lch

LCH, in color science, refers to the cylindrical representation of the CIE Lab color space. It uses three coordinates: L for lightness, C for chroma (colorfulness relative to a white), and h for hue angle. L ranges from 0 (black) to 100 (white); C is nonnegative and varies with the color’s distance from the neutral axis; h is an angle in degrees around the a-b plane, typically measured from the positive a axis.

The conversion from Lab to LCH is straightforward: C = sqrt(a^2 + b^2) and h = atan2(b, a) expressed in degrees, adjusted to the range [0, 360). The inverse transformation uses a = C cos(h) and b = C sin(h), with L remaining unchanged. This cylindrical form makes hue a continuous dimension and often improves interpretability for tasks involving color selection and editing.

Applications of LCH include color selection, color grading, and perceptual color difference measurements, where working in a representation that separates lightness, chroma, and hue can simplify comparisons and adjustments. It is commonly used in design, printing, and digital imaging, usually as a bridge between Lab-based color science and device-dependent color spaces like sRGB or CMYK.

Limitations include gamut constraints: not all Lab colors map to a displayable RGB color, so conversions may require clipping or gamut mapping. Hue continuity near the wrap-around point (0/360 degrees) can also require careful handling. LCH is a descriptive, perceptually informed coordinate system rather than a device-restricted color space.