Descreening printer-ready images

Abstract

In this paper we address the problem of taking a bilevel image prepared for one printer, and processing it such that when it is printed on a second printer, the outputs of the two printers are as visually similar as possible. We present novel algorithms for this processing, which includes descreening and rehalftoning. The potential application for this algorithm is the printing of a digital image on a printer that is different from the one the image was originally formatted for. Our algorithm segments the image into text and halftone areas based on gradient density. The halftone areas are analyzed through their Fourier power spectra to yield their repetitive frequencies. A smoothing filter is chosen based on the repetitive frequency to perform descreening. This results in an intermediate gray level image, which is then rehalftoned using a technique suitable for the second printer. We implemented this algorithm, and found that it works satisfactorily on several test images.