pnmtoxwd reads a PNM image as input and produces an X11 window dump as output. You can display this output with xwdu.
Normally, pnmtoxwd produces a StaticGray dump file for PBM and PGM files. For PPM, it writes a PseudoColor dump file if there are up to 256 colors in the input, and a DirectColor dump file otherwise. The -directcolor flag can be used to force a DirectColor dump. And the -pseudodepth flag can be used to change the depth of PseudoColor dumps from the default of 8 bits / 256 colors.