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19 lines
574 B
Python
19 lines
574 B
Python
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import math
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from imagekit.lib import Image
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def histogram_entropy(im):
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"""
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Calculate the entropy of an images' histogram. Used for "smart cropping" in easy-thumbnails;
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see: https://raw.github.com/SmileyChris/easy-thumbnails/master/easy_thumbnails/utils.py
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"""
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if not isinstance(im, Image.Image):
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return 0 # Fall back to a constant entropy.
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histogram = im.histogram()
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hist_ceil = float(sum(histogram))
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histonorm = [histocol / hist_ceil for histocol in histogram]
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return -sum([p * math.log(p, 2) for p in histonorm if p != 0])
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