How do I brighten a part of a picture with Gimp?
Say I wanted to bring out the colors in the shadowy bottom right hand part of the attached image, how would I go about it? I assume I need to restrict the processing to that part but I have no idea what technique I should use and how to limit the effect to part of the image.
For a smooth brightening (or darkening) of shadows (resp. highlights) I prefer the color curves tool (Shift+C) where you can define a non-linear curve for all channels, or a single RGB color channel.
In the example image I used a positive S-shaped curve for all values and a negative S-shaped curve to remove blue from the shadow parts of the image: