Hue

Hue is one of the main properties (called color appearance parameters) of a color, defined technically (in the CIECAM02 model), as 'the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow', (which in certain theories of color vision are called unique hues). Hue can typically be represented quantitatively by a single number, often corresponding to an angular position around a central or neutral point or axis on a colorspace coordinate diagram (such as a chromaticity diagram) or color wheel, or by its dominant wavelength or that of its complementary color. The other color appearance parameters are colorfulness, saturation (also known as intensity or chroma), lightness, and brightness. Hue is one of the main properties (called color appearance parameters) of a color, defined technically (in the CIECAM02 model), as 'the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow', (which in certain theories of color vision are called unique hues). Hue can typically be represented quantitatively by a single number, often corresponding to an angular position around a central or neutral point or axis on a colorspace coordinate diagram (such as a chromaticity diagram) or color wheel, or by its dominant wavelength or that of its complementary color. The other color appearance parameters are colorfulness, saturation (also known as intensity or chroma), lightness, and brightness. Usually, colors with the same hue are distinguished with adjectives referring to their lightness or colorfulness, such as with 'light blue', 'pastel blue', 'vivid blue'. Exceptions include brown, which is a dark orange. In painting color theory, a hue is a pure pigment—one without tint or shade (added white or black pigment, respectively). Hues are first processed in the brain in areas in the extended V4 called globs. In opponent color spaces in which two of the axes are perceptually orthogonal to lightness, such as the CIE 1976 (L*, a*, b*) (CIELAB) and 1976 (L*, u*, v*) (CIELUV) color spaces, hue may be computed together with chroma by converting these coordinates from rectangular form to polar form. Hue is the angular component of the polar representation, while chroma is the radial component. Specifically, in CIELAB while, analogously, in CIELUV where, atan2 is a two-argument inverse tangent. Preucil describes a color hexagon, similar to a trilinear plot described by Evans, Hanson, and Brewer, which may be used to compute hue from RGB. To place red at 0°, green at 120°, and blue at 240°,