LPI adaptive descreening method with Hadamard domain analysis

This paper presents a new line-per-inch (LPI) adaptive descreening algorithm for restoring a high-quality image when scanning a printed matter. The LPI of scanned image is estimated and image region is classified into flat or edge region by analyzing the distribution in Hadamard transform coefficients. Then, an LPI adaptive edge preserving filtering is applied to reduce the halftone patterns not only in flat region but also in edge region. Proposed method has hardware-friendly structure without iteration and cascades of filters, and also it needs only integer adder and shift operations. Experimental result shows that the proposed method performs adaptively for a variety of LPI contents.