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)