Method and system for improving compressed image chroma information
Methods, systems, and computer programs for improving compressed image chroma information. In one aspect of the invention, a resolution for a red color component of a color video image is used that is higher than the resolution for a blue color component of the color video image. Another aspect includes utilizing a lower or higher value of a quantization parameter (QP) for one or more chroma channels as compared to the luminance channel. Another aspect is use of a logarithmic representation of a video image to benefit image coding. Another aspect uses more than two chroma channels to represent a video image.
1. A method for coding a color space representation of video macroblocks in a computerized video system having at least a decoder, the method comprising:
receiving, at a decoder from an encoder, a coded bitstream including a luminance quantization parameter, a first chroma bias value and a second chroma bias value for a macroblock, wherein the first chroma bias value and the second chroma bias value differ from each other for the macroblock, and
constructing, with the decoder, first and second chrominance quantization parameters for the macroblock, wherein the constructing comprises:
determining the first chrominance quantization parameter using the first chroma bias value received in the coded bitstream and the luminance quantization parameter received in the coded bitstream; and
determining the second chrominance quantization parameter using the second chroma bias value received in the coded bitstream and the luminance quantization parameter received in the coded bitstream; and
decompressing the macroblock using the received luminance quantization parameter and the constructed first and second chrominance quantization parameters.
2. The method of claim 1 , further comprising receiving, at the decoder, the luminance quantization parameter with the first chroma bias value and the second chroma bias value for the macroblock.
3. The method of claim 1 , wherein the constructing comprises deriving the second chrominance quantization parameter by subtracting the second chroma bias value from the luminance quantization parameter, wherein the second chrominance quantization parameter differs from the luminance quantization parameter.
4. The method of claim 1 , wherein the macroblock comprises differential coding as a function of the luminance quantization parameter, the first chrominance quantization parameter, and the second chrominance quantization parameter.
5. The method of claim 1 , further comprising determining whether the decompressed macroblock has the first chrominance quantization parameter being different from the second chrominance quantization parameter.
6. The method of claim 1 , wherein the constructed first and second chrominance quantization parameters in the decoder are identical to first and second chrominance quantization parameters generated in an encoder.
7. The method of claim 1 , wherein the first chroma bias value is a negative value and the second chroma bias value is a positive value.
8. The method of claim 1 , wherein the first chroma bias value is a positive value and the second chroma bias value is a negative value.
9. The method of claim 1 , wherein the constructing further comprises utilizing a logarithmic lookup table to construct the first and second chrominance quantization parameters for the macroblock.
10. The method of claim 9 wherein the logarithmic lookup table comprises a first range of quantization parameter values that are mapped to a second range of quantization parameter values for performing decompression by utilizing at least a logarithmic-type factor between the first and second ranges of quantization parameter values.
11. A method for coding 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 bias value and a second chroma bias value for a macroblock, wherein the first chroma bias value and the second chroma bias value differ from each other for the macroblock, and
constructing, with the decoder, first and second chrominance quantization parameters for the macroblock, wherein the constructing comprises:
determining the first chrominance quantization parameter using the received first chroma bias value by deriving the first chrominance quantization parameter by subtracting the first chroma bias value from a luminance quantization parameter, wherein the first chrominance quantization parameter differs from the luminance quantization parameter; and
determining the second chrominance quantization parameter using the received second chroma bias value; and
decompressing the macroblock using a luminance quantization parameter and the constructed first and second chrominance quantization parameters.