pnmcomp


SYNOPSIS
       pnmcomp [-xoff=X | -align={left,center,right}]
       [-yoff=Y | -valign={top,middle,bottom}]
       [-alpha=alpha-pgmfile] [-invert]
       overlay [pnm-input] [pnm-output]

       Minimum unique abbreviations are acceptable.


DESCRIPTION
       pnmcomp reads two images and produces a composite image with one of the
       images overlayed on top of the other.  The images need not be the  same
       size.  The input and outputs are PNM format image files.

       In  its  simplest use, pnmcomp simply places the overlay file on top of
       the pnm-input file, blocking out the part of the pnm-input file beneath
       it.   If  you  specify  the  alpha-pgmfile, pnmcomp uses it as an alpha
       mask, which means it determines the level of transparency of each point
       in  the overlay image.  The alpha mask must have the same dimensions as
       the overlay image.  In places where the alpha mask defines the  overlay
       image  to be opaque, the composite output contains only the contents of
       the overlay image; the underlying image is  totally  blocked  out.   In
       places  where  the alpha mask defines the overlay image to be transpar-
       ent, the composite output contains  none  of  the  overlay  image;  the
       underlying  image  shows through completely.  In places where the alpha
       mask shows a value in between opaque  and  transparent  (translucence),
       the  composite  image  contains  a mixture of the overlay image and the
       underlying image and the level of translucence determines how  much  of
       each.

       The  alpha mask is a PGM file in which a white pixel represents opaque-
       ness and a black pixel transparency.  Anything in between  is  translu-
       cent.

       In some image file formats (PNG, for example), transparency information
       (the alpha mask) is part of the definition of the image.   In  the  PNM
       formats,  transparency is always embodied in a separate companion file.
       The PNM converter programs that convert from an image  format  such  as
       PNG have options that allow you to extract the transparency information
       to a separate file, which you can then use as input to pnmcomp.

       The output image is always of the same  dimensions  as  the  underlying
       image.   pnmcomp  only  uses parts of the overlay image that fit within
       the underlying image.

       To specify where on the underlying image to place  the  overlay  image,
       use  the  -xoff,  -yoff,  -align,  and  -valign options.  Without these
       options, the default horizontal position is flush left and the  default
       vertical position is flush top.

       The  overlay  and  underlying  images may be of different formats (e.g.
       overlaying a PBM text image over a full color PPM image) and have  dif-
       ferent maxvals.  The output image has the more general of the two input
       -xoff X

       -yoff Y
              These options position the overlay image  with  respect  to  the
              underlying  image.  X and Y are the horizontal and vertical dis-
              placements of the top left corner of the overlay image from  the
              top  left corner of the underlying image, in pixels.  A positive
              value means right or down; a negative value means  left  or  up.
              The  overlay need not fit entirely (or at all) on the underlying
              image.  pnmcomp uses only the parts that lie over the underlying
              image.

       -align=[left,center,right]
              This  option  is  an alternative to -xoff, in the style of HTML.
              It selects the horizontal position of the overlay image so  that
              it  is  flush  left,  centered, or flush right on the underlying
              image.

       -valign=[top,middle,bottom]
              This option is an alternative to -yoff, in the  style  of  HTML.
              It selects the vertical position of the overlay image so that it
              is flush top, centered, or flush bottom on the underlying image.


SEE ALSO
       ppmmix(1) and pnmpaste(1) are simpler, less  general  versions  of  the
       same tool.

       pnm(5), pbmmask(1)

AUTHOR
       Copyright (C) 1992 by David Koblas (koblas@mips.com).



                                 12 April 2000                      pnmcomp(1)
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