Change AVIF quality defaults

[zachleat]

Read: https://tsev.dev/posts/2023-11-10-should-avif-be-the-dominant-image-format/

As we discovered, AVIF often is more accurate and smaller in file size than competing image formats. A quality setting of 60-70% is a good place to start where perceivable accuracy is consistent enough across images without exploding in file size. At the cost of accuracy, we can lower it to 50%, but anything lower typically comes with bad artefacts. I recommend staying below 80% as any value higher is indistinguishable. If you care about improved pixel accuracy, JPEG might give you that at a smaller file size.

[zachleat]

I did find out later that the Sharp library we use upstream has a default quality of 50 so I think we can close this one as solved.

https://sharp.pixelplumbing.com/api-output#avif

[eeeps]

Different AVIF encoders have different effort and quality scales and I don't know how Sharp's are set up (it seems to use libaom, but maybe with a flipped "effort" (vs "speed") scale??)

Anyways when doing a test with one (1) image, I thought the output looked a bit crummy and turned up both the quality and effort – and was happier.

Here are some loosely-held beliefs:

• Many AVIF tools are built on AV1 toolchains, and have defaults tuned for video, which produce much lower quality than you'd want for images.
• (unless those images are being displayed at >=2x, then it might be fine, sometimes. Might not tho.)
• The last two effort/speed levels are almost never usable, in any AVIF encoder. Way too crappy at the fast end, and painfully slow at the slow end.

I chose effort 7 and quality 70 because they fit nicely within these guidelines and I used to always encode my JPEGs at Save for Web... quality 72 and you know 70 is pretty close to that.

Here are the images:

Original: https://o.img.rodeo/w_800/dogs/2.png
Default settings (quality 50, effort 4): https://o.img.rodeo/w3fr2wrmmrf3pfrtmal7.avif – compared to original
Custom settings (quality 70, effort 7): https://o.img.rodeo/vahj96nhy8xchvlodlbo.avif – compared to original

(Note that the comparison pages display the images at 1x...)

Clearly, some more rigorous investigation is in order. But this first experience with eleventy-img made me hypothesize that the defaults could and maybe should be higher.

[lovell]

Upstream discussion at lovell/sharp#4227