Automatic Segmentation And Descreening Of Scanned Color Documents

The conversion of existing books into digital form involves digitization of original hooks through scanning, which is a slow and labor-intensity process. Carci'uJ attention must be paid to maintain the qualily of the reproduced books and in particular of the images they contain. Halftone image areas in the original books cause the most reproduction problems, as there is the potential that moire patterns may form when these image areas are re-screened. In order to avoid these moire patterns, it is necessary to detect the image areas of the document and remove the screen patterns present in those areas.In the past, we have present techniques to perform these operations in the case of grayscale images. In this article, I extend these techniques to handle color images. I present techniques to segment a color document into halftone image areas, detect the presence and frequency of screen patterns in halftone areas and suppress the detected screens. Halftone imageareas are segmented by using a measure.of image activity, image activity is low in text areas and high in halftone areas. I use 2-D Fourier spectral analysis to identify the screen frequencies present. The screens are then suppressed by low-pass filtering. All these techniques are automatic processes which are recognized by my software. And these automatic techniques speed up the conversion process of books to digital form, and overcome quality problems in the reproduction of halftone images.