Syntax prediction using reconstructed samples

1. An apparatus for encoding a signal into a bitstream, the bitstream comprising a first signal sample and control information relating to encoding of a second signal sample, the apparatus comprising a processing circuitry configured to:

compress the first signal sample and reconstruct the compressed first signal sample;

select a semantic rule for assignment between control information contents and respective values of a syntax element according to the reconstructed first signal sample, the syntax element carrying control information content for the signal;

determine a value of the syntax element based on the semantic rule and a control information content relating to the encoding of the second signal sample; and

generate the bitstream by including into the bitstream the compressed first signal sample and the determined value of the syntax element.

2. The apparatus according to claim 1 , wherein the processing circuitry generates the bitstream by binarizing the compressed first signal sample or the determined value of the syntax element.

3. The apparatus according to claim 2 , wherein the processing circuitry is further configured to:

generate the control information content;

compress the second signal sample according to the generated control information content; and

binarize the compressed second signal sample and include the binarized second compressed signal sample into the bitstream.

4. The apparatus according to claim 2 , wherein the processing circuitry is configured to perform the binarization of the syntax element value by applying a context-adaptive binary arithmetic coding.

5. The apparatus according to claim 1 , wherein the semantic rule is selected as an index identifying one of a plurality of predefined tables associating the control information contents and the respective values of the syntax element, the index being determined as a function of the reconstructed first signal sample.

6. The apparatus according to claim 5 , wherein:

the semantic rule is either a first table or a second table;

the syntax element can take a first value or a second value;

the first table associates the first value of the syntax element with a first control information content and a second value with a second control information content; and

the second table associates the first value of the syntax element with the second control information content and the second value with the first control information content.

7. The apparatus according to claim 6 , wherein:

the signal is a video signal; and

the control information indicates with the first control information content a bi-prediction and with the second control information content a uni-prediction to be used in template matching to obtain a signal sample predictor.

8. The apparatus according to claim 7 , wherein the first table or the second table is selected according to a template matching cost function, which is based on a similarity between a template and a predictor based on bi-prediction and a predictor based on uni-prediction.

9. The apparatus according to claim 6 , wherein:

the signal is a video signal; and

the control information indicates with the first control information content a local illumination compensation switched on and with the second control information content the local illumination compensation switched off.

10. The apparatus according to claim 9 , wherein the first table or the second table is selected according to a similarity function between the reconstructed sample in a current image frame and the corresponding reconstructed sample in an image frame preceding the current image frame in the encoding order.

11. The apparatus according to claim 6 , wherein:

the signal is a video signal;

the control information indicates either a positive sign or a negative sign of a component of a motion vector, the component being a vertical component or a horizontal component.

12. The apparatus according to claim 11 , wherein the first table or the second table is selected according to a similarity function between prediction blocks pointed to by motion vectors with the respective positive sign and the respective negative sign and the samples surrounding the current prediction block.

13. An apparatus for decoding a signal from a bitstream, the bitstream comprising signal samples and control information relating to decoding of the signal samples, the decoder comprising a processing circuitry configured to:

parse from the bitstream a compressed first signal sample, of the signal samples, and a value of a syntax element;

reconstruct the compressed first signal sample;

select a semantic rule for assignment between control information contents and respective values of the syntax element according to the reconstructed first signal sample, the syntax element carrying control information content for the signal; and

determine a control information content, of the control information contents, based on the semantic rule and the parsed value of the syntax element.

14. The apparatus according to claim 13 , wherein the processing circuitry is further configured to:

parse from the bitstream a compressed second signal sample, of the signal samples; and

decompress the compressed second signal sample according to the determined control information content.

15. The apparatus according to claim 13 , wherein the processing circuitry is configured to perform the parsing of the syntax element value by applying a context-adaptive binary arithmetic decoding.

16. A method for encoding a signal into a bitstream, the bitstream comprising a first signal sample and control information relating to encoding a second signal sample, the method comprising:

compressing the first signal sample and reconstructing the compressed first signal sample;

selecting a semantic rule for assignment between control information contents and respective values of a syntax element according to the reconstructed first signal sample, the syntax element carrying control information content for the signal;

determining a value of the syntax element based on the semantic rule and control information content relating to the encoding of the second signal sample; and

generating the bitstream by including into the bitstream the compressed first signal sample and the determined value of the syntax element.

17. A method for decoding a signal from a bitstream, the bitstream comprising signal samples and control information relating to encoding of the signal samples, the method comprising:

parsing from the bitstream a compressed first signal sample, of the signal samples, and a value of a syntax element;

reconstructing the compressed first signal sample;

selecting a semantic rule for assignment between control information contents and respective values of the syntax element according to the reconstructed first signal sample, the syntax element carrying control information content for the signal; and

determining a control information content, of the control information contents, based on the semantic rule and the parsed value of the syntax element.

18. A non-transitory computer-readable medium storing instructions which when executed on a processor perform the method according to claim 17 .