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Chapter 17: Mapping and Adjusting Colors
What Is Color Mapping?
Color mapping is just a fancy name for shuffling colors around. For example, to map Color A to Color B simply means to take all the A-colored pixels and convert them to B-colored pixels. Photoshop provides several commands that enable you to map entire ranges of colors based on their hues, saturation levels, and most frequently, brightness values.
Color effects and adjustments
Why would you want to change colors around? For one thing, to achieve special effects. You know those psychedelic horror movies that show some guy’s hair turning blue while his face turns violet and the palms of his hands glow a sort of orange- yellow? No? Funny, me neither. But a grayscale version of this sort of effect appears in the second example of Figure 17-1. Although not the most attractive effect by modern standards — you may be able to harvest more tasteful results if you put your shoulder to the color wheel — what we think of as a “psychedelic” color effect qualifies as color mapping for the simple reason that each color shifts incrementally to a new color.
Figure 17-1: Nobody’s perfect, and neither is the best of scanned photos (top). You can modify colors in an image to achieve special effects (middle) or to simply fix the image with a few well-targeted corrections (bottom).
But the more common reason to map colors is to enhance the appearance of a scanned image or a digital photograph, as demonstrated in the third example in Figure 17-1. In this case, you’re not creating special effects; you’re just making straightforward repairs, alternatively known as color adjustments and corrections. Scans are never perfect, no matter how much money you spend on a scanning device or a service bureau. They can always benefit from tweaking and subtle adjustments, if not outright overhauls, in the color department.
Keep in mind, however, that Photoshop’s color adjustment functions can’t make something from nothing. In creating the illusion of more and better colors, most of the color adjustment operations that you perform actually take some small amount of color away from the image. Somewhere in your image, two pixels that were two different colors before you started the correction change to the same color. The image may look ten times better, but it will in fact be less colorful than when you started.
Remembering this principle is important because it demonstrates that color mapping is a balancing act. The first nine operations you perform may make an image look progressively better, but the tenth may send it into decline. There’s no magic formula; the amount of color mapping you need to apply varies from image to image. But if you follow my usual recommendations — use the commands in moderation, know when to stop, and save your image to disk before doing anything drastic — you should be fine.
| Note | Many of the commands I talk about in the following sections can also be applied as adjustment layers. Adjustment layers are an extremely flexible tool, giving you all the advantages of the color correction commands without the drawback of having your original image permanently altered. I discuss adjustment layers in full at the end of this chapter, but I wanted to alert you to their welcome presence from the outset. So now you know. |
The good, the bad, and the wacky
Photoshop stores all of its color mapping commands under the Image Adjustments submenu. (The one exception is Photoshop CS’s new Camera Raw dialog box, which can be accessed only by opening a Camera Raw file. We’ll take a look at this later in the chapter.) Basically, these commands fall into three categories:
Color mappers: Commands such as Invert and Threshold are quick-and-dirty color mappers. They don’t correct images, but they can be useful for creating special effects and adjusting masks.
Easy color correctors: Brightness/Contrast and Color Balance are true color correction commands, but they sacrifice functionality for ease of use. If I had my way, these two commands would be removed from the ImageAdjustments submenu and thrown in the dust heap.
Expert color correctors: The third, more complicated variety of color correction commands provides better control, but they take a fair amount of effort to learn. Levels, Curves, and Hue/Saturation are examples of color correcting at its best and most complicated.
This chapter contains little information about the second category of commands for the simple reason that some of them are inadequate and ultimately a big waste of time. There are exceptions, of course, most notably the Auto Color command, which usually does a passable job of adjusting an image’s midtones and removing color casts. Auto Levels and Auto Contrast are decent quick fixers, and Variations offers deceptively straightforward sophistication. But Brightness/Contrast and Color Balance sacrifice accuracy in their attempt to be straightforward. They are as liable to damage your image as to correct it, making them dangerous in a dull, pedestrian sort of way. I know because I spent my first year with Photoshop relying exclusively on Brightness/Contrast and Color Balance, all the while wondering why I couldn’t achieve the effects I wanted. Then, one happy day, I spent about half an hour learning Levels and Curves, and the quality of my images skyrocketed. So wouldn’t you just rather learn it correctly in the first place? I hope so, because that’s what you’re about to do.
