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RedHat 9 (Linux i386) - man page for pnmcrop (redhat section 1)

pnmcrop(1)						      General Commands Manual							pnmcrop(1)

pnmcrop - crop a portable anymap
pnmcrop [-white|-black|-sides] [-left] [-right] [-top] [-bottom] [pnmfile] All options may be abbreviated to their shortest unique prefix or specified with double hyphens.
Reads a PBM, PGM, or PPM image as input. Removes borders that are the background color, and produces the same type of image as output. If you don't specify otherwise, pnmcrop assumes the background color is whatever color the top left and right corners of the image are and if they are different colors, something midway between them. You can specify that the background is white or black with the -white and -black options or make pnmcrop base its guess on all four corners instead of just two with -sides. By default, pnmcrop chops off any stripe of background color it finds, on all four sides. You can tell pnmcrop to remove only specific borders with the -left, -right, -top, and -bottom options. If you want to chop a specific amount off the side of an image, use pnmcut. If you want to add different borders after removing the existing ones, use pnmcat or pnmcomp.
-white Take white to be the background color. pnmcrop removes borders which are white. -black Take black to be the background color. pnmcrop removes borders which are black. -sides Determine the background color from the colors of the four corners of the input image. pnmcrop removes borders which are of the background color. If at least three of the four corners are the same color, pnmcrop takes that as the background color. If not, pnmcrop looks for two corners of the same color in the following order, taking the first found as the background color: top, left, right, bottom. If all four corners are different colors, pnmcrop assumes an average of the four colors as the background color. The -sides option slows pnmcrop down, as it reads the entire image to determine the background color in addition to the up to three times that it would read it without -sides. -left Remove any left border. -right Remove any right border. -top Remove any top border. -bottom Remove any bottom border. -verbose Print on Standard Error information about the processing, including exactly how much is being cropped off of which sides.
pnmcut(1), pnmfile(1), pnm(5)
Copyright (C) 1989 by Jef Poskanzer. 18 March 2001 pnmcrop(1)