chroma key definition

This is a way of combining two images together. you put together two videos then you remove one of the track which makes it transparent. The green and blue is chosen because they are opposite to the skin color you can also use different colors but these seem to be the best. the actor also has to wear the opposite colors to screens color unless you want that part to disappear. this technique is also refereed to as color key. its also important to have even lighting on the background because shadows make it difficult to see the full image in the finial scene.