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G R A P H I C S - P R O. C O M F E B R U A R Y 2 0 2 3 • G R A P H I C S P R O 8 7 states that can be accessed at any time. e recorder for all the states is the History panel found in the Window menu. (Fig. 2). By default, when the image is opened, the History panel displays a snapshot of the image as it appeared when it was last saved. It is from this point on where you will make changes to the image. Each time you perform an operation, the History panel produces a state with the name of the operation or tool that was used — for example, Brush Tool, Levels, Smudge Tool, and so forth. The most recent state is at the bottom of the stack. e History panel is one of the most dynamic features and the one that can transport you forward and backwards in time to make observations or corrections. Click on any state and the image window displays the image as it was after a com- mand had been applied. Memory What enables Photoshop to remember all the History states is, of course, mem- ory. Each state is stored in your computer's R AM or on the scratch disk. When you exceed the current limit of states, the old- est state is deleted to make room for the most recent state. e number of History states is limited to fifty by default. at number can be increased or decreased by choosing Photoshop (Mac) or Edit Fig. 2. The History panel is the recorder for each step in the workflow. Fig. 3. The number of history states can be increased or decreased in the Performance Preferences. (Windows) > Preferences Performance >History States and entering a number from one to one thousand. (Fig. 3) Specif ying an excessive number of Histor y states earmarks memor y for the History cache and takes the alloca- tion away from Photoshop's other opera- tions. is could potentially compromise Photoshop's performance. W henever possible, keep the number of states at the default. Changing history Historians frequently rewrite history depending on their point of view and we've certainly seen a lot of revisionist Fig. 4. When you select a History state, by default all states below it in the History panel are grayed out. Fig. 5. Allow Non-Linear History to avoid losing subsequent history states. history through the years. In Photoshop and PaintShop Pro, changing history is a little more objective. If you want to move backward in time, click on the desired state in the History panel. The image window displays the image as it was after you applied the edit. All states below it in the History panel are grayed out. (Fig. 4) If you paint a stroke with the brush tool for example, all the grayed-out states disappear. To avoid losing the grayed-out states, choose History Options from the History panel menu and check the Allow Non- Linear History box. (Fig. 5) You can then eliminate or edit a state in the History panel and preserve all the states below it in the stack. A state can then be altered and saved as a snapshot or document. Work can then be resumed on the cur- rent document. I don't know why Non- Linear History isn't the default. It should be because it ensures that nothing is lost. at being said, check this box when you first start working and you will be certain that all is preserved.