Edge preservation with space-filling curve half-toning

Accurately displaying a grey-scale image on a printer requires that the image be half-toned. That is , the image is approximated by sets of white and black pixels whose local average intensity is similar to that of the original image. In the case of laser printers these black and white pixels should be clustered because pixels cannot be set independently. By using a space-filling curve it is possible to develop cl ustered sets of pixels that approximate the image . Unfortunately this technique can destroy the edges in the resulting image . In this paper we present two solutions to the edge destruction problem. The first solution uses an edge detection filter to determine when the region size should be changed. By ensuring that none of the regions cross an edge the resulting image will contain a good representation of the edges. The second solution uses a local sort of the region in order to determine where the black and white pixels are placed. When the regions are small t.he resulting black and white pixels are still clustered but are positioned in such a way that edges are highlighted .