HCL color to RGB and backward

Question

I need an algorithm to convert the HCL color to RGB and backward RGB to HCL keeping in mind that these color spaces have different gamuts (I need to constrain the HCL colors to those that can be reproduced in RGB color space). What is the algorithm for this (the algorithm is intended to be implemented in Wolfram Mathematica that supports natively only RGB color)? I have no experience in working with color spaces.

P.S. Some articles about HCL color:

M. Sarifuddin (2005). A new perceptually uniform color space with associated color similarity measure for content–based image and video retrieval.

Zeileis, Hornik and Murrell (2009): Escaping RGBland: Selecting Colors for Statistical Graphics // Computational Statistics & Data Analysis Volume 53, Issue 9, 1 July 2009, Pages 3259-3270

UPDATE: As pointed out by Jonathan Jansson, in the above two articles different color spaces are described by the name "HCL": "The second article uses LCh(uv) which is the same as Luv* but described in polar coordiates where h(uv) is the angle of the u* and v* coordinate and C* is the magnitude of that vector". So in fact I need an algorithm for converting RGB to Luv* and backward.

Answer 1

I was just learing about the HCL colorspace too. The colorspace used in the two articles in your question seems to be different color spaces though.

The second article uses L*C*h(uv) which is the same as L*u*v* but described in polar coordiates where h(uv) is the angle of the u* and v* coordiate and C* is the magnitude of that vector.

The LCH color space in the first article seems to describe another color space than that uses a more algorithmical conversion. There is also another version of the first paper here: http://isjd.pdii.lipi.go.id/admin/jurnal/14209102121.pdf

If you meant to use the CIE L*u*v* you need to first convert sRGB to CIE XYZ and then convert to CIE L*u*v*. RGB actually refers to sRGB in most cases so there is no need to convert from RGB to sRGB.

All source code needed

Good article about how conversion to XYZ works

Nice online converter

But I can't answer your question about how to constrain the colors to the sRGB space. You could just throw away RGB colors which are outside the range 0 to 1 after conversion. Just clamping colors can give quite weird results. Try to go to the converter and enter the color RGB 0 0 255 and convert to L*a*b* (similar to L*u*v*) and then increase L* to say 70 and convert it back and the result is certainly not blue anymore.

Edit: Corrected the URL Edit: Merged another answer into this answer