Video coding and decoding to improve signaling of an affine motion mode
The invention relates to signalling affine mode in an encoded video stream; in particular determining a list of merge candidates corresponding to blocks neighbouring a current block; and signalling affine mode for said current block; wherein signalling said affine mode comprises decoding a context encoded flag from the data stream, and wherein the context variable for said flag is determined based on whether or not said neighbouring blocks use affine mode. Related encoding and decoding methods and devices are also disclosed.
1. A method of decoding an image from a bitstream encoded using motion prediction, the method comprising:
determining, from a plurality of prediction modes including intra mode and inter mode, a prediction mode used to decode a current block of the image;
compiling a list of candidate motion predictors in the case where the inter mode is determined for the current block; and
placing a candidate for subblock affine prediction as a merge candidate lower in said list than a temporal motion vector candidate, the subblock affine prediction deriving one motion vector per subblock in a current block by using two or three motion vectors from a block which is of the same frame as the current block.
2. A method of encoding an image into a bitstream using motion prediction, the method comprising:
determining, from a plurality of prediction modes including intra mode and inter mode, a prediction mode used to encode a current block of the image;
compiling a list of candidate motion predictors in the case where the inter mode is determined for the current block; and
placing a candidate for subblock affine prediction as a merge candidate lower in said list than a temporal motion vector candidate, the subblock affine prediction deriving one motion vector per subblock in a current block by using two or three motion vectors from a block which is of the same frame as the current block.
3. An encoder for encoding an image into a bitstream using motion prediction, the encoder comprising:
a unit configured to determine, from a plurality of prediction modes including intra mode and inter mode, a prediction mode used to encode a current block of the image;
a unit configured to compile a list of candidate motion predictors in the case where the inter mode is determined for the current block; and
a unit configured to place a candidate for subblock affine prediction as a merge candidate lower in said list than a temporal motion vector candidate, the subblock affine prediction deriving one motion vector per subblock in a current block by using two or three motion vectors from a block which is of the same frame as the current block.
4. A decoder for decoding an image from a bitstream encoded using motion prediction, the decoder comprising:
a unit configured to determine, from a plurality of prediction modes including intra mode and inter mode, a prediction mode used to decode a current block of the image;
a unit configured to compile a list of candidate motion predictors in the case where the inter mode is determined for the current block; and
a unit configured to place a candidate for subblock affine prediction as a merge candidate lower in said list than a temporal motion vector candidate, the subblock affine prediction deriving one motion vector per subblock in a current block by using two or three motion vectors from a block which is of the same frame as the current block.
5. A non-transitory computer-readable storage medium storing a program for causing a computer to execute a method of decoding an image from a bitstream encoded using motion prediction, the method comprising:
determining, from a plurality of prediction modes including intra mode and inter mode, a prediction mode used to decode a current block of the image;
compiling a list of candidate motion predictors in the case where the inter mode is determined for the current block; and
placing a candidate for subblock affine prediction as a merge candidate lower in said list than a temporal motion vector candidate, the subblock affine prediction deriving one motion vector per subblock in a current block by using two or three motion vectors from a block which is of the same frame as the current block.
6. A non-transitory computer-readable storage medium storing a program for causing a computer to execute a method of encoding an image into a bitstream using motion prediction, the method comprising:
determining, from a plurality of prediction modes including intra mode and inter mode, a prediction mode used to encode a current block of the image;
compiling a list of candidate motion predictors; and
placing a candidate for subblock affine prediction as a merge candidate lower in said list than a temporal motion vector candidate, the subblock affine prediction deriving one motion vector per subblock in a current block by using two or three motion vectors from a block which is of the same frame as the current block.