Question for Rutt

XO-Studios

As I have been using many of the tips Rutt has been suggesting, one question keeps coming to mind. I have learned to love LAB, but why?

What is teh fundamental reason we should go to LAB for many things?

Any answer will do, lengthy online resources/links/articles, I am good with any and all.

My reasoning is that I want to learn and understand and get beyond 'because it works' type of answers and explanations.

Inquiringly,

XO,

pathfinder

XO-Studios wrote:

As I have been using many of the tips Rutt has been suggesting, one question keeps coming to mind. I have learned to love LAB, but why?

What is teh fundamental reason we should go to LAB for many things?

Any answer will do, lengthy online resources/links/articles, I am good with any and all.

My reasoning is that I want to learn and understand and get beyond 'because it works' type of answers and explanations.

Inquiringly,

XO,

Not sure what John will say, but I think one of LABs real advantages is that it seperates color tonalities from the luminosity values - allowing you to alter the contrast ratios without changing the color tonalities at all.

rutt

Pathfinder got there first. This was going to be my number one bullet point. Making big color moves in RGB or CMYK is a big pain because when you change the curve for each color you also change the brightness of every point. If are basically happy with the lumonosity of the image you have to change all the curves at once very carefully in order preserve it. It's a huge pain and often pretty darn hard.

Another thing that's great about LAB is that neutral colors are very easy to identify. A=0, B=0 and it's neutral no matter how bright. RGB is almost as easy but CMYK is much more subtle because cyan ink isn't as dark (for strange reasons) as mageneta or yellow. So CMYK white is C=5,M=3,Y=3 (believe it or not.)

Opponent color channels are an acquired taste, but I've learned to love them. At first, the A and B channels seem very arbitrary. And why no Cyan-Red channel? But my experience with landscapes and nature shots is that even very simple steepening of these curves often produces dramatic improvemetns in color contrast that can make an image come to life.

There are many more subtle good things about LAB. For one, it provides 3 more very different channels as grist for the plate blending mill. As always, Dan Margulis is a great resource for this sort of thing. Get his book, Professional Photoshop, if you don't already own it. You won't read it all in one sitting or even in one year, but it's a thing you'll slowly grow into. Dan says he will publish an advanced book focused on LAB this fall. In the mean time, he does have some online articles on the topic to check out:

http://www.ledet.com/margulis/PSW_Dan_Magic_of_LAB.pdf

Dan also write a column called "Make Ready". You'll find instructions for accessing these here:

http://www.dgrin.com/showthread.php?t=10150

XO-Studios

Thanks Rutt and Pathfinder, for the quick response.

XO,

lynnma

thanks Rutt and Path.. good to know.. great stuff here..

rutt

I thought of one more important advantage of LAB. It's sort of the flip side of the first advantage that Pathfinder raised. He said that you can change colors without having to think about brightness (luminosity). The flip side is that it's also easy to work make luminosity changes without thinking about colors. I do this all the time, steepen the L curve through areas where I want to bring out detail. Doing this in RGB or CMYK requires fussing with three or four differnet curves. In LAB, I only have to think about the L curve.

Look, the LAB curves adjustment is just one more tool in the toolbox. There are times when only the K curve in CMYK will do what I want. When it's what you need, it's great. When it isn't exactly what you need, there are other tools. But, like a hammer or a good sharp knife, LAB curve adjustment is a tool with a lot of good uses.