Hue

For the city in Vietnam, see Hue (city).

A hue refers to the gradation of color within the optical spectrum, or visible spectrum, of light. "Hue" may also refer to a particular color within this spectrum, as defined by its dominant wavelength. A color is defined by the central tendency of the light wave's wavelength. For example, a light wave with a central tendency within 565-590 nm will be yellow.

In painting color theory, a hue refers to a pure color —one without added white (tint) or black (shade) pigment.

In an RGB color space, hue can be thought of as an angle of rotation φ, such that φ=0° corresponds to red, φ=120° corresponds to green, and φ=240° corresponds to blue. Letting R, G, B be the color coordinates in RGB space, then after obtaining the brightness μ and the saturation σ, the hue could be obtained from

<math> \phi = \arccos \left( {R - \mu \over \sigma \sqrt{2}} \right) <math>.

Compare with standard score. The RGB coordinates should be derivable from the μ, σ, φ coordinates as follows:

<math> R = \mu + \sigma \sqrt{2} \cos \phi, <math>

<math> G = \mu + \sigma \sqrt{2} \cos \left( \phi + {4 \pi \over 3} \right), <math>

<math> B = \mu + \sigma \sqrt{2} \cos \left( \phi + {2 \pi \over 3} \right). <math>

Hue is a coordinate (an angle of rotation) in HSB color space.