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Strange B/W color desaturation

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  #1  
Old 01-28-2007, 08:48 PM
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saberlancer saberlancer is offline
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Strange B/W color desaturation

Hi,pls help..thks
1. Left image is RGB with Hue/Saturation adjustment layer - Sat 0%
2. Right image is CMYK with Hue/Saturation adjustment layer - Sat 0%
Qn: Why is there this reddish tint?

http://i176.photobucket.com/albums/w...soon/color.jpg

Last edited by saberlancer; 01-28-2007 at 08:59 PM.
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  #2  
Old 01-28-2007, 09:24 PM
BillFrey BillFrey is offline
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Re: Strange B/W color desaturation

I get the same results in cymk, never figured out why.

Sorry not to be of help, but at least you know you're not the only one.
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Old 01-28-2007, 10:07 PM
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saberlancer saberlancer is offline
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Re: Strange B/W color desaturation

I just found that clicking 'colorize'does remove the tint but its a bad conversion.
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Old 01-28-2007, 10:24 PM
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Re: Strange B/W color desaturation

ran a test and this is what i found ...

with desaturate on the hue-sat layer set to 0 the cmy numbers are the same when the eyedropper is moved around the image, when a solid color adjustment layer added and it's color set to black and the blend mode of this layer is set to color - the cmy numbers are not the same when the image is sampled. I am guessing this is but because the color profile is compensating for how the cyan, yellow and magenta inks need a different amount of density to appear grey when printed on a press. Just guessing but that is my vote

-Roger
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Old 01-28-2007, 10:39 PM
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saberlancer saberlancer is offline
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Re: Strange B/W color desaturation

Thks roger,
And I found that using a white solid and setting to 'color' blending produces the red tint effect I mentioned earlier!...

Not that I understand whats going on...
But it seems like using a black solid layer set to 'color' is the most flexible method if I want to a 'Grayscale CMYK image that is set by using just a layer'?
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Old 01-28-2007, 10:51 PM
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Re: Strange B/W color desaturation

When you desaturate in RGB, the 3 channels are equalized and youn get a pure grayscale result. In CMYK, the Cyan, Magenta and Yellow channels are also equalised while the Black channel is adjusted to ensure correct lightness is maintained. If you run your eyedropper around the image you will see that the CMY values are all equal. However, that will not produce gray because in the CMYK model, equal amounts of ink do not equal gray or black. So if you are looking to have a grayscale image, you should use one of the 10 ways in RGB or LAB to achieve the result.
Regards, Murray
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Old 01-29-2007, 01:07 AM
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roger_ele roger_ele is offline
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Re: Strange B/W color desaturation

Saber,

I don't know why you would want to specifically go to black & white in CMYK ...

Great explanation Murry!
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