INVERSE RENDERING FOR COMPUTER GRAPHICS Stephen

Creating realistic images has been a major focus in the study of computer graphics for much of its history. This eeort has led to mathematical models and algorithms that can compute predictive, or physically realistic, images from known camera positions and scene descriptions that include the geometry of objects, the reeectance of surfaces, and the lighting used to illuminate the scene. These images accurately describe the physical quantities that would be measured from a real scene. Because these algorithms can predict real images, they can also be used in inverse problems to work backward from photographs to attributes of the scene. Work on three such inverse rendering problems is described. The rst, inverse lighting, assumes knowledge of geometry, reeectance, and the recorded photograph and solves for the lighting in the scene. A technique using a linear least-squares system is proposed and demonstrated. Also demonstrated is an application of inverse lighting, called re-lighting, which modiies lighting in photographs. The second two i n verse rendering problems solve for unknown reeectance, given images with known geometry, lighting, and camera positions. Photographic texture measurement concentrates on capturing the spatial variation in an object's reeectance. The resulting system begins with scanned 3D models of real objects and uses photographs to construct accurate, high-resolution textures suitable for physically realistic rendering. The system is demonstrated on two complex natural objects with detailed surface textures. Image-based BRDF measurement takes the opposite approach to reeectance measurement , capturing the directional characteristics of a surface's reeectance by measuring the bidirectional reeectance distribution function, or BRDF. Using photographs of an object with spatially uniform reeectance, the BRDFs of paints and papers are measured with completeness and accuracy that rival that of measurements obtained using specialized devices. The image-based approach and novel light source positioning technique require only general-purpose equipment, so the cost of the apparatus is low compared to conventional approaches. In addition, very densely sampled data can bemeasured very quickly, when the wavelength spectrum of the BRDF does not need to be measured in detail. iii for Heidi iv Acknowledgements My rst thanks go to my advisor, Don Greenberg, for the support and encouragement he gave me during my stay at Cornell. His constant conndence in me and my work has been an inspiration, and he has surrounded me with the people and technology that made that work possible. I w ould also like to thank Len Gross and …