make fromHSL public, add toHSL

[Matthew Woehlke]

Olaf Schmidt wrote:
> [ Matthew Woehlke, Mi., 13. Jun. 2007 ]
>> IMO your color space is correctly termed H'C'Y' :-)
> 
> I have never heard of H'C'Y'. Earlier you called it H'S'Y', which is a group 
> of colour spaces.

Sorry... C = "chroma", which is what you calculate if I am understanding 
(1) correctly (link from Matt Newell, (2)). The difference between them 
is very slight, essentially a matter of nitpicking :-). I doubt I would 
use 'C' in a public name unless there was a 'true S' version also.

> Since we are taking about "correct" terminology:
> 
> sRGB and Adobe RGB are colour spaces. RGB is a group of colour spaces which 
> have a red, green and blue component. R'G'B' is a group of gamma-corrected 
> RGB colour spaces.
> 
> HSL is a group of colour spaces with hue, saturation and luminosity 
> components, where L=0 means black, L=MAX means white, V=0 means gray, and 
> V=MAX means full saturation. H'S'L' is a group of gamma-corrected HSL colour 
> spaces. For some of the H'S'L' colour spaces, the luminosity component is 
> hue-independent (which implies gamma-correction). This seems to be what you 
> call H'S'Y' or H'C'Y'. One example for such a colour space is sHSL (derived 
> from sRGB).

Right. Y = "luma" (technically "luminance" and Y' = "luma"); i.e. what 
you call "hue-independent". See (3). Hence why I feel that HSY is a more 
precise name for your HSL. To me "L" implies equal coefficients for R, 
G, and B :-). "Y" means something specific.

Anyway, while this is a fascinating intellectual discussion, it isn't 
terribly productive :-).

1: http://www.prip.tuwien.ac.at/~hanbury/CVWW02.pdf
2: http://lists.kde.org/?l=kde-core-devel&m=118099356007004&w=2
3: http://en.wikipedia.org/wiki/Luminance_(video)

-- 
Matthew
So, an astrophysicist, a quantum physicist, and an astrologer walk into 
a bar...