Intra-prediction-based image coding method and device therefor
A picture decoding method performed by a decoding apparatus according to the present disclosure includes detecting intra prediction modes of a plurality of luma blocks in a luma region corresponding to a current chroma block, generating a first predicted block for the current chroma block based on a first intra prediction mode of the intra prediction modes of the plurality of luma blocks, generating a second predicted block for the current chroma block based on a second intra prediction mode of the intra prediction modes of the plurality of luma blocks, generating a predicted block for the current chroma block based on a weighted sum using the first predicted block and the second predicted block, and generating a reconstructed block based on the predicted block for the current chroma block.
1. A picture decoding method performed by a decoding apparatus, the method comprising:
detecting intra prediction modes of a plurality of luma blocks in a luma region corresponding to a current chroma block;
deriving chroma prediction mode candidates for the current chroma block, wherein the chroma prediction mode candidates include a combined direct mode, a first intra prediction mode of the intra prediction modes of the plurality of the luma blocks, a second intra prediction mode of the intra prediction modes of the plurality of the luma blocks, intra prediction modes of neighboring chroma blocks of the current chroma block, and at least one of default prediction modes;
receiving index information regarding an intra chroma prediction mode;
selecting the intra chroma prediction mode of the current chroma block based on the chroma prediction mode candidates and the index information regarding the intra chroma prediction mode;
generating a predicted block for the current chroma block based on the selected intra chroma prediction mode of the current chroma block; and
generating a reconstructed block based on the predicted block for the current chroma block,
wherein the default prediction modes include at least one of a DC mode or a planar mode,
wherein, based on a value of the index information being 0, the combined direct mode is selected from among the chroma prediction mode candidates,
wherein a maximum number of the chroma prediction mode candidates is 5, and the value of the index information is one among 0 through 4,
wherein the value of the index information is derived based on binarization bits for the index information,
wherein for the value of the index information being 0, the binarization bits is represented by 0,
wherein for the value of the index information being 1, the binarization bits is represented by 100,
wherein for the value of the index information being 2, the binarization bits is represented by 101,
wherein for the value of the index information being 3, the binarization bits is represented by 110,
wherein for the value of the index information being 4, the binarization bits is represented by 111, and
wherein generating the predicted block for the current block comprises:
generating a first predicted block for the current chroma block based on the first intra prediction mode of the intra prediction modes of the plurality of the luma blocks, wherein the first predicted block includes first predicted pixels for the current chroma block,
generating a second predicted block for the current chroma block based on the second intra prediction mode of the intra prediction modes of the plurality of the luma blocks, wherein the second predicted block includes second predicted pixels for the current chroma block, and
generating the predicted block for the current chroma block based on a weighted sum using the first predicted block and the second predicted block, and
wherein a predicted pixel of the predicted block for the current chroma block is generated based on the weighted sum using a first predicted pixel of the chroma block and a second predicted pixel of the chroma block.
2. The picture decoding method of claim 1 , wherein a first weight and a second weight for the first predicted block and the second predicted block used to derive the weighted sum are equal to each other.
3. The picture decoding method of claim 1 , wherein the detecting of the intra prediction modes of the plurality of the luma blocks includes:
detecting the intra prediction modes of the plurality of the luma blocks based on at least one of a first luma block covering a center bottom-right sample position of the luma region, a second luma block covering a top-left sample position of the luma region, a third luma block covering a top-right sample position of the luma region, a fourth luma block covering a bottom-left sample position of the luma region, or a fifth luma block covering a bottom-right sample position of the luma region.
4. A decoding apparatus which performs picture decoding, the decoding apparatus comprising:
an entropy decoder configured to receive index information regarding an intra chroma prediction mode;
a predictor configured to:
detect intra prediction modes of a plurality of luma blocks in a luma region corresponding to a current chroma block,
derive chroma prediction mode candidates for the current chroma block, wherein the chroma prediction mode candidates include a combined direct mode, a first intra prediction mode of the intra prediction modes of the plurality of the luma blocks, a second intra prediction mode of the intra prediction modes of the plurality of the luma blocks, intra prediction modes of neighboring chroma blocks of the current chroma block, and at least one of default prediction modes,
derive the intra chroma prediction mode of the current chroma block based on the chroma prediction mode candidates and the index information regarding the intra chroma prediction mode, and
generate a predicted block for the current chroma block based on the derived intra chroma prediction mode of the current chroma block,
wherein the default prediction modes include at least one of a DC mode or a planar mode,
wherein, based on a value of the index information being 0, the combined direct mode is selected from among the chroma prediction mode candidates,
wherein a maximum number of the chroma prediction mode candidates is 5, and the value of the index information is one among 0 through 4,
wherein the value of the index information is derived based on binarization bits for the index information,
wherein for the value of the index information being 0, the binarization bits is represented by 0,
wherein for the value of the index information being 1, the binarization bits is represented by 100,
wherein for the value of the index information being 2, the binarization bits is represented by 101,
wherein for the value of the index information being 3, the binarization bits is represented by 110,
wherein for the value of the index information being 4, the binarization bits is represented by 111, and
wherein generating the predicted block for the current block comprises:
generating a first predicted block for the current chroma block based on the first intra prediction mode of the intra prediction modes of the plurality of the luma blocks, the first predicted block including first predicted pixels for the current chroma block,
generating a second predicted block for the current chroma block based on the second intra prediction mode of the intra prediction modes of the plurality of the luma blocks, the second predicted block including second predicted pixels for the current chroma block, and
generating the predicted block for the current chroma block based on a weighted sum using the first predicted block and the second predicted block,
wherein a predicted pixel of the predicted block for the current chroma block is generated based on the weighted sum using a first predicted pixel of the chroma block and a second predicted pixel of the chroma block; and
an adder configured to generate a reconstructed block based on the predicted block for the current chroma block.
5. An encoding apparatus which performs picture encoding, the encoding apparatus comprising:
a predictor configured to:
detect intra prediction modes of a plurality of luma blocks in a luma region corresponding to a current chroma block,
derive chroma prediction mode candidates for the current chroma block, wherein the chroma prediction mode candidates include a combined direct mode, a first intra prediction mode of the intra prediction modes of the plurality of the luma blocks, a second intra prediction mode of the intra prediction modes of the plurality of the luma blocks, intra prediction modes of neighboring chroma blocks of the current chroma block, and at least one of default prediction modes,
select an intra chroma prediction mode of the current chroma block based on the chroma prediction mode candidates,
generate index information regarding the intra chroma prediction mode, and
generate a predicted block for the current chroma block based on the selected intra chroma prediction mode of the current chroma block;
a residual processor configured to generate residual information based on the predicted block; and
an entropy encoder configured to encode image information including the index information regarding the intra chroma prediction mode and the residual information,
wherein the default prediction modes include at least one of a DC mode or a planar mode,
wherein a value of the index information being 0 indicates the combined direct mode from among the chroma prediction mode candidates,
wherein a maximum number of the chroma prediction mode candidates is 5, and the value of the index information is one among 0 through 4,
wherein the value of the index information is derived based on binarization bits for the index information,
wherein for the value of the index information being 0, the binarization bits is represented by 0,
wherein for the value of the index information being 1, the binarization bits is represented by 100,
wherein for the value of the index information being 2, the binarization bits is represented by 101,
wherein for the value of the index information being 3, the binarization bits is represented by 110,
wherein for the value of the index information being 4, the binarization bits is represented by 111, and
wherein, based on the combined direct mode being applied to the current chroma block, the predictor generates the predicted block by performing operations comprising:
generating a first predicted block for the current chroma block based on the first intra prediction mode of the intra prediction modes of the plurality of the luma blocks, wherein the first predicted block includes first predicted pixels for the current chroma block,
generating a second predicted block for the current chroma block based on the second intra prediction mode of the intra prediction modes of the plurality of the luma blocks, wherein the second predicted block includes second predicted pixels for the current chroma block, and
generating the predicted block for the current chroma block based on a weighted sum using the first predicted block and the second predicted block,
wherein a predicted pixel of the predicted block for the current chroma block is generated based on the weighted sum using a first predicted pixel of the chroma block and a second predicted pixel of the chroma block.