If you have ever photographed a high contrast scene, you know that selecting the correct exposure will not avoid blown out highlights and flat shadows. Photomatix Pro offers two ways to solve this problem:
32-bit Tone Mapping: Creates a High Dynamic Range Image from multiple exposures, then tones map it to compress its tonal range while preserving local contrast.
Exposure Blending: Merges differently exposed photographs into one image with increased dynamic range.
The freeware version of Photomatix comes with limited options compared with the existing commercial version you can find on the program author's website.