Re: AdobeRGB chromaticites (was CG220 emulating AdobeRGB)
Re: AdobeRGB chromaticites (was CG220 emulating AdobeRGB)
- Subject: Re: AdobeRGB chromaticites (was CG220 emulating AdobeRGB)
- From: Steve Upton <email@hidden>
- Date: Thu, 25 Aug 2005 09:51:19 -0700
At 11:15 AM -0400 8/25/05, Mike Eddington wrote:
>
>Maybe someone can clear this up for me. Comparing chromaticity coordinates of my CG220 with that of aRGB, I noticed that calculating the values from XYZ gave me different results than reported by Photoshop. I simply took XYZ tristimulus values XYZ tags the profile as reported by the Colorsync utility and plugged them into the x=(X/(X+Y+Z)), y=(Y/(X+Y+Z)) equation. I confirmed my results with that of the CIE Color Calculator at Bruce Lindbloom's site.
>
>So calculating chromaticities of the AdobeRGB profile in this manner, and comparing these values to those reported by Photoshop for AdobeRGB, you'll notice a difference:
>
>Calculated from XYZ
>Red: x=0.6484, y=0.3309
>Green: x=0.2302, y=0.7015
>Blue: x=0.1559, y=0.0660
>
>Photoshop reported
>Red: x=0.6400, y=0.3300
>Green: x=0.2100, y=0.7100
>Blue: x=0.1500, y=0.0600
>
>Its not an earth shaking difference, but it makes me wonder how the values are calculated. I find the same issue when calculating xy for my CG220 profile as well. Further, if I select a profile to emulate in Eizo's Color Navigator, the x,y values are identical to what I would get in Photoshop. Does anyone know how Photoshop/ColorNavigator are calculating chromaticity values?
chances are pretty good that the differences you are seeing are the result of chromatic adaptation.
in theory, the chromaticities are to be adapted to D50 before they are put into a profile. In reality - especially if the profile's white point is non-D50 - they may not be.
So you might be looking at one set that is and the other that isn't.
I'm not even sure how AdobeRGB values are encoded.... anyone at Adobe care to comment?
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
o ColorGear ColorThink ColorValet ColorSmarts ProfileCentral
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