Convert (320x200) RGB image to an Apple IIgs $C1 (Uncompressed SHR) file

genc1.py

# Invoke like:
# $ python genc1.py mypic.png output.shr

from PIL import Image
from math import sqrt
from sys import argv

img = Image.open(argv[1])
rgb_img = img.convert("RGB")	# create the pixel map

iigs_colors = set()
cvals = [0, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF]
for r in cvals:
	for g in cvals:
		for b in cvals:
			iigs_colors.add((r,g,b))

def distance3d((x1, y1, z1), (x2, y2, z2)):
	return sqrt((x2 - x1)**2 + (y2 - y1)**2 + (z2 - z1)**2)

def uniquepalette(image):
	hist = set()
	for j in range(image.size[1]):
		for i in range(image.size[0]):
			hist.add(image.getpixel((i,j)))
	return hist

def iigspalette(pal_set):
	new = set()
	for rgb in pal_set:
		new.add(min(iigs_colors, key=lambda x: distance3d(x, rgb)))
	return new

### MAIN
orig_pal = sorted(uniquepalette(rgb_img))	# source palette from gif/png
iigs_pal = iigspalette(orig_pal)			# our 4-bit colorspace versions
image_pal = list(iigs_pal)					# as a list to index palette colors
bytes = []
for j in range(rgb_img.size[1]):
	for i in range(rgb_img.size[0]/2):			# 2 horizontal pixels at a time to make a byte
		p1 = rgb_img.getpixel((i*2,j))
		p2 = rgb_img.getpixel(((i*2)+1,j))
		nearest_idx1 = image_pal.index(min(image_pal, key=lambda x: distance3d(x, p1)))
		nearest_idx2 = image_pal.index(min(image_pal, key=lambda x: distance3d(x, p2)))
		byte = (nearest_idx1*16) + (nearest_idx2)
		bytes.append(byte)

for _ in xrange(0,0x100):	# SCBs, all zero
	bytes.append(0)

# GB0R
for color in image_pal:		# write palette colors
	r,g,b = color
	gb = ((g/16)*16)+(b/16)	#actually need to step down these 8 bit values to 4 bits per color so /16
	r = r/16
	bytes.append(gb)
	bytes.append(r)

# now pad
print(0x200 - (len(image_pal)*2))
for _ in range(0x200 - (len(image_pal)*2)):
	bytes.append(0)

newFile = open(argv[2], "wb")
newFileByteArray = bytearray(bytes)
newFile.write(newFileByteArray)
print("Wrote {} bytes to {}.".format(len(bytes),argv[2]))