Excitation purity

Colorfulness or saturation in colorimetry and color theory refers to the perceived intensity of a specific color. Colorfulness is the visual sensation according to which the perceived color of an area appears to be more or less chromatic.Chroma is the colorfulness relative to the brightness of a similarly illuminated area that appears to be white or highly transmitting. Therefore, chroma should not be confused with colorfulness. Saturation is the colorfulness of a color relative to its own brightness. Though the general concept is intuitive, terms such as chroma, saturation, purity, and intensity are often used without great precision, and even when well-defined depend greatly on the specific color model in use.

A highly colorful stimulus is vivid and intense, while a less colorful stimulus appears more muted, closer to gray. With no colorfulness at all, a color is a “neutral” gray (an image with no colorfulness in any of its colors is called grayscale). Any color can be described using three color appearance parameters — colorfulness (or chroma or saturation), lightness (or brightness), and hue .

Saturation is one of three coordinates in the HSL and HSV color spaces.

The saturation of a color is determined by a combination of light intensity and how much it is distributed across the spectrum of different wavelengths. The purest (most saturated) color is achieved by using just one wavelength at a high intensity, such as in laser light. If the intensity drops, then as a result the saturation drops. To desaturate a color of given intensity in a subtractive system (such as watercolor), one can add white, black, gray, or the hue's complement.

Various correlates of saturation follow.

where (u′_n, v′_n) is the chromaticity of the white point, and chroma is defined below.

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