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Introduction

The advent of photography and computers has not replaced artists, illustrators, or draftsmen, despite rising salaries and the decreasing cost of photographic and computer rendering technology. Almost all manuals that involve 3D objects, e.g., a car owner's manual, have illustrations rather than photographs. This lack of photography is present even in applications where aesthetics are a side-issue, and communication of geometry is the key. Examining technical manuals, illustrated textbooks, and encyclopedias reveals illustration conventions that are quite different from current computer graphics methods. These conventions fall under the umbrella term technical illustrations . In this paper we attempt to automate some of these conventions. In particular, we adopt a shading algorithm based on cool-to-warm tones such as shown in the non-technical image in Figure 1. We adopt this style of shading to ensure that black silhouettes and edge lines are clearly visible which is often not the case when they are drawn in conjunction with traditional computer graphics shading. The fundamental idea in this paper is that when silhouettes and other edge lines are explicitly drawn, then very low dynamic range shading is needed for the interior. As artists have discovered, adding a somewhat artificial hue shift to shading helps imply shape without requiring a large dynamic range. This hue shift can interfere with precise albedo perception, but this is not a major concern in technical illustration where the communication of shape and form are valued above realism. In Section 2 we review previous computer graphics work, and conclude that little has been done to produce shaded technical drawings. In Section 3 we review the common technical illustration practices. In Section 4 we describe how we have automated some of these practices. We discuss future work and summarize in Section 5.


  
Figure 1: The non-photorealistic cool (blue) to warm (tan) transition on the skin of the garlic in this non-technical setting is an example of the technique automated in this paper for technical illustrations. Colored pencil drawing by Susan Ashurst.


next up previous
Next: Related Work Up: A Non-Photorealistic Lighting Model Previous: A Non-Photorealistic Lighting Model
Bruce or Amy Gooch
4/21/1998