LCh color space

The CIE-LCh color space is the CIELab color space , whereby instead of the Cartesian coordinates a * and  b *, the cylinder coordinates C * (relative color saturation , English chroma , chromaticity ' ) and h ° ( English hue angle , hue angle' ) must be specified. The color brightness  L * ( English lightness 'brightness' ) remains unchanged.

The simplified notations LCh , LCH and HLC (hue H - lightness L - saturation C) are common for this color space .

Coordinate transformation

Cartesian coordinates a and b of the two color axes; alternatively, color angle H and vector length C of the color saturation

The conversion of  a * and  b * in  C * and  h ° is performed according to the following formulas:

${\displaystyle C_{ab}^{*}={\sqrt {{a^{*}}^{2}+{b^{*}}^{2}}},\qquad h_{ab}^{\circ }=\arctan \left({\frac {b^{*}}{a^{*}}}\right)}$

Conversely, the polar coordinates can be converted into the Cartesian coordinates:

${\displaystyle a^{*}=C_{ab}^{*}\cdot \cos(h_{ab}^{\circ }),\qquad b^{*}=C_{ab}^{*}\cdot \sin(h_{ab}^{\circ })}$

The value for the brightness  L * remains.

Demarcation

The LCh color space is not identical to the HSV , HSL or HSB color space . Their values ​​can also be interpreted as the base color H, saturation S and brightness of a hue, but are derived from a polar coordinate transformation of the technically defined RGB color space and are therefore only slightly perceptual .

For example, H and  h are not identical, since the HSL space uses three colors as the basic color (additive primary colors red, green, blue with hue angle H = 0 °, 120 °, 240 °), but the LCh system uses four colors ( color-physiological elementary colors Red, yellow, green, and blue with h = 0 °, 90 °, 180 °, 270 °). h = 0 is the case for achromatic colors on the gray axis .

Individual evidence

1. ↑ In the variety of color systems, hue, lightness and saturation are logical quantities . In: FARBImpulse, May 10, 2006.