Determination of a co-located luminance sample of a color component sample, for HDR coding/decoding
A method for determining a luminance value used to process color samples in a decoder or encoder is provided comprising determining ( 33, 44 ) a luminance sample associated with a chroma sample position in a common space; and applying ( 34, 492 ) the determined luminance sample in a process that depends on luminance that is being applied to the chroma sample.
1. A method for reconstructing an HDR picture from reconstructed luma and chroma samples, comprising:
decoding luminance and chrominance samples representative of a SDR picture in a color space in which two chroma components have a spatial size that is half the size of a luminance component in width and/or in height, said SDR picture being a lower dynamic range depiction of said HDR picture;
determining a co-located luminance sample value for chrominance samples according to the spatial positions of said chrominance samples;
obtaining said reconstructed chroma samples by correcting the chrominance samples from said co-located luminance sample value; and
obtaining said reconstructed luma samples from said luminance samples.
2. The method of claim 1 , wherein obtaining a reconstructed luma sample from a luminance sample comprises:
determining a co-located chrominance sample values associated with said luminance sample according to the spatial position of said luminance sample; and
said reconstructed luma component is then a weighted linear combination of said luminance sample and said co-located chrominance sample values.
3. The method of claim 1 , wherein the color space comprises a non-linear luminance obtained when applying a standard transfer function.
4. The method of claim 3 , wherein the standard transfer function comprises a SMPTE ST2084 inverse electro-optical transfer function (EOTF).
5. The method of claim 1 , wherein determining a co-located luminance sample value comprises calculating an average value of the chrominance samples located at said spatial positions.
6. A device for reconstructing an HDR picture from reconstructed luma and chroma samples, comprising a processor configured to:
decode luminance and chrominance samples representative of a SDR picture in a color space in which two chroma components have a spatial size that is half the size of a luminance component in width and/or in height, said SDR picture being a lower dynamic range depiction of said HDR picture;
determine a co-located luminance sample value for chrominance samples according to the spatial positions of said chrominance samples;
obtain said reconstructed chroma samples by correcting the chrominance samples from said co-located luminance sample value; and
obtain said reconstructed luma samples from said luminance samples.
7. The device of claim 6 , wherein obtaining a reconstructed luma sample from a luminance sample comprises:
determining a co-located chrominance sample values associated with said luminance sample according to the spatial position of said luminance sample; and
said reconstructed luma component is then a weighted linear combination of said luminance sample and said co-located chrominance sample values.
8. The device of claim 6 , wherein the color space comprises a non-linear luminance obtained when applying a standard transfer function.
9. The device of claim 8 , wherein the standard transfer function comprises a SMPTE ST2084 inverse electro-optical transfer function (EOTF).
10. The device of claim 6 , wherein determining a co-located luminance sample value comprises calculating an average value of the chrominance samples located at said spatial positions.
11. A computer readable medium for storing instructions which, when executed by a computer, cause the computer to execute the following actions:
decode luminance and chrominance samples representative of a SDR picture in a color space in which two chroma components have a spatial size that is half the size of a luminance component in width and/or in height, said SDR picture being a lower dynamic range depiction of said HDR picture;
determine a co-located luminance sample value for chrominance samples according to the spatial positions of said chrominance samples;
obtain said reconstructed chroma samples by correcting the chrominance samples from said co-located luminance sample value; and
obtain said reconstructed luma samples from said luminance samples.