C code creates a postscript file that is fed to ghostscript to create a pnm file that is scaled to 50% with pnmscale to antialias and then converted to png by pnmtopng, and the original postscript output file is converted to pdf by ghostscript's ps2pdf14.

You'll need ghostscript installed in addition to netpbm for the other tools. Ghostscript itself could have been used to create a png, but the output file was much larger and the resulting image was not as visually appealing.