Using Photoshop s Time Machine


The history of a Photoshop image is simply a record of work that has been performed on it. Photoshop automatically records every edit, operation, or technique that you apply to an image. As you work, each event, called a state ”whether it s a paint stroke, filter, color correction, or any other operation ”is listed in the History palette (see Figure 11.1). You can target a specific state on the list and display its contents in the image window. Like riding in an H.G. Wells time machine, you can freely move through the history of the document, alter states, and in so doing affect the outcome of the final image.

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Figure 11.1: The opening History palette and menu: no changes have been applied to the image yet.
New  

The History states are not layers . They do not contain isolated parts of the image per se. Rather, each state is a record of how the image looked after a specific tool or operation was applied to it. The history is exclusively a record of the changes to the image during the current work session. After the image is closed, the history is wiped clean, and when you reopen the document, the history begins again. The history cannot be saved or transferred to another image. However, Photoshop CS has a new feature that enables you to record your history as metadata (information embedded in the file) or as a text file (see the General Preferences section in Chapter 5, Setting Up Photoshop, for more on the History log). Program changes to preferences, palettes, color settings, and Actions are not recorded.

Working with the History Palette

The recorder for all the states is the History palette, which you access by choosing Window History. By default, when the image is opened, the History palette displays a snapshot of the image as it appeared when it was last saved. It is from this point on where you will make changes to the image. Each time you perform an operation, the History palette produces a state with the name of the operation or tool that was used ” for example, Brush Tool, Levels, Smudge Tool, and so forth. The most recent state is at the bottom of the History stack; note that in Figure 11.2, the act of opening the document appears at the top. The higher the state appears in the stack, the earlier in the process the state was created.


Figure 11.2: The History palette after a few operations

Changing History

They say you can t change history, but in Photoshop you can. If you want to move backward in time and see a previous state, click it in the History palette. The image window will display the image as it was during the targeted state. All states below it in the History palette are grayed out.

Note  

Be careful! If you work on the image with a state targeted earlier than the most recent, all states below it will be deleted. You can still use the Undo and Step Backward features to get back to where you were, but you would lose all your new work.

For example, if you paint a brush stroke with the Brush tool while an earlier state is targeted, all states below it will be replaced by the state called Brush Tool. Later I ll show you how to avoid this by using the Allow Non-Linear History option.

Increasing History States

What enables Photoshop to remember all the History states is, of course, memory. Each state is stored in your computer s RAM or on the scratch disk. When you exceed the current limit on states, the oldest state is deleted to make room for the most recent state. The number of History states is limited to 20 by default. You can increase or decrease the default number of History states by choosing Edit Preferences General History States and entering a number from 1 to 1000.

Specifying an excessive number of History states earmarks memory for the History cache and takes the allocation away from Photoshop s other operations. This could compromise Photoshop s performance. Whenever possible, keep the number of states at the default.




Photoshop CS Savvy
Photoshop CS Savvy
ISBN: 078214280X
EAN: 2147483647
Year: 2004
Pages: 355

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