The Nonphotorealistic Rendering Project's purpose is to use computers to produce images that appear to have been drawn by hand. Computers are often used for precise rendering, computer-aided-design, and three-dimensional rendering, but, as evidenced in the art world, high precision isn't always the best way to convey ideas. Sometimes a quick sketch needs to look hasty to signify that the idea is fresh from the mind. A polished rendering gives a sense of finality which can be misleading or even frightening in some situations where an immediate solution has not been sought. The "sketched" look is instantly recognized as being an indication of intent with room for change and possible errors.
Our nonphotorealistic renderer can help make comprehensible but simple pictures of complicated objects by employing an economy of line. An important item to note is that this processing occurs in real-time because current nonphotorealistic rendering is primarily a batch process. This paper presents a real-time nonphotorealistic renderer that deliberately trades accuracy and detail for speed. Our renderer uses a method for determining visible lines and surfaces which is a modification of Appel's hidden-line algorithm, with improvements which are based on the topology of singular maps of a surface into the plane.
The method we describe for determining visibility has the potential to be used in any NPR system that requires a description of visible lines or surfaces in the scene. The major contribution of this paper is thus to describe a tool which can significantly improve the performance of these systems. We demonstrate the system with several nonphotorealistic rendering styles, all of which operate on complex models at interactive frame rates.
Lee Markosian, Michael A. Kowalski, Samuel J. Trychin, Lubomir D. Bourdev, Daniel Goldstein, and John F. Hughes. Real-Time Nonphotorealistic Rendering, Computer Graphics (Proceedings of SIGGRAPH '97), August, 1997.
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