Hydra is a program for Mac that is capable of mixing several overexposed and underexposed images to create one image whose appearance is similar to having taken a direct shot of the captured object.
This technique is known as HDR, or High Dynamic Range, and it requires the photographs that you are going to work with to have been taken with a tripod. Hydra includes algorithms that line them up automatically.
The program can run independently or as a plugin for Aperture. It can combine up to 10 images with different exposures and it supports photos of up to 20 megapixels.
For Mac OS X 10.5.4 or later. It requires a video card with at least 64 MB of memory.