Edge enhancement issues in half-toning

The correct display of edges in half-toned images is necessary for accurate image reproduction. This problem has been addressed by pre-processing the image to enhance the edges or by altering the half-toning algorithm to account for edges. In this paper we present a postprocessing edge enhancement technique that is applicable to all half-toning algorithms. We identify two types of edge pixels in the image; dark and light edge pixels. Edges in an image are highlighted by setting the dark/light edge pixels to black/white. Our method was tested on a modern laser printer and hence our evaluation of the technique is restricted to clustered half-toning methods. We evaluated the effect of enhancing edges by conducting a user survey to determine the perceived value of the different edge enhancement methods. The results of the user survey, while not statistically significant, indicate that our post-processing technique achieves comparable results to previous edge enhancement methods. Our technique is simple to implement and can be applied to any half-toning technique and thus is a good default edge-enhancing approach.