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What is wrong with this picture?

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BAY172-W3723A5A3D73B74A6D81... 25 Feb 09:47
  What is wrong with this picture? Liam R E Quin 22 Feb 04:28
1361475307.16477.10.camel@l... 25 Feb 09:47
  What is wrong with this picture? Richard Gitschlag 21 Feb 22:03
Richard Gitschlag
2013-02-21 22:03:29 UTC (almost 12 years ago)

What is wrong with this picture?

Subject: Re: [Gimp-user] What is wrong with this picture? From: liam@holoweb.net
To: strata_ranger@hotmail.com
CC: gimp-user-list@gnome.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?

Liam

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.

-- Stratadrake strata_ranger@hotmail.com
--------------------
Numbers may not lie, but neither do they tell the whole truth. =

Liam R E Quin
2013-02-22 04:28:16 UTC (almost 12 years ago)

What is wrong with this picture?

On Thu, 2013-02-21 at 14:03 -0800, Richard Gitschlag wrote:

You missed only one (very important) detail: The tool's Overlap setting.

No, I did it at 50% and mentioned that.

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.

Right - but only those pixels - and no, no magenta channel, they get their hue remapped. You could think of

I use the tool a lot.

Try it with the "master" colour selected and as you move the Hue slider you'll see it works just like Colours->Colourise, colouring the entire image to the hue you select.

With just Magenta and and overlap, it's like doing select by colour in Hue mode with a broad range, without feathering the selectoin, and then running colours->colorise on that selection.

Whether it's working as intended is another question, but I get the same sort of results regardless of which colour range I choose to remap.

Best,

Liam

Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
Pictures from old books: http://fromoldbooks.org/
Ankh: irc.sorcery.net irc.gnome.org freenode/#xml