Robert Krawitz wrote:
>    From: Christian <>
>    Date: Sun, 31 May 2009 17:53:43 +0200
>    Hi Michael
>    The HSL is one of the best color models. The colors are symmetrical
>    ordered. 
>    Advantages
>    1. symmetrical
>    2. color values are not rounded (you have more colors than in the HEX
>    model)
>    3. logical (no senselessly black axis)
>    4. equidistant colors in the color picker
>    5. the right color theory. In the middle is the neutral gray [1]
>    Bad's in the HSV color picker
>    1. not symmetrical
>    2. color values are rounded (in HEX a base color can have only a value
>    of 0 - 255)
>    3. not logical (a senselessly black axis)
>    4. not equidistant colors in the color picker, you can click too many
>    colors in the black area.
>    5. the color circle is correct but in the middle is not the neutral
>    gray.
> I favor HSL also, and it's what we use in Gutenprint to perform
> correction (actually, we perform parts of it in HL+G, but that amounts
> to the same thing).  I also added HSL decomposition to GIMP several
> years ago, and find it very useful -- a simple manipulation of the L
> curve can have a dramatic and predictable effect on the image.
> L conforms much more closely to perception than V, which is a major
> advantage when lightening or darkening an image -- in HSV space,
> there's no simple way to do that.

The representation certainly seems useful.  My major concern is that, as a 
photographer, "saturation" in HSL doesn't seem to usefully map to what we 
typically call "saturation" (hereafter, "psaturation") — if I'm talking about a 
"psaturated red sunset," a mostly-white sky with a touch of red isn't what I'm 

Put another way, a photographer's sense of psaturation is well-represented by 
saturation in HSV.  In HSL, the concept of psaturation is split across both 
saturation _and_ lightness — a color which is psaturated tends to have both 
HSL saturation and neutral lightness.

Note, however, that the HSV and HSL saturation would align to a useful extent 
HSL coordinates were defined in terms of a cylinder, but the color space were 
actually shaped like a double-cone (see [1]).  Or really, if it were any shape 
with single points at full-lightness (white) and zero-lightness (black), and 
with a circle/hexagon at neutral lightness.

In that case, a color could only be described as "fully saturated" when it has 
neutral lightness.  Colors that are between neutral lightness and extreme 
lightness have gradations of saturation, and the saturation is bounded such 
it must decrease as you approach one extreme or the other (of lightness).  Of 
course, when you do that, computations become harder.  *sigh*

I'll send out a mockup of what I mean shortly.



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