Navigating the history list in Photoshop

You can move up and down the history list even if the list isn’t visible on your screen. The Edit➪Step Forward and Edit➪Step Backward commands move forward and back in the history list. The best way to access these commands is to use the keyboard shortcuts:

-->Press Alt+Ctrl+Z (Option+Ô+Z on the Mac) to move backward in time (upward in the history list).

-->Press Shift+Ctrl+Z (Shift+Ô+Z on the Mac) to move forward in time (down the history list).

Looking at the History Options Dialog Box
The History palette has four options that change its behavior. To access these options, choose History Options from the History palette pop-up menu to open the History Options dialog box. The dialog box offers these options:

-->Automatically Create First Snapshot: This option, selected by default, tells Photoshop to create a snapshot of the image when you first open it, before you make any changes. You can return to this snapshot at any time by clicking its name in the History palette. Keep this option selected. That way, you can always return to your original image if necessary.

-->Automatically Create New Snapshot When Saving: This option tells Photoshop to create a new snapshot each time you save the image. If you’re like me and save every couple of minutes, you probably won’t want to select this option; otherwise, you end up with a palette full of unwanted snapshots.

-->Allow Non-Linear History: This option makes editing or deleting a state without removing all the states that follow it possible. When the Non-Linear History capability is active, you can make an editing change to an intermediate state in the history list, perhaps save the edited state as a snapshot, or even delete the state, leaving the other steps below it unchanged. (When you delete a state you’ve edited, the edit you made is added to the end of the history list.)

Use this option with caution because steps are interdependent. A change you’ve removed may form the basis for another edit later on, so deleting it can cause weird results.

-->Show New Snapshot Dialog by Default: This option ensures that Photoshop asks you for a name for any new snapshot you create. Applying names to snapshots makes reminding yourself of the state of the image when you saved the snapshot easy.


Keeping the New Snapshot dialog box close at hand
If you want the New Snapshot dialog box to open when you create a new snapshot by clicking the camera icon, select the Show New Snapshot Dialog by Default option described in the preceding section.
Hold down the Alt key (Option key on the Mac) when you click the camera icon to access the dialog box even when the Show New Snapshot Dialog by Default option is deselected. If you remember this technique, you can alternate between creating generic snapshots and using the dialog box.