HUSL/hsluv space

[petulla]

This is just a naive question I wasn't able to get an answer from Google about, but wondering why HUSL space isn't included. It claims to offer a uniform lightness color space like HCL/LAB.

There's an interpolator for V3. Is there a reason not to use on one's own in colorizing maps?

http://www.hsluv.org/comparison/
https://npm.hotlibs.com/d3-interpolate-husl/package/0.1.0

@mbostock Note the updated repo is below.

[mbostock]

See d3-hsv, d3-hcg and d3-cam02 for examples of how to define a new color space in D3. I’d be in favor of a new d3/d3-husl package that implements the HUSL color space, say, ported from the reference Haxe implementation or from the earlier d3-interpolate-husl. Though, I’d ask for a vanilla JavaScript implementation rather than CoffeeScript if you want to host it in the d3 organization.

[petulla]

👍 Will try to get this up. Do you have a preference for how a PR is made since everything's broken into repos?

[mbostock]

I would start by creating a new personal repo named d3-husl d3-hsluv, then send me a note say it’s ready, and then you can transfer it over to the d3 organization and I will contribute any finishing touches.

[MalcolmDwyer]

Just a note for anyone doing the work on adapting this color space to d3... I believe the preferred name is now HSLuv: http://www.hsluv.org/
(I've been reading a bunch about HSLuv lately and came across this issue and wondered at first if it was referring to the same thing).
Anyway, I'm looking forward to seeing it in D3.

[petulla]

@mbostock

I've setup a ported version in this repo that follows the guidelines you set forward. I have work still to do but wanted to send this over to get your eyes on it.

A few questions I have.

--I have some precision issues to work out in the conversion process. I saw some use of Math.round in d3-color. I have converted some floats to 32 byte (7 decimals). Still, in the tests, I'm getting values at 1.9e-12 instead of 0. I can coerce to a rounded value but wanted to see if you had specific guidance. I can provide more context if needed.

-- I use l,u,v as the returned values and the test values rather than h,s,l. I like that it distinguishes from h,s,l but perhaps it is too cute.

--I will finish the Readme. I think some additional documentation should be written. Because this creates a perceptually uniform space, I expect some interest in it.

--I need to review Brighter/Darker

--I did not create the interpolation method like in the HSV repo. Can do so if you like.

I will add that I think we should add hpluv as well (which has uniform, non-distorted Chroma, uniform lightness, and approximate HSL hue). Once a path forward for hsluv is chosen, I'll create this next.