How To Get An Undo After You’ve Closed The Document
As you probably already know, the History palette keeps track of the last 20 changes to your document, and you can use it for multiple undos when working on a project. The only bad part is that when you close your document, your undos (in History) are automatically deleted. However, there is a way to save an undo, as long as it’s a tonal adjustment (such as Curves, Levels, Color Balance, etc.), by creating adjustment layers. Just click on the half-white/half-black circle icon at the bottom of the Layers palette and choose your tonal adjustment from the pop-up menu to create an adjustment layer. These adjustment layers are saved along with your file. That way, the next time you open the file, you can go back and edit your Curves, Levels, etc., adjustment by double-clicking on the adjustment layer’s thumbnail. The last-applied adjustment will appear, and you can edit it live. If you decide you don’t want the original adjustment applied at all, you can drag the adjustment layer into the Trash icon at the bottom of the Layers palette. You can also add a Gradient fill, a Pattern fill, and even a Solid Color fill as an adjustment layer, giving you an undo at a later date, because again, they’re saved as layers with the file.