Edirol V-4 Owner's Manual page 30

Compositing two images
You cannot composite images via Luminance Key if there is no light or dark aspects in the image
to key off of. It may be difficult to extract correctly if contrast of light/dark is not sufficient or
consistent.
The default status of the Luminance Key of V-4 is set to extract the light part of the image. It is
possible to change setting to extract dark part. It is also possible to adjust the extraction level of blur
level of edges. For details, refer to p. 75 or later.
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