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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 panel 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. We'll also cover a few miscellaneous topics: using the Purge command, duplicating images, and closing documents.

Undo and Redo Commands

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

Undo

The Undo command will reverse 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 Tool or Undo Image Size.

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).

History Panel

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 panel 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.

Practice Exercise: History Panel

If the panel group containing the History panel is already displayed, click on the History tab to bring it to the front; otherwise, open the panel by going to Window > History. Assuming that you still have Cat.psd open from the previous lecture, your History panel should look like the one shown here. In the top row, a thumbnail of the image is displayed. This is the snapshot. To the left of it is the History Brush tool icon. We'll cover that function in a later lecture. 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.

1. Click once on the Open state. All of the resizing you did has been undone, leaving you with the original image.
2. Click on the last Image Size state in the panel. All of the states have been reapplied to the image.
   

The Snapshot

The thumbnail that appears in the History panel 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.

3. 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.
4. Click on the second Image Size state.
5. Click on the Create New Snapshot button at the bottom of the History panel. Now your panel should look like the one at the right. A second snapshot has been inserted below the first one and has been given the name "Snapshot 1".
   
6. Double-click on the snapshot name and it will become editable. Type Resize as the new name and click OK.
7. 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.
8. 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 panel 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.
9. Select the Brush tool and paint a scribble in your image with it. If you don't see it in the Toolbox, use the keyboard shortcut B to activate the tool.

Your History panel should now look like this. Notice that the Brush Tool 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.

10. Use the Undo command to undo the Brush Tool state.

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

Keep your cat image open. We'll resume the exercise after we review a few more commands.

History Panel Options

The History panel 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 Delete button (trashcan icon) at the bottom of the History panel.
• Drag a state and release it over the Delete button.

Clear History

Removes all states from the History panel 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 Create a New Document From Current State button.
• Drag a state or snapshot and release it over the Create a New Document From Current State 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 panel 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. This is enabled by default.

Automatically Create New Snapshot When Saving

When this is enabled, Photoshop will automatically take a snapshot of the image each time you use the File > Save or File > Save As commands. This will give you extra protection in case you forget to take snapshots along the way.

Allow Non-Linear History

Normally, 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 panel, separated from other groups by a black dividing line.

Show New Snapshot Dialog by Default

With this option enabled, you will always be prompted for snapshot names even when using the Create New Snapshot button on the History panel.

Make Layer Visibility Changes Undoable

Image layers can be visible or hidden. By default, when you change the layer visibility it is not recorded in the history. If you would like to store visibility changes so you can use the Undo command, enable this option.

Purge

This command frees up memory used by the Undo command, the History panel 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 panel's option menu.

All

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

Duplicate Image

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 is greyed out.)

11. Use the Duplicate command to make a copy of your cat image and accept the default file name Cat copy. Notice in the History panel that the new image has one state named Duplicate History.

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.

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.

12. Switch to Cat.psd by clicking on its tab (or title bar if it's floating).
13. Use the Revert command to remove all changes since the last save. The History panel will still display the Image Size states but the image itself will have will have been restored to its original dimensions. A new Revert state has been added to the history.

Closing Documents

We'll review closing documents in a little more detail this time. 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 haven't saved, you'll be asked 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 button.

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 (Option-Cmd-W).

If the Apply to All checkbox is checked, the action you choose (Save or Don't Save) will be applied to all open images at once before closing them. If left unchecked, Photoshop will prompt you what you want to do with each image, one at a time.

14. We'll be closing Cat.psd and Cat copy. Use the File > Close All command to display the dialog. Enable the Apply to All checkbox to lose the changes you made to Cat.psd and then click the Don't Save button.

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 panel.
• The Revert command will restore a document to the state it was in when it was last saved. This action can be undone.
• The History panel is Photoshop's Undo manager. It provides for multiple levels of Undo.
• Every change made to an image is recorded in the History panel as a state. You can return to an earlier or later state by clicking on its entry in the panel.
• A snapshot records the state of an image at a moment in time. It is represented by a thumbnail image in the History panel. 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 panel and assign names to them.
• The History panel has options that let you manage aspects of snapshots and states.
• An image's history is deleted once the image file is closed.
• The Purge command frees up memory used by the Undo command, the History panel 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)

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Photoshop - TOC - Introduction - Books -
New Images - Links - Questions -
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Photoshop - TOC - Introduction - Books -
New Images - Links - Questions -
1 - 2 - 3 - 4 - 5 - 6 - 7 - [ 8 ] - 9 -