Michael Reichmann has published a great article on his Luminous Landscape website which clearly explains how to use contrast masks in Photoshop to open up the shadow areas of an image. This looks like a brilliant and relatively simple technique that you will use again and again.

“Given that digital cameras have a dynamic range of 5-7 stops (about the same or slightly greater than transparency film), one often finds that the shadow areas of a frame are rendered darker than one would wish. What to do?

The solution is to use what is called a contrast mask. This is now done digitally, but it is nothing new. It’s been around since the early years of the 20th Century. This used to involve the production of a B&W negative copy of the original which was then placed in superimposition with the positive while a print was made. This caused a flattening of the contrast as shadows received extra exposure while highlights were held back.”

Website: Luminous Landscape - Understanding Contrast Masking