web-optimization
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JPEG XL vs. AVIF for web use-cases
research
49 min read
JPEG XL is now supported by all major browsers, but benchmarks run on a 2024 MacBook Pro with an M4 Pro found AVIF generally more efficient for lossy web images. Across tested photos, the best JPEG XL files were typically 15–25% larger than equivalent AVIF files at default encoder settings and 6–20% larger at maximum effort, although some images—including a weasel photo—favored JPEG XL. The newer jixel JPEG XL encoder generally outperformed libjxl, except on detailed transparency. AVIF produced substantially smaller files for screenshots, illustrations, and images with alpha channels, while also usually decoding two to three times faster at medium quality. AVIF 4:4:4 is recommended as the default over 4:2:0, whose reduced color resolution rarely cut file size and could limit quality. Higher effort settings improved AVIF and jixel results, whereas libjxl’s higher efforts often added large time and memory costs for little benefit. JPEG XL remains stronger for lossless compression and can transcode existing JPEGs without further quality loss, reducing their size by 9–20%. It can also provide progressive previews in Chrome and Firefox, while progressive AVIF currently renders only in Chrome. AVIF supports HDR gain maps in browsers; JPEG XL’s format supports gain maps, but browser decoders do not. For typical web delivery, AVIF 4:4:4 at a practical high-effort setting was the recommended default, with jixel worth testing for unusually large AVIF results.