pbmmask(1)

NAME

       pbmmask - create a mask bitmap from a regular bitmap

SYNOPSIS

       pbmmask [-expand] [pbmfile]

DESCRIPTION

       Reads  a portable bitmap as input.  Creates a corresponding mask bitmap
       and writes it out.

       The color to be interpreted as  "background"  is  determined  automati-
       cally.  Regardless of which color is background, the mask will be white
       where the background is and black where the figure is.

       This lets you do a masked paste like this, for  objects  with  a  black
       background:
           pbmmask obj > objmask
           pnmpaste < dest -and objmask <x> <y> | pnmpaste -or obj <x> <y>
       For  objects with a white background, you can either invert them or add
       a step:
           pbmmask obj > objmask
           pnminvert objmask | pnmpaste -and obj 0 0 > blackback
           pnmpaste < dest -and objmask <x> <y> | pnmpaste -or blackback <x> <y>
       Note that this three-step version works for objects  with  black  back-
       grounds too, if you don't care about the wasted time.

       You  can  also  use masks with graymaps and pixmaps, using the pnmarith
       tool.  For instance:
           ppmtopgm obj.ppm | pgmtopbm -threshold | pbmmask > objmask.pbm
           pnmarith -multiply dest.ppm objmask.pbm > t1.ppm
           pnminvert objmask.pbm | pnmarith -multiply obj.ppm - > t2.ppm
           pnmarith -add t1.ppm t2.ppm
       An interesting variation on this  is  to  pipe  the  mask  through  the
       pnmsmooth  script before using it.  This makes the boundary between the
       two images less sharp.

       -expand
              Expands the mask by one pixel out from the image.  This is  use-
              ful  if  you  want  a little white border around your image.  (A
              better solution might be to turn the pbmlife tool into a general
              cellular automaton tool...)

SEE ALSO

       pnmpaste(1), pnminvert(1), pbm(5), pnmarith(1), pnmsmooth(1)

AUTHOR

       Copyright (C) 1988 by Jef Poskanzer.

                                08 August 1989                      pbmmask(1)