Re: Lab in Photoshop
Re: Lab in Photoshop
- Subject: Re: Lab in Photoshop
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Fri, 12 Jul 2002 09:35:11 -0500
Tom Vanderlinden wrote:
>
Is this true of Photoshop 7?
>
When would the difference between ICC Lab & CIE Lab
>
make a difference in workflow?
>
Perhaps other applications assume differently about which Lab?
CIE Lab values are real numbers, and therefore have no bounds on the ranges
that the L*, a* and b* components may have. Furthermore, there are
infinitely many divisions between neighboring values.
ICC Lab (and Photoshop Lab) values are integers which have bounds on the
ranges that the a* and b* components may have (-128 to +127). There is a
finite number of divisions between them (1 delta E for 8-bit encoding, 1/256
delta E for 16-bit encoding).
As far as I know, "ICC Lab" and "Photoshop Lab" are the same (someone please
correct me if I'm wrong).
Neil Snape wrote:
>
Does this mean then that editing with Dan Margulis' techniques of doing some
>
trips to Lab for color corrections will have irreversible clipping from
>
Adobe 98?
With regard to Adobe 1998 specifically, there is only a very small amount of
clipping that will occur (pure Adobe 1998 green maps into an Lab value whose
a* value is -129, which is just barely outside the Photoshop range limit of
-128; all other parts of Adobe color space fit inside Photoshop Lab).
However, there will be some quantization of colors on the inside of the
gamut, but this is not "clipping." With other larger working spaces, such as
ProPhoto, clipping will be more severe.
--
Bruce J. Lindbloom
email@hidden
http://www.brucelindbloom.com
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