Found in the same toolbox flyout as the eyedropper, the color sampler tool looks like the eyedropper with a little crosshair target. But where the eyedropper lifts foreground and background colors, the color sampler merely measures the colors of pixels so that you can monitor how the pixels react to various color changes.
Select the color sampler and click somewhere inside the image window. Photoshop adds a crosshair target to indicate the point you clicked. The program also brings up the Info palette (if it isn't up already) and adds a new color measurement item labeled #1. This item corresponds to the target in the image, which is likewise labeled #1. Click again and you add a second target and a corresponding item #2 in the Info palette. You can add up to four targets to an image, as demonstrated in Figure 4-14.
The color sampler is primarily intended for printers and technicians who want to monitor the effects of color corrections on specific points in an image. If you apply Image ^ Adjust ^ Levels, for example, Photoshop constantly updates the items in the Info palette to reflect your changes (as I explain in more detail in Chapter 17). But you can also sample points in an image to monitor the effects of filters (Chapters 10 and 11, as well as Chapter A on the CD-ROM), blend modes (Chapter 13), and edit tools such as dodge and burn (Chapter 5). The color sampler is just another way to monitor changes to an image.
Here are a few more techniques of interest when color sampling:
♦ Photoshop limits you to four color targets. If you try to create a fifth one, the program generates an error message. If you want to measure a different point in the image, you can either hover your cursor over the point and note the top set of color values in the Info palette (as in Figure 4-14) or move one of the targets.
♦ To move a target inside the image window, drag it with the color sampler tool. You can also move a target by Ctrl-dragging it with the eyedropper tool.
♦ The Info palette grows to more than twice its normal size when you start clicking with the color sampler. To hide the sampler information without deleting targets, click the Info palette's collapse box or choose Hide Color Samplers from the palette menu. If you go the second route, you have to choose Show Color Samplers to bring the samples back.
♦ By default, the sampler items in the Info palette measure colors in the active color space. If you want to track a target in a different color space, click the item's eyedropper icon in the Info palette or right-click the target in the image window. Either way, you get a pop-up menu of color space alternatives, including Grayscale, RGB, and several others that you may recall from previous explanations in this chapter.
Tip To select the color sampler, press Shift+I when the eyedropper is active or Alt click the eyedropper icon. Or press I repeatedly to cycle between the eyedropper, color sampler, and measure tool (add Shift if you activated the Use Shift Key for Tool Switch option in the Preferences dialog box). You can also temporarily access the color sampler any time the eyedropper is active by pressing Shift. This little trick also works when a color correction dialog box such as Levels or Curves is open, as explained in Chapter 17. It's just the ticket when you're in the middle of an adjustment and you need to know how it's affecting specific portions of the image.
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