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by bscphil 1559 days ago
That's why the only acceptable way to compare codecs is to have two images of exactly the same size. At significantly different sizes, the compression artifacts will be different enough that the comparison becomes subjective, at best.

Here's a comparison that has AVIF, JPEG-XL, mozjpeg, and others: https://afontenot.github.io/image-formats-comparison/
1 comments
naoqj 1559 days ago
If you need images of the same exact size for them to look the same then there is no point to having new codecs.
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vlovich123 1559 days ago
OP is saying you need them to be the same to make the image quality difference more obvious. If you shrunk the other codecs to the size the AVIF version is at, you’d see much worse visual artifacts. If you increased AVIF to be the same size as the others, you’d get better relative image quality.

The article is trying to demonstrate how much more compression is achieved by trying to keep relative image quality the same. That’s fine normally but when you have a broad population looking at it then it’s going to be a lot of nitpicking which isn’t helpful when you’re trying to communicate about the codec quality (and no benchmark is perfect but it’s pretty clear that AVIF is roughly 20% or better than H265 if I recall correctly - good luck being able to measure a 20% relative difference in image quality by hand).

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bscphil 1558 days ago
Exactly. Many people are insensitive to blurring / smearing artifacts, and so what you very often see is a comparison between an old codec at a medium bitrate with noticeable artifacts (e.g. JPEG picking and ringing) and a new codec at a low bitrate with different artifacts that the author just didn't notice. It's no longer a 1:1 comparison. Is the modern codec still better? Probably, but unless the new codec is identical to the old one with less bitrate (hint: it rarely is), you can't prove it with differently sized comparison images.
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vlovich123 1558 days ago
It cuts both ways though which is what I’m trying to say. Humans can’t say “this artifact is 20% worse”. Everyone has a subjective opinion.

I disagree thought mostly about the codec characterization. H265/AV1 are definitely higher quality at the same bitrate. The test I used is to find the bitrate that artifacts started to be noticeable. H265 was 15-20% smaller bitrate consistently (across multiple people surveyed, not just me). I could definitely believe that AV1 manages a similar feat above that.

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