Ghostscript is a processor for PostScript and PDF files. It can rasterize these files to a wide variety of printers, devices for screen preview, and image file formats. Since applications tend to prepare pages for printing in a high-level format such as PostScript, most Unix users with low-level bitmap printers, such as inkjets, use GhostScript as part of the printing process. In addition, Ghostscript is capable of converting PostScript files, functionality comparable to Adobe Acrobat Distiller, but on the command line. In addition, Ghostscript is used for file import and viewing by a great many other applications, including xv, ImageMagick, gimp, and xdvi. Several GUI wrappers for viewing PostScript and PDF files exist, including GSview, ghostview, gv, ggv, and kghostview. This is far from a comprehensive list.
ICCLIB implements support for reading and writing of color profile files that conform to the International Color Consortium (ICC) Profile Format Specification, Version 3.4. The ICC Profile Format is a cross-platform device profile format that can be used to translate color data created on one device into another device's native color space. See the profile specification at color.org. In summary ICCLIB provides support for all version 3.4 header elements, Tags, and Tag Types, conversion to/from machine native representation of all data types, user-defined Tags, adding/deleting Tags, Tag type sharing within a file (often used for sharing LUTs amongst intents), reading/writing embedded profiles, a single function for transforming color values through a profile (including support for intents, forward and reverse transforms, gamut lookup or preview lookup), support and code examples for creating all profile types, monochrome, matrix, and Lut, and it loads Tag Types on demand to conserve memory space.
Ilib is an image manipulation library for developers. It's capable of reading and writing images (PPM/PGM, PNG, JPEG, GIF, XPM, BMP) and many drawing functions including drawing lines and text using any BDF (X11) font. It's great for generating GIFs/PNGs from a CGI or generating graphs. Ilib includes sample applications for generating graphs for HTTP access.log files and QuakeWorld server frag log files and a tool for creating image indices from a group of images.
Macfork can be used to both list and extract resources from a Macintosh resource fork under unix. Currently it supports icon families, pict resources and palettes, but the data from any resource may be extracted to a data file. It was written to port Macintosh icons and pictures over to unix, but has many other potential uses.