Select window and convert to PNG file:
xwd | ./xwd.py
XWDFile.h comes from http://www.opensource.apple.com/source/X11/X11-0.40.80/xc/include/XWDFile.h?txt
xwud -dumpheader can be a useful diagnostic.
Different windows may have dumps in different formats.
For example,
my Terminal dump has pixmap depth 32;
the display.im6 (ImageMagick) has pixmap depth 24.
(or possibly this is me taking dumps on different laptops; i'm
not sure)
Discovered that (on bay at any rate) trying to xwd an xmag
window creates a Visual Class 5 dump, which this module
currently fails to decode.
On a modern (2016) Linux box it seems that everything is either 24- or 32-bit.
file reports PixmapDepth. Not sure what "24-bit" means.
Both the 24-bit sample xwd file I have and
the 32-bit file
have 32-bits per pixel
in XRGB8 format.
Reading a series of 32-bit ints then masking off the top 8 bits
could be quite slow in Python.
Might be better to treat a row as an array of octets,
then remove every 4th octet: del a[0::4]