xv is an interactive image manipulation program for the X Window System. It can operate on images in the GIF, JPEG, TIFF, PBM, PGM, PPM, XPM, X11 bitmap, Sun Rasterfile, Targa, RLE, RGB, BMP, PCX, FITS, and PM formats on all known types of X displays. It can generate PostScript files, and if you have ghostscript (version 2.6 or above) installed on your machine, it can also display them.

xv lets you do a large number of things (many of them actually useful), including, but not limited to, the following:

• display an image in a window on the screen
• display an image on the root window, in a variety of styles
• grab any rectangular portion of the screen and turn it into an image
• arbitrarily stretch, compress, rotate or flip the image
• crop or pad images
• view files as ASCII text or hexadecimal data
• magnify any portion of the image by any amount, up to the size of the screen
• determine pixel values and x,y coordinates in the image
• adjust image brightness and contrast with a gamma correction function
• apply different gamma functions to the Red, Green, and Blue color components, to correct for non-linear color response
• adjust global image saturation
• perform global hue remapping
• perform histogram equalization
• run a number of image-processing algorithms on any rectangular portion of the image
• edit an image's colormap
• reduce the number of colors in an image
• dither in color and b/w
• crop off solid borders automatically
• convert image formats

Oddly enough, I'm still having a horrible time tracking down some minor bug in the Automatic Checkbook Balancing Module , and once again it fails to make it into the official xv distribution.