CIELCh is the cylindrical form of CIELAB. Instead of the rectangular a* and b* axes, it uses chroma (distance from the gray axis, i.e. colorfulness) and hue (an angle around the color wheel), which are more intuitive to adjust.

How is it computed from RGB?

RGB is converted to CIELAB first (gamma expand, sRGB-to-XYZ under D65, then the CIELAB function). Chroma is the hypotenuse of a* and b*, and hue is the arctangent of b* over a*, normalised to 0-360 degrees.

How does LCH differ from HSL?

HSL is a simple transform of RGB and is not perceptually uniform, so equal hue steps can look uneven. LCH is built on CIELAB, so its lightness and chroma track human perception far more closely, which is why it is preferred for accessible palettes.

What is the hue angle?

Hue is measured in degrees from 0 to 360. Roughly, 0 is reddish-magenta, 90 is yellow, 180 is cyan-green, and 270 is blue. Grays have no defined hue because their chroma is zero.

Is anything uploaded?

No. The full RGB to Lab to LCH pipeline runs in your browser. Nothing about your colors leaves your device.

RGB to LCH Color Converter

Convert a screen sRGB color into CIELCh — the cylindrical form of CIELAB built from Lightness, Chroma, and Hue. Because it is grounded in CIELAB, LCH separates a color into perceptually meaningful controls, which makes it ideal for building even, accessible palettes.

How it works

LCH is CIELAB expressed in polar coordinates, so RGB is first converted to Lab, then a* and b* are turned into chroma and hue:

RGB to Lab — gamma-expand each sRGB channel to linear light, apply the sRGB-to-XYZ matrix under the D65 white, then the CIELAB nonlinearity to get L*, a*, b*.
Lab to LCh:

L = L*
C = sqrt(a*^2 + b*^2)
H = atan2(b*, a*) in degrees, normalised to 0-360

L is unchanged; chroma is the radial distance from the neutral gray axis (how vivid the color is); hue is the angle around the wheel.

Example

Convert rgb(59, 130, 246):

Lab ≈ L* 55.6, a* 17.6, b* −64.4
C = √(17.6² + 64.4²) ≈ 66.8
H = atan2(−64.4, 17.6) ≈ −75° → normalised to 285° (blue)
Result: lch(55.6% 66.8 285)

Notes

Hue is undefined for true grays (chroma ≈ 0) and is reported as 0 in that case. The D65 white point is used to match CSS lch(). Everything runs in your browser — nothing is uploaded.