RGB to LCH converter

This RGB to LCH converter takes three sRGB channel intensities—red, green, and blue—each as an integer from zero through two hundred fifty-five, and returns CIE LCH coordinates (lightness L*, chroma C*, and hue angle h° in degrees) computed under the standard D65 white point used in web and print workflows. Designers, accessibility engineers, and students use LCH when a palette lives in eight-bit channels but the task needs a perceptually structured space where lightness, chroma, and hue can be edited independently without the rectangular a* and b* axes of Lab. The engine is fully deterministic: it inverse-compands each channel, multiplies by the D65 sRGB-to-XYZ matrix, normalizes by the D65 reference white, forms CIE Lab, then derives C* as the hypot of a* and b* and h° from atan2 of b* and a*—never calling the network, sampling randomness, or depending on the clock.

How RGB becomes lightness, chroma and hue

In the eight-bit sRGB model used by CSS and most web graphics, each of red, green, and blue is an integer channel from zero through two hundred fifty-five. CIE LCH is the polar form of CIE L*a*b*: the same stimulus is expressed as lightness L* (roughly zero for black through about one hundred for diffuse white), chroma C* measuring distance from the neutral axis, and hue h° as an angle around that axis in degrees from zero up to but not including three hundred sixty.

Conversion first scales each channel by dividing by two hundred fifty-five, then undoes sRGB gamma (the IEC six-one-nine-six-six inverse companding curve) so the values become linear light. Those linear channels pass through a fixed three-by-three matrix into CIE XYZ under illuminant D65; each tristimulus component is divided by the D65 reference white, then the CIE pivot function f is applied—cube root above a small threshold, linear branch below—to form L*, a*, and b*.

From Lab the cylindrical step is closed-form: C* equals the Euclidean length of the a*b* vector, and h° equals the two-argument arctangent of b* and a* converted to degrees and wrapped into the half-open interval from zero to three hundred sixty. When chroma is effectively zero the hue is undefined geometrically, so this calculator defines h° as zero for achromatic colors such as pure black, pure white, and neutral grays.

There is no path that accepts percentages or floating-point channels as input, and no silent clamp of two hundred fifty-six down to two hundred fifty-five.

Where RGB-to-LCH conversion fits in design, study, and software

Designers meet this mapping when a brand guide lists RGB swatches and a production or perceptual-editing workflow expects LCH targets, when lightness must stay fixed while hue rotates for tints and shades, or when a design system documents both screen RGB and LCH reference values side by side for ramp generation.

Accessibility engineers use L* and C* when reasoning about perceived lightness separately from chromatic strength, when checking that two UI states remain distinguishable after hue shifts, or when preparing notes that will later feed formal delta-E checks in Lab before re-expressing the same color as LCH for authoring.

Students see it in computer-graphics and color-science courses that introduce XYZ, Lab, and then the cylindrical LCH form, in digital photography classes that move between channel sliders and hue-chroma controls, and in interview warm-ups that ask for a mental convert of a short triple into polar Lab coordinates. Pair it with multi-format color tools when you need hex or CMYK, with the Lab converter when you need rectangular a* and b* only, and with other free deterministic converters when you are building a small lab for design-system hygiene.