Chroma key is also known as Blue Screening and is when the actor standing in front of a large blue screen and acts out the actions. The camera operators then switch the Blue Screen for the background that they want. You have to be careful what colour key is used so that you avoid colour bleeding. Traditionally the colour is blue but more frequently the colour is green as skins tones stands out well. also if the colour has bleed then is can be more covered up easier.
Luma Key is similar to Chroma Key but is do with the brightness levels. A brightness level is set then either higher or lower pixels from this point can be turned off. This works better with black and white as it is good at creating greyscale images.
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