Xwdtopnm User Manual(1) General Commands Manual Xwdtopnm User Manual(1)
NAME
xwdtopnm - convert an X11 or X10 window dump file to a PNM image
SYNOPSIS
xwdtopnm [-verbose] [-headerdump] [xwdfile]
DESCRIPTION
This program is part of Netpbm(1).
xwdtopnm reads an X11 or X10 window dump file as input and produces a
PNM image as output. The type of the output image depends on the input
file - if it's black and white, the output is PBM. If it's grayscale,
the output is PGM. Otherwise, it's PPM. The program tells you which
type it is writing.
Using this program, you can convert anything you can display on an X
workstation's screen into a PNM image. Just display whatever you're in-
terested in, run the xwd program to capture the contents of the window,
run it through xwdtopnm, and then use pamcut to select the part you
want.
Note that a pseudocolor XWD image (typically what you get when you make
a dump of a pseudocolor X window) has maxval 65535, which means the PNM
file that xwdtopnm generates has maxval 65535. Many older image pro-
cessing programs (that aren't part of the Netpbm package and don't use
the Netpbm programming library) don't know how to handle a PNM image
with maxval greater than 255 (because there are two bytes instead of one
for each sample in the image). So you may want to run the output of
xwdtopnm through pamdepth before feeding it to one of these old pro-
grams.
xwdtopnm can't convert every kind of XWD image (which essentially means
it can't convert an XWD created from every kind of X display configura-
tion). In particular, it cannot convert one with more than 24 bits per
pixel.
OPTIONS
In addition to the options common to all programs based on libnetpbm
(most notably -quiet, see ]8;;index.html#commonoptions\ Common Options]8;;\ ), xwdtopnm recognizes the
following command line options:
-verbose
This option causes xwdtopnm to display handy information about
the input image and the conversion process.
-headerdump
This option causes xwdtopnm to display the contents of the X11
header. It has no effect when the input is X10. This option was
new in Netpbm 10.26 (December 2004).
NOTES
Two Byte Samples
xwdtopnm sometimes produces output with a maxval greater than 255, which
means the maximum value of a sample (one intensity value, e.g. the red
component of a pixel) is greater than 255 and therefore each sample
takes 2 bytes to represent. This can be a problem because some programs
expect those bytes in a different order from what the Netpbm format
specs say, which is what xwdtopnm produces, which means they will see
totally different colors than they should. xv is one such program.
If this is a problem (e.g. you want to look at the output of xwdtopnm
with xv), there are two ways to fix it:
• Pass the output through pamendian to produce the format the pro-
gram expects.
• Pass the output through pamdepth to reduce the maxval below 256
so there is only one byte per sample.
Often, there is no good reason to have a maxval greater than 255. It
happens because in XWD, but not PNM, each color component of a pixel can
have different resolution, for example 5 bits for blue (maxval 31), 5
bits for red (maxval 31), and 6 bits for green (maxval 63), for a total
of 16 bits per pixel. In order to reproduce the colors as closely as
possible, xwdtopnm has to use a large maxval. In this example, it would
use maxval 31 * 63 = 1953, which requires two bytes per sample, to-
talling 48 bits per pixel.
Because this is a common and frustrating problem when using xwdtopnm,
the program issues a warning whenever it generates output with two byte
samples. You can quiet this warning with the -quiet ]8;;index.html#commonoptions\common option]8;;\ .
The warning was new in Netpbm 10.46 (March 2009).
SEE ALSO
pnmtoxwd(1), pamendian(1), pamdepth(1), pnm(1), xwd man page
AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML
source. The master documentation is at
http://netpbm.sourceforge.net/doc/xwdtopnm.html
netpbm documentation 08 January 2010 Xwdtopnm User Manual(1)
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