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LIGHTING CONTROLS FOR SYNTHETIC IMAGES David R. Warn Computer Science Department General Motors Research Laboratories Warren, Michigan 48090 ABSTRACT The traditional point source light used for synthetic image generation provides no adjustments other than position, and this severely limits the effects that can be achieved. It can be difficult to highlight particular features of an object. This paper describes new lighting controls and techniques which can be used to optimize the lighting for synthetic images. These controls are based in part on observations of the lights used in the studio of a professional photographer. Controls include a light direction to aim a light at a particular area of an object, light concen- tration to simulate spotlights or floodlights, and flaps or cones to restrict the path of a light. Another control relates to the color of the light source and its effect on the perceived color of specular highlights. An object color can be blended with a color for the highlights to simulate different materials, paints, or lighting conditions. This can be accomplished dynamically while the image is displayed, using the video lookup table to approximate the specular color shift. CR Categories and Subject Descriptors: 1.3.3 [Computer Graphics]: Picture/Image Generation - display algorithms; 1.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism - color, shading, shadowing, and texture; Additional Key Words and Phrases: light controls INTRODUCTION The lighting model and controls described in this paper are part of GMR AUTOCOLOR, a system developed at the General Motors Research Laboratories for automatic generation of color synthetic images. The major application for this Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. © ACM 0-89791-109-1/83/007/0013 $00.75 capability within GM is design evaluation, to view a realistic image prior to or in place of building a physical model in wood or clay. It can be used both to display automotive body surfaces to aid in their aesthetic evaluation and to display automotive parts constructed with the GMSolid [8] modeling system to aid in visualizing complex geometric shapes. GMR AUTOCOLOR can also be used to display color coded scalar values such as stress [14], pressure, or curvature [ii] on the surface of an object. The geometric shape of an object is approximated by a mesh of three or four sided planar polygons. The polygonal representation was selected both for its availability within GM and for its efficiency.
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