Nonlinear Editing

Chapter 7

Hole cutters

‘Hole cutters’ is a generic term which may be used to cover a number of techniques that are essentially image-compositing processes. The four techniques are:

•  luminance key;

•  chrominance key;

•  matte key;

•  alpha channels.

Luminance key

Luminance key is the process where a ‘hole’ can be cut in a background image based on the brightness of a second image. Historically, luminance keys were white on black captions, the white of the caption being used to cut a hole on the background video and then the white (or a colour from the vision mixer) being used to fill the hole. Luminance key is sometimes known as self key. In its simplest form a switching circuit would cut between the background and the key signal based on ...