History PaletteAs you can see, the History Options allows a non-linear option. The default behavior of the history palette is to eliminate the states that follow any state that you have reverted to as soon as you make another change to the image. By enabling the non-linear option, deleting a state deletes only the selected state, instead of all the states following it.
The history palette is a new feature added in Photoshop 5.0. The history palette tracks all the changes to your image and allows you to revert to a previous state at any time during an editing session. In other words, the history palette keeps a record of any changes from the time you opened your image to the time you close it. The number of edits saved is limited by the number you specify in the History Options (shown below).
http://0.tqn.com/d/graphicssoft/1/0/Q/6/ps005.gifThe history palette is shown to the right for an image to which I have applied a series of filters. In this example, you can see that I have reverted to the Fragment state. The Despeckle, Glass, and History Brush states are grayed out and will be deleted as soon as I make another change to the image. If the non-linear option had been selected in the History Options, only the Fragment state would have been removed. All other changes to the image would remain.
Snapshots
Part of the History Palette is the Snapshot command. Creating a snapshot saves a temporary reference point for the image that you can return to at any time until you close the image. A snapshot is retained even if the number of edits you've performed exceeds the maximum history states specified in the history options. Snapshots allow you freedom to experiment, the ability to compare the results of several techniques, and the ability to recover your work after using an action. You can also paint with snapshots, as described below.
History Brush http://0.tqn.com/d/graphicssoft/1/0/-/5/hb.gif
The History Brush tool allows you to paint with a snapshot of your image. For example, you may make a series of changes to an image, then later decide you only want to apply those changes to a portion of the image. It's simple... save a snapshot, revert to the previous state, and then paint with the snapshot onto specific areas of your image where you want the changes applied.
Espresso Graphics offers an excellent tutorial for one practical use of the History Brush - correcting a vintage black and white photo. Read on for my brief demonstration and a description of the history brush options.
http://0.tqn.com/d/graphicssoft/1/0/N/6/ps001.jpg A
http://0.tqn.com/d/graphicssoft/1/0/O/6/ps003.jpg C The image here was modified using the History Brush tool. Image A is the original image. I applied several different filters to the image, and Image B is the result. In image C, the History Brush was used to paint back in the details of the flower while leaving the rest of the image blurred.http://0.tqn.com/d/graphicssoft/1/0/_/6/ps032.gifTo the right you can see the History Brush Options. When you paint with the History Brush you have access to all the blending modes that are available with any other brush. You can also adjust the opacity of the brushstrokes. The Impressionist option applies an "impressionistic" style, smearing and blurring the pixels of the source file as you paint with it. Experiment with this option to see the effect... after all, you can always revert to the previous state with the history palette if you don't like the results.
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