pnmcomp(1)

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)

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Free and Open Source Software