Luminosity mask (GIMP)
From Wiki @ Karl Jones dot com
This article discusses luminosity masks in GIMP.
Description
Luminosity masks is to allow you to modify elements of a layer masked to a specific region of luminosity (or value).
Examples:
- Controlling the colors in the shadows of my image without modifying the mid tones or light tones
- Adjusting the light tones without affecting the other regions as well