Srgb -> Okhsl conversion results in NaN saturation

[ecton]

How To Reproduce

When converting from an Srgb value with 1.0 in all components into an Okhsl, the resulting saturation value is NaN. This test demonstrates the issue:

#[test]
fn okhsl_nan() {
    use palette::IntoColor;
    let hsl: palette::Okhsl = palette::Srgb::new(1.0, 1.0, 1.0).into_color();
    assert!(!hsl.saturation.is_nan());
}

Expected Outcome

I would expect anything except not a number. I think I'm expecting 1.0, but I'm not a color expert so I wouldn't be surprised if I was wrong.

Actual Outcome

The saturation component is not a number.

Additional Details

• Cargo.toml entry:

  Both of these reproduce the issue:

  palette = { git = "https://github.com/Ogeon/palette.git" }
  palette = "0.7.3"

• Rust version(s): rustc 1.75.0 (82e1608df 2023-12-21)

• Target platform: Arch Linux / x86_64-unknown-linux-gnu

Thank you for the wonderful library! This is my first time ever having any sort of problem with it. It's always my go-to when I need to work with colors.

[Ogeon]

Hi, thanks for pointing this out! The saturation should be 0 in that case (due to it being grayscale), but definitely not NaN. This should not be an unusual input, so I'm a bit surprised it wasn't discovered sooner.

Also, thanks for the kind words and I'm happy to see that it has been working so well so far! 🎉

[ecton]

Honestly, I was just as surprised as you that it was so simple to reproduce. You're absolutely right that 0.0 is the correct saturation. I was still having my morning coffee and hadn't figured that out yet 😆

I have a simple workaround in place for now, so this isn't a high priority for me to have resolved. Thanks again!

[Ogeon]

Ok, good to know that you aren't stuck on this. I will probably save it for the weekend, when I have time to have a proper look at where it comes from. It's usually a missing check for 0 or something similar, but finding it can be a bit tricky.

[Ogeon]

I found the issue and merged a fix. There was an edge case with saturated white or black input, as explained in #369. I'll just address a couple of requests from the Debian rust team before making a release, so I may end up postponing it a bit so they have a chance to respond.

[ecton]

Thank you! Definitely no rush needed on a release for me.