Luma to chroma quantization parameter table signaling
Compression technology comprises deriving chroma quantization parameter (Qpc) based on luma Qp using luma-to-chroma Qp mapping table. Such a table may be shared by the encoder and the decoder. However, in some cases, signaling such a table in the data stream instead of having it fixed by a standard may be advantageous. The syntax used to encode, signal and decode this table has a cost in terms of bitrate. The present principles propose to signaling of a luma-to-chroma mapping table in the data stream according to different embodiments.
1. A method comprising:
decoding a QP information for luma from a data stream;
obtaining a first luma-to-chroma QP mapping table from the data stream;
determining a second luma-to-chroma QP mapping table wherein the chroma value is an addition between a chroma value in the first luma-to-chroma QP mapping table and a corresponding luma value in the first luma-to-chroma QP mapping table; and
decoding a block of an image obtained from the stream using the second luma-to-chroma QP mapping table.
2. The method of claim 1 , wherein the QP information for luma indicates that the luma QP value at a position in the first luma-to-chroma QP mapping table corresponds to a first pivot point of a piecewise linear model is a difference from a regular QP.
3. The method of claim 1 , wherein the QP information for luma of the first luma-to-chroma QP mapping table indicates that the QP information for chroma is coded as a difference from luma value only for a first pivot point.
4. A non-transitory computer readable storage medium storing instructions, which, when executed by one or more processors, perform the method of claim 1 .
5. A device comprising a processor configured for:
decoding a QP information for luma from a data stream;
obtaining a first luma-to-chroma QP mapping table from the data stream;
determining a second luma-to-chroma QP mapping table wherein the chroma value is an addition between a chroma value in the first luma-to-chroma QP mapping table and a corresponding luma value in the first luma-to-chroma QP mapping table; and
decoding a block of an image obtained from the stream using the second luma-to-chroma QP mapping table.
6. The device of claim 5 , wherein the QP information for luma indicates that the luma QP value at a position in the first luma-to-chroma QP mapping table corresponds to a first pivot point of a piecewise linear model is a difference from a regular QP.
7. The device of claim 5 , wherein the QP information for luma of the first luma-to-chroma QP mapping table indicates that the QP information for chroma is coded as a difference from luma value only for a first pivot point.
8. A method comprising:
obtaining a first luma-to-chroma QP mapping table;
determining a second luma-to-chroma QP mapping table wherein the chroma value is a difference between a chroma value in the first luma-to-chroma QP mapping table and a corresponding luma value in the first luma-to-chroma QP mapping table; and
encoding, in a data stream, a block of an image and the second luma-to-chroma QP mapping table.
9. The method of claim 8 , wherein the QP information for luma indicates that the luma QP value at a position in the second luma-to-chroma QP mapping table corresponds to a first pivot point of a piecewise linear model is a difference from a regular QP.
10. The method of claim 8 , wherein the QP information for luma of the second luma-to-chroma QP mapping table indicates that the QP information for chroma is coded as a difference from luma value only for a first pivot point.
11. A non-transitory computer readable storage medium storing instructions, which, when executed by one or more processors, perform the method of claim 8 .
12. A device comprising a processor configured for:
obtaining a first luma-to-chroma QP mapping table;
determining a second luma-to-chroma QP mapping table wherein the chroma value is a difference between a chroma value in the first luma-to-chroma QP mapping table and a corresponding luma value in the first luma-to-chroma QP mapping table; and
encoding, in a data stream, a block of an image and the second luma-to-chroma QP mapping table.
13. The device of claim 12 , wherein the QP information for luma indicates that the luma QP value at a position in the second luma-to-chroma QP mapping table corresponds to a first pivot point of a piecewise linear model is a difference from a regular QP.
14. The device of claim 12 , wherein the QP information for luma of the second luma-to-chroma QP mapping table indicates that the QP information for chroma is coded as a difference from luma value only for a first pivot point.