World’s simplest band correlation visualizer

corr.py

#!/usr/bin/env python

# Simple script to scatterplot one band's values over another's into a third image.
# Usagi Yojimbo: corr.py band_1.tif band_2.tif 2_v_3.tif
# This is for quick testing; don't use it in place of proper statistics.
# It may overflow, will fail if the inputs are not identically formatted, etc.
# You may have to scale up the output (perhaps by increasing gamma).

import Image
from sys import argv

A = Image.open(argv[1])
B = Image.open(argv[2])

a, b = A.load(), B.load()
w, h = A.size

depth = 2**8 # assume the inputs are 8-bit by default
if A.mode == 'I;16': depth = 2**16 # check for 16-bit

C = Image.new('I;16', (depth, depth))
c = C.load()

for y in range(h):
  for x in range(w):
    c[a[x, y], b[x, y]] += 1 # can overflow

C.save(argv[3])