Comment by vardump | Hacker News Reader

Comment by vardump | Hacker News Reader

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I checked those images on a Macbook 16 M2 Max (standard P3-1600 nits preset), Chrome 120.0.6099.109. All of the WebP images had pretty bad posterization, while JPEG examples did not.

Edit: You have to actually click for a full size image to see the truth. Those inline images had pretty bad compression artefacts, even the supposed lossless versions.

So https://eng.aurelienpierre.com/wp-content/uploads/sites/8/20... (full size lossless WebP image) looks fine, but inline version of the same image https://eng.aurelienpierre.com/wp-content/uploads/sites/8/20... looks terrible.

Edit 2: The difference between...

https://eng.aurelienpierre.com/wp-content/uploads/sites/8/20... lossy-noise.jpg (216 kB JPEG)

https://eng.aurelienpierre.com/wp-content/uploads/sites/8/20... (150 kB WebP)

https://eng.aurelienpierre.com/wp-content/uploads/sites/8/20... (301 kB WebP)

... is pretty obvious. Both of the WebP examples, even that 301 kB version, show clearly visible posterization.

I wonder if there's some issue with the WebP encoder (or the settings) he is using?

Edit 3:

It should be noted that monitor gamma and color profile might affect gradient posterization visibility.

> I wonder if there's some issue with the WebP encoder (or the settings) he is using?

I played around with online optimizers and IrfanView which I had locally. IrfanView got the results they did, no matter what else I tuned, obvious degradation at 90. Online optimizers were not even comparable in how bad they were.

edit: I found Squoosh [0], which has WebP V2 compression marked as unstable. It’s far better, half the size of JPEG 90, but it’s still degraded in comparison. Also, it saves as wp2 file, which neither Chrome nor FF support natively.

[0]: https://squoosh.app/editor

They ceased development on WebP2.. don't think they could've come up with anything better than AVIF or JXL already have anyway.

The first link in your Edit 2 section (the JPEG) one is broken, it should be https://eng.aurelienpierre.com/wp-content/uploads/sites/8/20...

Thanks! Unfortunately I can't change it anymore.

> I wonder if there's some issue with the WebP encoder (or the settings) he is using?

He's re-encoding the JPEG compressed images. That is a huge mistake.

From the article:

> It’s not 100 % clean either, but much better. Granted, this is WebP re-encoding of an already lossy compressed JPEG, so we stack 2 steps of destructive compression. But this is what Google Page Speed insights encourage you to do and what a shitload of plugins enable you to do, while pretending it’s completely safe. It’s not.

Addendum:

Tried it with a Windows laptop connected to a Samsung LS32A800 32" 4k display. Laptop has factory default settings. Chrome 120. The monitor is pretty low end for a 4k model.

Monitor's picture settings: Custom, brightness 81, contrast 75, sharpness 60, gamma mode1 and response time fastest.

Switched between those three "Edit 2" images blindly, yet the issues are obvious also on this combination.

The JPEG version looks better compared to WebP ones. (Also, this goes against my prior general assumptions about JPEG vs WebP quality.)

the second image and the third image are half resolution of the other, yeah some posterization is visible in Shoot-Antoine-0044-_DSC0085-lossless-1200x675.webp, but it's half resolution and he purposefully added a high frequency noise for his test then averaged the noise point trough resizing, and well, of course it's blurry.

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