jp2_dims.py

#!/usr/bin/env python3
from io import open
from collections import deque
IHDR = b'\x69\x68\x64\x72' # See I.5.3.1 Image Header box
with open('tests/fixtures/images/color.jp2', 'rb') as jp2:
    window = deque([], 4)
    while bytes(b''.join(window)) != IHDR:
        window.append(jp2.read(1))
    # The image header box is the only place in the spec where height comes
    # first. Go figure.
    image_height = int.from_bytes(jp2.read(4), byteorder='big', signed=False)
    image_width = int.from_bytes(jp2.read(4), byteorder='big', signed=False)
print(image_width, image_height)