L*a*b Color definitions and differenzes in PS-CS

DP
Posted By
Daniel Pfeiffer
Mar 2, 2005
Views
246
Replies
1
Status
Closed
Hello Everyone!

I’m wondering about a peculiarity of P.Shop-CS.
I’m defined my own cmyk colors with precise lab coordinates. But if i fill after the color setup a selection with one of my primary colors i get slightly different lab values shown in the PS-info window. For example: Cyan is defined L*(54) a*(-36) b*(-49). The color in the selection shows L*(54) a(-40) b*(-49) So i get a dE*(4). It’s too blue. Now i’m printing this color with my proofer and i get exactly this delta a* as shown in the info before.
For information:
The set up profile is attached to my picture.
Picture is in CMYK format
Rendering intent is relative colormetric
ICM: Adobe

Do you know this problem or maybe a solution?

Thanks,
Daniel
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m.golner
Mar 3, 2005
Daniel Pfeiffer wrote:
Hello Everyone!

I’m wondering about a peculiarity of P.Shop-CS.
I’m defined my own cmyk colors with precise lab coordinates. But if i fill after the color setup a selection with one of my primary colors i get slightly different lab values shown in the PS-info window. For example: Cyan is defined L*(54) a*(-36) b*(-49). The color in the selection shows L*(54) a(-40) b*(-49) So i get a dE*(4). It’s too blue. Now i’m printing this color with my proofer and i get exactly this delta a* as shown in the info before.
For information:
The set up profile is attached to my picture.
Picture is in CMYK format
Rendering intent is relative colormetric
ICM: Adobe

Do you know this problem or maybe a solution?

Thanks,
Daniel
Daniel,

I’m not confident this is the answer, but perhaps the issue is with the Relative Colorimetric rendering intent. If I understnd, you have a source profile. This should contain a ‘source’ white definition. Not clear what you have as an output or proof profile, but it should have a ‘destination’ white definition. To quote from Real World Color Management, 2nd Edition, Fraser, et. al, p. 91, "Relative colorimetric rendering scales the source white to the destination white and adjusts all other colors proportionately. Perhaps this is where your color shift is coming from. Just a thought….

Mike

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