Method and device for predictive picture encoding and decoding
A method for encoding a block of a picture is disclosed. The method comprises for at least one sample of the block and for one current component: —obtaining a prediction value; —determining a mapped residual value from a source value of the sample and from the prediction value responsive to a mapping function; and —encoding the mapped residual value into a bitstream; wherein the mapping function is derived to obtain at least one of a reduction of a bit cost of the bitstream for a given quality of reconstruction or an increase of quality of reconstruction for a given bit cost of the bitstream.
1. A method for encoding comprising:
obtaining a prediction value of a source value of a current color component of a sample of a block of a picture;
determining a mapped residual value from the source value of the current color component and from the prediction value using a mapping function; and
encoding the mapped residual value into a bitstream;
wherein determining the mapped residual value comprises:
mapping the prediction value with the mapping function to obtain a mapped prediction value;
mapping the source value with the mapping function to obtain a mapped source value; and
determining the mapped residual value representative of a subtraction of the mapped prediction value and the mapped source value.
2. The method of claim 1 , wherein the mapping function is derived such that an amplitude of a residual value is increased more for large amplitude values of the source value than for small amplitude values of the source value.
3. The method of claim 1 , wherein the mapping function is a pre-defined quantization adjustment table or a quantization adjustment function configured to improve perceptual or objective coding performance.
4. The method of claim 1 , wherein the mapping function is derived such that the source values are better distributed in an overall codeword range.
5. The method of claim 1 , wherein the mapping function is configured to improve compression performance.
6. A method for decoding comprising:
obtaining a prediction value of a current color component of a sample of a block of a picture;
decoding a residual value for the sample; and
determining a reconstructed value for the sample from the decoded residual value and from the prediction value using both a mapping function and an inverse mapping function that is the inverse of the mapping function;
wherein determining the reconstructed value comprises:
mapping the prediction value with the mapping function to obtain a mapped prediction value;
obtaining an intermediate value representative of a sum of the mapped prediction value and the residual value; and
obtaining the reconstructed value by mapping the intermediate value with the inverse mapping function.
7. The method of claim 6 , wherein the mapping function is a pre-defined quantization adjustment table or a quantization adjustment function.
8. The method of claim 6 , wherein the mapping function is derived such that the source values are better distributed in an overall codeword range.
9. The method of claim 6 , wherein the mapping function is configured to improve compression performance.
10. A device for encoding comprising electronic circuitry configured to:
obtain a prediction value of a source value of a current color component of at least a sample of a block of a picture;
determine a mapped residual value from the source value of the current color component and from the prediction using a mapping function; and
encode the mapped residual value into a bitstream;
wherein determining the mapped residual value comprises:
mapping the prediction value with the mapping function to obtain a mapped prediction value;
mapping the source value with the mapping function to obtain a mapped source value; and
determining the mapped residual value representative of a subtraction of the mapped prediction value and the mapped source value.
11. The device of claim 10 , wherein the mapping function is derived such that an amplitude of a residual value is increased more for large amplitude values of the source value than for small amplitude values of the source value.
12. The device of claim 10 , wherein the mapping function is a pre-defined quantization adjustment table or a quantization adjustment function configured to improve perceptual or objective coding performance.
13. The device of claim 10 , wherein the mapping function is derived such that the source values are better distributed in an overall codeword range.
14. The device of claim 10 , wherein the mapping function is configured to improve compression performance.
15. A device for decoding comprising electronic circuitry configured to:
obtain a prediction value of a current color component of a sample of a block of a picture;
decode a residual value for the sample; and
determine a reconstructed value for the sample from the decoded residual value and from the prediction value using both a mapping function and an inverse mapping function that is the inverse of the mapping function;
wherein determining the reconstructed value comprises:
mapping the prediction value with the mapping function to obtain a mapped prediction value;
obtaining an intermediate value representative of a sum of the mapped prediction value and the residual value; and
obtaining the reconstructed value by mapping the intermediate value with the inverse mapping function.
16. The device of claim 15 , wherein the mapping function is a pre-defined quantization adjustment table or a quantization adjustment function.
17. The device of claim 15 , wherein the mapping function is derived such that the source values are better distributed in an overall codeword range.
18. The device of claim 15 , wherein the mapping function is configured to improve compression performance.
19. A non-transitory information storage medium storing program code instructions for implementing a processor-executable method for encoding comprising:
obtaining a prediction value of a source value of a current color component of a sample of a block of a picture;
determining a mapped residual value from the source value of the current color component and from the prediction value using a mapping function; and
encoding the mapped residual value into a bitstream;
wherein determining the mapped residual value comprises:
mapping the prediction value with the mapping function to obtain a mapped prediction value;
mapping the source value with the mapping function to obtain a mapped source value; and
determining the mapped residual value representative of subtraction of the mapped prediction value and the mapped source value.
20. A non-transitory information storage medium storing program code instructions for implementing a processor-executable method for decoding comprising:
obtaining a prediction value of a current color component of a sample of a block of a picture;
decoding a residual value for the sample; and
determining a reconstructed value for the sample from the decoded residual value and from the prediction value using both a mapping function and an inverse mapping function that is the inverse of the mapping function;
wherein determining the reconstructed value comprises:
mapping the prediction value with the mapping function to obtain a mapped prediction value;
obtaining an intermediate value representative of a sum of the mapped prediction value and the residual value; and
obtaining the reconstructed value by mapping the intermediate value with the inverse mapping function.