import ImageFilter, math

class GaussianBlurFilter(ImageFilter.Kernel):
	def __init__(self, radius=5.0):
		# cf. http://mikecheng.d2.net.au/selgauss/selgauss.c
		nconv = int(radius * math.sqrt(-math.log(0.1)/math.log(2.0))) + 1
		size = 2 * nconv - 1
		kernel = [ 0 ] * size * size
		
		def store(x, y, v):
			i = size * y + x
			#print x, y, i
			kernel[i] = v
		
		k = nconv - 1
		for y in xrange(0, nconv):
			for x in xrange(0, nconv):
				r = math.sqrt(x*x + y*y)
				v = math.exp(-math.log(2)*math.pow(r/radius,2))
				store(k-x, k-y, v)
				store(k+x, k-y, v)
				store(k-x, k+y, v)
				store(k+x, k+y, v)
		if 0:
			for i in xrange(0, len(kernel)):
				print '%4.2f' % kernel[i],
				if (i+1) % size == 0: print
			print
		norm = reduce(lambda a,b: a+b, kernel)
		self.filterargs = (size, size), norm, 0, kernel