Open CASCADE Technology  7.5.0

Quantity_TypeOfColor.hxx File Reference


enum  Quantity_TypeOfColor {
  Quantity_TOC_RGB, Quantity_TOC_sRGB, Quantity_TOC_HLS, Quantity_TOC_CIELab,
 Identifies color definition systems. More...

Enumeration Type Documentation

◆ Quantity_TypeOfColor

Identifies color definition systems.


Normalized linear RGB (red, green, blue) values within range [0..1] for each component.


Normalized non-linear gamma-shifted RGB (red, green, blue) values within range [0..1] for each component.


Hue + light + saturation components, where:

  • First component is the Hue (H) angle in degrees within range [0.0; 360.0], 0.0 being Red; value -1.0 is a special value reserved for grayscale color (S should be 0.0).
  • Second component is the Lightness (L) within range [0.0; 1.0]
  • Third component is the Saturation (S) within range [0.0; 1.0]

CIE L*a*b* color space, constructed to be perceptually uniform for human eye. The values are assumed to be with respect to D65 2° white point.

The color is defined by:

  • L: lightness in range [0, 100] (from black to white)
  • a: green-to-red axis, approximately in range [-90, 100]
  • b: blue-to-yellow axis, approximately in range [-110, 95]

Note that not all combinations of L, a, and b values represent visible colors, and RGB cube takes only part of visible color space.

When Lab color is converted to RGB, a and b components may be reduced (with the same proportion) to fit the result into the RGB range.


CIE L*c*h* color space, same as L*a*b* in cylindrical coordinates:

  • L: lightness in range [0, 100] (from black to white)
  • c: chroma, approximately in range [0, 135], 0 corresponds to greyscale
  • h: hue angle, in range [0., 360.]

The hue values of standard colors are approximately:

  • red at 40,
  • yellow at 103,
  • green at 136,
  • cyan at 196,
  • blue at 306,
  • magenta at 328.

When Lch color is converted to RGB, chroma component may be reduced to fit the color into the RGB range.