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

   1. symmetrical
   2. color values are not rounded (you have more colors than in the HEX
   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

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.

I'd ideally like to see an HSL-based correction pack in GIMP using the
Gutenprint algorithm, where it's possible to correct all three
channels as a single operation.  The correction adjustments (+/- delta
for H, multiplicative factors with soft clipping for S and L) are done
with curves, where the X axis is the starting hue and the Y axis is
the correction.  This would allow selective hue shifting along with
saturation and lightness adjustments in one shot, with only one loss
of precision.

Robert Krawitz                                     <>

Tall Clubs International  -- or 1-888-IM-TALL-2
Member of the League for Programming Freedom -- mail
Project lead for Gutenprint   --

"Linux doesn't dictate how I work, I dictate how Linux works."
--Eric Crampton
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