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)