HSV and HSL are cylindrical transformations of the RGB color cube model. 

**HSV (hue, saturation and value)** and **HSL (hue, saturation and lightness)** were first described by Smith, Joblove and Greenberg in two articles in an ACM SIGGRAPH Computer Graphics issue from 1978. 

Smith gave algorithms for conversion between HSV and RGB and between HSL and RGB in his article. Smith gave a formulation of HSV based on a **hexcone representation** and HSL based on a **triangle representation**. 

Joblove and Greenberg gave an alternative formulation of the HSV color space based on a **cylindrical representation**. 

Metrick and the graphic standards planning committee later gave a **double-hexcone representation** for HSL and improved the algorithm for conversion between HSL and RGB with one that does not require `sqrt()`, `cos()`, and `arctan()`. Fishkin finally improved the performance for conversion from HSL to RGB. It converts HSL to HSV and then uses the steps in the HSV to RGB conversion algorithm.

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- Alvy Ray Smith (1978): "Color Gamut Transform Pairs", in: ACM SIGGRAPH Computer Graphics, Volume 12 Issue 3, August 1978, pp. 12-19, http://alvyray.com/Papers/CG/color78.pdf

- George H. Joblove, Donald Greenberg (1978): "Color Spaces for Computer Graphics", in: ACM SIGGRAPH Computer Graphics, Volume 12 Issue 3, August 1978, pp. 20-25, http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.413.9004

- Lee Metrick, et. al. (1979): "Raster Extensions to the Core System", in: ACM SIGGRAPH Computer Graphics , Volume 13 Issue 3, August 1979, pp. III-6-7, pp. III-37-38, http://dl.acm.org/citation.cfm?id=988497.988498

- Ken Fishkin (1990): "A Fast HSL-to-RGB Transform", in: Graphics Gems I, pp. 448–449, http://www.gameenginegems.net/gemsdb/article.php?id=751

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According to Wikipedia there are two uses of the term **Map Coloring**:

>The first is in **cartography**, choosing the colors to be used when producing a map. The second is in **mathematics**, where the problem is to determine the minimum number of colors needed to color a map so that no two adjacent features have the same color.

This stream is primarily about the former.

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I wonder if the color model declared as HSL in Smith's paper is actually the color model common known as HSI. The formulas in [1] and the detailed information in [2] suggest this.

- [1] Plataniotis, Venetsanopoulos: "Color Image Processing and Applications", pp. 27-28.
- [2] "HSI and HSV color space", http://stackoverflow.com/questions/20853527/hsi-and-hsv-color-space/30007313#30007313