Lightening an underexposed image, method 1
When I’m shooting concert images, the lighting often changes quickly, and I end up with an image that’s just a little too dark. One of the simplest and most effective tricks to lighten an image is to use the Screen layer blend mode. Open the image, duplicate the Background layer by pressing Command-J (PC: Ctrl-J), and then change the blend mode of the new layer to Screen. Then simply adjust the Opacity of the new layer until it suits your needs.