Keying

Keying is defining transparency by a particular color value or luminance value in an image. When you key out a value, all pixels that have colors or luminance values similar to that value become transparent. Keying makes it easy to replace a background, which is especially useful when you work with objects too complex to mask easily. When you place a keyed layer over another layer, the result forms a composite, in which the background is visible wherever the keyed layer is transparent

• Information on Keying
• This is accessed in the Effect menu Effects>Keying
  • Color Keying - keying out a background of a consistent color
    • This is where greenscreening or bluescreening comes in because these are not usually natural colors and thus easier to sample
  • Luminance Keying - Sampling light or dark areas. Most effective with solid black or white
  • Difference Keying - Defines transparency with respect to a particular baseline background image. Quick overview
• What is the difference between matting and keying
  • Keying defines the transparent area of the video with the chroma or luma values
  • Matting uses two separate layers to create the desired transparency. A matte can define either the transparent or the opaque pixels on a clip.
• Best Effects in After Effects Great video on keying
  • Keylight (1.2)
  • Key Cleaner
  • Advanced Spill Suppressor