[PatrickMcCluskey]

I'll try to explain this as best as I can, I have seen this technique used but don't know how to.

I have a Landscape photo of Buachaille Etive Mor and is unfortunately Backlit
I'd arrived too late and the sun was at the wrong end to lighten the mountain

I'd like to drag a screen down from top to halfway while holding the mouse so
that I can lighten the top half of the image only as the forground is exposed okay

Hope someone knows what I'm talking about.