Adds a bumpmap-like effect to images (works best on low-res [~16x16] textures).

imgbump.py

#!/usr/bin/env python
import sys
from PIL import Image

FCT = 8

def diff2(a, b):
	return abs(a-b)

def avg3(a, b, c, d=0):
	return (a + b + c) / 3.0

def pxlmlower(ar, x, y, n):
	v = list(ar[x, y])
	v[0] = int((v[0] / 256.0) * float(256-n))
	v[1] = int((v[1] / 256.0) * float(256-n))
	v[2] = int((v[2] / 256.0) * float(256-n))
	ar[x, y] = tuple(v)

if len(sys.argv) <= 2:
	print("Usage: %s <input> <output>" % sys.argv[0])
else:
	im = Image.open(sys.argv[1])
	#if im.mode == 'P':
	#	im = im.convert(im.palette.mode)
	#if not im.mode.startswith("RGB"):
	im = im.convert("RGBA")
	ims = im.size
	imp = im.load()
	out = im.resize((ims[0]*FCT, ims[1]*FCT))
	outp = out.load()
	for x in range(ims[0]):
		for y in range(ims[1]):
			pxl = imp[x, y]
			if x > 0:
				opx = imp[x-1, y]
				n = diff2(avg3(*pxl), avg3(*opx))
				xx = x*FCT
				for yy in range(y*FCT, y*FCT+FCT):
						pxlmlower(outp, xx, yy, n)
			if y > 0:
				opx = imp[x, y-1]
				n = diff2(avg3(*pxl), avg3(*opx))
				yy = y*FCT
				for xx in range(x*FCT, x*FCT+FCT):
						pxlmlower(outp, xx, yy, n)
			if x < ims[0]-1:
				opx = imp[x+1, y]
				n = diff2(avg3(*pxl), avg3(*opx))
				xx = x*FCT+FCT
				for yy in range(y*FCT, y*FCT+FCT):
						pxlmlower(outp, xx, yy, n)
			if y < ims[1]-1:
				opx = imp[x, y+1]
				n = diff2(avg3(*pxl), avg3(*opx))
				yy = y*FCT+FCT
				for xx in range(x*FCT, x*FCT+FCT):
						pxlmlower(outp, xx, yy, n)
	out.save(sys.argv[2])