Document image segmentation and quality improvement by moiré pattern analysis

MoireH patterns are distortions on the results of scanning printed documents. However, the patterns can be utilized in document image segmentation and quality improvement. The moireH phenomenon comes from sampling periodical structures in images, such as halftone screens, color components, and text galleys which often appear in printed magazines and newspapers. The generated moireH patterns appear in the scanning result in the form of obvious periodical patterns, color skew, and color noise on the edges of artworks. The moireH pattern degrades the scanning result and makes document analysis more di$cult. A new approach to document image segmentation and quality improvement by moireH pattern analysis is proposed. A scanning resolution, called the conductor of screen sharing, is proposed to control the moireH pattern. With the resolution, moireH patterns are generated and enhanced in certain designed areas in the frequency domain. Then, a logical "lter, called the comb "lter, is proposed to detect the moireH pattern. The new method, which is based on the sampling theory and moireH analysis in the frequency domain, is actually performed in the spatial domain by re-sampling and logical "ltering. The proposed method can e$ciently extract gray or color pictures, artworks, and text paragraphs in printed documents. Moreover, the moireH patterns on the segmented document components can be easily suppressed. The suppression yields better image quality for further analysis and image compression. Experimental results are shown to demonstrate the feasibility of the proposed approach. ( 2000 Elsevier Science B.V. All rights reserved.