bbox - compute bounding rectangle
fb/bbox [ -s ] [ -cchannel ] [ -vvalue ] [ picture ]
Bbox reads the given picture file (default standard input) and prints
on its standard output the minimum bounding box of the interesting pix-
els of the image. `Interesting' pixels are those for which a given
channel, specified by the -c option, does not have a given value, spec-
ified by the -v option. -v defaults to 0, and -c defaults to the
channel (letter 'a' in the CHAN= header line) if the image contains
one, or the `m' channel otherwise. If the image has neither nor `m',
option -c is not optional. By default, therefore, bbox prints the
bounding box of the visible parts of an image with an channel, or the
non-black parts of a monochrome image.
Option -s causes bbox to instead copy its input to standard output,
clipping the image to the bounding rectangle.