Progressive decoding: JPEG vs JPEG XL vs AVIF
Why Hacker News recommends it
HN uses it as visual evidence that JPEG XL decodes progressively while AVIF shows nothing until fully loaded.
What it is
A short side-by-side demo of a large image loading over a slow connection in JPEG, progressive mozjpeg, JPEG XL and AVIF. It shows how each codec renders partial data.
Recommended by 1 HN commenters across 1 different months, 2021 to 2026.
What Hacker News said
Recommends 149765 · 2024-03 · on “JPEG XL and the Pareto Front”
A couple of videos comparing progressive decoding of jpeg, jxl and avif: [this video] [LINK] There's more on the same channel, generation loss ones are really interesting.
Cites twotwotwo · 2021-06 · on “JPEG XL”
Some notable features of JPEG XL that don't show up in side-by-sides: 1) Progressive decoding. Like the original .jpg, .jxl can give you a low-quality image when a fraction of the file is loaded, then a decent-quality image, then the final image. This can give JPEG XL the edge in perceived load speed even when the full .avif is smaller than the full .jxl. (Old demo from a JXL contributor at [this video] ) 2) Fast conversion: JPEG XL encoding/decoding is fast without dedicated hardware. Facebook found encode/decode speed and progressive decoding to be points in favor of JPEG XL for their use: [LINK] 3) .jpg repacking: JPEG XL can pack a JPEG1 about 20% smaller without any additional loss; the orig
Cites cubefox · 2023-07 · on “JPEG XL: How It Started, How It’s Going”
Apart from limited resolution probably the biggest problem with AVIF: It doesn't support progressive decoding. Which could effectively cancel out its smaller file size for any web applications. AVIF only shows when it is 100% finished. See [this video] This comparison video is admittedly a little unfair though, because AVIF would have easily 30% lower file size than JPEG XL on ordinary images with medium quality.
Cites supermatt · 2023-09 · on “First automatic JPEG-XL cloud service”
High quality progressive decoding at reduced filesizes is a big positive for me. There is no other format that supports that. [this video]
Cites cubefox · 2026-07 · on “Regressive JPEGs”
Progressive decoding isn't expected to speed up decoding, it's expected to speed up displaying large image files, especially for downloads via slow mobile connections. Example: [this video]