When you work with the eraser, you can select from four eraser styles: Paintbrush, Airbrush, Pencil, and Block. Block is the old 16 x 16-pixel square eraser that's great for hard-edged touch-ups. The other options work exactly like the tools for which they're named.
In earlier versions of Photoshop, pressing E cycled you through the eraser styles. That shortcut now cycles through the eraser, magic eraser, and background eraser, all of which share a flyout menu and keyboard shortcut (E) in Version 6. You now must select the eraser style from the Mode pop-up menu on the Options bar, as shown in Figure 7-28 (press Enter with the eraser selected in the toolbox to display the bar).
In addition to four styles, the Options bar provides the Brush palette, the Opacity control, and the Brush Dynamics palette, all of which work as described in Chapter 5. When the Paintbrush option is active, you even have access to the Wet Edges check box, also covered in Chapter 5. The only thing you can't do is choose a brush mode (Normal, Overlay, Darken, Lighten, and so on) — although, as I mentioned a little while ago, you can apply the Fade command after the fact to fade and blend your eraser strokes.
Although the eraser is pretty straightforward, there's no sense in leaving any stone unturned. So here's everything you ever wanted to know about the art of erasing:
* Erasing on a layer: When you're working on the Background layer, the eraser merely paints in the background color. Big whoop. What distinguishes the eraser tool from the other brushes is layers. If you drag on a layer and deselect the Lock check boxes for transparency and image pixels in the Layers palette, the eraser tool removes paint and exposes portions of the underlying image. The eraser tool suddenly performs like a real eraser.
If you select the transparency Lock check box in the Layers palette, Photoshop won't let the eraser bore holes in the layer or alter areas that are already transparent. Instead, the eraser can paint opaque pixels with the background color. If you select the check box for locking image pixels, you can't erase or paint any part of the layer. For more information on the check boxes in the Layers palette, read Chapter 12.
* Erasing lightly: Change the Opacity setting on the Options bar to make portions of a layer translucent in inverse proportion to the Opacity value. For example, if you set the Opacity to 90 percent, you remove 90 percent of the opacity from the layer and, therefore, leave 10 percent of the opacity behind. The result is a nearly transparent stroke through the layer.
* Erasing versus using layer masks: As described in the "Creating layer-specific masks" section of Chapter 12, you can also erase holes in a layer using a layer mask. But unlike the eraser—which eliminates pixels for good — a layer mask doesn't do any permanent damage. On the other hand, using the eraser tool doesn't increase the size of your image as much as a layer mask does. (You can argue that any operation — even a deletion — increases the size of the image in RAM because the History palette has to track it. But the eraser is still more memory-efficient than a layer mask.) So it's a trade-off.
* Erasing with the pencil: When you work with the pencil tool and select the Auto Erase check box on the Options bar, you draw in the background color any time you click or drag a pixel colored in the foreground color. This technique can be useful when you're drawing a line against a plain background. Set the foreground color to the color of the line; set the background color to the color of the background. Then use the pencil tool to draw and erase the line until you get it just right. I use this feature all the time when preparing screen shots. Adobe engineers call the Auto Erase check box their "ode to Fatbits," from the ancient MacPaint zoom function.
Like the eraser, the pencil tool is affected by the Lock check boxes in the Layers palette. Unlike the eraser, the pencil always draws either in the foreground or background color, even when used on a layer.
* Erasing to history: Press Alt as you drag with the eraser to paint with the source state identified by the history brush icon in the History palette. (By default, Photoshop sets the source state to the image as it appeared when first opened.) It's like scraping away the paint laid down by the operations following the source state, as demonstrated quite graphically in Figure 7-29.
Alternatively, you can select the Erase to History check box on the Options bar. In this case, dragging with the eraser reverts and Alt-dragging paints in the background color.
Note Many people use the term "magic eraser" to refer to the eraser set in revert mode. But Photoshop 5.5 introduced an official magic eraser, which erases background pixels instead of erasing to history. So be careful not to get the two confused.
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