Cross-component planar prediction in image and video compression
Methods and apparatuses for video coding are provided. Processing circuitry in one of the apparatuses receives a coded video bitstream that includes prediction information of a chroma block to be reconstructed in a current picture. The prediction information indicates that the chroma block is predicted based at least on a luma block in the current picture. The luma block is reconstructed and collocated with the chroma block. The processing circuitry predicts one or more first chroma samples in the chroma block based on one or more luma samples in the luma block and predicts a second chroma sample in the chroma block based on the predicted one or more first chroma samples and at least one reference chroma sample of the chroma block. The second chroma sample is different from the one or more first chroma samples. The at least one reference chroma sample is adjacent to the chroma block.
1 . A method of video decoding in a decoder, comprising:
receiving a coded video bitstream that includes prediction information of a chroma block to be reconstructed in a current picture, the prediction information indicating that the chroma block is predicted based at least on a luma block in the current picture, the luma block being reconstructed and collocated with the chroma block;
predicting one or more first chroma samples in the chroma block based on one or more luma samples in the luma block; and
predicting a second chroma sample in the chroma block based on the predicted one or more first chroma samples and at least one reference chroma sample of the chroma block, the second chroma sample being different from the one or more first chroma samples, the at least one reference chroma sample being adjacent to the chroma block.
2 . The method of claim 1 , wherein
the one or more first chroma samples is a bottom-right corner chroma sample in the chroma block; and
the predicting the second chroma sample includes:
predicting, based on the bottom-right corner chroma sample and the at least one reference chroma sample, at least one of (i) chroma samples in a bottom row of the chroma block or (ii) chroma samples in a right most column of the chroma block;
when the chroma samples in the bottom row of the chroma block are predicted, generating a vertical predictor of the second chroma sample based on a top reference chroma sample in the at least one reference chroma sample and a predicted bottom chroma sample in the predicted chroma samples in the bottom row, the second chroma sample, the top reference chroma sample, and the predicted bottom chroma sample being in a same column in the chroma block; and
when the chroma samples in the right most column of the chroma block are predicted, generating a horizontal predictor of the second chroma sample based on a left reference chroma sample in the at least one reference chroma sample and a predicted right chroma sample in the predicted chroma samples in the right most column, the second chroma sample, the left reference chroma sample, and the predicted right chroma sample being in a same row of the chroma block.
3 . The method of claim 2 , wherein
the predicting the at least one of (i) the chroma samples in the bottom row of the chroma block or (ii) the chroma samples in the right most column of the chroma block includes predicting the chroma samples in the bottom row of the chroma block and the chroma samples in the right most column of the chroma block; and
the predicting the second chroma sample includes predicting the second chroma sample based on the vertical predictor and the horizontal predictor.
4 . The method of claim 2 , wherein
a width of the chroma block is larger than a height of the chroma block or the height of the chroma block is less than a threshold;
the predicting the at least one of (i) the chroma samples in the bottom row of the chroma block or (ii) the chroma samples in the right most column of the chroma block includes predicting the chroma samples in the bottom row of the chroma block; and
the predicting the second chroma sample includes predicting the second chroma sample based on the vertical predictor.
5 . The method of claim 2 , wherein
a width of the chroma block is less than a height of the chroma block or a threshold;
the predicting the at least one of (i) the chroma samples in the bottom row of the chroma block or (ii) the chroma samples in the right most column of the chroma block includes predicting the chroma samples in the right most column of the chroma block; and
the predicting the second chroma sample includes predicting the second chroma sample based on the horizontal predictor.
6 . The method of claim 2 , wherein the predicting the one or more first chroma samples comprises:
predicting the bottom-right corner chroma sample in the chroma block based on at least one of a bottom-right corner luma sample in the luma block or luma samples in the luma block that are collocated with the bottom-right corner chroma sample.
7 . The method of claim 1 , wherein
the one or more first chroma samples include (i) chroma samples in a bottom row of the chroma block and (ii) chroma samples in a right most column of the chroma block; and
the predicting the second chroma sample includes:
generating a vertical predictor of the second chroma sample based on a top reference chroma sample in the at least one reference chroma sample and a predicted bottom chroma sample in the predicted chroma samples in the bottom row, the second chroma sample, the top reference chroma sample, and the predicted bottom chroma sample being in a same column in the chroma block;
generating a horizontal predictor of the second chroma sample based on a left reference chroma sample in the at least one reference chroma sample and a predicted right chroma sample in the predicted chroma samples in the right most column, the second chroma sample, the left reference chroma sample, and the predicted right chroma sample being in a same row in the chroma block; and
predicting the second chroma sample based on the vertical predictor and the horizontal predictor.
8 . The method of claim 1 , wherein
a width of the chroma block is larger than a height of the chroma block or the height of the chroma block is less than a threshold;
the one or more first chroma samples include chroma samples in a bottom row of the chroma block; and
the predicting the second chroma sample includes:
generating a vertical predictor of the second chroma sample based on a top reference chroma sample in the at least one reference chroma sample and a predicted bottom chroma sample in the predicted chroma samples in the bottom row, the second chroma sample, the top reference chroma sample, and the predicted bottom chroma sample being in a same column in the chroma block; and
predicting the second chroma sample based on the vertical predictor.
9 . The method of claim 1 , wherein
a width of the chroma block is less than a height of the chroma block or a threshold;
the one or more first chroma samples include chroma samples in a right most column of the chroma block; and
the predicting the second chroma sample includes:
generating a horizontal predictor of the second chroma sample based on a left reference chroma sample in the at least one reference chroma sample and a predicted right chroma sample in the predicted chroma samples in the right most column, the second chroma sample, the left reference chroma sample, and the predicted right chroma sample being in a same row in the chroma block; and
predicting the second chroma sample based on the horizontal predictor.
10 . The method of claim 1 , wherein
the predicting the one or more first chroma samples includes predicting the one or more first chroma samples in the chroma block based on the one or more luma samples in the luma block that are collocated with the one or more first chroma samples using a cross-component linear model prediction (CCLM) mode; and
the predicting the second chroma sample in the chroma block includes predicting the second chroma sample in the chroma block using a planar mode.
11 . The method of claim 1 , wherein
the at least one reference chroma sample includes at least one of a top reference chroma sample that is a top neighbor of the chroma block or a left reference chroma sample that is a left neighbor of the chroma block.
12 . A method of video encoding, comprising:
predicting one or more first chroma samples in a chroma block to be encoded in a current picture based on one or more luma samples in a luma block in the current picture, the chroma block being predicted based at least on the luma block in the current picture, the luma block being reconstructed and collocated with the chroma block;
predicting a second chroma sample in the chroma block based on the predicted one or more first chroma samples and at least one reference chroma sample of the chroma block, the second chroma sample being different from the one or more first chroma samples, the at least one reference chroma sample being adjacent to the chroma block;
encoding prediction information in a bitstream indicating that the chroma block is predicted based at least on the luma block in the current picture; and
encoding the chroma block in the bitstream based on the predicted second chroma sample.
13 . The method of claim 12 , wherein
the one or more first chroma samples is a bottom-right corner chroma sample in the chroma block; and
the predicting the second chroma sample includes:
predicting, based on the bottom-right corner chroma sample and the at least one reference chroma sample, at least one of (i) chroma samples in a bottom row of the chroma block or (ii) chroma samples in a right most column of the chroma block;
when the chroma samples in the bottom row of the chroma block are predicted, generating a vertical predictor of the second chroma sample based on a top reference chroma sample in the at least one reference chroma sample and a predicted bottom chroma sample in the predicted chroma samples in the bottom row, the second chroma sample, the top reference chroma sample, and the predicted bottom chroma sample being in a same column in the chroma block; and
when the chroma samples in the right most column of the chroma block are predicted, generating a horizontal predictor of the second chroma sample based on a left reference chroma sample in the at least one reference chroma sample and a predicted right chroma sample in the predicted chroma samples in the right most column, the second chroma sample, the left reference chroma sample, and the predicted right chroma sample being in a same row of the chroma block.
14 . The method of claim 13 , wherein
the predicting the at least one of (i) the chroma samples in the bottom row of the chroma block or (ii) the chroma samples in the right most column of the chroma block includes predicting the chroma samples in the bottom row of the chroma block and the chroma samples in the right most column of the chroma block; and
the predicting the second chroma sample includes predicting the second chroma sample based on the vertical predictor and the horizontal predictor.
15 . The method of claim 13 , wherein
a width of the chroma block is larger than a height of the chroma block or the height of the chroma block is less than a threshold;
the predicting the at least one of (i) the chroma samples in the bottom row of the chroma block or (ii) the chroma samples in the right most column of the chroma block includes predicting the chroma samples in the bottom row of the chroma block; and
the predicting the second chroma sample includes predicting the second chroma sample based on the vertical predictor.
16 . The method of claim 13 , wherein
a width of the chroma block is less than a height of the chroma block or a threshold;
the predicting the at least one of (i) the chroma samples in the bottom row of the chroma block or (ii) the chroma samples in the right most column of the chroma block includes predicting the chroma samples in the right most column of the chroma block; and
the predicting the second chroma sample includes predicting the second chroma sample based on the horizontal predictor.
17 . The method of claim 13 , wherein the predicting the one or more first chroma samples comprises:
predicting the bottom-right corner chroma sample in the chroma block based on at least one of a bottom-right corner luma sample in the luma block or luma samples in the luma block that are collocated with the bottom-right corner chroma sample.
18 . The method of claim 12 , wherein
the one or more first chroma samples include (i) chroma samples in a bottom row of the chroma block and (ii) chroma samples in a right most column of the chroma block; and
the predicting the second chroma sample includes:
generating a vertical predictor of the second chroma sample based on a top reference chroma sample in the at least one reference chroma sample and a predicted bottom chroma sample in the predicted chroma samples in the bottom row, the second chroma sample, the top reference chroma sample, and the predicted bottom chroma sample being in a same column in the chroma block;
generating a horizontal predictor of the second chroma sample based on a left reference chroma sample in the at least one reference chroma sample and a predicted right chroma sample in the predicted chroma samples in the right most column, the second chroma sample, the left reference chroma sample, and the predicted right chroma sample being in a same row in the chroma block; and
predicting the second chroma sample based on the vertical predictor and the horizontal predictor.
19 . The method of claim 12 , wherein
the predicting the one or more first chroma samples includes predicting the one or more first chroma samples in the chroma block based on the one or more luma samples in the luma block that are collocated with the one or more first chroma samples using a cross-component linear model prediction (CCLM) mode; and
the predicting the second chroma sample in the chroma block includes predicting the second chroma sample in the chroma block using a planar mode.
20 . A non-transitory computer-readable storage medium storing instructions which when executed by a processor cause the processor to perform an encoding method comprising:
predicting one or more first chroma samples in a chroma block to be encoded in a current picture based on one or more luma samples in a luma block in the current picture, the chroma block being predicted based at least on the luma block in the current picture, the luma block being reconstructed and collocated with the chroma block;
predicting a second chroma sample in the chroma block based on the predicted one or more first chroma samples and at least one reference chroma sample of the chroma block, the second chroma sample being different from the one or more first chroma samples, the at least one reference chroma sample being adjacent to the chroma block;
encoding prediction information in a bitstream indicating that the chroma block is predicted based at least on the luma block in the current picture;
encoding the chroma block in the bitstream based on the predicted second chroma sample; and
transmitting the bitstream.