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Item A Dual Light Stage(The Eurographics Association, 2005) Hawkins, Tim; Einarsson, Per; Debevec, Paul; Kavita Bala and Philip DutreWe present a technique for capturing high-resolution 4D reflectance fields using the reciprocity property of light transport. In our technique we place the object inside a diffuse spherical shell and scan a laser across its surface. For each incident ray, the object scatters a pattern of light onto the inner surface of the sphere, and we photograph the resulting radiance from the sphere s interior using a camera with a fisheye lens. Because of reciprocity, the image of the inside of the sphere corresponds to the reflectance function of the surface point illuminated by the laser, that is, the color that point would appear to a camera along the laser ray when the object is lit from each direction on the surface of the sphere. The measured reflectance functions allow the object to be photorealistically rendered from the laser s viewpoint under arbitrary directional illumination conditions. Since each captured re- flectance function is a high-resolution image, our data reproduces sharp specular reflections and self-shadowing more accurately than previous approaches. We demonstrate our technique by scanning objects with a wide range of reflectance properties and show accurate renderings of the objects under novel illumination conditions.Item Relighting Human Locomotion with Flowed Reflectance Fields(The Eurographics Association, 2006) Einarsson, Per; Chabert, Charles-Felix; Jones, Andrew; Ma, Wan-Chun; Lamond, Bruce; Hawkins, Tim; Bolas, Mark; Sylwan, Sebastian; Debevec, Paul; Tomas Akenine-Moeller and Wolfgang HeidrichWe present an image-based approach for capturing the appearance of a walking or running person so they can be rendered realistically under variable viewpoint and illumination. In our approach, a person walks on a treadmill at a regular rate as a turntable slowly rotates the person s direction. As this happens, the person is filmed with a vertical array of high-speed cameras under a time-multiplexed lighting basis, acquiring a seven-dimensional dataset of the person under variable time, illumination, and viewing direction in approximately forty seconds. We process this data into a flowed reflectance field using an optical flow algorithm to correspond pixels in neighboring camera views and time samples to each other, and we use image compression to reduce the size of this data.We then use image-based relighting and a hardware-accelerated combination of view morphing and light field rendering to render the subject under user-specified viewpoint and lighting conditions. To composite the person into a scene, we use an alpha channel derived from back lighting and a retroreflective treadmill surface and a visual hull process to render the shadows the person would cast onto the ground. We demonstrate realistic composites of several subjects into real and virtual environments using our technique.Item Digital Reunification of the Parthenon and its Sculptures(The Eurographics Association, 2003) Stumpfel, Jessi; Tchou, Christopher; Yun, Nathan; Martinez, Philippe; Hawkins, Timothy; Jones, Andrew; Emerson, Brian; Debevec, Paul; David Arnold and Alan Chalmers and Franco NiccolucciThe location, condition, and number of the Parthenon sculptures present a considerable challenge to archeologists and researchers studying this monument. Although the Parthenon proudly stands on the Athenian Acropolis after nearly 2,500 years, many of its sculptures have been damaged or lost. Since the end of the 18th century, its surviving sculptural decorations have been scattered to museums around the world. We propose a strategy for digitally capturing a large number of sculptures while minimizing impact on site and working under time and resource constraints. Our system employs a custom structured light scanner and adapted techniques for organizing, aligning and merging the data. In particular this paper details our effort to digitally record the Parthenon sculpture collection in the Basel Skulpturhalle museum, which exhibits plaster casts of most of the known existing pediments, metopes, and frieze. We demonstrate our results by virtually placing the scanned sculptures on the Parthenon.Item Estimating Specular Roughness and Anisotropy from Second Order Spherical Gradient Illumination(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ghosh, Abhijeet; Chen, Tongbo; Peers, Pieter; Wilson, Cyrus A.; Debevec, PaulThis paper presents a novel method for estimating specular roughness and tangent vectors, per surface point, from polarized second order spherical gradient illumination patterns. We demonstrate that for isotropic BRDFs, only three second order spherical gradients are sufficient to robustly estimate spatially varying specular roughness. For anisotropic BRDFs, an additional two measurements yield specular roughness and tangent vectors per surface point. We verify our approach with different illumination configurations which project both discrete and continuous fields of gradient illumination. Our technique provides a direct estimate of the per-pixel specular roughness and thus does not require off-line numerical optimization that is typical for the measure-and-fit approach to classical BRDF modeling.Item Real-Time High-Dynamic Range Texture Mapping(The Eurographics Association, 2001) Cohen, Jonathan; Tchou, Chris; Hawkins, Tim; Debevec, Paul; S. J. Gortle and K. MyszkowskiThis paper presents a technique for representing and displaying high dynamic-range texture maps (HDRTMs) using current graphics hardware. Dynamic range in real-world environments often far exceeds the range representable in 8-bit per-channel texture maps. The increased realism afforded by a highdynamic range representation provides improved fidelity and expressiveness for interactive visualization of image-based models. Our technique allows for realtime rendering of scenes with arbitrary dynamic range, limited only by available texture memory. In our technique, high-dynamic range textures are decomposed into sets of 8- bit textures. These 8-bit textures are dynamically reassembled by the graphics hardware s programmable multitexturing system or using multipass techniques and framebuffer image processing. These operations allow the exposure level of the texture to be adjusted continuously and arbitrarily at the time of rendering, correctly accounting for the gamma curve and dynamic range restrictions of the display device. Further, for any given exposure only two 8-bit textures must be resident in texture memory simultaneously. We present implementation details of this technique on various 3D graphics hardware architectures. We demonstrate several applications, including high-dynamic range panoramic viewing with simulated auto-exposure, real-time radiance environment mapping, and simulated Fresnel reflection.Item Rapid Acquisition of Specular and Diffuse Normal Maps from Polarized Spherical Gradient Illumination(The Eurographics Association, 2007) Ma, Wan-Chun; Hawkins, Tim; Peers, Pieter; Chabert, Charles-Felix; Weiss, Malte; Debevec, Paul; Jan Kautz and Sumanta PattanaikWe estimate surface normal maps of an object from either its diffuse or specular reflectance using four spherical gradient illumination patterns. In contrast to traditional photometric stereo, the spherical patterns allow normals to be estimated simultaneously from any number of viewpoints. We present two polarized lighting techniques that allow the diffuse and specular normal maps of an object to be measured independently. For scattering materials, we show that the specular normal maps yield the best record of detailed surface shape while the diffuse normals deviate from the true surface normal due to subsurface scattering, and that this effect is dependent on wavelength. We show several applications of this acquisition technique. First, we capture normal maps of a facial performance simultaneously from several viewing positions using time-multiplexed illumination. Second, we show that highresolution normal maps based on the specular component can be used with structured light 3D scanning to quickly acquire high-resolution facial surface geometry using off-the-shelf digital still cameras. Finally, we present a realtime shading model that uses independently estimated normal maps for the specular and diffuse color channels to reproduce some of the perceptually important effects of subsurface scattering.Item Animatable Facial Reflectance Fields(The Eurographics Association, 2004) Hawkins, Tim; Wenger, Andreas; Tchou, Chris; Gardner, Andrew; Göransson, Fredrik; Debevec, Paul; Alexander Keller and Henrik Wann JensenWe present a technique for creating an animatable image-based appearance model of a human face, able to capture appearance variation over changing facial expression, head pose, view direction, and lighting condition. Our capture process makes use of a specialized lighting apparatus designed to rapidly illuminate the subject sequentially from many different directions in just a few seconds. For each pose, the subject remains still while six video cameras capture their appearance under each of the directions of lighting. We repeat this process for approximately 60 different poses, capturing different expressions, visemes, head poses, and eye positions. The images for each of the poses and camera views are registered to each other semi-automatically with the help of fiducial markers. The result is a model which can be rendered realistically under any linear blend of the captured poses and under any desired lighting condition by warping, scaling, and blending data from the original images. Finally, we show how to drive the model with performance capture data, where the pose is not necessarily a linear combination of the original captured poses.