST matrices based on a modified intra prediction mode by the wide angle intra prediction mode mapping process;
- and
- performing a matrix operation based on one LFNST matrix,
- wherein the updated intra prediction mode is derived as an intra prediction mode corresponding to a specific position in the luma block,
- wherein the specific position is set to ((xTbY+(nTbW*SubWidthC)/2), (yTbY+(nTbH *SubHeightC)/2)),
- wherein xTbY and yTbY denote top-left coordinates of the luma block,
- wherein nTbW and nTbH denote the width and the height of the chroma block, and
- wherein SubWidthC and SubHeightC denote variables corresponding to a color format.
15 more elements
Dependencies are inferred from the claim text.