Easily Brighten Underexposed Areas of a Photo

In Overlay an Inverted Layer Onto a Photo to Brighten Underexposed Areas, PetaPixel shows how to do precisely that. I applied the method to a quite arbitrary underexposed photo and this is what I got:

Original image

Lit up using overlay method

Lit up, white balance applied

White balance only

A nice method indeed and it should work with any image processing program that's worth being used – in the article it's Photoshop while I have been using the Gimp.