A transparency designation memory is provided in parallel with color loop-up tables (CLUTs) corresponding to a plurality of frames. When color value data are set in the CLUTs, a transparency designation memory section detects if the color value is transparency or not, and writes data indicating the presence...http://www.google.com/patents/US4853681?utm_source=gb-gplus-sharePatent US4853681 - Image frame composing circuit utilizing color look-up table
