An extremely useful feature of the GIMP is its ability to perform
multiple undos and redos. The Undo
function is found in the Image:Edit menu, as is the Redo function. These two functions are so
useful and are employed so often that you will want to immediately
memorize their keyboard shortcuts. These are C-z for undo and
C-r for redo.
The number of undos that can be performed in the GIMP is controlled by
the Interface branch of the Preferences dialog, and the Preferences dialog is found in the Toolbox:File menu. Figure
1.12
Figure 1.12:
Setting the Number of Undo Levels
 |
illustrates the dialog with the Interface branch highlighted. The
default value for the number of undos is 5, but for the size of images
I work with and the amount of RAM I have available on my computer, I
like to have 25 levels of undo. If I were working with large images
with many layers, this would not be possible, and I would change the
number of undos to a lower value. See Section
![[*]](cross_ref_motif.gif)
in the
README for more on how to budget your RAM.
An amazing feature of the GIMP is the Undo History
function found in the Image:View
menu. When invoked, this function displays a palette of thumbnails,
each representing an image state in the sequence of operations
performed on your image. Figure
1.13
Figure 1.13:
Working with the Undo History Dialog
 |
illustrates such a sequence. Figures
1.13(a), (b),
and (c) show the successive application of a selection, followed by a
color fill. Figures
1.13(d), (e), and (f) show the
respective entries in the
Undo History dialog as the
operations are performed.
In Figure
1.13, note how the highlighted thumbnail in
the Undo History dialog indicates the current status of the
image displayed in the image window. Performing an undo by typing
C-z in the image window moves the highlighted thumbnail to a
layer higher in the thumbnail stack, and performing redo with a C-r moves the highlighted thumbnail a layer lower. Furthermore, you
can select any layer in the Undo History dialog at any time
by clicking on it.
In this way, you have access to any prior version of the image
available in the Undo History by one of two separate methods.
The first is by repeatedly pressing C-z in the image window
until arriving at the desired state. The second is by directly
clicking on the corresponding thumbnail in the Undo History
dialog.
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