Method and system for improving compressed image chroma information

A method for decoding a color space representation of video macroblocks in a computerized video system having at least a decoder, the method comprising:

• receiving, at a decoder, a first chroma quantization parameter bias value for a first chroma channel and a second chroma quantization parameter bias value for a second chroma channel for a macroblock,
• wherein the first chroma quantization parameter bias value and the second chroma quantization parameter bias value differ from each other for the macroblock, and
• wherein the first chroma quantization parameter bias value, the second chroma quantization parameter bias value, and a luminance quantization parameter relates to the macroblock;
• and
• constructing, with the decoder, a first chrominance quantization parameter for the macroblock by determining the first chrominance quantization parameter using the received first chroma quantization parameter bias value and the luminance quantization parameter;
• constructing, with the decoder, a second chrominance quantization parameter for the macroblock by determining the second chrominance quantization parameter using the received second chroma quantization parameter bias value and the luminance quantization parameter;
• and
• decompressing the macroblock using the luminance quantization parameter, the constructed first chrominance quantization parameter and the constructed second chrominance quantization parameter;
• applying the first chrominance quantization parameter to derive a first scaling coefficient for an AC coefficient of a transform output;
• and
• applying the first chrominance quantization parameter to derive a second scaling coefficient for a DC coefficient of the transform output.