Imagemagick

Is a command-line image converter processor. While it does have a GUI display called Display, it is powerful in three ways:

• A batch conversion application.
• Ability to handle a wide range of image formats.
• The newest versions understand color management and use littlecms, just like Scribus.

Imagemagick is kind of a black box for image processing, but incredibly powerful when used properly. Versions for Linux, Windows and MacOSX are available.