Selecting the Undo command will restore the active picture to the state it was in prior to your most recent edit. Use this command when you make a mistake such as using the wrong tool, erasing more than you meant, etc.
PixelNEO includes a dynamic, multi-level undo/redo feature that can keep track of multiple changes made to your pictures. The state of the undo buffer can be viewed by selecting the Show Undo History command from the Options menu.
The Undo History, which can remain open while you work, displays all available undo choices for the active picture. Each open picture has its own Undo History. The total number of items that can be stored here depends on the settings you specified in PixelNEO's Preferences screen. Each item in the list represents an edit made to your picture. The edits are listed in chronological order with the most recent ones at the bottom of the list. The history item that matches the current state of your picture will appear highlighted - normally this will be the last item in the list.
You may jump backward to one of your picture's previous states by clicking on one of the items in the history list. Your picture will change to reflect its state at that point in history. If history items exist ahead of your current location, you also may click any of those items to move forward or "redo" those edits. Once you go backwards to a previous state and then make changes, you will loose all history items that existed after that point.
The Undo feature can be turned off or on at any time by clicking the button located in the upper right of the Undo History window. It sometimes can be beneficial to temporarily turn off the Undo feature when making a series of minor changes to a large image. This will speed up the process as you will not have to wait for PixelNEO to update the undo buffer after each edit. When finished with the changes, the Undo feature can be turned on again.
If you no longer need the current contents of the Undo History, you can click the button and free up some memory by purging those unneeded items.