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Xwdtopnm User Manual(0)                                Xwdtopnm User Manual(0)

       xwdtopnm - convert an X11 or X10 window dump file to a PNM image

       xwdtopnm [-verbose] [-headerdump] [xwdfile]

       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 interested 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  processing
       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 programs.

              This option causes xwdtopnm to display handy information about the input image and the  conversion  pro-

              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).

   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 that 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 program 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,  byte  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 31 * 63 =
       1953, and use 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 common option .  The warn-
       ing was new in Netpbm 10.46 (March 2009).

       pnmtoxwd(1), pamendian(1), pamdepth(1), pnm(1), xwd man page

       Copyright (C) 1989, 1991 by Jef Poskanzer.

netpbm documentation            21 January 2009        Xwdtopnm User Manual(0)