Visualising two-dimensional vector fields using directed halftone cells

Digital halftoning is a technique for converting an image with multiple levels of grey into a bi-level (bitmap) image, typically in preparation for printing on paper. It is standard practice to optimize the halftoning process to reduce the visibility of artifacts that appear as textures within what should be a region of uniform or slowly varying intensity. This paper describes a method of manipulating the halftoning process to cause the texture to give an indication of field direction, while the field magnitude is displayed using the intensity. The method is very fast, and gives an unambiguous indication of direction everywhere in the field. It is suitable for displaying up to about 100×100 samples on a normal size page.