NConvert is a batch utility to convert graphics files. Supports more than 400 graphics formats.

Features
Import about 400 graphic file formats
Export about 40 graphic file formats
Multipage TIFF, Animated GIF, Animated ICO support
Resize
Adjust brightness, contrast...
Modify number of colors
Apply filters (blur, average, emboss, ...)
Apply effects (lens, wave, ...)
And many many other things...