HSL color space

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Image:Color cones.png

The HSL color space, also called HLS or HSI, stands for Hue, Saturation, Lightness (also Luminance or Luminosity) / Intensity. While HSV (Hue, Saturation, Value) can be viewed graphically as a color cone or hexcone, HSL is drawn as a double cone or double hexcone. Both systems are non-linear deformations of the RGB colour cube. The two apexes of the HSL double hexcone correspond to black and white. The angular parameter corresponds to hue, distance from the axis corresponds to saturation, and distance along the black-white axis corresponds to lightness.

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Converting from RGB

The (R, G, B) values must be expressed as numbers from 0 to 1. Let MAX equal the maximum of the (R, G, B) values, and MIN equal the minimum of those values. The formula can then be written as

<math> H = \begin{cases} \mbox{undefined} & \mbox{if } MAX = MIN \\ 60 \times \frac{G - B}{MAX - MIN} + 0, & \mbox{if } MAX = R \\ &\mbox{and } G \geq B \\ 60 \times \frac{G - B}{MAX - MIN} + 360, & \mbox{if } MAX = R \\ &\mbox{and } G < B \\ 60 \times \frac{B - R}{MAX - MIN} + 120, & \mbox{if } MAX = G \\ 60 \times \frac{R - G}{MAX - MIN} + 240, & \mbox{if } MAX = B \end{cases} </math>

<math> S = \begin{cases} 0 & \mbox{if } MIN = MAX \\ \frac{MAX-MIN}{MAX+MIN} = \frac{MAX-MIN}{2L}, & \mbox{if } 0 < L \leq \frac{1}{2} \\ \frac{MAX-MIN}{2-(MAX+MIN)} = \frac{MAX-MIN}{2-2L}, & \mbox{if } L > \frac{1}{2} \end{cases} </math>

<math>L = \begin{matrix} \frac{1}{2} \end{matrix} (MAX + MIN)</math>


<math>H=0</math> is often used instead of leaving <math>H</math> undefined. HSL and HSV have the same definition of hue, but the other components differ. The other two components of HSV are defined as follows:

<math>S = \frac {MAX - MIN} {MAX}= 1- \frac {MIN} {MAX}</math>

<math>V = MAX \,</math>

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Comparison of HSL and HSV

HSL is similar to HSV but better reflects the intuitive notion of "saturation" and "lightness" as two independent parameters, and is therefore more suitable for use by artists. The CSS3 specification from the W3C states, "Advantages of HSL are that it is symmetrical to lightness and darkness (which is not the case with HSV for example)..." This means that:

  • In HSL, the Saturation component always goes from fully saturated color to the equivalent gray (in HSV, with V at maximum, it goes from saturated color to white, which may be considered counterintuitive).
  • The Lightness in HSL always spans the entire range from black through the chosen hue to white (in HSV, the V component only goes half that way, from black to the chosen hue).

In software, a hue-based color model (HSV or HSL) is usually presented to the user in the form of a linear or circular hue chooser and a two-dimensional area (usually a square or a triangle) where you can choose saturation and value/lightness for the selected hue. With this representation, the difference between HSV or HSL is irrelevant. However, many programs also let you select a color via linear sliders or numeric entry fields, and for those controls, usually either HSL or HSV (not both) are used. HSV is traditionally more common. Here are some examples:

  • Applications that use HSV (HSB):
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Examples

The RGB values are shown in the range 0.0 to 1.0.

RGB HSL HSV Result
(1, 0, 0) (0°, 1, 0.5) (0°, 1, 1)                   
(0.5, 1, 0.5) (120°, 1, 0.75) (120°, 0.5, 1)                   
(0, 0, 0.5) (240°, 1, 0.25) (240°, 1, 0.5)    
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See also

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External links

fr:Teinte saturation lumière nl:HSL (kleurruimte) pl:HLS

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