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 com­
       pletely.  In places where the alpha mask shows a value  in
       between opaque and transparent (translucence), the compos­
       ite 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 repre­
       sents opaqueness and a black pixel transparency.  Anything
       in between is translucent.

       In some image file  formats  (PNG,  for  example),  trans­
       parency  information (the alpha mask) is part of the defi­
       nition 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 trans­
       parency 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.

       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 for­
       mats (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 posi­
              tive  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.  pnm­
              comp uses only the parts that lie over the underly­
              ing 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, cen­
              tered, 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,  cen­
              tered, or flush bottom on the underlying image.


SEE ALSO

       ppmmix(1)  and  pnmpaste(1) are simpler, less general ver­
       sions of the same tool.



AUTHOR

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


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