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HSL and HSV are two related representations of points in an RGB color space that attempt to describe perceptual color relationships more accurately than RGB, while remaining computationally simple. HSL stands for hue, saturation and lightness, while HSV stands for hue, saturation and value.

HSI and HSB are alternative names for these concepts, substituting intensity and brightness for lightness and/or value; their definitions are less standardized, but they are typically interpreted to be synonymous with HSL and HSV.

Both HSL and HSV can be thought of as describing colors as points in a cylinder whose central axis ranges from black at the bottom to white at the top with neutral colors between them, where angle around the axis corresponds to “hue”, distance from the axis corresponds to “saturation”, and distance along the axis corresponds to “lightness”, “value”, or “brightness”.

The two representations are similar in purpose, but differ somewhat in approach. Both are mathematically cylindrical, but while HSV (hue, saturation, value) can be thought of conceptually as an inverted cone of colors (with a black point at the bottom, and fully-saturated colors around a circle at the top), HSL conceptually represents a double-cone or sphere (with white at the top, black at the bottom, and the fully-saturated colors around the edge of a horizontal cross-section with middle gray at its center). Note that while “hue” in HSL and HSV refers to the same attribute, their definitions of “saturation” differ dramatically.

Because HSL and HSV are simple transformations of device-dependent RGB, the color defined by a (h, s, l) or (h, s, v) triplet depends on the colors of the red, green, and blue primaries produced by the device, and on the gamma compression used to represent the amounts of those primaries. Each unique RGB device therefore has unique HSL and HSV spaces to accompany it. An (h, s, l) or (h, s, v) triplet can however become definite when it is tied to a particular RGB color space, such as sRGB.

Both models were first formally described in 1978 by Alvy Ray Smith, though the concept of describing colors in three dimensions dates to the 18th century (see section below).

Usage

[[Image:HSV triangle and cone.png|

1. Gonzalez, Rafael C. (2007). Digital Image Processing. Prentice Hall. p. 954. ISBN 013168728X, 9780131687288. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
2. "The HSB/HLS Color Model - Color Models - Technical Guides". Adobe. Retrieved 2009-06-29.
3. Jewett, Tom (1997–2009). "Colors: HSB". Retrieved 2009-06-29.{{cite web}}: CS1 maint: date format (link)
4. Alvy Ray Smith (August 1978). "Color Gamut Transform Pairs". Computer Graphics. 12 (3): 12. doi:10.1145/965139.807361. {{cite journal}}: Unknown parameter |curly= ignored (help)
5. Kuehni, Rolf G. (February 2002). "The early development of the Munsell system". Color Research and Application. 27 (1): 20–27. doi:10.1002/col.10002. {{cite journal}}: Unknown parameter |curly= ignored (help)CS1 maint: date and year (link).