Removing Dust and Noise

Photoshop includes several ways to remove dust spots, noise, and other artifacts from an image. Three of them, the Reduce Noise, Despeckle, and Dust & Scratches filters, don't lend themselves to this particular image, so I'll describe them and get them out of the way first.

Reduce Noise

Noise shows up in conventional photographs as grain, although that kind of graininess comes from the silver halide clumps in the photosensitive media when the photo is taken and processed. Noise can be added to a film image or print as it is scanned and converted to digital form, because electronic noise is an inherent part of the digital process. Any time an electronic signal is converted from analog form to digital, or is amplified, some random information gets mixed in with the actual picture data in the form of noise.

Noise is often removed by the electronic gadget, such as a digital camera, that produces it. The process involves comparing the image data with a "blank" image exposed under the same conditions. Certain kinds of fuzziness that appear in the blank version and the image can be assumed to be noise and safely removed. Photoshop has its own noise reduction function, which can be summoned using the Filters > Noise > Reduce Noise command. The dialog box shown in Figure 4.10 pops up.

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