Hue

This article refers to the gradation of color; for the city in Vietnam, see Huế.

An image with the hue altered

The hue of this Painted Bunting is adjusted over the spectrum.

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, or the central tendency of its combined wavelengths. 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 φ in standard position. To calculate φ, let R, G, B be the color coordinates in RGB space, defined on a scale from zero to one. Then, after obtaining the brightness μ and the saturation σ, the hue could be obtained from

$\phi =\arccos \left({R-\mu \over \sigma {\sqrt {2}}}\right)$

(Compare with standard score). Using this formula, φ = 0° [0^c] would corresponds to red, while φ = 120° [2π/3^c] would correspond to blue, and φ = 240° [4π/3^c] would correspond to green.

The RGB coordinates should be derivable from the μ, σ, φ coordinates as follows:

$R=\mu +\sigma {\sqrt {2}}\cos \phi ,$

$G=\mu +\sigma {\sqrt {2}}\cos \left(\phi +240^{\circ }\;\lbrack {4\pi \over 3}^{c}\rbrack \right),$

$B=\mu +\sigma {\sqrt {2}}\cos \left(\phi +120^{\circ }\;\lbrack {2\pi \over 3}^{c}\rbrack \right).$

Hue is a coordinate (an angle of rotation) in HSL color space and HSV color space.

Manufacturer's of pigments use the word hue e.g. 'Cadmium Yellow (hue)' to indicate that the original pigmentation ingredient, often toxic, has been replaced by safer (or cheaper) alternatives whilst retaining the hue of the original. Replacements are often used for Chromium, Cadmium and Alizarin.

See also

• Brightness
• Bezold-Brücke shift

External link

• Editing of hue in photography