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This chapter is from the book

The Recipe and Its Ramifications

Now that we're set up, and know the implications of the LAB numbering system, we can make more sense of the recipe and why and how it works—and we can also make its impact more specific.

The objectives of curve-based corrections in LAB are the same as they would be in any other colorspace: full range, no impossible colors, and allocation of as much contrast as reasonable to the main focus of interest. Let's consider these three points in turn.

  • Full range means that the lightest and darkest significant points of the image get handled appropriately.

Most people call this step setting highlight and shadow. The task is a little more onerous in other colorspaces, where we generally have to be sure that the highlight and shadow are also neutral—in RGB, equal values in all three channels; in CMYK, equal magenta and yellow, a bit more cyan, with black irrelevant. In either one, if we decide that the highlights and shadows should be something other than neutral, we have to scratch our heads to come up with different numbers.

With LAB, which defines range independently of color, there's no such problem. If the L channel's numbers are good, you can set a neutral highlight and shadow (or not) by establishing values of 0A0B in them.

On the other hand, there are workflow issues that don't exist in other colorspaces.

The strength of LAB is that it can make dramatic changes almost inconceivably quickly. If you have only one minute to fix an image, LAB gives the biggest bang for the buck. If you've got more time than that, there can be room for an argument, because LAB's strength is also a weakness.

Dramatic, instantaneous changes for the better, as in Figure 3.2A, are possible because the L channel is a bull, far more powerful than the black of CMYK, which is itself much more potent than anything in RGB. If there's something seriously wrong with contrast, the bull is strong enough to fix it, provided that you have a little tolerance for what may happen to the china shop of endpoints.

With one minute to fix an image, use LAB and hope for the best—with almost any original. If you have more time than that, first of all there are a whole slew of images that RGB and CMYK will handle better. We'll discuss these cases in Chapters 6 and 7. But even if it's the type of image that LAB does well with, sooner or later it has to come back to RGB or CMYK for output. And when it does, it can almost always be made slightly better by optimizing the highlights and shadows in a way too delicate for a bull.

The real question is, therefore, have you budgeted time to finalize the correction in RGB or CMYK after you hit it in LAB? Because if you have, you should be more conservative with endpoint values. Blowing out highlights and/or plugging shadows is a disaster more easily accomplished in the L channel than by any competitive method. If you're certain that you're going to be correcting in RGB or CMYK afterward, play it safe. Use 95L and 10L as your endpoints, and fine-tune later.

Lastly, remember that the purpose of end-points is to maximize range while retaining highlight and shadow detail. If the lightest point of the image has no detail of any value, you may as well use 100L for the light point. If you don't care whether the shadow plugs, you should use 0L for the black.

  • No impossible colors sounds easy, and sometimes actually is. If fortune is on our side, she provides something that we know ought to be a neutral color—a gray. If such an object is found, the recipe is like one for duck soup, much easier than in RGB and CMYK, where all channels interact in a more complicated way. But 0A0B is neutral, no matter what's up with the L.

Sometimes we find something that's approximately neutral, but we're not sure exactly. In Figure 3.1A, I'm not positive that the winding road is gray, but it certainly should be fairly close. Furthermore, we can rule out certain possibilities. I've seen roads that are gray, bluish gray, and brownish gray, but I'd sooner follow a recipe for jalapeño pepper ice cream than make the road greenish gray.

And we sometimes spot colors that can't be right. In Figure 3.1A, we know little about the exact color of the trees and the grass—except that they'd better both be some flavor of green. That means a negative A channel (more green than magenta), and a positive B, because all natural greens are more yellow than they are blue. In fact, we are so accustomed to greens being biased toward yellow that we might describe the top half of the A as being more of a teal than a green. Therefore, the B could actually be further away from zero than the A is, and we'd still buy the overall hue as a yellowish green. But if it's more than half again as far away, it's a greenish yellow, which isn't appetizing.

  • Allocation of contrast was covered in Chapter 1. It's related to, but not the same as, setting range. The L channel curve has to establish light and dark points, yes, but beyond that it helps if it's steepest where the most important parts of the image live. It's not always possible. Often the image's entire range of tonalities is important, in which case there's nothing more to be done than establish the endpoints. Up until now, the images have been specially selected to avoid this inconvenience—each one has had the interest object in a small range, easily exploited in the L.

We'll move beyond that, and we'll move beyond canyons, too, ending this part with images of two subjects that not only strongly suggest LAB every time you see them, but demonstrate that the A and B channels should not always be handled identically.

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