Enhance visual similarity comparison for lossy compression

[irv]

Use SSIMULACRA 2 to calculate visual similarity

One big caveat is that it doesn't work with tiff, and likely never will

When possible, cjxl/djxl are able to read/write the following image formats: OpenEXR (.exr), GIF (.gif), JPEG (.jpg/.jpeg), NetPBM (.pam/.pgm/.ppm), Portable FloatMap (.pfm), PGX Test Format (.pgx), Portable Network Graphics (.png), Animated PNG (.png/.apng), and JPEG XL itself (.jxl).

This would mean instead of roundtripping the jp2 back to tiff, we'd need to use ppm,pgm,pfm or pgx

[mel-mason]

The TIFF restriction seems like it could be a dealbreaker, considering our original copies are almost all TIFFs. The visual similarity check is intended to check the TIFF to JP2 conversion - is there a reason why we would be able to trust that the conversion from TIFF to ppm etc more than the JP2 conversion? Or why we could rely on the conversions not having the same change/loss and thus masking it?

Also, not sure what lossy compression you're referring to - isn't TIFF to JP2 always done losslessly?