> Subject: Re: [Gimp-user] What is wrong with this picture?
> From: l...@holoweb.net
> To: strata_ran...@hotmail.com
> CC: firstname.lastname@example.org
> Date: Thu, 21 Feb 2013 14:35:07 -0500
> I don't know where you get your "results should be like this"... you are
> not "increasing the magenta channel by 30%", you are mapping all pixels
> whose colour value in RGB space is within 30 degrees of magenta to a
> completely different hue, to a different location in HSV space....
> The effect you show happens with all the colour "channels".
> I think you are wanting to increase saturation.
> Or am I missing something?
You missed only one (very important) detail: The tool's Overlap setting.
IF we left the overlap setting at zero, then we would get exactly what you
described -- only those pixels within absolutely 30 degrees of Magenta would be
affected, everything else remains the same.
BUT with an Overlap setting of 50%, this "blurs" the threshold between Magenta
and Red (and likewise between Magenta and Blue). All pixels with hues falling
between a 15° ~ 45° deviation from Magenta (a 30° range, or 50% of the 60°
between Magenta and its neighbors) will receive a variable percentage (100% ~
0%, respectively) of the Magenta channel's adjustment.
Test it yourself: Paint a simple red-to-yellow gradient, then go to the
Hue-Saturation tool and (with overlap = 0) drain all saturation out of Red.
Next, slowly increase the Overlap slider and watch how the pixel-sharp
threshold between the two channels becomes a smooth fade. It's very useful
behavior when you're using this tool on photographs or other images with smooth
color transitions around the hue thresholds; it just happens to make one epic
screwup in this particular usecase.
Numbers may not lie, but neither do they tell the whole truth.
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