This is a great package of command-line based image manipulation utilities, originally written by Jef Poskanzer as pbmplus. Included are programs for conversion to/from nearly all the popular (and unpopular) image formats (JPEG the only notable exception (see cjpeg)), as well as a number of image manipulation utilities. All of the programs operate as standard Unix filters, reading from stdin and writing to stdout, so you pipe the output of one program into another program, and thus perform fairly complex operations on one command-line.
Pretty cool, and perfect for all your batch-image-processing needs. This one should be on everybody's machine!
Note: the above link is for the March 1994 version, which is the last version I've personally used. If you go here you'll see that there are newer versions available, which you may wish to try out. I know nothing about them, and it's quite possible that they may have been forced to remove GIF support, so they may not be as useful to certain people. But that's just idle conjecture on my part.
This is a freely-available PostScript interpreter, written and maintained by L. Peter Deutsch of Aladdin Enterprises. It reads PostScript and can display it in an X window, or write it out in a number of image formats. As far as xv is concerned, you need to get and install this program if you want xv to be able to 'load' PostScript files. xv calls upon ghostscript to convert the PostScript into an image format that xv natively understands. Once you've got ghostscript installed, you'll need to edit xv's config.h file, tell it where to find the gs executable, and rebuild xv.
The newest versions of ghostscript (and plenty of related software, information, and such) may be found at http://www.cs.wisc.edu/~ghost. While I haven't personally tested xv with any of these, there's no reason to believe they won't work with xv.
Note: If you get a sufficiently hip version of ghostscript (read: a non-GNU version), you'll find that it supports PDF files as well. If you'd like xv to support PDF files, you'll just need this trivial little patch (as well as the aforementioned version of ghostscript!)
The latest versions that I have personally tested with xv 3.10a may be found here (you need both files):
cjpeg and djpeg
These are a pair of programs which convert between JPEG and a number of standard image file formats (ppm, etc.). They are included in the IJG JPEG distribution, which in turn is included in the xv distribution. As such, you should already have them. They are mentioned here primarily as the missing piece that enables you to get JPEG files in and out of the netpbm package.
The GIMP is an image manipulation program suitable for photo retouching, image composition and image authoring, in many of the ways that xv is not. It's definitely cool, and well-worth having.
gzip and gunzip have long been the de-facto standard file compression utilities on Unix machines, replacing compress and uncompress in functionality. Despite this fact, there are still machines out there that inexplicably fail to have gzip and gunzip installed. You'll need gunzip in order to uncompress any files with a '.gz' suffix, which is most of them, these days.
Larry Wall's most-excellent patch program is another required program for Unix systems. It is used to apply patch files to source code. Patch files allow authors to make minor changes to a distribution without putting out a whole new distribution. Patch files tend to be small (a few KB at most) and easily downloaded, which is handy for folks with slow Internet connections.
This is a handy little C program that, among other things, lets you make the background color in a GIF file transparent, for use on web pages and the like. This is particularly useful, since xv 3.10a doesn't let you do that!
(Well, XVscan isn't new, it's just a new addition to this page...)
Sean Reifschneider's keen scanner-enhanced version of XV. Currently runs on HPs, Suns, and Intel systems (Linux, FreeBSD, etc.)