trezor-firmware/tools/png2toi

#!/usr/bin/env python3
from PIL import Image
import sys
import struct
import zlib

if len(sys.argv) < 2:
    print('Usage png2toi image.png [mode]')
    sys.exit(1)

ifn = sys.argv[1]

gray = False
if len(sys.argv) >= 3 and sys.argv[2] == 'g':
    gray = True

if not ifn.endswith('.png'):
    print('Must provide PNG file')
    sys.exit(2)

im = Image.open(ifn)
w, h = im.size
print('Opened  %s ... %d x %d @ %s' % (ifn, w, h, im.mode))

if not gray:
    if not im.mode == 'RGB':
        print('PNG file must use RGB mode')
        sys.exit(3)
else:
    if not im.mode == 'L':
        print('PNG file must use grayscale mode')
        sys.exit(3)
    if w % 2 > 0:
        print('PNG file must have width divisible by 2')
        sys.exit(4)

pix = im.load()

ofn = '%s.toi' % ifn[:-4]
with open(ofn, 'wb') as f:
    if not gray:
        f.write(bytes('TOIa', 'ascii'))
    else:
        f.write(bytes('TOIg', 'ascii'))
    f.write(struct.pack('>HH', w, h))
    data = bytes()
    if not gray:
        for j in range(h):
            for i in range(w):
                r, g, b = pix[i, j]
                c = ((r & 0xF8) << 8) | ((g & 0xFC) << 3) | ((b & 0xF8) >> 3)
                data += struct.pack('>H', c)
    else:
        for j in range(h):
            for i in range(w // 2):
                l1, l2 = pix[i * 2, j], pix[i * 2 + 1, j]
                c = (l1 & 0xF0) | (l2 >> 4)
                data += struct.pack('>B', c)
    z = zlib.compressobj(level=9, wbits=10)
    zdata = z.compress(data) + z.flush()
    zdata = zdata[2:-4] # strip header and checksum
    f.write(zdata)

print('Written %s ... %d bytes' % (ofn, 4 + 4 + len(zdata)))