Hi,
I was wondering, does anyone use LAB in PSD/PHOTO etc? I like it because it keeps the contrast (L) channel separate from the color (AB).

God Bless,
Rodi

G-5 imac
PSD CS
DTS1030ai Drum Scanner
soon a Fuji Pictrography!
Rarely enough time :cat:

Yes, LAB is an excellent color space for doing certain types of editing. There is a new book just out by Dan Margulis called "Photoshop LAB Color". It is one of the most detailed, cutting edge color editing books ever written for Photoshop and is, apparently, the #1 selling Photoshop book at Amazon this week. It has gotten rave reviews from some Photoshop gurus like Scott Kelby and David Beidny (author of the classic "Channel Chops" book).

It would be helpful to have read "Professional Photoshop - 4th Ed." by Margulis before diving into his "LAB", however. This is one "heavy" book that I think will become a classic on a subject largely ignored by other authors.

The book mentioned is extrodinary. I do all my color correction in LAB and will do more and more as I better understand the possibilities presented :) ...skip

Yeah,
I got it and it is superb. Just on quick review it is really a deep book, much more than what I understand. Dan Margulis is also a great writer. You can get his column "MakeReady" for free by subscribing up for Electronic Publishing magazine. He is in 6 issues a year and the subscription is free.

LAB is great because just basic moves enhance many pictures and removes color casts.

God Bless,
Rodi :cat:

Even Margulis cautions that LAB (or any color space for that matter) is not best for all situations. His book "Professional Photoshop 4th Ed." nicely explores RGB, CMYK and LAB and compares the strength and weaknesses of each. In other words, don't always reach for a hammer if a saw works better for what you need to do.

Perhaps to mdavis point, a considerable body of work has been built over time re RGB grey point corrections, CMYK skin tone corrections. Not having read Margulis' new book, I suspect it still lacks some of the acquired "intuitiveness" of the other spaces. Will it ever have the 1,2,3 relative simpleness? I am awaiting my book with great anticipation but think it may be others who may find a "simple" beauty in working in LAB.

Dave

acquired "intuitiveness" [/QUOTE]

Interesting postulation, seems more like applied knowledge. :) Having actually read the book—on my third reading, it may take twenty—I find LAB as presented therein—offers faster correction, greater control, and endless opportunity for application. No doubt one draws on all Photoshop experience, and it easy to imagine how that knowledge could be ported. A simple Curves adjustment in LAB might require numerous adjustment layers and mask by conventional methods. Then you say, "well what if I added that other stuff on top of this stuff...oh my!" Early days at any rate; no tool fits—or is necessary—for every job, some are just more adaptable...skip

Any colorspace can be "intuitive" if you learn it, just as Spanish is intuitive in Mexico or English (in its many variations) in the U.S., Australia, G.B. and Canada. Since we all probably learned RGB (or English) first, all else is less than intuitive.

LAB is quite logical, and Margulis make the point that it is actually more like the way we see colors than RGB. All color spaces make use of the color wheel. The only difference is how the information is divided into the grayscale "channels" used to hold color and detail information. We have all probably used the HSB (hue, saturation, brightness) sliders in our imaging editors. LAB is essentially the same idea. The first couple of chapters of "Photoshop LAB Color" give you the basics of HOW to use LAB for color correction. The rest of the book gives you the basics of why it works. Using LAB is very simple. Using it creatively with advanced channel blending and such gets a bit hairy, but no more so than in RGB/CMYK.

So, if you understand the L channel (lightness) and you can understand the relation of colors on the color wheel, you can use LAB curves to do some amazing things that you just can't do in RGB/CMYK. As long as you keep the center of the a* and b* channel curves centered, all remains balanced with respect to color casts. It's a "no brainer" as long as you don't go twisting the curves when you don't need to.

Hi,
Breaking contrast from color is the strength of LAB and really blowing casts away is relatively simple. Also it is easy to add contrast/color enhancement while keeping the neuterals neuteral.


God Bless,
Rodi:cat:

As mentioned already, lab is unmatched for removing color casts. The other thing it does that cannot be duplicated in other spaces is the way it effortlessly pulles hues apart and clarifies them. The only comparable moves in CMYK and RGB are to use Saturation, which is nowhere close.

I started using lab around the time Margulis' "Professional Photoshop" came out for version 5. He had an exercise there that showed how to separate and enance colors, and though I really didn't understand what was going on at the time, I was able to put the technique to good use anyway. He also used a more precise method for removing casts, which he seems to have abandoned in his new book, for a more intuitive approach.

It's not a subtle space. Fine tuning face tones or contrasts can be done much better in CMYK or RGB, particularly if you split up your curves into luminosity mode and color mode, borrowing some of the utility of lab but allowing much fines moves. But when you need a major makeover, nothing comes close.

OK. So I've read up to page 75 for the third time..had a little success with removing color cast. This image though I'm having trouble. No problem correcting in the other spaces but can the LAB pros post a correction including curves.

Thanks
Dave

OK. So I've read up to page 75 for the third time..had a little success with removing color cast. This image though I'm having trouble. No problem correcting in the other spaces but can the LAB pros post a correction including curves.

Thanks
Dave

This one is tricky, but not impossible. Keep in mind that the lab techniques referenced, all deriving from Dan Margulis' approach, are based on his personal preference for avoiding at all costs local corrections until the very end of the process. An image this badly damaged probably is worth the trouble to just go ahead and cut masks and apply corrections locally.

However, lab does present some options. The three versions below show the three-step process that I took. The first image on the left has a curve applied to it that removes the cast from the highlights and seriously reduces it in the quartertones. As you can see, the rest of the image is still crap. The middle version has a second curve adjustment layer applied that removes the cast using the black of the phone as a reference. Using blending options, I restricted the effect of this curve to the shadows and faded it away through the mid-tones. The third version has a third adjustment layer added using a drastic color enhancement curve, pulling both anchor points in towards the center 40 units each on both a and b channels. Then, using blending options, I removed the effects of this curve from the highlights and shadows. That enabled me to go back to the b curve and favor the yellow end of the spectrum. I put the opacity of this layer at around 50%.

This is a first shot effort. The variables are the areas affected through blending options, the intensity of the third curve and the opacity of that layer. More experimentation might yield better results. There were no contrast moves in the lightness channel, and once the color comes out, other serious problems appear, such as the extra-greenish band on the right side. I would probably wait to go into CMYK and push the black channel to get some contrast, or perhaps make a copy, convert to CMYK and borrow the black channel as a layer mask in LAB or RGB to heighten shadows. But, like I said, this is just an example of lab curves, not an effort to produce a print-ready masterpiece.

Here's what I've ended up so far in LAB. Fairly nauseating a curve. Not as good but perhaps it can be brought closer after converting back to CMYK and/or RGB for further manipulation. Lots of reading yet ahead. Thanks for your effort.

Cheers

Dave

The problem with your curve for the a channel is that, while it certainly eliminates the red cast, pulling the entire bottom half of the curve above the center line turns ALL the red in the image to green. So now you have a green cast.

Ya, pretty nasty. Are you able to send your curves?

Dave

The method for removing the color cast comes from the chapter on LAB color in Dan Margulis' earlier book, Professional Photoshop. He seems to have abandoned this technique for the more intuitive approach he takes in his latest work, but I find it's an incredibly simple and powerful way to kill whatever cast you have.

The white of her dress is reading a:9, b:9. The black phone (front panel) is reading a:54, b:17. Right off we see that shadows and highlights will need a separate treatment. While RGB and CMYK allow curves that address different tonal ranges, the lightness channel in lab allows you to target highlight, shadows or midtones specifically, using blending options. I used one curve for the highlights, then placed an adjustment layer on top targeting the shadows. The approach is identical for both curves. I've included the second set of curves, as well as the blending settings.

Make sure that the light/dark gradient on the curve window has darks set at the left. (This is contrary to the method Dan uses in his LAB book, but it is necessary to match the Info readouts). Since the highlights read 9 in both color channels, the curve will be the same. Click somewhere in the midrange, and in the input/output windows, plug in the values; 9 for inupt, 0 for output. Do this for both a and b curves.

Now the highlights read 0 0 and the phone reads 47 9. So the second curve uses those values to address the shadow cast. Those are included below. Then, double clicking to the right of the layer name brings up the blending options window. Setting the channel to lightness, the settings shown will begin fading out the effects of this curve at the first white arrow and totally exclude it by the second arrow. These settings are intuitive and to some extent a judgement call. I was concerned that the drastic moves did not affect the highlights that the first curve had already fixed. The quartertones had been helped by that curve but still needed further moves. The fade-out was set to address both those needs.

The third curve is a straight color enhancement curve, as described in the early chapters of Dan's book. For this, I reversed the light/dark gradient. Note that the blending options emphasize the midtones, leaving the highlights and shadows, previously adjusted, intact. Note also that the curves do not move through the center point. Ordinarily this would cause the highlights and shadows to take on a serious cast, but the exclusion of the blending options prevents this from happening. I favored the green in the a curve and the yellow in the blue. The curve moves are pretty extreme, and so I set the opacity of this layer to 36%.

These settings are all variable, and a matter of judgement. Any number of modifications could produce a better result, I'm sure. But the approach, the ability to address highlights, shadows and midtones separately, while not unique to LAB, is much more effective when coupled with the power of it's cast killing curves.

What is obvious, now that there is some definition to the colors, is that this is one seriously messed up image. It's going to be impossible to address the rest of the issues without making some local selections. In addition to the green band at the right, the rug along the left side is also disastrous. Contrast sucks and dozens of other glitches show up. These could be addressed in LAB as well, but for this stuff, LAB doesn't offer much of an advantage over RGB or CMYK and for the local color moves, might not be as good. LAB is a battering ram. From here on, something more subtle would be called for.