import sys

from PIL import Image

def two_bpp_index(px):
    indices = {0x00: 0, 0x55: 1, 0xaa: 2, 0xff: 3}
    assert px in indices, px
    return indices[px]

def convert(image):
    assert image.mode == 'L', image.mode
    width, height = image.size

    buf = bytearray(width * height // 2)

    for cell_y in range(height//8):
        for cell_x in range(width//8):
            for y in range(8):
                for x in range(8):
                    px = im.getpixel((cell_x * 8 + x, cell_y * 8 + y))
                    index = two_bpp_index(px)
                    buf_ix = x//2 + (4 * (cell_x * 8 + (cell_y * width) + y))
                    buf[buf_ix] |= (index << 4 * (1 - (x % 2)))
    return buf

def debug(buf):
    for row in range(len(buf) // 4):
        for x in range(4):
            px = buf[row * 4 + x]
            print((px >> 4) & 0xf, end='')
            print((px >> 0) & 0xf, end='')
        print()
        if (row % 8 == 7):
            print()

im = Image.open(sys.argv[1])
buf = convert(im)
with open(sys.argv[2], 'wb') as f:
    f.write(buf)