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valbros  
#1 Posted : Thursday, February 23, 2006 12:06:53 AM(UTC)
valbros

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Hello,
I'm trying to mimic Photoshop HSL adjustments online and have noticed
that Graphics Mill's results seem uneven compared to Photoshop.
Example here:

http://www.terajet.com/images/targets.jpg

The orginal file had a saturation adjustment of -50 in Photoshop, and
-2.55*50 with Graphics Mill, which should be same adjustment.

Any suggestions for getting more consistent results?

Thanks,
Bobby
Andrew  
#2 Posted : Thursday, February 23, 2006 1:19:54 PM(UTC)
Andrew

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It seems photoshop works smarter and avoid rounding errors or maybe it applies the effect non-linearly. We need to investigate it more detailed.
jeremy llewiff  
#3 Posted : Tuesday, March 28, 2006 3:51:52 PM(UTC)
jeremy llewiff

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Perhaps GraphicsMill uses HSL?

Photoshop uses the HSB model to convert RGB to human values. This is different from HSL, and Saturation and Brightness have slightly different meaning. Paint Shop Pro, for example, uses HSL. Some programs offer both methods, like the little 3D tool Bryce.

Most notable is that a colour like #FF0000 (full red) is 100% "bright" in HSB, but only 50% "light" in HSL. In HSL the remaining 50% is taken up by the ramp from #FF0000 to #FFFFFF.

#ff8080 is 50% saturated in HSB (photoshop), but 100% saturated in HSL.

They cover the same color space, though. It's basically a deformation of the S/B square you see when you open the colour picker in Photoshop.



Quote:
a saturation adjustment of -50 in Photoshop, and
-2.55*50 with Graphics Mill, which should be same adjustment.


Not necessarily.

Photoshop scales the saturation values, which causes a smoothly desaturated image. Low saturation pixels are less influenced than high saturation pixels.

If GraphicsMill simply shifts them, then the image would more quickly show fully grey spots while other pixels are still relatively colourful.
Andrew  
#4 Posted : Sunday, April 02, 2006 1:13:19 PM(UTC)
Andrew

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Thank you for your input, Jeremy! I think we will consider providing alternative transform which provides HSB conversion functionality.
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