APPARATUS AND METHOD OF PROCESSING IMAGE

A reference value memory circuit 552 in a video switch control circuit 550 stores upper threshold values DU and lower threshold values DL of respective colors defining a predetermined range of chromaticity. A color comparator circuit 554 compares these upper threshold values DU and the lower threshold values DL with a second video signal LSMEM. When a color represented by the second video signal is within the predetermined range of chromaticity, a color comparison signal S1, which is an output of the color comparator circuit 554, becomes at H level, while the color comparison signal S1 becomes at L level when the color is out of the predetermined range of chromaticity. A selection signal S2 is generated according to the color comparison signal S1 and a switcher signal CNT. A video switch 510 selects one of a first video signal LSPC output from a computer and a second video signal LSDA output from a video memory 310 in response to the selection signal S2. As a result, only a desirable portion of the second video image is superimposed over the first video image.