US Patent 11019339 Fractional quantization parameter offset in video compression

A method of coding includes receiving a bitstream, obtaining a chroma quantization parameter range offset, a luma quantization parameter, quantization parameter offsets, and coefficients; calculating first intermediate chroma quantization parameters using the chroma quantization parameter range offset, the luma quantization parameter, and the quantization parameter offsets; where the first intermediate chroma quantization parameters have non-integer values; determining second intermediate chroma quantization parameters based on the first intermediate chroma quantization parameters, where the second intermediate chroma quantization parameters have non-integer values; calculating final chroma quantization parameters based on the second intermediate chroma quantization parameters and the chroma quantization parameter range offset; calculating a quantization step using the final chroma quantization parameters; quantizing the coefficients using the quantization step to produce quantized coefficients and transforming the quantized coefficients to residual pixels; and combining the residual pixels with prediction pixels to obtain reconstructed pixels.