Signal reshaping and coding for HDR and wide color gamut signals
In a method to improve the coding efficiency of high-dynamic range (HDR) images, a decoder parses sequence processing set (SPS) data from an input coded bitstream to detect that an HDR extension syntax structure is present in the parsed SPS data. It extracts from the HDR extension syntax structure post-processing information that includes one or more of a color space enabled flag, a color enhancement enabled flag, an adaptive reshaping enabled flag, a dynamic range conversion flag, a color correction enabled flag, or an SDR viewable flag. It decodes the input bitstream to generate a preliminary output decoded signal, and generates a second output signal based on the preliminary output signal and the post-processing information.
1. A method to generate video data in a processor, the method comprising:
receiving an input bitstream comprising coded data and metadata, wherein the metadata comprises information indicating whether adaptive reshaping is enabled or not in the input bitstream;
parsing the input bitstream; and upon detecting that adaptive reshaping is enabled in the input bitstream:
extracting adaptive reshaping metadata from the input bitstream, wherein the adaptive reshaping metadata comprise at least parameters related to a piece-wise polynomial representation of a reshaping function; and
decoding the input bitstream to generate an output decoded signal based on the coded data and the adaptive reshaping metadata.
2. The method of claim 1 , wherein generating the output decoded signal comprises:
decoding the input bitstream to generate a preliminary output decoded signal without taking into consideration the adaptive reshaping metadata; and
generating the output decoded signal based on the preliminary output decoded signal and the adaptive reshaping metadata.
3. The method of claim 1 , wherein the adaptive reshaping metadata comprise:
a first parameter based on a total number of polynomial functions used to define the reshaping function, and for each (p i ) polynomial function in the reshaping function, further comprising:
a starting pivot point for the polynomial function;
a second parameter based on the order of the polynomial function, wherein the order of the polynomial function can't exceed the value of two; and
one or more non-zero coefficients for the polynomial function.
4. The method of claim 3 , wherein, for a first polynomial function in the reshaping function following a second adjoining polynomial function, the coefficients for the first polynomial function comprise:
a second order coefficient (c i ), if the order of the first polynomial function is two; and
a first order coefficient (b i ), if the order of the first polynomial function is two and the order of the second adjoining polynomial function is not two, or if the order of the first polynomial function is one.
5. The method of claim 4 , wherein if the coefficients for the first polynomial function do not include the first order coefficient (b i ), then if the order of the first polynomial function is two, the first order coefficient is computed based on the first order and second order coefficients of the second adjoining polynomial function, the third order coefficient of the first polynomial function, and the starting pivot point for the first polynomial function.
6. The method of claim 5 , wherein the first order coefficient (b i ) for the first polynomial is computed as:
b i =b i−1 +2( c i−1 −c i ) x i ,
wherein b i−1 and c i−1 denote the first order and second order coefficients of the second adjoining polynomial function, c i denotes the third order coefficient of the first polynomial function, and x i denotes the starting pivot point for the first polynomial function.
7. The method of claim 5 , wherein the zero order coefficient (a i ) for the first polynomial function is computed based on the coefficients of the second adjoining polynomial function, the second order and third order coefficients of the first polynomial function, and the starting pivot point for the first polynomial function.
8. The method of claim 7 , wherein the zero order coefficient (a i ) for the first polynomial function is computed as:
a i =a i−1 +( b i−1 −b i ) x i +( c i−1 −c ) x i 2 ,
wherein a i−1 , b i−1 and c i−1 denote the zero order, first order, and second order coefficients of the second adjoining polynomial function, b i and c i denotes the second order and third order coefficients of the first polynomial function, and x i denotes the starting pivot point for the first polynomial function.
9. The method of claim 1 , further comprising:
parsing slice header data in the input bitstream and extracting slice-related reshaping metadata.
10. The method of claim 1 , wherein the piece-wise polynomial representation comprises N linear (first order) segments, wherein N is an integer larger than 0.
11. The method of claim 1 , wherein the piece-wise polynomial representation comprises N linear or second order segments, wherein N is an integer larger than 0.
12. The method of claim 1 , wherein the metadata comprise sequence parameter set (SPS) data, picture parameter set (PPS) data, or supplemental enhancement information (SEI) data.
13. A non-transitory computer-readable storage medium having stored thereon computer-executable instructions that, when executed by one or more processors, execute the method of claim 1 .
14. A computer program product, comprising instructions which, when executed by a computer, cause the computer to perform the method of claim 1 .