Photoshop's incredible selective Undo

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Here is one major difference between Photoshop and other programs you use. Almost all programs have some form of Undo, enabling you to reverse the most recent command or action (or mistake). Like many programs, Photoshop uses the ^+Z/Ctrl+Z shortcut for Undo/Redo (but remember that you can change the shortcut, as described in Chapter 3). Photoshop also has, however, a couple of great features that let you partially undo.

Painting to undo with the History Brush

You can use the Photoshop History Brush to partially undo just about any filter, adjustment, or tool by painting. You select the History Brush, choose a history state (a stage in the image development) to which you want to revert, and then paint over areas of the image that you want to change back to the earlier state.

You can undo as far back in the editing process as you want, with a couple of limitations: The History palette (where you select the state to which you want to revert) holds only a limited number of history states. In the Photoshop PreferencesOGeneral pane, you specify how many states you want Photoshop to remember (to a maximum of 1,000). Keep in mind that storing lots of history states takes up computer memory that you might need for processing filters and adjustments. That can slow things down. The default of 20 history states is good for most projects, but when using painting tools or other procedures that involve lots of repetitive steps, a larger number (perhaps as many as 60) is generally a better idea.

The second limitation is pixel dimensions. If you make changes to the image's actual size (in pixels) with the Crop tool or the Image Size or Canvas Size commands, you cannot revert to prior steps with the History Brush. You can choose as a source any history state that comes after the image's pixel dimensions changed but none that come before.

Here's one example of using the History Brush as a creative tool. You open a photograph in Photoshop. You desaturate the image to make it appear to be grayscale, which gives it the appearance of a black-and-white photo. In the History palette, you click in the left column next to the Open step to designate that as the source state, the appearance of the image to which you want to revert. You select the History Brush and paint over your eyes, lips, and hair, restoring them to the original (color) appearance (see Figure 1-11). There you have it — a grayscale image with a couple of areas of color, compliments of the History Brush!

Reducing to undo with the Fade command

Immediately after applying a filter or adjustment or using most of Photoshop's tools, you can choose the EditOFade command and change the opacity or blending mode with which the previous step was performed. You might, for example, apply a sharpening filter and then use the EditO

Fade Unsharp Mask command to change the blending mode from Normal to Luminosity. (Sharpening only the luminosity of your image, whether with this technique or in the L*a*b color mode, prevents unwanted color shifts along edges in your images. Color modes are discussed in Chapter 6.) Or you might apply the Motion Blur filter and then use EditOFade Motion Blur (yes, the Figure 1-12: Compare the original blur with a reduction using the name of the command Fade command.

choose as a source any history state that comes after the image's pixel dimensions changed but none that come before.

©2002 PhotoSpin, PhotoSpin image #0770118

Figure 1-11: Painting to undo with the History Brush.

©2002 PhotoSpin, PhotoSpin image #0770118

Figure 1-11: Painting to undo with the History Brush.

actually changes for you) to reduce the opacity of the blur to 75%. That gives you the appearance of a back-and-forth motion while leaving the subject recognizable (see Figure 1-12).

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