[Image-SIG] Estimating compression quality of existing JPEG files

[Franz Buchinger]

I want to estimate the quality of uploaded JPEG files by analyzing their
Quantization Tables (DQTs).

Is there a way to do this with PIL? I already figured out the
Image.quantization property, but without some quantization array ==> JPEG
quality mapping I can't make assumptions on the quality.

Exiftool provides an enormous amount of JPEG DQT checksums in this module:

http://cpansearch.perl.org/src/EXIFTOOL/Image-ExifTool-7.82/lib/Image/ExifTool/JPEGDigest.pm

I really like to build on that dataset, but this implies that I make my
quantization hashing function compatible to the one of Exiftool and
eventually need to access the raw DQT.

Any hints on that?

nice regards,

Franz
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