From Chroma Software:
Shadow Control is a Photoshop and Photoshop Elements plugin designed to bring out detail out of dark areas of deep shadow in your digital photos. Plug-in works by selectively increasing gamma and contrast on dark areas of deep shadow of the image using the mask: plug-in analyzes the image and creates the mask that shows which areas of the image will be affected by processing (marked black on the mask view). After the mask is created, plug-in applies desired correction to the affected areas of the image and displays the result. You can then adjust the settings and preview the result in real-time. Plug-in is designed to work with images from all digital cameras, but cameras capable of capturing image in 16 bit will yield higher quality result.