On Fri, Apr 28, 2017 at 10:44:25AM -0400, Elle Stone wrote: > On 04/28/2017 04:35 AM, Marco Ciampa via gimp-docs-list wrote: > > >Is this right? > > > >src/menus/colors/desaturate/desaturate.xml:108(phrase) > > > > <para>The shades of gray will be calculated as</para> > > <informalequation> > > <mediaobject> > > <textobject> > > <phrase> > > Lightness (HSL)) = ½ × (max(R,G,B) + min(R,G,B)) > > </phrase> > > </textobject> > > </mediaobject> > > </informalequation> > > </listitem> > > > > If you mean the formula for Lightness, it's correct: > > From 2.8 docs: > Lightness > > The graylevel will be calculated as > Lightness = ½ × (max(R,G,B) + min(R,G,B)) > > From posted 2.9 docs: > Lightness (HSL) > > The shades of gray will be calculated as > Lightness (HSL)) = ½ × (max(R,G,B) + min(R,G,B)) > > From Wikipedia (https://en.wikipedia.org): > In the HSL "bi-hexcone" model, lightness is defined as the average of the > largest and smallest color components (fig. 12c). > > From GIMP code (app/operations/gimpoperationdesaturate.c): > case GIMP_DESATURATE_LIGHTNESS: > /* This is the formula for Lightness in the HSL "bi-hexcone" > * model: https://en.wikipedia.org/wiki/HSL_and_HSV > */ > while (samples--) > { > gfloat min, max, value; > > max = MAX (src[0], src[1]); > max = MAX (max, src[2]); > min = MIN (src[0], src[1]); > min = MIN (min, src[2]); > > value = (max + min) / 2; > > Not to be confused with LAB/LCH Lightness, which is calculated from XYZ, not > from RGB (http://brucelindbloom.com/index.html?Eqn_XYZ_to_Lab.html). Many thanks Elle! Sorry for the noise! Just a very minor typo: I think there is a spurious parenthesis after HSL ... bye -- Marco Ciampa I know a joke about UDP, but you might not get it. ------------------------ GNU/Linux User #78271 FSFE fellow #364 ------------------------ _______________________________________________ gimp-docs-list mailing list gimp-docs-list@xxxxxxxxx https://mail.gnome.org/mailman/listinfo/gimp-docs-list
