Does alpha affect the LAB output?

No. The CIE LAB color space has no alpha channel. Alpha (opacity) is a compositing concept, not a colorimetric property. This tool passes the alpha value through and displays it separately, but it has no effect on L*, a*, or b*.

What do L*, a*, and b* mean?

L* is perceptual lightness (0 = black, 100 = white). a* runs from negative (green) to positive (red). b* runs from negative (blue) to positive (yellow). Equal numerical distances in LAB correspond roughly to equal perceived color differences.

What illuminant does this tool use?

This tool uses the CIE D65 standard illuminant (6500 K daylight), with reference white Xn=0.95047, Yn=1.00000, Zn=1.08883. D65 is the standard for sRGB and is the most common choice for web and display color work.

What is the expected LAB for pure red (255, 0, 0)?

rgba(255, 0, 0, 255) converts to approximately L*=53.24, a*=80.09, b*=67.20. You can verify this in the tool by entering R=255, G=0, B=0.

Why are the XYZ values less than 1?

XYZ values are normalized so that pure white (R=255, G=255, B=255) maps to approximately X=0.9505, Y=1.0000, Z=1.0890. Most colors produce XYZ values in the range 0–1.

Does this tool send data to a server?

No. All conversion math runs entirely in your browser using JavaScript. No data is transmitted to any server.

RGBA to LAB Converter

Enter RGBA values (0–255) and instantly see the CIE LAB (L*, a*, b*) result with intermediate XYZ values and a color preview swatch.

RGBA Input

Red (R) 255

Green (G) 0

Blue (B) 0

Alpha (A) 255

rgba(255, 0, 0, 255)

CIE LAB Output

L* (Lightness)

a* (green–red)

b* (blue–yellow)

Alpha: 255 / 255 (100.0%) — passed through, does not affect L*a*b*

Conversion Pipeline

1 sRGB gamma decode (linearize): Rl=1.0000, Gl=0.0000, Bl=0.0000
2 Linear RGB → XYZ (D65 matrix): X=0.4125, Y=0.2126, Z=0.0193
3 Normalize by D65 white (Xn=0.95047, Yn=1.00000, Zn=1.08883): X/Xn=0.4340, Y/Yn=0.2126, Z/Zn=0.0178
4 XYZ → CIE LAB: lab(53.24 80.09 67.20)

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Summary

This tool converts RGBA color values (red, green, blue each 0–255, alpha 0–255) to CIE LAB (L*, a*, b*), a device-independent perceptual color space. The conversion follows the standard pipeline: sRGB gamma decoding (linearization) → multiplication by the sRGB-to-XYZ D65 matrix → normalization against the D65 reference white and the CIE f() cube-root function. Alpha is passed through but does not affect the Lab result, since LAB has no alpha channel. Intermediate XYZ values are displayed so you can inspect every step of the pipeline.

How it works

Enter R, G, B values (0–255) and Alpha (0–255) in the input fields or drag the sliders.
Each RGB channel is linearized by reversing the sRGB gamma curve: values ≤ 0.04045 are divided by 12.92; values above that use ((v + 0.055) / 1.055)^2.4.
The three linear-light values are multiplied by the standard sRGB-to-XYZ D65 matrix to produce X, Y, Z tristimulus values.
XYZ is normalized against the D65 reference white (Xn=0.95047, Yn=1.00000, Zn=1.08883) and passed through the CIE f() function (cube root or linear segment).
L*, a*, and b* are computed as: L*=116·f(Y/Yn)−16, a*=500·(f(X/Xn)−f(Y/Yn)), b*=200·(f(Y/Yn)−f(Z/Zn)).
The color swatch previews the RGB color at the specified alpha. Alpha passes through unchanged and is shown separately.

Use cases

Convert screen or CSS RGBA colors to CIE LAB for perceptual color analysis.
Compute color-difference (ΔE) inputs from RGBA values used in design tools.
Cross-reference colors between sRGB display space and device-independent LAB.
Inspect the intermediate XYZ values for ICC profile or color management work.
Generate lab() CSS Color Level 4 values from existing rgba() color strings.
Validate RGBA → LAB conversions when implementing color science algorithms.
Check perceptual lightness (L*) and chroma axes (a*, b*) for any RGBA color.
Build perceptual color palettes by comparing L* values across RGBA swatches.

Frequently Asked Questions

Last updated: 2026-05-28 · Reviewed by Nham Vu