Interactive Non-Photorealistic Technical Illustration  

Current interactive modeling systems allow users to view models in wireframe or Phong-shaded images. However, the wireframe is based on the model's parameterization, and a model's features may get lost in a nest of lines. Alone, a fully rendered image may not provide enough useful information about the structure or model features. Human technical illustrators follow certain visual conventions that are unlike Phong-shaded or wireframe renderings, and the drawings they produce are subjectively superior to conventional computer renderings. This thesis explores lighting, shading, and line illustration conventions used by technical illustrators. These conventions are implemented in a modeling system to create a new method of displaying and viewing complex NURBS models. In particular, silhouettes and edge lines are drawn in a manner similar to pen-and-ink drawings, and a shading algorithm is used that is similar to ink-wash or air-brush renderings for areas inside the silhouettes. This shading has a low intensity variation so that the black silhouettes remain visually distinct, and it has a cool-to-warm hue transition to help accent surface orientation. Applying these illustration methods produces images that are closer to human-drawn illustrations than is provided by traditional computer graphics approaches.

Gooch, Amy. University of Utah (1998). Design>Graphic Design>Technical Illustration

Interactive Technical Illustration

A rendering is an abstraction that favors, preserves, or even emphasizes some qualities while sacrificing, suppressing, or omitting other characteristics that are not the focus of attention. Most computer graphics rendering activities have been concerned with photorealism, i.e., trying to emulate an image that looks like a high-quality photograph. This laudable goal is useful and appropriate in many applications, but not in technical illustration where elucidation of structure and technical information is the preeminent motivation. This calls for a different kind of abstraction in which technical communication is central, but art and appearance are still essential instruments toward this end. Work that has been done on computer generated technical illustrations has focused on static images, and has not included all of the techniques used to hand draw technical illustrations. A paradigm for the display of technical illustrations in a dynamic environment is presented. This display environment includes all of the benefits of computer generated technical illustrations, such as a clearer picture of shape, structure, and material composition than traditional computer graphics methods. It also includes the three-dimensional interactive strength of modern display systems. This is accomplished by using new algorithms for real time drawing of silhouette curves, algorithms which solve a number of the problems inherent in previous methods. We incorporate current non-photorealistic lighting methods, and augment them with new shadowing algorithms based on accepted techniques used by artists and studies carried out in human perception.

Gooch, Bruce, Peter-Pike J. Sloan, Amy Gooch, Peter Shirley and Richard Riesenfeld. University of Utah (1997). Design>Graphic Design>Technical Illustration

A Non-Photorealistic Lighting Model For Automatic Technical Illustration  

Phong-shaded 3D imagery does not provide geometric information of the same richness as human-drawn technical illustrations. A non-photorealistic lighting model is presented that attempts to narrow this gap. The model is based on practice in traditional technical illustration, where the lighting model uses both luminance and changes in hue to indicate surface orientation, reserving extreme lights and darks for edge lines and highlights. The lighting model allows shading to occur only in mid-tones so that edge lines and highlights remain visually prominent. In addition, we show how this lighting model is modified when portraying models of metal objects. These illustration methods give a clearer picture of shape, structure, and material composition than traditional computer graphics methods.

Gooch, Amy, Bruce Gooch, Peter Shirley and Elaine Cohen. University of Utah (1998). Design>Graphic Design>Technical Illustration