Scanning a halftone image introduces halftone artifacts, known as Moiré patterns, which significantly degrade the image quality. Printers that use amplitude modulation (AM) screening for halftone printing position dots in a periodic pattern. Therefore, frequencies relating halftoning are easily identifiable in the frequency domain. This paper proposes a method for descreening scanned color halftone images using a custom band reject filter designed to isolate and remove only the frequencies related to halftoning while leaving image edges sharp without image segmentation or edge detection. To enable hardware acceleration, the image is processed in small overlapped windows. The windows are filtered individually in the frequency domain, then pieced back together in a method that does not show blocking artifacts.
Stanger, C. J.; Tran, Thanh; and Barney Smith, Elisa H.. (2011). "Descreening of Color Halftone Images in the Frequency Domain". Proceedings of SPIE-IS&T Electronic Imaging, 7866. http://dx.doi.org/10.1117/12.872158