Implementation of chroma key composition or mixing is trivial, but results are often not perfect since it is difficult to have a clean separation between pixels belonging to the foreground (which must be rendered over a background image) and pixels that must be considered transparent or translucent (which shouldn't be rendered) due to antialias effects, compression artifacts or other reasons. Problems may also occur when the transparent or translucent region is not homogeneous, which makes the determination of the transparency/translucency values hard or imprecise.