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HSL (hue-saturation-lightness) is one of the most common cylindrical-coordinate representations of points in an RGB color model. Developed in the 1970s for computer graphics applications, HSL is used today in color pickers, in image editing software, and less commonly in image analysis and computer vision.
The representation rearranges the geometry of RGB in an attempt to be more intuitive and perceptually relevant than the cartesian (cube) representation, by mapping the values into a cylinder loosely inspired by a traditional color wheel. The angle around the central vertical axis corresponds to "hue" and the distance from the axis corresponds to "saturation". These first two values give the two schemes the 'H' and 'S' in its name. The height corresponds to a third value, the system's representation of the perceived luminance in relation to the saturation.