A perceptually validated model for surface depth hallucination

Capturing detailed surface geometry currently requires specialized equipment such as laser range scanners, which despite their high accuracy, leave gaps in the surfaces that must be reconciled with photographic capture for relighting applications. Using only a standard digital camera and a single view, we present a method for recovering models of predominantly diffuse textured surfaces that can be plausibly relit and viewed from any angle under any illumination. Our multiscale shape-from-shading technique uses diffuse-lit/flash-lit image pairs to produce an albedo map and textured height field. Using two lighting conditions enables us to subtract one from the other to estimate albedo. In the absence of a flash-lit image of a surface for which we already have a similar exemplar pair, we approximate both albedo and diffuse shading images using histogram matching. Our depth estimation is based on local visibility. Unlike other depth-from-shading approaches, all operations are performed on the diffuse shading image in image space, and we impose no constant albedo restrictions. An experimental validation shows our method works for a broad range of textured surfaces, and viewers are frequently unable to identify our results as synthetic in a randomized presentation. Furthermore, in side-by-side comparisons, subjects found a rendering of our depth map equally plausible to one generated from a laser range scan. We see this method as a significant advance in acquiring surface detail for texturing using a standard digital camera, with applications in architecture, archaeological reconstruction, games and special effects. © 2008 ACM

A case study evaluation: perceptually accurate textured surface models

This paper evaluates a new method for capturing surfaces with variations in albedo, height, and local orientation using a standard digital camera with three flash units. Similar to other approaches, captured areas are assumed to be globally flat and largely diffuse. Fortunately, this encompasses a wide array of interesting surfaces, including most materials found in the built environment, e.g., masonry, fabrics, floor coverings, and textured paints. We present a case study of naïve subjects who found that surfaces captured with our method, when rendered under novel lighting and view conditions, were statistically indistinguishable from photographs. This is a significant improvement over previous methods, to which our results are also compared. © 2009 ACM

Modelling appearance and geometry from images

Acquisition of realistic and relightable 3D models of large outdoor structures, such as buildings, requires the modelling of detailed geometry and visual appearance. Recovering these material characteristics can be very time consuming and needs specially dedicated equipment. Alternatively, surface detail can be conveyed by textures recovered from images, whose appearance is only valid under the originally photographed viewing and lighting conditions. Methods to easily capture locally detailed geometry, such as cracks in stone walls, and visual appearance require control of lighting conditions, which are usually restricted to small portions of surfaces captured at close range.This thesis investigates the acquisition of high-quality models from images, using simple photographic equipment and modest user intervention. The main focus of this investigation is on approximating detailed local depth information and visual appearance, obtained using a new image-based approach, and combining this with gross-scale 3D geometry. This is achieved by capturing these surface characteristics in small accessible regions and transferring them to the complete façade. This approach yields high-quality models, imparting the illusion of measured reflectance. In this thesis, we first present two novel algorithms for surface detail and visual appearance transfer, where these material properties are captured for small exemplars, using an image-based technique. Second, we develop an interactive solution to solve the problems of performing the transfer over both a large change in scale and to the different materials contained in a complete façade. Aiming to completely automate this process, a novel algorithm to differentiate between materials in the façade and associate them with the correct exemplars is introduced with promising results. Third, we present a new method for texture reconstruction from multiple images that optimises texture quality, by choosing the best view for every point and minimising seams. Material properties are transferred from the exemplars to the texture map, approximating reflectance and meso-structure. The combination of these techniques results in a complete working system capable of producing realistic relightable models of full building façades, containing high-resolution geometry and plausible visual appearance.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Transfer of albedo and local depth variation to photo-textures

Acquisition of displacement and albedo maps for full building façades is a difficult problem and traditionally achieved through a labor intensive artistic process. In this paper, we present a material appearance transfer method, Transfer by Analogy, designed to infer surface detail and diffuse reflectance for textured surfaces like the present in building façades. We begin by acquiring small exemplars (displacement and albedo maps), in accessible areas, where capture conditions can be controlled. We then transfer these properties to a complete phototexture constructed from reference images and captured under diffuse daylight illumination. Our approach allows super-resolution inference of albedo and displacement from information in the photo-texture. When transferring appearance from multiple exemplars to façades containing multiple materials, our approach also sidesteps the need for segmentation. We show how we use these methods to create relightable models with a high degree of texture detail, reproducing the visually rich self-shadowing effects that would normally be difficult to capture using just simple consumer equipment. Copyright © 2012 by the Association for Computing Machinery, Inc

Image based surface reflectance remapping for consistent and tool independent material appearence

Physically-based rendering in Computer Graphics requires the knowledge of material properties other than 3D shapes, textures and colors, in order to solve the rendering equation. A number of material models have been developed, since no model is currently able to reproduce the full range of available materials. Although only few material models have been widely adopted in current rendering systems, the lack of standardisation causes several issues in the 3D modelling workflow, leading to a heavy tool dependency of material appearance. In industry, final decisions about products are often based on a virtual prototype, a crucial step for the production pipeline, usually developed by a collaborations among several departments, which exchange data. Unfortunately, exchanged data often tends to differ from the original, when imported into a different application. As a result, delivering consistent visual results requires time, labour and computational cost. This thesis begins with an examination of the current state of the art in material appearance representation and capture, in order to identify a suitable strategy to tackle material appearance consistency. Automatic solutions to this problem are suggested in this work, accounting for the constraints of real-world scenarios, where the only available information is a reference rendering and the renderer used to obtain it, with no access to the implementation of the shaders. In particular, two image-based frameworks are proposed, working under these constraints. The first one, validated by means of perceptual studies, is aimed to the remapping of BRDF parameters and useful when the parameters used for the reference rendering are available. The second one provides consistent material appearance across different renderers, even when the parameters used for the reference are unknown. It allows the selection of an arbitrary reference rendering tool, and manipulates the output of other renderers in order to be consistent with the reference

Illuminance-proxy high dynamic range imaging: a simple method to measure surface reflectance

A technique to measure arbitrarily complex patterns of diffuse surface reflectance under real-world illumination conditions is presented. The technique is founded on high dynamic range (HDR) imaging whereby the luminance values in an HDR image are used to derive average and/or per-pixel values of surface reflectance. Two variants of the method are described and the results from both are compared with analytical solutions. Whilst the technique has general application for the measurement of reflectance, the authors make the case that there is a pressing need to survey occupied building spaces since the notional/typical reflectance values commonly employed in simulation for compliance testing may be quite different from those found in real buildings

Polarization imaging reflectometry in the wild

We present a novel approach for on-site acquisition of surface reflectance for planar, spatially varying, isotropic materials in uncontrolled outdoor environments. Our method exploits the naturally occuring linear polarization of incident illumination: by rotating a linear polarizing filter in front of a camera at 3 different orientations, we measure the linear polarization reflected off the sample and combine this information with multiview analysis and inverse rendering in order to recover per-pixel, high resolution reflectance maps. We exploit polarization both for diffuse/specular separation and surface normals estimation by combining polarization measurements from at least two near orthogonal views close to Brewster angle of incidence. We then use our estimates of surface normals and albedos in an inverse rendering framework to recover specular roughness. To the best of our knowledge, our method is the first to successfully extract a complete set of reflectance parameters with passive capture in completely uncontrolled outdoor environments

Visualizing 3D models with fine-grain surface dept

The Daedalus Project has devised new methods for recovering 3D models of scenes from wide-baseline photographs. Current work is focused on developing novel shape-fromshading methods (referred to as Depth Hallucination) to add fine-grain surface detail to the reconstructed models. In doing this, our goal is to reconstruct models that appear visually correct under varying illumination, including subtle effects such as surface self-shadowing. Output from the current software is in the form of a dense polygon mesh and corresponding albedo and normal-depth maps. The main goal of this thesis is to explore GPU algorithms for rendering such models in real time or at interactive frame rates. The aspects explored include rendering with relief textures, and how best to store the raw data and process it on the GPU. We also study the best way to illuminate the scene in a realistic way, keeping the interactive frame-rates as the most important characteristic. Evaluation includes measures of performance, and test cases with varying illumination to compare the results of the project with those achieved with a global illumination algorithm. Another goal of the project is to use only free software. This will concern from the programming environment to the libraries used including the programs that we use for working with image