Method and apparatus to transform/inverse transform and quantize/dequantize color image, and method and apparatus to encode/decode color image using it

The color image converting / inverse transform and the quantization / inverse quantization method and an apparatus for encoding of the color image using the same / decoding method and apparatus. The transformation and quantization method comprising the steps of: converting the color image to the image in the frequency domain; Applying according to whether a residue conversion of the color image and a macroblock prediction mode, different from the conversion for the removal of redundancy in the DC component of the frequency domain image; And it is characterized in that the DC component redundancy, including the removal of quantizing the image. According to the present invention, regardless of inter or intra prediction mode applied to the residue conversion can increase the compression efficiency. Further, by the quantization suitable for the residue conversion, thereby increasing the compression efficiency.