Halftone screen frequency and magnitude estimation for digital descreening of documents

摘要

A highly efficient method and system for eliminating halftone screens from scanned documents while preserving the quality and sharpness of text and line-art is disclosed. The method and system utilizes a single channel screen frequency estimator module, which generates a screen frequency estimate for image data. The module generates a signal based on the highly filtered image signal at low contrast levels, and based on a reliable estimate to the halftone frequency at higher contrast levels. The single channel screen estimate module has adequate performance in resolution ranges from 300 to 600 dpi.