Adaptive chroma quantization in video coding for multiple color imaging formats
Methods to improve the quality of coding high-dynamic range (HDR) signals are presented. Instead of using a single chroma quantization table for all color formats, a video encoder may adaptively use separate tables for each one, and transmit the table's ID to a decoder. Examples for chroma quantization tables for video content encoded in the YCbCr (PQ) and ICtCp (PQ) color formats under a variety of color gamut containers are provided.
1. In a video decoder, a method to decode a coded bitstream with a processor, the method comprising:
receiving an input coded bitstream;
extracting from the input coded bitstream a table identifier for selecting a chroma quantization table among two or more chroma quantization tables, wherein the two or more chroma quantization tables comprise a first table for the YCbCr (gamma) color format and a second table for the YCbCr (PQ) color format, wherein each chroma quantization table is associated with a different color format, and wherein in each chroma quantization table an input index quantization value (qPi) is mapped to an output chroma quantization value (Qp C ), wherein for input qPi values larger than a first value, the corresponding output Qp C values for the first table are higher than the corresponding output Qp C values for the second table;
selecting a chroma quantization table using the table identifier; and
generating a decoded output signal using the selected chroma quantization table and the input coded bitstream.
2. The method of claim 1 , wherein the first value is between 19 and 24.
3. The method of claim 1 , wherein the two or more quantization tables comprise a first table for the YCbCr (gamma) color format and a second table for the ICtCp (PQ) color format.
4. The method of claim 3 , wherein for input qPi values smaller than a second value, the corresponding output Qp C values for the first table are smaller than the corresponding output Qp C values for the second table.
5. The method of claim 1 , wherein the second value is between 24 and 30.
6. An apparatus comprising a processor and configured to decode a coded bitstream, wherein decoding comprises:
receiving an input coded bitstream;
extracting from the input coded bitstream a table identifier for selecting a chroma quantization table among two or more chroma quantization tables, wherein the two or more chroma quantization tables comprise a first table for the YCbCr (gamma) color format and a second table for the YCbCr (PQ) color format, wherein each chroma quantization table is associated with a different color format, and wherein in each chroma quantization table an input index quantization value (qPi) is mapped to an output chroma quantization value (Qp C ), wherein for input qPi values larger than a first value, the corresponding output Qp C values for the first table are higher than the corresponding output Qp C values for the second table;
selecting a chroma quantization table using the table identifier; and
generating a decoded output signal using the selected chroma quantization table and the input coded bitstream.
7. A non-transitory computer-readable storage medium having stored thereon computer-executable instructions for decoding a coded bitstream with one or more processors, wherein decoding comprises:
receiving an input coded bitstream;
extracting from the input coded bitstream a table identifier for selecting a chroma quantization table among two or more chroma quantization tables, wherein the two or more chroma quantization tables comprise a first table for the YCbCr (gamma) color format and a second table for the YCbCr (PQ) color format, wherein each chroma quantization table is associated with a different color format, and wherein in each chroma quantization table an input index quantization value (qPi) is mapped to an output chroma quantization value (Qp C ), wherein for input qPi values larger than a first value, the corresponding output Qp C values for the first table are higher than the corresponding output Qp C values for the second table;
selecting a chroma quantization table using the table identifier; and
generating a decoded output signal using the selected chroma quantization table and the input coded bitstream.