If you'll be printing to an inkjet printer, sending photos to a lab for prints, or posting your image on the Web, you need RGB color mode. (Despite the CMYK inks that you load into your inkjet printer, the printer's software expects and must receive RGB color data.) If you're prepping an image for inclusion in a page layout document destined for a commercial offset press, you need CMYK. You select the image's color mode from the Image

Warning

Converting between color modes or gamuts (done with the Image

Although the image itself has a single color mode, you can use any of the available color models when defining a color in Photoshop. Say, for example, that you're preparing to use the Brush tool to paint some artistic elements for your latest project. The project is in RGB mode because you'll be printing it with your inkjet printer. You can use the Color panel to define your foreground color any way you please — RGB, CMYK, Grayscale, Lab, or even HSB (hue/saturation/brightness, which isn't available as a color mode, just a color model). It doesn't matter how you set up the Color panel, which you do through the panel's menu, as shown in Figure 6-4. When you add the color to your image, Photoshop uses the nearest RGB (or CMYK) equivalent.

Figure 6-4. Choose your preferred color model from the Color panel menu.

Notice that the Color panel menu in Figure 6-4 doesn't list Duotone or Multichannel. Those are color modes only, not color models. A couple of other things to note about working with the Color panel: The warning triangle visible in Figure 6-4 in the lower-left corner of the panel indicates that the selected color is outside the CMYK color gamut. (Clicking the swatch to the right would select the nearest equivalent color. If, that is, you were actually working in CMYK mode.) Also note that the background swatch is selected in the panel, highlighted with a black outline — click the foreground swatch to make changes to the foreground color.

Color depth is the actual number of different colors that you have available. (Remember that each pixel can be only one color at any time.) When you work in 8-bit/channel color, simply called 8-bit color, each of the component colors is recorded with exactly 8 bits of information in the computer file. (At the beginning of this chapter, I mention digits. These are the actual numbers — the zeros and ones recorded on the hard drive to track each pixel's color.) In an 8-bit RGB image, each pixel's color is recorded with three strings of eight characters. When you work with 16-bit/channel, or 16-bit color, each of the component colors is recorded with 16 characters. The larger numbers mean more possible ways to record each color, which means more possible variations of color, as well as files that take up more space on your hard drive.

What that means to you, in practical terms, is possibly a better-looking image when working in 16-bit color. You'll have smoother transitions between colors throughout your image, no banding in gradients (those annoying areas in a gradient where you can actually see one color stop and the next color start), and no splotchy shadows. Posterization, which I explain in Chapter 5, is the degradation of your image's appearance when similar colors are forced to the same color, making transitions between colors more abrupt. Many tonal and color corrections that produce posterization in your 8-bit images won't harm a 16-bit image in the least. Take a look at Figure 6-5. To the left, a Levels adjustment is increasing a 16-bit image's tonal range. When the same adjustment is applied to an 8-bit version of the image, some rather substantial posterization becomes visible in the Histogram panel (represented by the gaps in the histogram).

Figure 6-5. Compare the Histogram panels to see posterization (right).

So, should you use 16-bit color all the time? No. You can't post a 16-bit image on the Web, and 16-bit color is rarely used for CMYK images. Digital photos taken in JPEG format are 8-bit because that file format doesn't support 16-bit color. And with most inkjet printers, you won't see any improvement in the final print. You might, however, see a dramatic increase in printing time because there's twice as much image data to process.

If you shoot in 16-bit color, whether TIFF or Raw, it makes sense to process the image in 16-bit color. When the image is perfect, you might want to convert a copy of the file to 8-bit color for printing (Image

One other note on color depth: Photoshop can work with 32-bit/channel images. These monstrous files are called high dynamic range (HDR) images and are typically constructed by combining different exposures of the same photo. In Photoshop, you can work with two or more exposures in the Merge to HDR feature (presented in Chapter 10). You probably will never be called upon to create an HDR image for any of the esoteric 3D or video programs that use them, but you might find some benefit in combining multiple exposures of a difficult shot. Afterward, so that you have a file of reasonable size and access to more of Photoshop's features, use the Image

The three "auto" adjustments, found in the Image menu rather than Image

The Brightness/Contrast adjustment works with the tonality of an image rather than color. While making adjustments to the tonal range may improve the overall appearance of your photo, don't rely on this feature for color adjustment.

The Levels adjustment, which is discussed in detail in Chapter 5, uses three slider controls to individually adjust the shadows, highlights, and overall tonality of your image. It's generally used to control the brightness/darkness of the image by making changes to the RGB (or CMYK) channel, but it can be used for color correction by adjusting the color channels individually.

The Curves command is also discussed at length in Chapter 5. However, for color correction (rather than tonal adjustment), you want to work on each channel individually, choosing each in turn from the pop-up menu at the top of the Curves dialog box (see Figure 6-8).

Although working on each channel with Curves can be very effective, it can also be rather time consuming, with lots of flipping back and forth among the channels as one adjustment makes another channel correction look like a bad decision. While it may be inconvenient, Curves is a very powerful color correction tool.

Note, in Figure 6-8, the Preset pop-up menu at the top of the Curves dialog box. In that menu, you'll find some ready-made Curves adjustments that — if they don't solve the problem immediately — give you some pretty good starting points. In addition to color correction presets such as Darker, Lighter, Increase Contrast, and Strong Contrast, you'll find special effects like Cross Process (developing film in the wrong chemicals — intentionally) and Color Negative (which, unfortunately, creates the appearance of a scanned negative rather than removing the orange from an actual scanned negative).

Figure 6-8. Correct each channel individually with Curves to adjust color in your image.

The Exposure adjustment, discussed in Chapter 5, is a tonal adjustment that simulates a change in the camera's exposure setting when taking a photo.

Often overlooked and rarely exploited to the fullest, Hue/Saturation is a very powerful tool. Using the three sliders together, you can adjust the hue to eliminate a color cast, increase saturation so that your colors appear richer and more vibrant, and adjust lightness to improve your image's tonality. (See Figure 6-9.) Keep in mind that when you adjust something that's very dark, start with the Lightness slider so that you can evaluate the other changes (Hue and Saturation) properly. Remember, too, that you can apply Hue/Saturation (like a number of other adjustments) to a specific range of colors in the image, selected in the pop-up menu at the top of the dialog box.

Using the pop-up menu at the top, you can elect to apply an adjustment to only a certain part of the color in your image. Once a color is selected, the eyedroppers become active, to add to or subtract from the range of color being adjusted, and sliders become active between the gradients at the bottom, giving you yet another way to control the range of color being adjusted.

Note

New in Photoshop CS4 and visible in Figure 6-9 is the Adjustments panel, which you now use to add adjustment layers to your images. (It's discussed in more depth in Chapter 8.) The content of the panel offers the same options as the Image

Figure 6-9. Hue/Saturation can cure three problems at once.

The Color Balance command (as shown in Figure 6-10) presents you with three sliders that you use to make changes to the balance between your color opposites. If the image is too blue, you drag the third slider away from Blue and toward Yellow. (This is also a great way to remember which colors are opposite pairs!)

You can control the highlights, midtones, and shadows of your image individually by using radio buttons at the bottom of the Color Balance dialog box. And, in almost all cases, you'll want to leave the Preserve Luminosity check box marked so that the brightness of the individual pixels is retained.

You can also use Color Balance to throw an image out of whack for special effects or (getting back to the adjustment's roots) compensating for a color cast being introduced by the printing device.

Figure 6-10. Color Balance gives you direct control over opposites.

The Black & White adjustment creates outstanding grayscale copies of your color images. This feature provides even more control than using Channel Mixer with the Monochrome box checked. As you can see in Figure 6-11, you can control the amount of each major range of color used to create the grayscale copy. In this particular example, the original consists primarily of greens and browns, so the top three sliders are key. Reducing Reds and increasing Yellows both lighten the browns and greens and increases contrast among the brown tones.

Figure 6-11. Black & White enables you to determine grayscale tones by mixing color values.

The Photoshop Photo Filter is actually an image adjustment rather than a filter. The filter in the name refers to those actual photographic filters that you screw onto the end of a lens. This adjustment is a great way to correct problems with temperature in an image — the perceived warmth or coldness of an image. When the camera takes a picture under unexpected lighting conditions, a color problem is apparent. (Say, for example, that the camera is set to Daylight when shooting indoors.) When an image is too blue, it's too cool; conversely, an image that's orangey is too warm. (Remember that these are perceptual evaluations — blue light is technically hotter than yellow or red light.)

In Photo Filter, you select a preset filter from a pop-up menu or select a color of your choice. As you can see in Figure 6-12, both preset filters and custom colors can be effective in neutralizing a color cast. (You could, of course, also use these filters to add a color cast . . . if you wanted to, that is.)

Designed to repair a defective channel in an image, Channel Mixer lets you use sliders to replace some or all of the intensity of one color channel with content from the others. Should you come across an image with damage in one channel, you can certainly use the Channel Mixer adjustment to work on it (with some degree of success). You reduce the value of the target channel by dragging the slider to the left. You then drag one or both of the other sliders toward the right. Generally speaking, you want to add an amount (combined between the two other channels) just about equal to what you subtract from the target channel.

Figure 6-12. Neutralize a color cast with a filter of the opposite color in Photo Filter.

More creative than corrective, the Invert command (no dialog box) simply reverses the colors in your image or the selected area. Although inverting areas of an image (like desaturating) can draw attention to the subject of the image, it's an edgier technique and generally requires touch-up after inverting. You'll find that any specular highlight — a pure-white area (mainly reflections) — becomes a distracting black spot.

The Posterize command forces your image's broad range of colors into a few selected colors (as shown in Figure 6-13). You automatically get black and white, and then a limited number of additional colors, based on the content of the original. You pick the number of colors that you want to use, and Photoshop picks which colors to use. You can use as few as two colors (plus black and white) or as many as 255, which pretty much gives you your original image. Posterize can create a rather pleasing rendering of a photo with very few colors.

Threshold converts each pixel to either black or white (no colors, no grays). You adjust the border between black and white with a slider or by entering a value in the Threshold Level box. For an eye-catching special effect, open a color image and make a selection of the background (or the subject!) and apply Threshold, mixing color and black and white.

Figure 6-13. Reduce colors with Posterize for a special effect.

Again, more creative than corrective, the Gradient Map feature re-creates your image by using a gradient. The leftmost color stop (the anchor points where a gradient color is assigned) in the gradient is mapped to the shadows, the right-most to the highlights, and any color stops in between are appropriately assigned to the rest of the tonal range. In Figure 6-14, you can see how a two-color gradient (upper left) lacks detail compared with the four-color gradient being created for the lower image.

Generally speaking, you use darker colors for the color stops on the left and lighter colors for the color stops on the right (although you can create extremely interesting effects by mixing things up). Using a black-to-white gradient produces a grayscale image.

To edit the gradient, simply click directly on the sample gradient in the Gradient Map dialog box. Click to add color stops, drag to move color stops, and click the color swatch near the bottom to change the color of the selected stop. (You can find more detailed information on creating and working with gradients in Chapter 14.)

Figure 6-14. Using more colors in your gradient produces more detail.

Although designed to help you compensate for the vagaries of printing presses, Selective Color can do other great things for you! The command's dialog box, shown in Figure 6-15, has a pop-up menu that offers the six basic colors of Photoshop, as well as Whites, Neutrals, and Blacks. You select which range of colors to adjust and then drag the sliders. You can work on one set of colors, switch to another and make adjustments, switch to another, and so on without having to click OK in between. For example, you can adjust the reds in the image and leave the blues untouched, or you can adjust the reds and then tweak the blues without having to exit the dialog box.

When you have reasonably small adjustments to make, select the Relative radio button at the bottom. If you have substantial changes — rather radical alterations — select the Absolute radio button.

Figure 6-15. Tweaking the Neutrals can adjust the overall appearance of an image.

The Shadow/Highlight adjustment is discussed at length in Chapter 5 as a tonal-correction tool, the job for which it was designed. However, keep in mind that the Shadow/Highlight dialog box also includes the Color Correction slider. After you lighten shadows or tone down highlights, you can increase or decrease the saturation of the colors in the adjusted areas of your image with the Color Correction slider.

Variations is a semi-automated way to make adjustments to your image's color and tonal range. It's discussed in detail later in this chapter.

The Photoshop Desaturate command creates a grayscale representation of a color image without changing the color mode. However, with no dialog box or adjustments, it doesn't offer the control you get by using Black & White.

Now this is a feature to savor! There you are, adding Cousin Joe to the family reunion photo because he wasn't bailed out in time, and you see that the lighting is all kinds of different and he sticks out like a sore thumb (or bum). Or you return from a major shoot only to find that something wasn't set correctly in the camera, and all your images have a nasty color cast.

Match Color lets you adjust one image to another (and you can even use selections to identify areas to adjust or areas of the images to use as the basis for adjustment), but keep in mind that you get better results with images that are already rather similar. You can also fix one shot and use that shot as a standard by which others are corrected. (Like most image adjustments, you can record a change in an Action and use Photoshop's Batch command to apply that adjustment to a series of images. Read more about Actions in Chapter 16.) Take a look at Figure 6-16 to see the Match Color dialog box.

Figure 6-16. The small image to the upper-right shows the results of using Match Color.

Because the Match Color dialog box is such a powerful tool, it's worth taking at look at what's going on there:

In Figure 6-16, an area of water is selected in the target image and a comparable area of water is selected in the source image. (The selection in the source image is visible in Figure 6-16 for illustrative purposes only — a selection in an inactive image window isn't normally visible.) With the two selections, I tell Match Color to adjust the target image based on the difference between the water color in the two images. Using selections prevents any skewing of the adjustment that would be caused by the colors in the sail (source image) and the trees (target image). But with the Ignore Selection When Applying Adjustment check box enabled as well, I make sure the entire target image is adjusted, not just the areas within the selection.

Sort of a cross between the Select

The Replace Color dialog box, as shown in Figure 6-17, has two separate parts: Selection and Replacement. Click with the left eyedropper in either the preview area or in the image windows and adjust the Fuzziness slider (how much variation counts as "selected") to make your initial selection. Use the middle eyedropper to add colors or shades of your initial color, and use the right eyedropper to subtract from the selection. Choose only variations of one color. Then drag those Hue, Saturation, and Lightness sliders in the Replacement section of the dialog box to produce your new look.

Figure 6-17. Make a selection and change the selection's hue, saturation, and lightness.

When you select the Equalize adjustment, Photoshop finds the darkest pixel in the image and maps it to black, maps the lightest pixel to white, and distributes the rest of the tonal values between. You can pretty much skip Equalize — use Auto Color instead.