fprintf (stderr, "Usage: png2pnm [options] <file>.png [<file>.pnm]\n");
fprintf (stderr, " or: ... | png2pnm [options]\n");
fprintf (stderr, "Options:\n");
fprintf (stderr, "Usage: png2pnm [options] <file>.png [<file>.pnm]\n");
fprintf (stderr, " or: ... | png2pnm [options]\n");
fprintf (stderr, "Options:\n");