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Chapter 10. Photo Restorations > Removing a Halftone Screen

Removing a Halftone Screen

We looked at removing a halftone screen earlier in this book, in terms of uses for blurring and sharpening. However, trying to get decent photos from halftones can be a serious concern. Sometimes, the only existing version of a photo may be a halftoned version. That can be a problem.

In Chapter 9, you learned a bit about the limitations of printing photographs in newspapers, magazines, and books. As a refresher, keep in mind that for a black-and-white image, every tone you see must be reproduced using pure black ink and the white of the paper. Any photograph must be converted to a series of dots called a halftone. Our eyes blend these dots together to produce the illusion of a grayscale (or color) image with smooth gradations of tone. A problem arises when you want to reuse a photograph and don’t have access to the original. Scanners can capture the halftone dots, but the resulting image usually has an unpleasant pattern, called moiré. You can see this effect in Figure 10.19.


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