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ameingast / cocoaimagehashing

Perceptual Image Hashing for macOS, iOS, tvOS and watchOS
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Fixed ignoring frequencies in pHash #13

Closed artyom-razinov closed 5 years ago

artyom-razinov commented 6 years ago

15 of lowest 64 frequencies were ignored instead of suggested 1. This caused images with low details produce 0 hash (e.g.: screenshots of UI).

Note that this breaks compatibility with previously generated values of pHash. I've added tests that check future possible regression of values.

My reference to the algorithm was: http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html#c1410

artyom-razinov commented 6 years ago

It seems that calculation is platform-dependent: tests fail on a different platform (it reproduces locally as well).

artyom-razinov commented 6 years ago

This test fails on 32-bit iPhone 4S (iOS 9.3): testResizedRGBABitmapDataScanline aHash and dHash calculation is different on different devices. E.g. aHash values for same image: on Mac OS: -8608481637110868033 64 bit iPhone Sim: -8608472703578630209 32 bit iPhone Sim: -8608191228601917505

  1. Would you make an issue?
  2. Is my fix in pHash worth merging? If so, I'll remove tests from the PR, because they don't work (I didn't do it to show you the issue).
ameingast commented 5 years ago

Is my fix in pHash worth merging?

Absolutely, but I don't want to break backwards compatibility.

If you provide a new hash-type (.pHashNoFrequencies ? - I can't think of a better name) we can talk about merging this in.

ameingast commented 5 years ago

Closing due to inactivity.