Tektronix Grass Valley 3000 - Manual (Page 126)

3-18
Section 3 — Switcher Concepts
Coring
Coring is a video noise-reducing operation in which pixels below
a predetermined luminance threshold are replaced by “clean”
black pixels. During keying, the black eliminates any noise
surrounding the fill video that might otherwise add to the
background, causing noisy key edges.
A menu selection enables or disables the coring function and
allows adjustment of the coring level to ensure that video is fully
removed in the key area.