Snapshots and History
As you work on an image, you can take snapshots of it at regular intervals so you have versions saved to use with the History Brush. To make a snapshot, click the New Snapshot button at the foot of the History palette. A new snapshot appears at the top of the History palette (see Figure 9).
Figure 9 Make snapshots of the image at various stages to use as sources for the History Brush.
One situation where this technique is handy is if you want to make different changes to different parts of an image. For example, you can apply the Hue/Saturation adjustment to an image, set the Saturation to −100 to remove the color, and then save this version as a snapshot. Undo this action and repeat the adjustment, this time increasing the saturation, and save this version as a snapshot also. Now you can selectively paint either of the adjustments onto the image by using the History Brush; just select the relevant snapshot as the source for the History Brush and start painting.