Method and apparatus of video coding with prediction offset
A method and apparatus for video encoding and decoding with prediction offset in a video coding system are disclosed. A prediction offset for a current block is derived from a reconstructed residual signal of one or more coded blocks. At the encoder side, a residual signal for the current block is calculated by subtracting a prediction signal and the prediction offset from an original signal of the current block, and the residual signal is encoded to generate an encoded bitstream. At the decoder side, a residual signal for the current block is obtained from input data, a reconstructed signal for the current block is calculated by adding a prediction signal and the prediction offset to the residual signal, and the current block is decoded using the reconstructed signal.
1. A method of encoding video data in a video coding system, comprising:
receiving input data associated with a current block in a current picture, the current block being coded according to a merge mode using motion information of a merge candidate;
deriving a prediction offset for the current block from a reconstructed residual signal of the merge candidate that is spatially adjacent to the current block;
calculating a residual signal for the current block by subtracting a prediction signal obtained according to the motion information of the merge candidate and the prediction offset from an original signal of the current block; and
encoding the residual signal for the current block to generate an encoded bitstream.
2. The method of claim 1 , wherein the prediction offset is derived as a mean value of the reconstructed residual signal of the merge candidate.
3. The method of claim 2 , wherein the mean value of the reconstructed residual signal of the merge candidate is pre-calculated and stored before the mean value is used for deriving the prediction offset for the current block.
4. The method of claim 1 , wherein the merge candidate corresponds to a coding block, a prediction block, a 4×4 block, or a block with a predefined block size.
5. The method of claim 1 , further comprising selecting the merge candidate from a plurality of candidate coded blocks by comparing motion information of the candidate coded blocks with motion information of the current block.
6. The method of claim 5 , wherein the merge candidate selected from the candidate coded blocks has a candidate motion vector and a candidate reference picture index same as a current motion vector and a current reference picture index of the current block.
7. The method of claim 1 , further comprising:
deriving and applying the prediction offset in a case that the current block belongs to a predefined category; and
calculating the residual signal for the current block by subtracting only the prediction signal from the original signal of the current block in a case that the current block does not belong to the predefined category,
wherein the current block belongs to the predefined category if the current block is a luma component, a predetermined partition size, coded in merge mode, or a combination thereof.
8. The method of claim 1 , further comprising incorporating a syntax element to explicitly signal whether the prediction offset is applied.
9. The method of claim 1 , further comprising:
setting the prediction offset to zero or a preset value if the derived prediction offset is larger than a first threshold, if the merge candidate is smaller than the current block, or if a variance of the merge candidate is larger than a second threshold.
10. A method of decoding a video bitstream in a video coding system, comprising:
receiving input data associated with a current block in a current picture, the current block being coded according to a merge mode using motion information of a merge candidate;
obtaining a residual signal for the current block from the input data;
deriving a prediction offset for the current block from a reconstructed residual signal of the merge candidate that is spatially adjacent to the current block;
calculating a reconstructed signal for the current block by adding a prediction signal obtained according to the motion information of the merge candidate and the prediction offset to the residual signal for the current block; and
decoding the current block using the reconstructed signal for the current block.
11. The method of claim 10 , wherein the prediction offset is derived as a mean value of the reconstructed residual signal of the merge candidate.
12. The method of claim 11 , wherein the mean value of the reconstructed residual signal of the merge candidate is pre-calculated and stored before the mean value is used for deriving the prediction offset for the current block.
13. The method of claim 10 , wherein the merge candidate corresponds to a coding block, a prediction block, a 4×4 block, or a block with a predefined block size.
14. The method of claim 10 , further comprising selecting the merge candidate from a plurality of candidate coded blocks.
15. The method of claim 14 , wherein the merge candidate selected from the candidate coded bocks has a candidate motion vector and a candidate reference picture index same as a current motion vector and a current reference picture index of the current block.
16. The method of claim 10 , further comprising:
deriving and applying the prediction offset in a case that the current block belongs to a predefined category; and
calculating the reconstructed signal for the current block by only adding the prediction signal to the residual signal for the current block in a case that the current block does not belong to the predefined category,
wherein the current block belongs to the predefined category if the current block is a luma component, a predetermined partition size, coded in merge mode, or a combination thereof.
17. The method of claim 10 , further comprising retrieving a syntax element from the input data to determine whether the prediction offset is applied.
18. The method of claim 10 , further comprising:
setting the prediction offset to zero or a preset value if the derived prediction offset is larger than a first threshold, if the merge candidate is smaller than the current block, or if a variance of the merge candidate is larger than a second threshold.
19. An apparatus of decoding a video bitstream, the apparatus comprising:
processing circuitry configured to:
receive input data associated with a current block in a current picture, the current block being coded according to a merge mode using motion information of a merge candidate;
obtain a residual signal for the current block from the input data;
derive a prediction offset for the current block from a reconstructed residual signal of the merge candidate that is spatially adjacent to the current block;
calculate a reconstructed signal for the current block by adding a prediction signal obtained according to the motion information of the merge candidate and the prediction offset to the residual signal for the current block; and
decode the current block using the reconstructed signal for the current block.