Читать книгу Adobe Photoshop CC For Dummies - Peter Bauer - Страница 20

Here’s one major difference between Photoshop and other programs. Almost all programs have some form of Undo, enabling you to reverse the most recent command or action (or mistake). Photoshop also has, however, a great feature that lets you partially undo. The History Brush tool can 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 panel (where you select the state to which you want to revert) holds only a limited number of history states. In the Photoshop Preferences ⇒ Performance pane, you can 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 50 history states is good for most projects, but when using painting tools or other procedures that involve lots of repetitive steps (such as touching up with the Dodge, Burn, or Clone Stamp tools), a larger number (perhaps as high as 200) 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, the Image ⇒ Crop command, or the Image Size or Canvas Size commands (both in the Image menu), you cannot revert to prior steps with the History Brush tool. You can choose as a source any history state that comes after the image’s pixel dimensions change but none that come before.

Here’s one example of using the History Brush as a creative tool. You open a copy of a photograph in Photoshop. You edit as necessary. You use the Black & White adjustment on the image to make it appear to be grayscale. In the History panel, you click in the left column next to a snapshot (a saved history state) or the step prior to Black & White to designate that as the source state, the appearance of the image to which you want to revert. You select the History Brush tool and paint over specific areas of the image to return them to the original (color) appearance (see Figure 1-5). There you have it — a grayscale image with areas of color, compliments of the History Brush tool!

FIGURE 1-5: Painting to undo with the History Brush, with the original in the upper-right.

Photoshop has another very powerful partial Undo in the Fade command. Found in the Edit menu, Fade can be used immediately after just about any tool or adjustment or filter or, well, almost anything that changes the appearance of the image. (You can even fade the History Brush tool.) The Fade command enables you to change the opacity, blending mode, or both of whatever alteration you most recently made to the appearance of your artwork with tools or commands. You might, for example, use a Sharpen filter and then use the Fade command to change the filter’s blending mode to Luminosity. That’s the functional equivalent of sharpening the L channel in Lab color mode without having to switch color modes at all. Keep in mind that when I use the word immediately, I really mean it — you can’t even use the Save command between applying a filter and using the Fade command.