[Documentation] Broken link and missing config examples

[dmyersturnbull]

Describe the bug

Hi,

The readme contains a broken link: https://github.com/calibreapp/image-actions#Configuration.

I'm also wondering if the documentation on the options/arguments could be more clear; I wasn't sure about some aspects. Apologies if I misuse any terminology!

• How the *Quality (e.g. jpegQuality) options are used. My understanding at first was that the compression can be constrained to result in no perceptible quality loss; that is, pseudo-lossless or nominally lossy.
• Whether options available other than *Quality (e.g. jpegQuality). I confirmed none were, but only from action.yml.
• (A related feature request): The Sharp docs list AVIF support, along with HEIF.
  Would introducing AVIF support only need these options to be passed along?

Also, thanks for maintaining this tool for the community. I'm happy to contribute if it's useful.

Code of Conduct

• I agree to follow this project’s Code of Conduct

[benschwarz]

Hey @dmyersturnbull, thanks for raising these clarifications.

I agree, the quality options could probably be better documented. Here's the TLDR version of how the quality arguments are used:

*Quality (e.g.) jpegQuality configuration is passed directly to sharp. There's also pngQuality and webpQuality

At the moment image-actions re-encodes/compresses existing images in a repository. In theory image-actions can support AVIF and HEIF resources (thanks to sharp), though it would require users to add AVIF or HEIF files to their repositories.

Personally, I have no issue in adding AVIF and HEIF as options, though haven't had much motivation to make such a change as I've not seen these compression algorithms in regular use outside CDNs.

Generally speaking, I think a better approach is to create primary image resources using well-deployed formats (e.g. webp, png. sidenote: webp are a bit of a pain without specialist tools!), then use a CDN to transcode images on the fly, based on what the end users browser supports.

@dmyersturnbull, if you've interest and time to contribute, I'd happily accept PRs to address the points you've raised in this issue. Thanks again 🥞

[dmyersturnbull]

@benschwarz Thanks! That's very helpful. I'll try it out and also add a clarification to the readme.

In Chrome, I'm now regularly seeing AVIF and occasionally some HEIF in the wild (presumably mostly from CDNs). I end up with AVIFs naturally as AV1 snapshots, though admittedly I have no motivation to keep those in Git :)