Publications
47 results found
Guarnera D, Guarnera GC, Ghosh A, et al., 2016, BRDF Representation and Acquisition, Computer Graphics Forum, Vol: 35, ISSN: 1467-8659
Photorealistic rendering of real world environments is important in a range of different areas; including Visual Special effects,Interior/Exterior Modelling, Architectural Modelling, Cultural Heritage, Computer Games and Automotive Design.Currently, rendering systems are able to produce photorealistic simulations of the appearance of many real-world materials.In the real world, viewer perception of objects depends on the lighting and object/material/surface characteristics, the waya surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact thesecharacteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interactwith light. Thus the representation and acquisition of material models has become such an active research area.This survey of the state-of-the-art of BRDF Representation and Acquisition presents an overview of BRDF (Bidirectional Re-flectance Distribution Function) models used to represent surface/material reflection characteristics, and describes currentacquisition methods for the capture and rendering of photorealistic materials.
Fyffe G, Graham P, Tunwattanapong B, et al., 2016, Near-instant capture of high-resolution facial geometry and reflectance, Computer Graphics Forum, Vol: 35, ISSN: 1467-8659
We present a near-instant method for acquiring facial geometry and reflectance using a set of commodity DSLR cameras andflashes. Our setup consists of twenty-four cameras and six flashes which are fired in rapid succession with subsets of thecameras. Each camera records only a single photograph and the total capture time is less than the 67ms blink reflex. Thecameras and flashes are specially arranged to produce an even distribution of specular highlights on the face. We employ thisset of acquired images to estimate diffuse color, specular intensity, specular exponent, and surface orientation at each pointon the face. We further refine the facial base geometry obtained from multi-view stereo using estimated diffuse and specularphotometric information. This allows final submillimeter surface mesostructure detail to be obtained via shape-from-specularity.The final system uses commodity components and produces models suitable for authoring high-quality digital human characters.
Riviere J, Peers P, Ghosh A, 2016, Mobile Surface Reflectometry, Computer Graphics Forum, Vol: 35, Pages: 191-202, ISSN: 1467-8659
We present two novel mobile reflectometry approaches for acquiring detailed spatially varying isotropic surfacereflectance and mesostructure of a planar material sample using commodity mobile devices. The first approachrelies on the integrated camera and flash pair present on typical mobile devices to support free-form handheldacquisition of spatially varying rough specular material samples. The second approach, suited for highly specularsamples, uses the LCD panel to illuminate the sample with polarized second order gradient illumination. Toaddress the limited overlap of the front facing camera’s view and the LCD illumination (and thus limited samplesize), we propose a novel appearance transfer method that combines controlled reflectance measurement of a smallexemplar section with uncontrolled reflectance measurements of the full sample under natural lighting. Finally,we introduce a novel surface detail enhancement method that adds fine scale surface mesostructure from close-upobservations under uncontrolled natural lighting. We demonstrate the accuracy and versatility of the proposedmobile reflectometry methods on a wide variety of spatially varying materials.
Riviere J, Reshetouski I, Ghosh A, 2016, Polarization imaging reflectometry in the wild, Departmental Technical Report: 16/8, Publisher: Department of Computing, Imperial College London, 16/8
We present a novel approach for on-site acquisition of surface reflectancefor planar, spatially varying, isotropic materials in uncontrolledoutdoor environments. Our method exploits the naturallyoccuring linear polarization of incident illumination: by rotating alinear polarizing filter in front of a camera at 3 different orientations,we measure the linear polarization reflected off the sampleand combine this information with multiview analysis and inverserendering in order to recover per-pixel, high resolution reflectancemaps. We exploit polarization both for diffuse/specular separationand surface normals estimation by combining polarization measurementsfrom at least two near orthogonal views close to Brewsterangle of incidence. We then use our estimates of surface normalsand albedos in an inverse rendering framework to recover specularroughness. To the best of our knowledge, our method is the firstto successfully extract a complete set of reflectance parameters withpassive capture in completely uncontrolled outdoor environments.
Nagano K, Fyffe G, Alexander O, et al., 2015, Skin microstructure deformation with displacement map convolution, ACM Transactions on Graphics, Vol: 34, ISSN: 1557-7368
We present a technique for synthesizing the effects of skin microstructure deformation by anisotropically convolving a high-resolution displacement map to match normal distribution changes in measured skin samples. We use a 10-micron resolution scanning technique to measure several in vivo skin samples as they are stretched and compressed in different directions, quantifying how stretching smooths the skin and compression makes it rougher. We tabulate the resulting surface normal distributions, and show that convolving a neutral skin microstructure displacement map with blurring and sharpening filters can mimic normal distribution changes and microstructure deformations. We implement the spatially-varying displacement map filtering on the GPU to interactively render the effects of dynamic microgeometry on animated faces obtained from high-resolution facial scans.
Wang P, Bicazan D, Ghosh A, 2014, Rerendering Landscape Photographs, CVMP '14 11th European Conference on Visual Media Production (CVMP 2014), Publisher: Association for Computing Machinery
We present a practical approach for realistic rerendering of landscape photographs. We extract a view dependent depth map from single input landscape images by examining global and local pixel color distributions and demonstrate applications of depth dependent rendering such as novel viewpoints, digital refocusing and dehazing.We also present a simple approach to relight the input landscape photograph under novel sky illumination. Here, we assume diffuse reflectance and relight landscapes by estimating the irradiance due the sky in the input photograph. Finally, we also takeinto account specular reflections on water surfaces which are common in landscape photography and demonstrate a semiautomatic process for relighting scenes with still water.
Tunwattanapong B, Fyffe G, Graham P, et al., 2013, Acquiring Reflectance and Shape from Continuous Spherical Harmonic Illumination, ACM Transactions on Graphics, Vol: 32
Zhu Y, Garigipati P, Peers P, et al., 2013, Estimating diffusion parameters from polarized spherical-gradient illumination, IEEE Computer Graphics and Applications, Vol: 33, Pages: 34-43, ISSN: 0272-1716
The proposed method acquires subsurface-scattering parameters of heterogeneous translucent materials. It directly obtains dense per-surface-point scattering parameters from observations under cross-polarized spherical-gradient illumination of curved surfaces. This method does not require explicit fitting of observed scattering profiles. A variety of heterogeneous translucent objects illustrate its validity. © 1981-2012 IEEE.
Graham P, Tunwattanapong B, Busch J, et al., 2013, Measurement Based Synthesis of Facial Microgeometry, Computer Graphics Forum, Vol: 32, Pages: 335-344
Guarnera GC, Peers P, Debevec P, et al., 2012, Estimating Surface Normals from Spherical Stokes Reflectance Fields, ECCV Workshop on Color and Photometry in Computer Vision (CPCV) 2012
Stratou G, Ghosh A, Debevec P, et al., 2012, Exploring the effect of illumination on automatic expression recognition using the ICT-3DRFE database, Image and Vision Computing, Vol: 30, Pages: 728-737, ISSN: 0262-8856
Ghosh A, Fyffe G, Tunwattanapong B, et al., 2011, Multiview face capture using polarized spherical gradient illumination, ACM Transactions on Graphics, Vol: 30, Pages: 1-10, ISSN: 0730-0301
<jats:p> We present a novel process for acquiring detailed facial geometry with high resolution diffuse and specular photometric information from multiple viewpoints using polarized spherical gradient illumination. Key to our method is a new pair of linearly polarized lighting patterns which enables <jats:italic>multiview</jats:italic> diffuse-specular separation under a given spherical illumination condition from just two photographs. The patterns -- one following lines of latitude and one following lines of longitude -- allow the use of fixed linear polarizers in front of the cameras, enabling more efficient acquisition of diffuse and specular albedo and normal maps from multiple viewpoints. In a second step, we employ these albedo and normal maps as input to a novel multi-resolution adaptive domain message passing stereo reconstruction algorithm to create high resolution facial geometry. To do this, we formulate the stereo reconstruction from multiple cameras in a commonly parameterized domain for multiview reconstruction. We show competitive results consisting of high-resolution facial geometry with relightable reflectance maps using five DSLR cameras. Our technique scales well for multiview acquisition without requiring specialized camera systems for sensing multiple polarization states. </jats:p>
Ghosh A, Chen T, Peers P, et al., 2010, Circularly polarized spherical illumination reflectometry, ACM Transactions on Graphics, Vol: 29, ISSN: 0730-0301
Ghosh A, Heidrich W, Achutha S, et al., 2010, A Basis Illumination Approach to BRDF Measurement, International Journal of Computer Vision, Vol: 90, Pages: 183-197, ISSN: 0920-5691
Wilson CA, Ghosh A, Peers P, et al., 2010, Temporal upsampling of performance geometry using photometric alignment, ACM Transactions on Graphics, Vol: 29, Pages: 1-11, ISSN: 0730-0301
<jats:p> We present a novel technique for acquiring detailed facial geometry of a dynamic performance using extended spherical gradient illumination. Key to our method is a new algorithm for <jats:italic>jointly</jats:italic> aligning two photographs, under a gradient illumination condition and its complement, to a full-on tracking frame, providing dense temporal correspondences under changing lighting conditions. We employ a two-step algorithm to reconstruct detailed geometry for <jats:italic>every</jats:italic> captured frame. In the first step, we coalesce information from the gradient illumination frames to the full-on tracking frame, and form a temporally aligned photometric normal map, which is subsequently combined with dense stereo correspondences yielding a detailed geometry. In a second step, we propagate the detailed geometry back to every captured instance guided by the previously computed dense correspondences. We demonstrate reconstructed dynamic facial geometry, captured using moderate to video rates of acquisition, for every captured frame. </jats:p>
Ghosh A, Chen T, Peers P, et al., 2009, Estimating Specular Roughness and Anisotropy from Second Order Spherical Gradient Illumination, Computer Graphics Forum, Vol: 28, Pages: 1161-1170, ISSN: 0167-7055
<jats:title>Abstract</jats:title><jats:p>This 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.</jats:p>
Ghosh A, Hawkins T, Peers P, et al., 2008, Practical modeling and acquisition of layered facial reflectance, ACM Transactions on Graphics, Vol: 27, ISSN: 0730-0301
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