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kornelski / cavif-rs

AVIF image creator in pure Rust
https://lib.rs/cavif
BSD 3-Clause "New" or "Revised" License
582 stars 29 forks source link

minor color shifting of large areas #20

Closed tomByrer closed 3 years ago

tomByrer commented 3 years ago

I would assume a large area would not color shift at all (aside from edges perhaps), but unfortunately it does. I can test on what ever test images you want.

Good news: not as bad as Squoosh, which uses their own WASM version of libavif.

Thanks for for your tool! I'll have to try it on Cloudflare Workers sometime ;)

source: codepen io-2021-02-15

cavif.exe -Q 80 -s 8 codepen io-2021-02-15 avif

kornelski commented 3 years ago

I'm not seeing any shift at all. Maybe it's something caused by color profile processing?

I'll have to try it on Cloudflare Workers sometime ;)

BTW, Cloudflare uses this encoder internally: https://developers.cloudflare.com/images/resizing-with-workers

tomByrer commented 3 years ago

color profile processing

That could be, I'm on Win10, but happens on both monitors. There is a bug linked in the Squoosh thread I linked to Firefox. I'll test on another machine with Chrome & Manjaro; have a test suite of images?

kornelski commented 3 years ago

On my macOS it looks the same in Firefox nightly and Chrome canary. There is a little bit of posterization in the gradient on gray background, but that is just a compression artifact.

tomByrer commented 3 years ago

Solid backgrounds on both source & rendered.

kornelski commented 3 years ago

Can you add a screenshot of a decoded image? I'm not sure if we're looking at the same image and disagreeing what a color shift is, or whether it's a decoder-specific issue.

tomByrer commented 3 years ago

Might be ChromaSubsampling not being 444; something I found testing other AVIF tools.

I'm not sure how to config ChromaSubsampling : 444; not in your readme & I can't read Rust that well now. (Though I understand the filesize will increase; I'm trying to isolate browser bugs, so perhaps CS444 is not good for production.)

kornelski commented 3 years ago

It's definitely 444, and I'd never use anything less with AVIF.

File size does not increase with 444 in AV1. AV1 has chroma-from-luma. OTOH 420 is a total mistake, because chroma upsampling algorithm has been left undefined, so there's large error that can't be avoided.