Lab Color Range

CR
Posted By
Chris.Radley
Oct 15, 2008
Views
233
Replies
4
Status
Closed
Hi

In Photoshop the a and b values in Lab color range from -128 to 127, but on wikipedia ( http://en.wikipedia.org/wiki/Lab_color#Range_of_L.2Aa.2Ab.2A _coordinates) they are -0.86 to 0.98 and -1.07 to 0.94 respectively. Is this just a usability thing in Photoshop? Can I plot the Photoshop values on a graph (http://en.wikipedia.org/wiki/Image:CIExy1931.svg) by using ratios to convert the values?

Thanks!

Chris
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M
mistermonday
Oct 16, 2008
Hello Chris,
What are you trying to do? Do you want to get into all the math and complexities of 3 dimensional space and Euclidean Distances or are you interested in understanding and using LAB for practical purposes. If it’s the latter, then there are a lot of tutorials floating around and the Photoshopper’s bible on lAB – a book by Dan Margulis called "The Canyon Conundrum and Other Adventures in the World’s Most Powerful Color Space". If however you want to get into all the math and science, you would probably be better off checking out the CIE org.
Regards, MM
CC
Chris_Cox
Oct 17, 2008
The wikipedia entry is pretty messed up right now.

The a and b ranges in Photoshop are as stated, and match the CIELAB definitions for a* and b*.
DM
dave_milbut
Oct 17, 2008
hi chris, great to see you! hope the release went well, i can’t wait to try it out!
BJ
Bill_Janes
Oct 18, 2008
Bruce Lindbloom < http://www.brucelindbloom.com/index.html?LabGamutDisplayHelp .html> has an informative post on integer encoding if *a and *b values in L*a*b as used in Photoshop and some other applications. The full L*a*b gamut can not be encoded with these integers, but it is doubtful that commonly encountered real world colors are affected.

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