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Next: 1.6 Recalling the Last Up: 1. GIMP Basics Previous: 1.4 RGB, Grayscale, and

# 1.5 Undoing and Redoing

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 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.

Next: 1.6 Recalling the Last Up: 1. GIMP Basics Previous: 1.4 RGB, Grayscale, and
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