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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 even so, the eraser remains more memory-efficient than a layer mask.) With the speed and power of most modern computers, though, this is hardly the issue that it once was. Erasing with the pencil: When you work with the pencil tool not the Pencil mode but the actual pencil tool Photoshop presents you with an Auto Erase check box in the Options bar. Turn it on to draw in the background color any time you click or drag on a pixel that is already 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 once called the Auto Erase check box their "ode to Fatbits," from the ancient MacPaint zoom function.Note Unlike the eraser, the pencil tool always draws either in the foreground or background color, even when used on a layer.
Erasing to history: Press Alt (Option on the Mac) as you drag with the eraser to paint with the source state identified by the history brush icon in the History palette. It's like scraping away the paint laid down by the operations following the source state. For example, in Figure 7-28, I used the rectangular marquee tool along with the eraser to paint a frame around a frame job inside this picture of a picture window. I began by creating a new layer and then selecting various rectangular areas and filling them with black or gray. In the second image, I selected a few more areas and filled them with white. At this point, however, I decided the white was too garish and elected to erase portions of it using history. I clicked in front of the last state before I added the white to make it the source state. Then I pressed Alt (or Option) and painted with the eraser to erase through the white rectangles while leaving the black and gray rectangles unchanged.
Figure 7-28: I created a geometric frame by selecting areas with the rectangular marquee tool and filling them with black or gray (left). Then I added a series of white rectangles (middle). By identifying the state just before the first white rectangle as the source state, I was then able to use the history eraser function to erase away the white and leave the black and gray unharmed.
Instead of pressing Alt, you can select the Erase to History check box in the Options bar. In this case,
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Part II: Painting and Retouching
dragging with the eraser reverts and Alt-dragging (Option-dragging on the Mac) paints in the background color or erases the active layer.Note
In the old days, folks used the term "magic eraser" to mean the eraser set to the revert mode. But when Photoshop 5.5 introduced the official magic eraser, which deletes a range of similarly colored pixels each time you click in the image window (see Chapter 9), this use of the term died away. So the old magic eraser is the modern history eraser don't you dare get the two confused.The history brush Painting with the history brush tool which you can select from the keyboard by pressing the Y key is like painting with the eraser when Erase to History is turned on. Just drag with the history brush to selectively revert to the source state targeted in the History palette. You also can vary the translucency of your strokes using the Opacity setting in the Options bar. But that's where the similarities end. Unlike the part-time history eraser, the dedicated history brush lets you take advantage of brush modes. By choosing a different brush mode from the Mode pop-up menu in the Options bar, you can mix pixels from the changed and saved images to achieve interesting, and sometimes surprising, effects.
I advise you to get in the habit of using the history brush instead of using the eraser's Erase to History function. Granted, with Pencil and Block, the eraser offers more styles. But when weighed against brush modes, these styles aren't much of an advantage. The history brush is also more intuitive because its icon matches the source state icon in the History palette.Tip
As you play with the history brush, keep in mind that you don't have to limit yourself to painting into the past. Just as the History palette lets you skip back and forth along the train track of time, the history brush lets you paint to any point in time. The following steps provide an example of how you can use the History palette to establish an alternative reality and then follow up with the history brush to merge that reality with the present. It can be a lot to keep track of, but I'm confident that with a little effort, you can give that post-modern brain of yours a half twist and wrap it around these steps like a big, mushy Mobius strip.STEPS: Brushing to a Parallel Time Line