Why we use descreening
There may come a time when something important is printed, or displayed in a magazine or newspaper that you want to scan into your computer to save or manipulate. This may at first seem to be a simple process when you go about setting up your scan. What could be easier than just putting the document into the scanner, and then scanning it into a computer? Well many people don’t understand that the images that appear so clean and crisp in the magazine or newspapers are printed using a method known as halftoning. Those photos are printed using a series of overlapping dots that fool your eyes into seeing more colors than are actually there. Because of these overlapping dots, scanning these documents or images will produce something known as Moiré pattern (pronounced more-ay).
A Moiré pattern happens when two identical patterns of lines, circles, or array of dots are overlapped with imperfect alignment creating an interference pattern (resembles an optical illusion). Scanning these images into the computer will result in a wavy pattern that garbles the original image leaving you with a useless image. What makes things worse is scanning the image or document slightly off alignment can increase the effects of this wavy pattern, not only that, but the pitch of the scanners sensors will enhances the pattern even more. This will happen with any scanner, so don’t go blame it on the manufacturer just yet for the pitch of the scanner sensors.
To counter this attack on our visual spectrum Art-Scan was designed with two counters to this Moiré pattern. Art-Scan was designed with a descreening function that when used removes the halftone dot pattern from the printed material during scanning by defocusing the image. This effectively eliminates the Moiré pattern and the color shifting patterns. The downside to this process is the image will become slightly less detailed due to the blurring effect caused by the descreening process. This is where Art-Scan’s Sharpen Image setting comes in. By setting the unsharp mask after performing a descreening operation the image can be restored to its original sharpness.
Information on image descreening.