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Photoshop

New Images

Undoing Changes

There are a number of ways to undo your editing changes if you make a mistake or change your mind. Photoshop has Undo and Redo commands as well as a Revert command that will return you to the last saved version of your document. It also has a powerful History palette that allows for multiple undos and lets you take 'snapshots' of an image at a moment in time to which you can return during your editing session.

Undo and Redo Commands

In addition to these two commands there are also the Step Backward and Step Forward commands, all found in the Edit menu.

Undo

The Undo command will undo the last operation performed. The keyboard shortcut is Ctrl-Z (Cmd-Z). When displayed in the Edit menu, the command will be followed by the name of the last tool or command used; e.g., Undo Brush or Undo Crop.

Redo

The Redo command is only available after the Undo command has been used and will replace it in the Edit menu. Redo will reapply the action that was just undone. Its keyboard shortcut is also Ctrl-Z (Cmd-Z); therefore, the shortcut toggles between Undo and Redo. Like the Undo command, it will be displayed in the Edit menu along with the name of the tool or command action that was just undone using the Undo command.

Step Backward

This is similar to Undo except that it lets you continue to move backwards through multiple editing changes, undoing one at a time. The keyboard shortcut is Alt-Ctrl-Z (Option-Cmd-Z).

Step Forward

This is similar to Redo except that it lets you continue to move forward through multiple undone changes, redoing them one at a time. The keyboard shortcut is Shift-Ctrl-Z (Shift-Cmd-Z).

Revert

This command is used to restore an image back to the state it was in when it was last saved. To apply it, go to File > Revert. This command can be undone.

History Palette

By default, Photoshop stores the 20 most recent editing changes (called states) in memory. This is called the image's history. The Undo, Redo, Step Backward and Step Forward commands all access this history to perform their functions. The History palette displays a list of the states in the history and lets you perform multiple Undos and Redos with a single click as well as delete a particular state without undoing any other states.

When more than 20 states have been recorded in the history, older states are deleted. You can change the number of states that are stored in the General Preferences. Keep in mind that an image's history only exists during the current editing session. Once you close the document, the history is deleted.

If the palette group containing the History palette is already displayed, click on the History tab to bring it to the front; otherwise, open the palette by going to Window > Show History. Assuming that you still have Cat.psd open from the previous lecture, your History palette should look like the one shown here. In the top row, a thumbnail of the image is displayed. This is the snapshot. The image states are listed underneath the snapshot with the earliest state at the top of the list.

The States

Our cat image has four states: the Open command and three Image Size commands. You can revert to any state by clicking on it in the list. When you do this, the states underneath become greyed out, taking all changes away except the one that was selected. Click once on the Open state. All of the resizing you did has been undone, leaving you with the original image. Click on the last Image Size state in the palette. All of the states have been reapplied to the image.

The Snapshot

The thumbnail that appears in the History palette represents a snapshot of that image at a particular moment in time. When an image is opened or first created, a snapshot is generated automatically. You can create new snapshots for reference at any time and you may return to any one of them at any given time. To return to a specific snapshot, simply click once on the thumbnail. This is a powerful feature that can provide a level of security if you wish to experiment with an image but need to be able to return to a pre-defined snapshot of the image. It's also handy in case you've exceeded the 20 levels of Undo but need to go further back in the history to a state no longer in the history list. For our cat image we have a snapshot of the original image. Let's experiment with this a little.

1. Try clicking on the snapshot. All of the states, including the Open state, will become greyed out and the cat image will return to its original appearance.
2. Click on the second Image Size state.
3. Click on the Create New Snapshot button at the bottom of the History palette. Now your palette should look like this:

4. A second snapshot has been inserted below the first one and has been given the name Snapshot 1. Double-click on the snapshot name and the Rename Snapshot dialog will open. Type Resize as the new name and click OK.
5. Click on the last Image Size state. Even though you reverted to a previous state to create the snapshot, you can still return to a later state.
6. There is a slider control to the left of the states. Try dragging it up and down the list. This is an alternate way of moving back and forth between states. When the state area of the palette is active, the slider appears there. When the snapshot area is active, the slider appears there. Drag the slider to the first Image Size state on the history list.
7. Select the Brush tool and paint a scribble in your image with it. It's located in the second column of the Toolbox, the fourth tool down.

Your History palette should now look like this. Notice that the Brush state has overwritten the last two Image Size states. Once you return to an earlier state in the history, a new change will replace all states that came after the state you returned to. Also, the snapshot that was taken of one of the replaced states is still available, allowing you to return to that state even though it no longer appears in the list of states.

8. Use the Undo command to undo the Brush state.

If you look at the History palette now, you'll see that not only has the Brush action been undone, the states that it had replaced have reappeared in the palette!

History Palette Options

The History palette menu has some important options that can be configured to assist in managing the various states of your image.

Step Forward

This does the same thing as the command in the Edit menu. It moves forward to the next state in the history.

Step Backward

This takes you back to the previous state in the history.

New Snapshot

Using this command instead of clicking on the Create New Snapshot button will present you with some options before creating a snapshot. The New Snapshot dialog will open, allowing you to assign a name to the snapshot. You can also determine what content should be included in the snapshot. The choices are:

• Full Document: Includes all layers separately in the image
• Merged Layers: Stores the image with its layers merged (flattened)
• Current Layer: Includes the current layer only

Delete

Deletes a snapshot or a state and those that followed it after prompting you if you're sure. This option can be undone. An alternate method for deleting a state or snapshot is:

• Select a state or snapshot and click on the trashcan icon at the bottom of the History palette.
• Drag a state and release it over the trashcan icon.

Clear History

Removes all states from the History palette without changing the image. This operation can be undone.

New Document

Creates a new image document based on the currently selected state or snapshot. Alternate methods are:

• Select a state or snapshot and click the New Document button.
• Drag a state or snapshot and release it over the New Document button.
• Drag a state or snapshot into another image window to copy the state or snapshot into that document.

History Options

Selecting this command from the History palette menu opens the History Options dialog that contains the following items:

Automatically Create First Snapshot

With this option checked, Photoshop will automatically take a snapshot of the image before any modifications have taken place, meaning that you can restore the image to its original form at any time.

Automatically Create First Snapshot When Saving

Photoshop will automatically take a snapshot of the image when you select File > Save (or Save As) so that you may revert to any of a multitude of snapshots when working with a particular image.

Allow Non-Linear History

As you add states to an image, they relate to each other. By undoing one, the rest below it become greyed out. Selecting Allow Non-Linear History allows the relationship to break, giving you the option to remove one state without affecting the others. Related states will be grouped together in the History palette, separated from other groups by a black dividing line.

Show New Snapshot Dialog By Default

Forces Photoshop to prompt you for snapshot names even when using Create New Snapshot button on the palette.

Purge

This command frees up memory used by the Undo command, the History palette or the clipboard. It is useful when the buffer is so full that the performance of Photoshop is noticeably affected. Since purging can't be undone, be cautious using it. When you select Edit > Purge there are four options to choose from in the submenu:

Undo

Purges the last Undo from memory. Once purged, the Redo option isn't available and Can't Undo will be displayed in a dimmed state in the Edit menu.

Clipboard

Removes information from the computer's clipboard.

Histories

The history states in all open documents are deleted and removed from memory. The image won't change and snapshots are unaffected. To clear only the history from the active document, hold down the Alt (Option) key and choose Clear History from the History palette's option menu.

All

Purges the last Undo, the clipboard and the history states in all open documents.

Duplicate

This command lets you create a copy of the active image with its separate layers, masks and channels intact. To access this command, go to Image > Duplicate and the Duplicate Image dialog will appear.

• The name of the image you are copying is displayed: e.g., Duplicate: Cat.psd. You can enter a new file name in the As field or accept the name assigned by Photoshop: e.g., Cat copy.
• If you don't need to retain separate layers, you can disable the Duplicate Merged Layers Only check box. (Since there is only a single layer in this document, this option will be greyed out.)

To duplicate the image and bypass the Image > Duplicate and the Duplicate Image dialog, hold down the Alt (Option) key while choosing the command from the Image menu. The word "copy" will be appended to the original file name and any layers will remain intact in the duplicate image.

Closing Documents

You can close one image document at a time or close all open documents with a single command. If there are changes you've made and not saved, you'll be prompted if you want to save them before closing the document(s). If you change your mind about closing, choose the Cancel button from the prompt message. Otherwise, choose the Save or Don't Save buttons.

Close

Located in the File menu, this command will close the active document window. The keyboard shortcut is Ctrl-W (Cmd-W).

Close All

To close all open documents, go to File > Close All or use the keyboard shortcut Shift-Ctrl-W (Shift-Cmd-W).

Undoing Changes Summary

• The Undo command reverses the last editing change in the active document.
• Redo will reapply a change reversed by Undo.
• Step Backward is like Undo except you can continue using this command to move backwards through the history one step at a time.
• Step Forward is similar to Redo but it lets you redo multiple editing changes that were reversed using the History palette.
• The History palette is Photoshop's Undo manager. It provides for multiple levels of Undo.
• Every change made to an image is recorded in the History palette as a state. You can return to an earlier or later state by clicking on its entry in the palette.
• A snapshot records the state of an image at a moment in time. It is represented by a thumbnail image in the History palette. Clicking on a snapshot will cause your image to revert to the state it was in when the snapshot was taken.
• You can store multiple snapshots in the History palette.
• The History palette has options that let you manage aspects of snapshots and states.
• An image's history is deleted once the image file is closed.
• The Revert command restores an image to the way it was during the last save.
• The Purge command frees up memory used by the Undo command, the History palette or the clipboard.
• Documents can be closed individually or you can close all open documents at once.

Undoing Changes Keyboard Shortcuts:

• Undo/Redo: Ctrl-Z (Cmd-Z)
• Step Backward: Alt-Ctrl-Z (Option-Cmd-Z)
• Step Forward: Shift-Ctrl-Z (Shift-Cmd-Z)
• Close active document: Ctrl-W (Cmd-W)
• Close all open documents: Shift-Ctrl-W (Shift-Cmd-W)

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Photoshop - TOC - Introduction - Books -
New Images - Links - Questions - Quiz -
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Photoshop - TOC - Introduction - Books -
New Images - Links - Questions - Quiz -
1 - 2 - 3 - 4 - 5 - 6 - [ 7 ] - 8 -