CIE L*a*b* is a device-independent, perceptually uniform color space. L* is lightness (0 black to 100 white), a* runs green to red, and b* runs blue to yellow. Equal distances in Lab roughly match equal perceived color differences.

How is the conversion done?

sRGB is gamma-expanded to linear RGB, multiplied by the sRGB-to-XYZ matrix under the D65 white point, then XYZ is normalised to that white and passed through the CIELAB cube-root function to give L*, a*, and b*.

Why convert through XYZ?

CIELAB is defined relative to CIE XYZ tristimulus values, not RGB. You cannot go straight from RGB to Lab, so the color must first be linearised and transformed into XYZ using the correct matrix and white point.

What white point does this use?

It uses the D65 illuminant, the standard daylight white point for sRGB, with reference white Xn=95.047, Yn=100, Zn=108.883. This matches CSS lab() and most design tools.

Is anything uploaded?

No. All gamma, matrix, and cube-root math runs locally in your browser. Nothing about your colors leaves your device.

RGB to CIE L*a*b* Color Converter

Convert a screen sRGB color into CIE L*a*b*, a perceptually uniform color space where equal numeric distances correspond to roughly equal perceived color differences. Useful for color-difference (Delta E) work, gradients, and matching.

How it works

RGB cannot be turned into Lab directly — it must pass through linear light and CIE XYZ:

Gamma expand each sRGB channel to linear RGB:

c <= 0.04045 ?  c / 12.92  :  ((c + 0.055) / 1.055) ^ 2.4

Linear RGB to XYZ using the sRGB / D65 matrix:

X = 0.4124*r + 0.3576*g + 0.1805*b
Y = 0.2126*r + 0.7152*g + 0.0722*b
Z = 0.0193*r + 0.1192*g + 0.9505*b

XYZ to Lab — normalise by the D65 white (Xn 95.047, Yn 100, Zn 108.883), apply the CIELAB nonlinearity f(t), then:

L* = 116*f(Y/Yn) - 16
a* = 500*(f(X/Xn) - f(Y/Yn))
b* = 200*(f(Y/Yn) - f(Z/Zn))

where f(t) = t^(1/3) for t > (6/29)^3, otherwise a linear segment.

Example

Convert rgb(59, 130, 246) (a blue): L* ≈ 55.6, a* ≈ 17.6, b* ≈ −64.4 — high lightness, slightly toward red on a*, strongly toward blue on b*.

Notes

Values use the D65 white point to match CSS lab() and common design tools. The whole pipeline runs in your browser — nothing is uploaded.