Reads a portable anymap as input. Rotates it by the specified angle and produces a portable anymap as output. If the input file is in color, the output will be too, otherwise it will be grayscale. The angle is in degrees (floating point), measured counter-clockwise. It can be negative, but it should be between -90 and 90. Also, for rotations greater than 45 degrees you may get better results if you first use pnmflip to do a 90 degree rotation and then pnmrotate less than 45 degrees back the other direction
the shearing by moving pixels without changing their values. If you want anti-aliasing and don't care about the precise colors, but still need a limited number of colors, you can run the result through ppmquant.