pbmmask(1) | General Commands Manual | pbmmask(1) |
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 background:
For objects with a white background, you can either invert them or add a step:
pbmmask obj > objmask
pnmpaste < dest -and objmask <x> <y> | pnmpaste -or obj <x> <y>
Note that this three-step version works for objects with black backgrounds too, if you don't care about the wasted time.
pbmmask obj > objmask
pnminvert objmask | pnmpaste -and obj 0 0 > blackback
pnmpaste < dest -and objmask <x> <y> | pnmpaste -or blackback <x> <y>
You can also use masks with graymaps and pixmaps, using the pnmarith tool. For instance:
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.
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
ppmcolormask(1), pnmpaste(1), pnminvert(1), pbm(5), pnmarith(1), pnmsmooth(1)
Copyright (C) 1988 by Jef Poskanzer.
08 August 1989 |