This program is part of Netpbm.
ximptoppm reads an Xim file as input and produces a PPM image as output. The Xim toolkit is included in the contrib tree of the X.V11R4 release.
You can abbreviate any option to its shortest unique prefix.
If you specify - as the filename, ximtoppm writes the alpha output to Standard Output and discards the image.
Actually, an Xim image can contain an arbitrary fourth channel -- it need not be an Alpha channel. ximtoppm extracts any fourth channel it finds as described above; it doesn't matter if it is an alpha channel or not.
See pamcomp for one way to use the alpha output file.
Copyright (C) 1991 by Jef Poskanzer.