Dust removal is a fairly common problem if you're scanning images that have damage or if the scanner itself has particles on its flatbed. One of the first tools to reach for to remove dust is the Dust & Scratches filter. This filter finds pixels that are drastically different from the surrounding pixels and eliminates them by blurring them to match their neighbors.
In addition to dust, it's designed to help with removing hair, halftone dots, and other blemishes from scanned images. Your success with this filter may vary depending on the image — in some cases, it might get everything right on the first try; in others, you might have to retouch the image manually by using the Healing Brush and other techniques discussed in Chapter 18.
Open the filter's dialog box (see Figure 17.8) by choosing FilterDust & Scratches. Adjust the Radius slider (the maximum value is 100 pixels) to increase the size of the area that is examined for dissimilar pixels. The Threshold slider controls which pixels receive the effect of the filter — a lower threshold setting restricts the filter to just those pixels that are dramatically different from their neighbors.
When applying the Dust & Scratches filter, it's best to stick with fairly low values for the Radius —anything below 16 should be enough. Once you've found a Radius value that reduces the most noticeable blemishes, slowly increase ...