Re: Eye-One Pro and Profilemaker 4 Emissive Meaurement Errors
Re: Eye-One Pro and Profilemaker 4 Emissive Meaurement Errors
- Subject: Re: Eye-One Pro and Profilemaker 4 Emissive Meaurement Errors
- From: "John Hollenberg" <email@hidden>
- Date: Sun, 24 Nov 2002 19:43:54 -0800
- Priority: Normal
On Sun, 24 Nov 2002 19:43:45 -0700, Chris Murphy wrote:
>
The measured values are correct. The numbers from Photoshop are bogus
>
because they are based on RelCol rendering. Example:
>
>
Go into the color picker and create a LAB color 50,0,0 which in Adobe
>
RGB corresponds to 118 for R, G, and B. Make a new RGB document made up
>
of 118 for R, G, and B. Using the info palette set to LAB and confirm
>
that these RGB values equate to 50,0,0 in LAB. Now go into the Color
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Settings, check the advanced mode, and change the conversion options
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rendering intent to Absolute Colorimetric and click OK. Now check the
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info palette measurement and it will read 50, -1, -11. The discrepency
>
in L* has to do with L* not being absolute. It's relative - I forget to
>
what, maybe it's vendor specific, but it's uncommon to get L*=100 from
>
a measurement device as there's always something that could have a
>
higher L*.
Fascinating, but not sure it applies to my example. I created the color
patches in photoshop in L*a*b* mode, rather than creating in RGB mode
and reading the L*a*b* values with the eyedropper. So, my L*a*b* patch
of 50,0,0 WAS 50,0,0 since no conversion would be needed (I understand
that L*a*b* is the device independent color space used by Photoshop).
Also, while your example does work with Adobe RGB, if I choose Ektaspace
as my RGB space it doesn't matter whether I use Perceptual or Absolute
Rendering in the Color Settings. Either one still shows the L*a*b* value
as 50,0,0. Why would perceptual vs absolute rendering make a difference
when there is only one color (neutral gray) in the image, and that is in gamut?
And why would this behavior show up with Adobe RGB, but not Ektaspace?
Still, it strikes me as very strange that two different explanations (D65 vs D50,
perceptual vs absolute) would match the numbers I have!
--John
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