SIP provides image processing, pattern recognition, and computer vision routines for SciLab, a Matlab-like matrix-oriented programming environment. SIP is able to read/write images in almost 90 major formats, including JPEG, PNG, BMP, GIF, FITS, and TIFF. It includes routines for filtering, segmentation, edge detection, morphology, curvature, fractal dimension, distance transforms, multiscale skeletons, and more.
UFRaw is a utility for converting and manipulating raw images from digital cameras. It can be used as a stand-alone tool or as a Gimp plugin, and images can be batch processed using the commandline interface. UFRaw reads most existing raw formats using Dave Coffin's raw conversion utility DCRaw, and it supports basic color management using Little CMS, allowing the user to apply color profiles. For Nikon users, UFRaw has the advantage that it can read the camera's tone curves. Even if you don't own a Nikon, you can still apply a Nikon curve to your images.
The Geospatial Data Abstraction Library (GDAL) is a unifying C/C++ API for accessing raster geospatial data, and currently includes formats like GeoTIFF, Erdas Imagine, Arc/Info Binary, CEOS, DTED, GXF, and SDTS. It is intended to provide efficient access, suitable for use in viewer applications, and also attempts to preserve coordinate systems and metadata. Python, C, and C++ interfaces are available.
pngquant is a batch conversion utility to quantize and dither truecolor PNG images, especially those with a full alpha channel, down to "RGBA-palette" PNGs (i.e., PLTE + tRNS in PNG parlance). Such images are usually two to four times smaller than the full 32-bit versions, and partial transparency is preserved quite nicely. This makes pngquant especially useful both for Web sites and for PlayStation 2 development, where one of the texture formats is RGBA-palette-based (though not PNG-compressed).
Asciidia generates bitmap or vector files from simple ASCII diagrams. It was inspired by ditaa but has a plugin based architecture, which allows it to draw specialized diagrams. Currently-supported diagram types are simple ASCII diagrams and directory trees. Asciidia can directly output SVG and MVG. For additional file formats, an ImageMagick installation is required.
Potrace is a utility for tracing a bitmap (that is, transforming a bitmap into a smooth, scalable image). The input is a portable bitmap (PBM), and the default output is an encapsulated PostScript file (EPS). A typical use is to create EPS files from scanned data, such as company or university logos, handwritten notes, etc. The resulting image is not "jaggy" like a bitmap, but smooth. It can then be rendered at any resolution.
RPhoto is a handy image editor to simplify cropping of digital camera pictures and avoid white borders introduced by incorrect height/width ratios. It also has lossless rotate and flip features, as well as a unique way to rectify a bad angle by only drawing a horizontal or vertical line.
Image Viewer is a multi-frame (animated) image viewer with real-time interactive pan and zoom viewing that uses the GTK+ toolkit and Imlib. It is capable of opening and saving to any image format supported by Imlib. It features screenshots (screen capture), crop, resizing, print, fullscreen display, display on the desktop (root window), animation (creating animated GIFs), color leveling, drawing font/text strings, and editing image header information.