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Use Photoshop LAB to Spice Up Your Image's Colors

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The best cooks never follow recipes, or at least not literally. A pinch of something extra here, a little bit of something not in the list of ingredients there, and presto, a culinary masterpiece. It's that way with LAB, too. In this sample chapter, you'll learn how to wipe out casts while enhancing other colors, exclude brilliant colors without formally selecting them or using a mask, and choose certain colors for more of a boost than others.
This chapter is from the book

The simple, symmetrical curves of Chapter 1 are powerful, but they're just the beginning. By using different mixes of ingredients, LAB curving can become considerably more spicy, emphasizing certain colors more than others.

The best cooks never follow recipes, or at least not literally. A pinch of something extra here, a little bit of something not in the list of ingredients there, adjust the quantity of this, delete all mention of that, and presto, a culinary masterpiece, although when I do it, there always seem to be more carbohydrates in the result than the original recipe suggested.

It's that way with LAB, too. Chapter 1 presented the basic recipe, the fundamental method of using LAB to bring out the natural colors of an image. Because I was trying to assume that you had never been in a kitchen before and didn't know the difference between a truffle and a habanero pepper, the recipe was necessarily simple—and inflexible. Several contingencies could derail it, such as a cast in the original, the presence of brilliant colors, or a subject that was excessively busy in the L channel.

Now that we've had an introduction to how LAB operates and what its numbers mean, we're in a position to expand the recipe's usefulness. We can wipe out casts while enhancing other colors; we can exclude brilliant colors without formally selecting them or using a mask; we can choose certain colors for more of a boost than others.

Getting to that happy point requires some preparation of Photoshop settings, but before doing that, let's review the recipe. Figure 3.1 demonstrates LAB's knack of smashing its way through any kind of haze. The bottom version follows the recipe, and therefore is made up of four basic moves. We will now look at each in isolation, to see how the whole is greater than the sum of its parts.

sequoia_a_only.jpg

Figure 3.1 (opposite) LAB excels at cutting through haze. The bottom version was prepared in much the same way as the canyon images of Chapter 1.

As we know, LAB, unlike RGB and CMYK, treats color and contrast as separate ingredients. Figure 3.2A has greatly improved detail in comparison to Figure 3.1A, but there has been no change in color because the A and B channels were left untouched.

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Figure 3.2 Changes to the L channel affect contrast, not color. Above, the curve shown at left enhances contrast. Then (below) an application of unsharp masking to the L channel enhances focus.

The L curve that provided the extra detail was derived in the same way as in Chapter 1, by steepening the area of major interest. To find that area, I held down the mouse button and, with the Curves dialog open, ran the cursor across key parts of the image, which yields a moving circle that indicates the range in which the objects fall.

As with the Chapter 1 images, this very flat original falls in a narrow range. The part of the curve that affects that range can be quite steep, and the increase in contrast (Figure 3.2A) dramatic.

In principle, it would be nice to show a version with sharpening applied to the original image only. The result would be deceptive because, with everything so flat, the sharpening wouldn't be nearly as pronounced as it would be after the L curve was applied. Therefore, Figure 3.2B sharpens not the original file, but rather Figure 3.2A.

Both of these L-only moves repeat a sad story about images that are too dark, too light, or too flat: they also tend to be colorless. If a picture is too dark, merely lightening it won't make it acceptable, because it's almost always too gray as well. The same thing is happening here. A haze hurts not just contrast but color. By the time we reach Figure 3.2B, there's so much snap that the tepid colors look artificial. We need more vivid greens. The A and B channels will give them to us.

To get the final version (Figure 3.1B), I steepened the A and B curves by moving their endpoints three gridlines horizontally toward the center. This is almost exactly the same procedure as in Figure 1.10, the picture of Yellowstone Lake. Figure 3.3A shows how the picture would look if the curve were applied to the A alone without any change to the other two channels; and Figure 3.3B does the same for the B alone.

43_fig3_3.jpg

Figure 3.3 Top, an image modified only by altering the A channel. Bottom, if the modification is only to the B.

Three Channels, One Image

These four intermediate images are the ingredients. But, as with anything involving seasonings, the chef's good taste must come into play. Let's discuss some of the options, because there are some things about Figure 3.1B that I don't particularly like.

The L curve shown in Figure 3.2 is definitely of the right shape. It places the entire scene in a steep part, but opinions could vary as to how steep the slope should be. You may feel that it gives the image too much bite, in which case a less extreme steepening is called for. Or, you may wish to go further than I did, making the curve even more vertical. I wouldn't, because I think that the grassy areas are getting too light already, and that the trees are getting so dark as to be threatening to lose all detail.

Sharpening is the most irritatingly subjective item in all of color correction. We'll discuss some of the considerations in more depth in Chapter 5. For now, it's enough to say that you could sharpen this image more than I did, or less, or not at all.

As for the color changes, they're hard to evaluate without seeing them in conjunction with the move in the L channel. One way to begin, however, is with this question: if the choice is between hanging and poison (that is, between Figures 3.3A and 3.3B), which one would you choose?

If these two were the only choices, which I thank the gods of color they are not, I'd go with Figure 3.3A. Green is a pleasing hue in the context of this image. Yellow isn't.

Figure 3.1B is far better than the foggy original, true, but—at least to my taste—some of the grassy areas at the center of the image seem too yellow. So, we could alter the recipe. All the images in Chapter 1 used different angles for the curves, but the angle was always the same in both the A and B channels. They don't throw us in prison for applying different ones, and that's what we might do here. We could use the existing curve for the A channel, but something milder, less vertical, for the B.

There's another option, too. Making the B less vertical tones down not just the yellow component of the image, but the blue also. Personally, I happen to like how the background has picked up a blue shade at its top right. If we wanted to preserve that increased blue but keep the yellow where it was, Chapter 4 will explain how to do it.

Expertise with the AB curves gives us enormous flexibility. Before we turn to their magic, let's verify our system settings.

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