Hue, saturation, and brightness are aspects of color in the red, green, and blue ( RGB ) scheme. These terms are most often used in reference to the color of each pixel in a cathode ray tube ( CRT ) display. All possible colors can be specified according to hue, saturation, and brightness (also called brilliance ), just as colors can be represented in terms of the R, G, and B components.
Most sources of visible light contain energy over a band of wavelengths. Hue is the wavelength within the visible-light spectrum at which the energy output from a source is greatest. This is shown as the peak of the curves in the accompanying graph of intensity versus wavelength. In this example, all three colors have the same hue, with a wavelength slightly longer than 500 nanometers, in the yellow-green portion of the spectrum.
Saturation is an expression for the relative bandwidth of the visible output from a light source. In the diagram, the saturation is represented by the steepness of the slopes of the curves. Here, the red curve represents a color having low saturation, the green curve represents a color having greater saturation, and the blue curve represents a color with fairly high saturation. As saturation increases, colors appear more "pure." As saturation decreases, colors appear more "washed-out."
Brightness is a relative expression of the intensity of the energy output of a visible light source. It can be expressed as a total energy value (different for each of the curves in the diagram), or as the amplitude at the wavelength where the intensity is greatest (identical for all three curves). In the RGB color model, the amplitudes of red, green, and blue for a particular color can each range from 0 to 100 percent of full brilliance. These levels are represented by the range of decimal numbers from 0 to 255, or hexadecimal numbers from 00 to FF.