If you haven't used Photoshop's Eraser tool much, you may think it's a tool for, well, erasing things. But, in fact, the Eraser's purpose is more subtle. It's best used to isolate images from their backgrounds, an essential technique for building image collages.

This month we introduce the Eraser tool and focus on using the Background Eraser to remove an unwanted background. Then we'll show you how to use that isolated image to create a collage.

To begin, open the sample photograph of a zebra that comes with Photoshop. Find it on your computer at this location: C:/PROGRAM FILES/ADOBE/PHOTOSHOP 6.0/SAMPLES/Zebra.psd. Save it as Zebra.jpg to back it up. You'll work with this file.

Next, go to Window and select Show Tools and then Show Layers. In the Layers menu, right-click the Background layer and select Duplicate Layer. Click OK. Click and drag the original Background layer to the trash can in the Layers menu. This important step unlocks image settings.

Introducing The Eraser

Click the Eraser tool, which looks like a rectangular block. Under the main menu bar you'll see settings. Here's where you define Eraser mode (Paintbrush, Airbrush, Pencil, or Block) and brush size. Opacity determines how thoroughly you wish to erase. For example, 100% opacity erases the entire image, whereas 25% opacity renders the image semi-translucent. Wipe the Eraser tool over the zebra image now. Try different modes and brush sizes. To undo your experiments, click the Erase to History box and wipe over the image again.

Erase Backgrounds

There are various ways to turn a background transparent, but our favorite method uses the Background Eraser tool. It works best when there is good contrast between the image and the background, as we have with the zebra.

Hold the mouse down on the Eraser tool and select the Background Eraser. Select a soft-edged brush for erasing around fuzzy edges, such as the zebra's mane. (We chose number 17.) For Limits, select Find Edges. Set Tolerance to 50%. Low tolerance erases colors very similar to those found in the center or "hot spot" of the Eraser tool. High tolerance erases a wider range of colors.

For the Sampling option, select Continuous. The option to protect foreground color makes it more difficult to accidentally erase a uniformly colored edge. Because our zebra is striped, we leave this option unchecked.

The task is easier with a close-up view. Select the Magnifier tool. Click the image to enlarge it 200%. Reselect the Background Eraser. Now, carefully run the Eraser brush around the edge of the zebra. Watch the placement of the cross-hair mark at the center of the brush; it controls the colors you erase.

Don't try to outline the zebra in a single stroke. That way if you make a mistake and need to select Edit/Undo, you won't undo all your work. Also, remember that you can change brushes or settings at any time. You'll need a small brush and a steady hand to erase around the zebra's whiskers.

To return the image to its original size, reselect the Magnifier, hold down the CTRL key, and click the image again.

Select, Copy & Paste

Once you've erased around the image, you can select it, copy it, and paste it into another Photoshop file. Click the Polygonal Lasso tool. Draw a rough outline around the zebra, making sure your line stays within the transparent perimeter of the zebra image. To close the selection, click the original starting point. A small circle will appear next to the tool when you hold the cursor over the correct spot.

Once you've selected the zebra, use the Copy command found in the Edit menu. Next, select File, New to open a new file. When prompted, specify that the new file have a transparent background. Finally, paste the selection into a new file.

Layer Images

Here's the fun part. Working in the new file, click the New Layer icon at the bottom right of the Layers window. Click the Edit menu and select Paste. Voila! It's a pair of zebras. Use the Move tool (the arrow-and-cross icon in the toolbar) to place the new zebra strategically. If you like, create another layer and paste in a third zebra.