Pruning method for history-based affine parameters

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• derive, for a conversion between a current block of a video and a bitstream of the video, a first set of affine parameters associated with affine model for the current block;
• compare the first set of affine parameters to one or more of sets of affine parameters stored in a buffer for storing affine parameters to make a determination whether the first set of affine parameters is same or similar to at least one set of affine parameters;
• and
• decide whether or how to update the buffer for storing affine parameters based on the determination,
• wherein, in response to the determination indicating that the first set of affine parameters is not same or similar to at least one set of affine parameters stored in the buffer, storing the first set of affine parameters in the buffer,
• wherein the first set of affine parameters comprises variables a, b, c or d, or variables a, b, c, d, e, f,
• a
• =
• (
• mv
• 1
• h
• -
• mv
• 0
• h
• )
• w
• ,
• b
• =
• (
• mv
• 1
• v
• -
• mv
• 0
• v
• )
• w
• ,
• c
• =
• (
• mv
• 2
• h
• -
• mv
• 0
• h
• )
• h
• ,
• d
• =
• (
• mv
• 2
• v
• -
• mv
• 0
• v
• )
• h
• ,
• e=mv0h, f=mv0v, or (e, f)=(mvx, mvy), where (mvx, mvy) is any motion vector used for coding a first block, wherein (mvh0, mvv0) is a motion vector of a top-left corner control point, (mvh1, mvv1) is a motion vector of a top-right corner control point, and (mvh2, mvv2) is a motion vector of a bottom-left corner control point, and wherein w and h are width and height of the current block, respectively.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• deriving, for a current block of the video, a first set of affine parameters associated with affine model for the current block;
• comparing the first set of affine parameters to one or more of sets of affine parameters stored in a buffer for storing affine parameters to make a determination whether the first set of affine parameters is same or similar to at least one set of affine parameters;
• deciding whether or how to update the buffer for storing affine parameters based on the determination;
• and
• generating the bitstream based on the deciding,
• wherein, in response to the determination indicating that the first set of affine parameters is not same or similar to at least one set of affine parameters stored in the buffer, storing the first set of affine parameters in the buffer,
• wherein the first set of affine parameters comprises variables a, b, c or d, or variables a, b, c, d, e, f,
• a
• =
• (
• mv
• 1
• h
• -
• mv
• 0
• h
• )
• w
• ,
• b
• =
• (
• mv
• 1
• v
• -
• mv
• 0
• v
• )
• w
• ,
• c
• =
• (
• mv
• 2
• h
• -
• mv
• 0
• h
• )
• h
• ,
• d
• =
• (
• mv
• 2
• v
• -
• mv
• 0
• v
• )
• h
• ,
• e=mv0h, f=mv0v, or (e, f)=(mvx, mvy), where (mvx, mvy) is any motion vector used for coding a first block, wherein (mvh0, mvv0) is a motion vector of a top-left corner control point, (mvh1, mvv1) is a motion vector of a top-right corner control point, and (mvh2, mvv2) is a motion vector of a bottom-left corner control point, and wherein w and h are width and height of the current block, respectively.