This documentation assumes knowledge of channels. And terminologies are for Foundry Nuke; as same operation have different names over different packages, but the work is same. Multiply Multiply multiplies each channel information of one image to another. The result is subtractive as we multiply.. Plus Plus adds pixel value from background to the foreground. Screen The screen is a conditional operation. It multiplies if pixel if higher than 50% threshold and plus if the value if the value if lower than 50%.