Keir Rice wrote:
> Ian, I was basing my code off Fredrik Lundh post on comparing images.
> http://effbot.org/zone/pil-comparing-images.htm
> return math.sqrt(sum([h*i*i for i,h in enumerate(histogram)]) /
> self.Area())
>
> Ran at the same speed as my 'fast' version and without the square brackets
> was slower.
It looks like len(histogram) will always be 256. If so, you can factor out
[i*i for i in range(256)]. For number-crunching tasks considering numpy
might also be a good idea:
# untested
import numpy
deltas = numpy.arange(256, dtype=float)
squares = deltas * deltas
class Whatever:
def RMSBand(self, histogram):
return math.sqrt((squares*histogram).sum()/self.Area())
If it works this should be quite fast.
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