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 an encoder, the method comprising:
accessing a video image comprising a luminance channel, a first chroma channel, and a second chroma channel;
generating a compressed bitstream of a first image region in the video image, comprising:
compressing the luminance channel of the first image region using a first luminance quantization parameter;
compressing the first chroma channel of the first image region using a first chrominance quantization parameter; and
compressing the second chroma channel of the first image region;
generating a compressed bitstream of a second image region in the video image, comprising:
compressing the luminance channel of the second image region using a second luminance quantization parameter, wherein the first luminance quantization parameter is different from the second luminance quantization parameter;
compressing the first chroma channel of the second image region using a second chrominance quantization parameter; and
compressing the second chroma channel of the second image region; and
signaling the compressed bitstream of the first image region and the second image region, the first luminance quantization parameter, the second luminance quantization parameter, and a first quantization bias from the encoder to a decoder,
wherein the first quantization bias indicates a difference between the first chrominance quantization parameter and the first luminance quantization parameter, and wherein the first chrominance quantization parameter is less than or equal to a predetermined maximum value.
2. The method of claim 1 , wherein the first quantization bias is positive.
3. The method of claim 1 , wherein the first quantization bias is negative.
4. The method of claim 1 ,
wherein compressing the second chroma channel of the first image region further comprises compressing the second chroma channel of the first image region using a chrominance quantization parameter for second chroma channel of the first image region that is different from the first chrominance quantization parameter, and
wherein the method further comprises:
signaling a second quantization bias from the encoder to the decoder for decompressing the compressed bitstream of the first image region, wherein the second quantization bias indicates a difference between the chrominance quantization parameter for second chroma channel of the first image region and the first luminance quantization parameter.
5. A method for a decoder, the method comprising:
receiving a compressed bitstream of an image comprising a luminance channel, a first chroma channel, and a second chroma channel;
receiving from an encoder a first luminance quantization parameter and a first quantization bias for a first image region and a second luminance quantization parameter for a second image region in the compressed bitstream, wherein the first quantization bias was determined by the encoder and was signaled to the decoder by the encoder, and wherein the first luminance quantization parameter is different from the second luminance quantization parameter;
decompressing the luminance channel of the first image region in the bitstream using the first luminance quantization parameter;
determining a first chroma quantization parameter by adding the first quantization bias to the first luminance quantization parameter;
decompressing the first chroma channel of the first image region in the bitstream using the first chroma quantization parameter;
determining a second chroma quantization parameter by adding the first quantization bias to the second luminance quantization parameter; and
decompressing the first chroma channel of the second image region in the bitstream using the second chroma quantization parameter.
6. The method of claim 5 , further comprising:
receiving from the encoder a second quantization bias for the first image region in the compressed bitstream, wherein the second quantization bias was determined by the encoder and was signaled to the decoder by the encoder;
determining a chroma quantization parameter for the second chroma channel of the first image region by adding the second quantization bias to the first luminance quantization parameter; and
decompressing the second chroma channel of the first image region in the bitstream using the chroma quantization parameter for the second chroma channel of the first image region.