SAM Coupé PNG bitmap converter

cool.py

#!/usr/bin/python

from PIL import Image				# open PNG and get raw (bitmap) data bytes
import struct						# we use struct to convert between integers and byte values

im = Image.open("input.png")		# input file
filea = open('framea.bin','wb')		# field A output file
fileb = open('frameb.bin','wb')		# field B output file

filepointer = fileb
mod = 128							# 256 pixel row in bytes (4bpp)

bytes = im.tobytes()				# raw bitmap bytes from PNG

for i in range(len(bytes)/2):
	left = ord(bytes[i*2])			# high nibble (left pixel)
	right = ord(bytes[(i*2)+1])		# low nibble (right pixel)
	sam = (left*16) + right			# combined byte
	filepointer.write(struct.pack('<B',sam))	 #write to file

	# switch file A/B for every display row
	if i % mod == 0:
		if filepointer==fileb: filepointer = filea
		else: filepointer = fileb

filea.close()
fileb.close()