History
Palette
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.
A D V E R T I S E M E N T
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.
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