av1-avif VS libjxl

The article is about avif not webp. Note the editors for the AOM avif specification don't even include Google https://aomediacodec.github.io/av1-avif/

This reminds me of something similar from the guy who implemented AVIF in Firefox. He gives a talk about the implementation [1] where he talks about the CLAP privacy problem. Basically the spec adds a field that allows for cropping of the image, but the binary file would still contain the original. This would lead users to believe some image data was deleted when it really wasn't. I always thought he spent a lot of time and effort on this for little gain, but now I'm starting to think it was worth his effort.

[1]: https://youtu.be/BUkRlfkv2D8?t=2199

And the related GitHub issue: https://github.com/AOMediaCodec/av1-avif/issues/188

So actually the same images I linked above are in the AOMediaCodec repo as well, under Link-U: https://github.com/AOMediaCodec/av1-avif/tree/master/testFiles/Link-U And I see the same issue with the yuv422 images there as well. I'm guessing Apple's AVIF implementation must be incomplete?

Created by Alliance for Open Media and worked on by Netflix, Microsoft, and Google developers, AVIF is open source - you can even weigh in on image processing and spec issues.

I've been trying to find a way edit 14bit RAW files (.ARW) to an HDR capable format (HEIF/AVIF). In the process I found out there's an official AVIF encoder (1) by AOM that seems like it should be capable of creating HDR PQ stills.

Others samples are available here : https://github.com/AOMediaCodec/av1-avif/tree/master/testFiles/Netflix/avif

AVIF can do something that resembles hierarchical JPEG and that could be useful for progressive decoding: you can have multiple layers/scales, where e.g. first a 1:4 image is encoded, then residuals to get to 1:2, then residuals to get to 1:1. Examples of this were recently added to the AVIF spec: https://github.com/AOMediaCodec/av1-avif/pull/134

https://github.com/libjxl/libjxl/blob/main/doc/format_overvi... is a pretty detailed but good overview. The highlights are variable size DCT (up to 128x128), ANS entropy prediction, and chroma from luminance prediction. https://github.com/libjxl/libjxl/blob/main/doc/encode_effort... also gives a good breakdown of features by effort level.

For JPEG XL, refer to its format overview [1]. In short its lossless mode uses a combination of multiple techniques: the rANS coding with an alias table, LZ77, reversible color transforms, a general vector quantization that subsumes palettes, a modified Haar transform and a learnable meta-adaptive decision tree for context modelling.

One good thing about JPEG XL is that its lossy mode also largely uses the same tool, with a major addition of specialized quantization and context modelling for low- and high-frequenty components.

[1] https://github.com/libjxl/libjxl/blob/main/doc/format_overvi...

The cjxl source is here. If you spot any reason why -x strip=exif may not work, tell me.

The problem is that the instructions for actually running the WASM file are not that clear... the docs the author mentions shows how to compile to WASM, which is easy enough, but then here's the instructions to make that actually work in the browser:

https://github.com/libjxl/libjxl/blob/main/tools/wasm_demo/R...

Yeah, you need some mysterious Python script, a JS service worker at runtime, choose whether you want the WASM or WASM_SIMD target, use a browser that supports Threads and SIMD if you chose that, make sure to serve everything with the appropriate custom HTTP headers... just reading that, I can see that to get this stuff working on non-browser WASM targets would likely require expertise in WASM, which is the point of the OP. WASM's UX is just not there yet.

https://github.com/libjxl/libjxl#usage

> Specifically for JPEG files, the default cjxl behavior is to apply lossless recompression and the default djxl behavior is to reconstruct the original JPEG file (when the extension of the output file is .jpg).

I mean compiling a bleeding edge kicad, inkscape or jpeg-xl is easy. But will probably trash your system if you already have an older version installed.

But you look at your image viewer that could have the lossless indicator? (and there is an issue open to add this indicator to the jxl files)

https://github.com/libjxl/libjxl/issues/432

You might want to use libjxl directly, e.g. for visually lossless images: cjxl --effort 9 --brotli_effort 11 --distance 1.0 --num_threads (nproc) --lossless_jpeg 0 input.png output.jxl on linux (if you're on windows/mac, just replace the (nproc) with the number of cpu threads you have, e.g. --num_threads 16).