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NAME

       pnmcomp - composite (overlay) two portable anymap files together

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
       transparent, 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
       opaqueness and a black pixel  transparency.   Anything  in  between  is
       translucent.

       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
       different  maxvals.   The  output image has the more general of the two
       input formats and a maxval that is the least common  multiple  the  two
       maxvals  (or  the maximum maxval allowable by the format, if the LCM is
       more than that).

OPTIONS

       -invert
              This option inverts the sense of the values in the  alpha  mask,
              which  effectively  switches  the roles of the overlay image and
              the underlying image in places where the two intersect.

       -xoff X

       -yoff Y
              These options position the overlay image  with  respect  to  the
              underlying  image.   X  and  Y  are  the horizontal and vertical
              displacements 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)