Suggested target values for LAB skin correction?

ajava

I am eagerly awaiting the arrival of Dan Margulis's book on the LAB color space. In the meantime, can anybody tell me the general ratio of balanced caucasian skin in LAB? I believe that the b channel is supposed to be slightly higher than the a channel...and that's all I've been able to discover, so far. Any more detail, while I'm waiting for the book?

Thanks!
Andrea

Richard

You are correct. Both positive, B slightly greater than A is the usual target. But don't insist on that as there is a lot of natural variation. In Spain, for example, a slightly redder complexion is not unusual, and plentiful sun and good, cheap wine only accentuate it.

Dan's book is great if you want to learn LAB. You should look for some of the many threads on Dgrin that have discussed it, including a chapter-by-chapter reading group.

arodney

Note, you can keep the data in RGB and just set the info for Lab. Looking over most of the good skin tone reference files I have, including the Roman 16*, aStar and bStar are often numerically very close and never more than 15 values difference. In Photoshop, this is a good bet. In Lightroom and ACR, you’ll have to use RGB ratio’s (no Lab readouts).
*http://www.roman16.com/en/
http://digitaldog.net/files/LR_Skintone_Ratio.jpg

BinaryFx

It obviously depends on many factors, including but not limited to
lighting, ethnicity, age, hair & eye colour combinations, body part,
make-up etc.

That being said, I agree with Andrew that the A and B values are often
close, with the B channel sometimes being slightly to a little bit higher.

I also agree that one can work in RGB and simply use Lab value info
palett readings in Photoshop - however that would be missing out on the
value of Lab mode as an editing space (in the book Dan notes many of the
pros/cons of where, when and why to use Lab mode and RGB mode).

This topic is a couple of years old, so I am sure that the OP has Dan's
book by now. For those that don't, two free sample chapters are linked below:

http://www.ledet.com/margulis/PLC_Ch02.pdf
http://www.ledet.com/margulis/PLC_Ch09.pdf



Best,

Stephen Marsh

http://binaryfx.customer.netspace.net.au/ (coming soon!)
http://members.ozemail.com.au/~binaryfx/
http://prepression.blogspot.com/