lab ranges different from CSS Color Module 4

[drwpow]

Problem

The lab ranges (code) are set as following:

	ranges: {
		l: [0, 100],
		a: [-100, 100],
		b: [-100, 100]
	},

But in CSS Color Module 4, they’re defined as -125 and 125:

Percent reference range
for L: 0% = 0.0, 100% = 100.0
for a and b: -100% = -125, 100% = 125

Further, the lab65 ranges are (I’m guessing) the same ranges, just converted?

	ranges: {
		l: [0, 100],
		a: [-86.182, 98.234],
		b: [-107.86, 94.477]
	}

Is this an intentional deviation?

[danburzo]

The ranges property in spaces’ definition is only used for two things:

• when clamping a color to a gamut, the gamut’s c (chroma) range is the basis of the ε value.
• when using culori.random(), the random values are produced within the component’s range.

The parse methods, e.g. parseLab, use the reference ranges from the CSS spec when interpreting percentages in component values, and they’re hardcoded in each parse method.

That being said, I couldn’t tell you why those ranges don’t read [-125, 125], and I don’t see an issue with updating them.
The lab65 space, not being part of css-color-4 per se, was left with the default ranges corresponding to the approximate extent of the sRGB gamut, but it would probably make sense to update the ranges to match lab.

[drwpow]

Thanks for the explanation! I only noticed this running into #261, not realizing you couldn’t clamp toGamut using Lab.

That makes sense though that it likely wouldn’t impact anything. Perhaps only someone that was accessing these directly somehow, but that seems unlikely. All the same, I could open a PR to change, just for no other reason than “there’s not a reason for them to not match the spec”

[danburzo]

I’ve added the correct ranges along wit the other fix in the commit above.

[drwpow]

Awesome, thank you!

[danburzo]

Available in culori@v4.0.2.