1. A method for extracting chrominance shape pixels from luminance shape pixels for an interlaced video having two fields, comprising the steps of: a) setting every four adjacent luminance shape pixels in two consecutive scan lines within a first field of the interlaced video to a first sub-sampling unit of a video coder; and b) extracting an associated chrominance shape pixel on the basis of said four adjacent luminance shape pixels in the first sub-sampling unit.