Halftoning and Stippling
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One important origin of non-photorealistic computer graphics comes from printing technology. Halftoning is a reproduction technique for photography in printing. The continuous tones of the images are represented by fulltone dots of varying size, shape, and density. While printing technology brought this to perfection over time, computer graphics researchers developed methods that modified this process for artistic purposes. For purposes of halftoning, dots are distributed in repetitive patterns. Stippling, an artistic illustration technique, distributes them in a random but expressive way. Illustrators aim at representing tone and texture of an object by such patterns. Interestingly, the distributions can be described mathematically and a simple optimization scheme allows computers to imitate the artistic process quite well. The method can be extended towards distributing other shapes. In this case the optimization is extended to move and rotate the objects. This allows users not only to create other forms of illustrations but also to generate mosaics.