Calculate hash of image pixels

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Bilge
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Calculate hash of image pixels

Post by Bilge »

Is there a way to calculate a hash of the decoded image information only? That is, for two identical images with different metadata, the hash will be the same.

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magick
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Re: Calculate hash of image pixels

Post by magick »

ImageMagick already does this for you. Type 'identify -verbose myimage.png' for example.

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anthony
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Re: Calculate hash of image pixels

Post by anthony »

Note tat this is only a hash of the image data. It ignores difference in meta-data (which will always be different due to file dates)

Also the slightest difference will produce a different hash. If the data may have slight differences (say from jpeg compressions), then a image comparision will probably be better for identical image testing.
http://www.imagemagick.org/Usage/compare/
Anthony Thyssen -- Webmaster for ImageMagick Example Pages
https://imagemagick.org/Usage/

Wolfgang Woehl
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Re: Calculate hash of image pixels

Post by Wolfgang Woehl »

Anthony, in some use cases having a image-data-only hash is extremely useful. Now if the hash algorithm used was configurable ...

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magick
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Re: Calculate hash of image pixels

Post by magick »

We have existing algorithms to support configurable hashes but so far we have not found a use case that justifies the distribution bloat. The default is SHA 256.

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