pnmcomp(1)pnmcomp(1)NAMEpnmcomp - composite (overlay) two portable anymap files
together
SYNOPSISpnmcomp [-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.
DESCRIPTIONpnmcomp 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.
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 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 ALSOppmmix(1) and pnmpaste(1) are simpler, less general ver
sions of the same tool.
pnm(5), pbmmask(1)AUTHOR
Copyright (C) 1992 by David Koblas (koblas@mips.com).
12 April 2000 pnmcomp(1)
