pbmmask



Pbmmask User Manual(0)                                  Pbmmask User Manual(0)




NAME

       pbmmask - create a mask bitmap from a regular bitmap



SYNOPSIS

       pbmmask [-expand] [pbmfile]



DESCRIPTION

       This program is part of Netpbm(1).

       pbmmask  reads  a PBM image as input and Generates a corresponding mask
       of the foreground areas as another PBM image.

       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 | pamditherbw -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  pnmsmooth
       before  using  it.  This makes the boundary between the two images less
       sharp.



OPTIONS

       -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 program into a gen-
              eral cellular automaton tool...)





SEE ALSO

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



AUTHOR

       Copyright (C) 1988 by Jef Poskanzer.



netpbm documentation            08 August 1989          Pbmmask User Manual(0)

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