Convert hpi files into pngs -- based on Ed Halley's Method: http://www.halley.cc/ed/linux/interop/hemera.html

convert.sh

#! /bin/sh
#  depends on ImageMagick 6.8.9-9 

for name in *.hpi; do

	echo $name

	# split hpi into component jpg & png
	./split.py $name

	wait

	# clean up jpg
	convert $name.jpg -type truecolormatte matted.$name.png

	# use png as mask for jpg (ala hpi's formatting)
	convert matted.$name.png $name.png \
		-alpha off -compose CopyOpacity -composite \
		final.$name.png

	wait

	# clean up files generated during this process
	rm -f matted.$name.png $name.jpg $name.png
	mv final.$name.png ${name%%.*}.png


done;

split.py

#! /usr/bin/env python
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
# note: tested with python 2.7, may need tweaked for python 3+

import sys, re

name = sys.argv[1]

try:
    if name:
        # read hpi file
        f = open(name, "r");
        imgs = f.read()
        # split image with regex
        imgs = re.search(r"^.{32}(.*)(\211PNG.*)$", imgs, re.S)
        # write first match as JPG
        j = open(name + ".jpg", "w");
        j.write(imgs.group(1));
        # write second match as PNG
        p = open(name + ".png", "w");
        p.write(imgs.group(2));
        # close all the files we've opened.
        j.close()
        p.close()
        f.close()
    else:
        print name + " not found"
except:
    print "could not split " + name