This isn't an in depth tutorial it's more of an overview of options available to brighten dark screen captures and pictures.
There are a few ways to brighten dark screen caps in Gimp which I will show you in this entry.
Here is a dark screen cap from
1. ) Screen Layer - Easy & most popular way to brighten up caps.
2.) Auto White Balance - Extremely easy and gets good results with dark contrast.
3.) Hard Light Layer set over a color filled layer (light or pale colors work best). This can be used to add different color tones/hues instead or just use white.
4.) Filled color layer set on Overlay (also works with light colored gradient)
5.) Curves Tool
Takes a little time to work with but you can get some pretty results.
6.) SmartCurves plug in (may not work with all programs) similar results as using the Curves tool.
Curves can be adjusted using the built in Curves tool or if you prefer you can download the SmartCurve plug in is here. I personally find it easy to use with Gimp 2.6.
Alternate examples using a screen cap from
Color Layer/Hard Light