Adobe Photoshop Basics

Now that we've learned some basic commands for modifying images, it's important to understand how to undo these changes and correct mistakes. In learning about the Canvas Size command and crop tool, I snuck in a couple of ways for undoing your changes. These were Ctrl-Z/Command-Z for Undo and the File > Revert command.

You may have noticed already that the Undo command acts as a toggle for Undo and Redo, so you can only Undo the last action taken. And the Revert command takes you all the way back to the state of your image when it was last saved. So what if you want to undo more than one action, but you don't want to completely revert to the last saved state? That's where the History Palette comes in.

Let's look at the history palette now. At the top of the palette is a small thumbnail icon and the file name of your image. Whenever you open an image, Photoshop creates a initial "snapshot" of the image and lists it here in the history palette. A quick way to revert your image is to click this initial snapshot. You can add new snapshots to the history palette at any point by choosing new snapshot from the History palette menu or clicking the new snapshot button.

Try it now. Open any image, make some obvious editing changes such as changing the image size or cropping. Create a snapshot. Now click the first snapshot in the list. The image reverts to its original state. Click the second snapshot and you'll be returned to the edited version. Combined with the History Brush, snapshots can be a very powerful tool. We'll learn more about that later. For now, let's get back to looking at the History palette.

Below the snapshots there is a dividing line, and a list of all the recent changes you have made to the image. You can undo any of these recent changes just by clicking the last change you want to revert to, or by dragging the tiny arrow slider that appears next to each state. The slider is useful if you're not sure how far back you need to go because it allows you to preview the changes as you move it up or down.

By default, Photoshop only lists the last 20 actions you have performed on an image and anything older is purged from the list to allow more memory for Photoshop. If you have a lot of memory, you can increase this number through the History Options command in the History palette menu. If you'd prefer to keep more memory available for Photoshop, it's a good idea to get in the habit of creating snapshots of your image at key points throughout the editing process, then you can still revert to an earlier state.

Along the bottom of the History palette are three buttons. The first button creates a new document and works just like the duplicate command When you duplicate the image, all history states are deleted for the duplicate. The next button creates a new snapshot. This is quicker than using the menu command but it does not give you dialog box to name the snapshot. The snapshots will automatically be named in numeric sequence. The third button deletes the current state or snapshot depending on what is selected in the palette.

There's a lot more I could tell you about the History palette, but it is all explained very well in your User Guide (Pages 167-172 in the Photoshop 5.0 User Guide and pages 69-73 in the Photoshop 6.0 User Guide). We'll cover more about the History palette as required in future lessons, but if you want to learn more you can read these pages in your User Guide or the online help.

But before we move on, I just want to point out some important things you should know about the history palette and Snapshots:

• History and snapshots are not saved with an image. Closing and reopening an image will clear all history states and snapshots.
• Reverting to a previous state and then editing your image eliminates all history states that had come after it.
• Deleting a state deletes everything after it, unless the non-linear option is selected.
• Ctrl-Alt-Z/Command-Option-Z moves backward through the history states.
• Ctrl-Shift-Z/Command-Shift-Z moves forward through the history states.

Next > Saving Images