What is all the fuss with cositing of chroma components?
A. It is moderately important to properly co-site chroma samples, otherwise a sort of chroma shifting effect (exhibited as a halo) may result when the reconstructed video is displayed. In MPEG-1 video, the chroma samples are exactly centered between the 4 luminance samples (Fig 1.) To maintain compatibility with the CCIR 601 horizontal chroma locations and simplify implementation (eliminate need for phase shift), MPEG-2 chroma samples are arranged as per Fig.2. Y Y Y Y Y Y Y Y YC Y YC Y C C C C Y Y X Y Y Y Y Y YC Y YC Y Y Y Y Y Y Y Y Y YC Y YC Y C C C C Y Y Y Y Y Y Y Y YC Y YC Y Fig.1 MPEG-1 Fig.2 MPEG-2 Fig.3 MPEG-2 and 4:2:0 organization 4:2:0 organization CCIR Rec.
