Output quality loss information

[JamieMason]

Types of Changes

What types of changes does your issue require? Put an x in all the boxes that apply:

• [x] feat: A new feature
• [ ] fix: A bug fix
• [ ] docs: Documentation only changes
• [ ] style: Changes that do not affect the meaning of the code
• [ ] refactor: A code change that neither fixes a bug or adds a feature
• [ ] perf: A code change that improves performance
• [ ] test: Adding missing tests
• [ ] chore: Changes to the build process or auxiliary tools/libraries

Description

This was a feature in <2.0.0 of imageoptim-cli that needs reinstating.

Suggested Solution

If ImageMagick's compare is installed, or a NodeJS alternative exists, output quality loss information if the stats option is enabled.

[kornelski]

I would advise against using IM's compare command. It only offers naive pixel-by-pixel comparison methods, which reward distortions that are blurry, and penalize good texture-preserving codecs.

In TID2013 benchmark these methods have 30-40% correlation with human judgement, while for JPEG compression DSSIM achieves 94%: https://github.com/kornelski/dssim

[JamieMason]

perfect, thanks @kornelski I will use that.