Fun With Dots: Non-Interactive Stippling of Greyscale Images and Animations

Introduction The artistic tradition of stippling has a long history, particularly in the field of scientific illustration. Stippled drawings are made up of thousands of small ink dots or stipples that combine to give the impression of continuous tone. The artist can control the placement and size of the stipples precisely to delineate particular details and clarify structures that might be lost in a photograph. Recently computers have been used to approximate and extend traditional artistic methods and styles. This project is an attempt to generate stippled drawings quickly from greyscale images and animations. Wood discusses many advantages of traditional stippling in this text on scientific illustration. Among the most important are the ease at which stippled drawings can be reproduced by many different methods of varying quality and still maintain their visual impact. Black and white are faithfully reproduced by most methods, unlike continuous tones. Stippled drawings can be greatly reduced without losing their detail. Indeed, stipple drawings are typically created 25-100% larger than the intended final reproduction so the reduction process will smooth away small imperfections. Since stipple drawings are normally black and white, they are inexpensive to reproduce. Fine detailing is possible with stippling, up to the resolution of the stipples on the reproduced page. Finally, stippling mixes easily and effectively with other presentation techniques, especially line drawings, which share many of stippling's advantages. Stippling is often used when illustrating shaded smooth surfaces which are difficult to render well with only lines. In particular, textured surfaces such as stone or old metal are well-represented by stipples. The stipples suggest the high-frequency information of the surface texture without inducing much visual complexity. In a mixed stipple and line drawing, the lines can show overall structure (silhouettes in particular) while the stipples fill in shading and surface texture. The resulting images can be extremely striking and efficient in conveying information without being complicated. Traditional artists use either a stiff crowquill or mechanical pen when creating stipple drawings. The crowquill pen is a slightly flexible nibbed pen which translates hand pressure into line thickness, allowing variable line thicknesses or stipple sizes. The mechanical pen is a refined version of the familiar ball-point pen which produces very regular stipple sizes. The placement follows fairly strict guidelines to produce the correct effect. Stipples should be placed evenly with a sufficient density to approximate the desired tone. However, the stipples cannot form regular …