Chroma keying is a technique where in a specific color is removed from one image to reveal another “behind” it. We have a main image over which an overlay image which is usually smaller than the main image is overlaid.When the phase of the chroma signal in the overlay image corresponds to the
pre-programmed state associated with the background color(s) behind the principal subject, the signal from the alternate background (which in this case comes from the main image channel) is inserted in the composite signal and presented at the output.
For Chroma keying feature, the transparency control bit in the PIXC_CTL register is enabled. The transparent colour values are loaded in the PIXC_TC register. The colour samples in the overlay image data with the same values as that programmed in the PIXC_TC register are ignored and the background/main image is presented at the output.