The VIPS library/image processing system is well suited for larger than RAM true and false-colour images. VIPS can be used for image format conversion, colour calibration, image filtering, transformation and analysis, thumbnail generation, small object recognition and many other image processing
... [More] tasks. VIPS is well suited for medical and scientific research & development and batch image processing. It is not so good for retouching photographs. The system has two main parts: libvips is the library, and nip2 is the GUI. Both execute common image processing tasks faster than other image processing systems because of sophisticated memory/task management and multicore compatibility.
VIPS runs in batch (command line) mode on *nix, Windows, Mac and other OSes. [Less]
nip2, the "free love child of Photoshop and Excel," is the GUI of vips. You don't directly edit images --- instead, like a spreadsheet, you build relationships between objects. nip2 actively manages these relationships: if you change an object property, the change is propagated "spreadsheet-style."
Like vips, nip2 is fast and needs little memory. You can comfortably work with multi-gigabyte images on very modest hardware.
In addition to the visual programming interface accessible through the GUI, nip2 has command-line and batch modes. It even has its own functional programming language (for writing extensions). [Less]