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PBMMASK.MAN
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1991-08-11
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pbmmask(1) Unix Programmer's Manual pbmmask(1)
NNNAAAMMMEEE
pbmmask - create a mask bitmap from a regular bitmap
SSSYYYNNNOOOPPPSSSIIISSS
pppbbbmmmmmmaaassskkk [-eeexxxpppaaannnddd] [_p_b_m_f_i_l_e]
DDDEEESSSCCCRRRIIIPPPTTTIIIOOONNN
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:
pbmmask obj > objmask
pbmpaste < dest -and objmask <x> <y> | pbmpaste -or obj <x> <y>
For objects with a white background, you can either invert them or add a
step:
pbmmask obj > objmask
pnminvert objmask | pbmpaste -and obj 0 0 > blackback
pbmpaste < dest -and objmask <x> <y> | pbmpaste -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 _p_n_m_a_r_i_t_h
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
_p_n_m_s_m_o_o_t_h script before using it. This makes the boundary between the
two images less sharp.
---eeexxxpppaaannnddd
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 _p_b_m_l_i_f_e tool into a general cellular
automaton tool...)
SSSEEEEEE AAALLLSSSOOO
pbmpaste(1), pnminvert(1), pbm(5), pnmarith(1), pnmsmooth(1)
AAAUUUTTTHHHOOORRR
Copyright (C) 1988 by Jef Poskanzer.
08 August 1989 1