Layer mask (GIMP)
From Wiki @ Karl Jones dot com
This article discusses how to use layer masks in GIMP.
Description
Layer masks are a fundamental tool in image manipulation.
They allow you to selectively modify the opacity (transparency) of the layer they belong to.
This differs from the use of the layer Opacity slider as a mask has the ability to selectively modify the opacity of different areas across a single layer.
The modification of a layer’s transparency through a mask is non-destructive to the layer itself.
This flexibility to define the opacity of different areas of a layer is the basis for more interesting image manipulation techniques such as selective coloring and luminosity masking.
