Compositing:
Compositing is the combining of visual elements from separate sources into single images, often to create the illusion that all those elements are parts of the same scene. Live-action shooting for compositing is variously called "chroma key", "blue screen", "green screen" and other names. Today, most, though not all, compositing is achieved through digital image manipulation. All compositing involves the replacement of selected parts of an image with other material, usually, but not always, from another image. In the digital method of compositing, software commands designate a narrowly defined color as the part of an image to be replaced. Then every pixel within the designated color range is replaced by the software with a pixel from another image, aligned to appear as part of the original. For example, a TV weather person is recorded in front of a plain blue or green screen, while compositing software replaces only the designated blue or green color with weather maps.