Gianni Rosato works on image compression at Halide Compression, with a background in AV1 and AVIF tooling. He spent years as a JPEG XL advocate — he endorsed the format for Interop 2024 and speaks well of its authors — and this essay is a public reversal, argued from measurements rather than the browser-politics framing that usually carries the debate.

The case against, in his numbers:

  • AVIF now dominates the entire fidelity range, so JPEG XL’s one real advantage — better lossy quality at medium-high fidelity — has disappeared.
  • Lossless was never the Web’s problem. JXL’s lossless gains are roughly 12% over lossless WebP, measured on a dataset that does not resemble Web image traffic.
  • Decode time is the disqualifier. In size-matched encodes, WebP came in about 90KB larger and still decoded more than 10x faster than the Rust JPEG XL decoder.
  • The format itself is disadvantaged, not merely its reference encoder: no directional prediction modes, no deblocking loop filter, and XYB colorspace savings that come partly from aggressively quantizing the blue channel.
  • Non-photographic content is awkward — patches cost far more bitstream overhead than AV1’s Intra Block Copy, and can exceed the savings.
  • Expressivity is a foot-gun. He demonstrates a 1,918-byte JXL that takes 17.4 seconds of user time to decode on an M5 Pro, which makes cheap denial-of-service against low-end devices possible now that the Rust decoder is shipping in Chrome and Firefox.
  • JPEG recompression still saves bits, but costs about 33% more decode time, so it is not free.

He separates the engineering from the politics carefully. His read is that most of the argument for JPEG XL in browsers comes from wanting a Web with more developer choice after the WebP and AVIF fights — a legitimate goal, but a different claim than technical superiority. Both formats are royalty-free, and JPEG XL came out of Cloudinary and Google as much as anywhere.

The conclusion is scoped rather than dismissive: Web codecs should be purpose-built and narrow, while JPEG XL stays genuinely compelling off the Web — professional tooling, cameras, archival. Worth reading as a model for changing your mind in public, with the evidence attached.