pnmcomp(1) - man - phpman

pnmcomp(1)                             General Commands Manual                            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  for‐
       mat 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  im‐
       age.   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 composite image contains a mixture of the overlay image and the  underly‐
       ing 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 max‐
       vals (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 en‐
              tirely (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 horizon‐
              tal 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 AT mips.com).



                                            12 April 2000                                 pnmcomp(1)