Provided by: netpbm_10.0-12.2_i386 bug


       pbmmask - create a mask bitmap from a regular bitmap


       pbmmask [-expand] [pbmfile]


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

       The  color  to   be   interpreted   as   "background"   is   determined
       automatically.   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
           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
       backgrounds 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.


              Expands the mask by one pixel  out  from  the  image.   This  is
              useful  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...)


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


       Copyright (C) 1988 by Jef Poskanzer.

                                08 August 1989                      pbmmask(1)