The History panel shows the list of every change made to a file. By clicking on an item in the list, you can revert the file to a previous state.
At the top of the panel, next to the thumbnail of an image, there is information about the file: its name, size (in pixels), color mode, profile, date and time of creation.
The history of changes is arranged in a linear fashion. This means that if you return to any intermediate state and apply an action, all actions on the list after it will be permanently removed, except for the control points (which will be placed at the top of the list). Selecting Open from the list returns the file to its initial state (before changes were applied).
All changes made are shown with their corresponding icon. Any successive changes made by the same tool (two or more) are arranged in a group; the number of elements in a group is shown by a number to the right of the icon. The list of elements in a group can be collapsed and reopened by pressing the "+" icon to the left of the tool’s icon.
After applying the filter or effect in the program, you can back to it and edit the result. To do this, click the "+" icon in the History panel next to the effect's name and choose Result. The opened Effect dialog box displays the last used settings. After the editing is done, all the subsequent history states are deleted.
The possible number of states in the History panel can be adjusted in the Preferences.
The following buttons are at the bottom of the History panel:
You can also edit the history using the Edit menu commands:
History clears the whole history, except the initial and current states, as well as checkpoints.
Clipboard deletes the contents of the clipboard.
Clear All clears both the history and the clipboard.
Attention: The commands in the Purge menu cannot be canceled!