REDUCTION OF MOIRE IN SCREENED IMAGES USING HIERARCHICAL EDGE DETECTION AND ADAPTIVE-LENGTH AVERAGING FILTERS

In an image reproduction system, an image processor analyzes a hierarchy of image representations of different resolutions to detect edges. In regions having edges that are detected in all hierarchical representations, little or no filtering is applied to the image. In regions having no edges or edges that are detected in only the highest-resolution representation, greater amounts of filtering are applied to the image. In regions having edges detected in two or more but not all hierarchical representations, an intermediate amount of filtering is applied to the image. In preferred embodiments, two-dimensional averaging filters of varying size are applied to the image. The size of the averaging filter is selected according to the number of hierarchical representations in which an edge is detected.