Image reshaping in video coding using rate distortion optimization
Given a sequence of images in a first codeword representation, methods, processes, and systems are presented for image reshaping using rate distortion optimization, wherein reshaping allows the images to be coded in a second codeword representation which allows more efficient compression than using the first codeword representation. Syntax methods for signaling reshaping parameters are also presented.
1. A method to reconstruct coded video data with one or more processors, the method comprising:
receiving a coded bitstream comprising one or more coded reshaped images in a reshaped codeword representation;
receiving reshaping parameters for the one or more coded reshaped images in the coded bitstream, wherein the reshaping parameters comprise parameters to generate a forward reshaping function based on the reshaping parameters, wherein the forward reshaping function maps pixels of an image from an input codeword representation to the reshaped codeword representation, wherein the reshaping parameters comprise:
a delta-index parameter to determine an active maximum bin index used for reshaping, wherein the active maximum bin index is smaller or equal to a predefined maximum bin index, wherein the delta-index parameter represents a difference between the active maximum bin index and the predefined maximum bin index;
a min-index parameter indicating a minimum bin index being used in the reshaping;
absolute delta codeword values for each active bin used in the reshaping; and
signs of the absolute delta codeword values for each active bin used in the reshaping.
2. The method of claim 1 , wherein the forward reshaping function is reconstructed as a piece-wise linear function with linear segments derived by the reshaping parameters.
3. The method of claim 1 , wherein determining the active maximum bin index used for representing the input codeword representation comprises computing a difference between the predefined maximum bin index and the delta-index parameter.
4. The method of claim 1 , wherein the predefined maximum bin index is one of 15, 31, or 63.
5. A method to generate reshaping parameters for an encoded bitstream, the method comprising:
receiving a sequence of video pictures in an input codeword representation;
for one or more pictures in the sequence of video pictures applying a forward reshaping function to generate reshaped pictures in a reshaped codeword representation, wherein the forward reshaping function maps pixels of an image from the input codeword representation to the reshaped codeword representation;
generating reshaping parameters for the reshaped codeword representation; and
generating a coded bitstream based at least on the reshaped pictures, wherein the reshaping parameters comprise:
a delta-index parameter to determine an active maximum bin index used for reshaping, wherein the active maximum bin index is smaller or equal to a predefined maximum bin index, wherein the delta-index parameter represents a difference between the active maximum bin index and the predefined maximum bin index;
a min-index parameter indicating a minimum bin index being used in the reshaping;
absolute delta codeword values for each active bin used in the reshaping; and
signs of the absolute delta codeword values for each active bin used in the reshaping.
6. The method of claim 5 , wherein the forward reshaping function comprises a piece-wise linear function with linear segments derived by the reshaping parameters.
7. The method of claim 5 , wherein determining the active maximum bin index used for representing the input codeword representation comprises computing a difference between the predefined maximum bin index and the delta-index parameter.
8. The method of claim 5 , wherein the predefined maximum bin index is one of 15, 31, or 63.
9. An apparatus comprising:
a processor;
one or more non-transitory computer-readable media storing instructions for generating and recording a bitstream in a recording medium, the instructions, when executed by the processor, causing the processor to perform a video encoding method to generate the bitstream,
the encoding method comprising:
receiving a sequence of video pictures in an input codeword representation;
for one or more pictures in the sequence of video pictures applying a forward reshaping function to generate reshaped pictures in a reshaped codeword representation, wherein the forward reshaping function maps pixels of an image from the input codeword representation to the reshaped codeword representation;
generating reshaping parameters for the reshaped codeword representation; and
generating a coded bitstream based at least on the reshaped pictures, wherein the reshaping parameters comprise:
a delta-index parameter to determine an active maximum bin index used for reshaping, wherein the active maximum bin index is smaller or equal to a predefined maximum bin index, wherein the delta-index parameter represents a difference between the active maximum bin index and the predefined maximum bin index;
a min-index parameter indicating a minimum bin index being used in the reshaping;
absolute delta codeword values for each active bin used in the reshaping; and
signs of the absolute delta codeword values for each active bin used in the reshaping.
10. The apparatus of claim 9 , wherein the forward reshaping function comprises a piece-wise linear function with linear segments derived by the reshaping parameters.
11. The apparatus of claim 9 , wherein determining the active maximum bin index used for representing the input codeword representation comprises computing a difference between the predefined maximum bin index and the delta-index parameter.
12. The apparatus of claim 9 , wherein the predefined maximum bin index is one of 15, 31, or 63.
13. One or more non-transitory computer-readable media storing instructions for generating and recording a bitstream in a recording medium, the instructions, when executed by the processor, causing the processor to perform a video encoding method to generate the bitstream,
the encoding method comprising:
receiving a sequence of video pictures in an input codeword representation;
for one or more pictures in the sequence of video pictures applying a forward reshaping function to generate reshaped pictures in a reshaped codeword representation, wherein the forward reshaping function maps pixels of an image from the input codeword representation to the reshaped codeword representation;
generating reshaping parameters for the reshaped codeword representation; and
generating a coded bitstream based at least on the reshaped pictures, wherein the reshaping parameters comprise:
a delta-index parameter to determine an active maximum bin index used for reshaping, wherein the active maximum bin index is smaller or equal to a predefined maximum bin index, wherein the delta-index parameter represents a difference between the active maximum bin index and the predefined maximum bin index;
a min-index parameter indicating a minimum bin index being used in the reshaping;
absolute delta codeword values for each active bin used in the reshaping; and
signs of the absolute delta codeword values for each active bin used in the reshaping.