For estimating JPEG quality, ExifTool uses a heuristic that is adapted from ImageMagick. There are several problems with this method, and I just created an issue for this (see links to blog posts for details):
In the issue description I suggest an alternative quality estimation algorithm, for which I also provide a Python implementation. If there's any interest in this, feel free to port this to ExifTool.
boardhead
commented
5 days ago
For estimating JPEG quality, ExifTool uses a heuristic that is adapted from ImageMagick. There are several problems with this method, and I just created an issue for this (see links to blog posts for details):
https://github.com/ImageMagick/ImageMagick/issues/7732
In the issue description I suggest an alternative quality estimation algorithm, for which I also provide a Python implementation. If there's any interest in this, feel free to port this to ExifTool.