Piece-wise-linear mapping for in-loop reshaping in image coding
AssigneeDolby Laboratories Licensing Corporation
InventorsTaoran Lu, Peng Yin
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Abstract
Given a representation of a forward reshaping function in an M-piecewise linear representation (M-PWL), methods, processes, and systems are presented for generating the forward reshaping function in an N-PWL representation (where N<M), by properly adjusting the first and last segments, and for generating a decoded bitstream using the adjusted N-PWL reshaping representation. Syntax methods for signaling reshaping parameters are also presented.
Claims16
A method for in-loop reshaping of a video sequence with a processor, the method comprising:
- generating a first piece-wise linear representation of a forward reshaping function using N segments all of an equal length, wherein the forward reshaping function maps luma pixel values of the video sequence from a first codeword representation to a second codeword representation, wherein the codeword start of the first segment is zero and the codeword end of the last segment is 2Bitdepth−1, where Bitdepth denotes the bit-depth of the luma pixels of the video sequence;
- in the first piece-wise linear representation, adjusting the codeword start of the first segment to generate an adjusted first segment of less than the equal length and adjusting the codeword end of the last segment to generate an adjusted last segment of less than the equal length to generate an output piece-wise linear representation of the forward reshaping function using the adjusted first segment, the adjusted last segment and zero or more remaining unadjusted segments of the N segments;
- generating syntax elements related to the output piece-wise linear representation of the forward reshaping function;
- and
- generating a coded bitstream using the output piece-wise linear representation of the forward reshaping function, wherein the coded bitstream includes the syntax elements related to the output piece-wise linear representation of the forward reshaping function.
A method to decode a coded bitstream using reshaping in a decoder, the method comprising:
- receiving syntax elements for a piece-wise linear representation of a forward reshaping function using N segments, wherein the forward reshaping function maps luma pixel values of the coded bitstream from a first codeword representation to a second codeword representation, wherein the syntax elements comprise one or more pivot parameters to adjust the codeword start of the first segment from 0 to a second codeword start greater than 0 and to adjust the codeword end of the last segment from 2Bitdepth−1, to a second codeword end different from 2Bitdepth−1, where Bitdepth denotes the bit-depth of the luma pixels of the coded bitstream;
- determining the second codeword start of the first segment and the second codeword end of the last segment based on the one or more pivot parameters to generate an adjusted piece-wise linear representation of the forward reshaping function;
- and
- decoding the coded bitstream based on the adjusted piece-wise linear representation of the forward reshaping function.
Dependencies are inferred from the claim text.