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     BBOX(9.1)                                               BBOX(9.1)

          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 pixels of the image.  `Interesting' pix-
          els are those for which a given channel, specified by the -c
          option, does not have a given value, specified by the -v
          option.  -v defaults to 0, and -c defaults to the α channel
          (letter 'a' in the CHAN= header line) if the image contains
          one, or the `m' channel otherwise.  If the image has neither
          α nor `m', option -c is not optional.  By default, there-
          fore, bbox prints the bounding box of the visible parts of
          an image with an α 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.