Updating image entropy implementations #529
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As of version 6.1.0, the Pillow imaging library’s C module includes an optimized native entropy method: • https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst#610-2019-07-01 This change detects and selects this new native method, if it is available in the version of Pillow upon which `easy-thumbnails` finds itself running. Additionally, an optimized version of the existing Python image-entropy method is furnished as a fallback: rather than summing the entire histogram value set, the function calculates the product of the image dimensions and band count to arrive at the same number. It also uses generator expressions and the specialized `math.fsum(…)` and `math.log2(…)` library calls to improve on the performance of its predecessor without altering the algorithm. The appropriate image-entropy function is then conditionally ensconced in the `easy_thumbnails.utils` module, at module-load time. I also made a slight tweak to the `pil_image` function, found in `easy_thumbnails.source_generators` – the call to `PIL.Image.Image.load()` was raising the exception noted in comments in that functions’ source while I was running the testsuite; now all such calls have these exceptions swallowed and everything works OK.
Mogost
suggested changes
Dec 23, 2019
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| # Select the Pillow native image entropy function - if available - | ||
| # and fall back to our Python implementation: | ||
| image_entropy = hasattr(Image.Image, 'entropy') \ |
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Please don't break lines with \
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| from django.utils import six |
| hist_size = float(sum(hist)) | ||
| hist = [h / hist_size for h in hist] | ||
| return -sum([p * math.log(p, 2) for p in hist if p != 0]) | ||
| from math import log2, fsum |
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| try: | ||
| from PIL import Image, ImageMode | ||
| except ImportError: |
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As of version 6.1.0, the Pillow imaging library’s C module includes an optimized native entropy method:
• https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst#610-2019-07-01
This change detects and selects this new native method, if it is available in the version of Pillow upon which
easy-thumbnailsfinds itself running.Additionally, an optimized version of the existing Python image-entropy method is furnished as a fallback: rather than summing the entire histogram value set, this new function calculates the product of the image dimensions and band count, arriving at the same number. The new function also uses generator expressions and the specialized
math.fsum(…)andmath.log2(…)library calls to improve on the performance of its predecessor without altering the algorithm.The appropriate image-entropy function is then conditionally ensconced in the
easy_thumbnails.utilsmodule, at module-load time.I also made a slight tweak to the
pil_imagefunction, found ineasy_thumbnails.source_generators– the call toPIL.Image.Image.load()was raising the exception noted in comments in that functions’ source while I was running the testsuite; now all such calls have these exceptions swallowed and everything works OK.