This paper presents a new reflectance model for rendering computer synthesized images. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. The paper presents a method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material and discusses a procedure for accurately reproducing the color associated with the spectral energy distribution. The model is applied to the simulation of a metal and a plastic.

A reflectance model for computer graphics

Clinical Trials: A Practical Approach

Computer graphics systems are capable of generating stunningly realistic images of objects that have never physically existed. In order for computers to create these accurately detailed images, digital models of appearance must include robust data to give viewers a credible visual impression of the depicted materials. In particular, digital models demonstrating the nuances of how materials interact with light are essential to this capability. 

This is the first comprehensive work on the digital modeling of material appearance: it explains how models from physics and engineering are combined with keen observation skills for use in computer graphics rendering.

Written by the foremost experts in appearance modeling and rendering, this book is for practitioners who want a general framework for understanding material modeling tools, and also for researchers pursuing the development of new modeling techniques. The text is not a "how to" guide for a particular software system. Instead, it provides a thorough discussion of foundations and detailed coverage of key advances.

Practitioners and researchers in applications such as architecture, theater, product development, cultural heritage documentation, visual simulation and training, as well as traditional digital application areas such as feature film, television, and computer games, will benefit from this much needed resource.

ABOUT THE AUTHORS
Julie Dorsey and Holly Rushmeier are professors in the Computer Science Department at Yale University and co-directors of the Yale Computer Graphics Group. Francois Sillion is a senior researcher with INRIA (Institut National de Recherche en Informatique et Automatique), and director of its Grenoble Rhone-Alpes research center.

* First comprehensive treatment of the digital modeling of material appearance;
* Provides a foundation for modeling appearance, based on the physics of how light interacts with materials, how people perceive appearance, and the implications of rendering appearance on a digital computer;
* An invaluable, one-stop resource for practitioners and researchers in a variety of fields dealing with the digital modeling of material appearance.

Digital Modeling of Material Appearance

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 way a surface interacts with the light and on how the light is reflected, scattered, absorbed by the surface and the impact these characteristics have on material appearance. In order to re-produce this, it is necessary to understand how materials interact with 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 Reflectance Distribution Function) models used to represent surface/material reflection characteristics, and describes current acquisition methods for the capture and rendering of photorealistic materials.

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BRDF representation and acquisition

Interesting textures form on the surfaces of objects as the result of external chemical, mechanical, and biological agents. Simulating these textures is necessary to generate models for realistic image synthesis. The textures formed are progressively variant, with the variations depending on the global and local geometric context. We present a method for capturing progressively varying textures and the relevant context parameters that control them. By relating textures and context parameters, we are able to transfer the textures to novel synthetic objects. We present examples of capturing chemical effects, such as rusting; mechanical effects, such as paint cracking; and biological effects, such as the growth of mold on a surface. We demonstrate a user interface that provides a method for specifying where an object is exposed to external agents. We show the results of complex, geometry-dependent textures evolving on synthetic objects.

Context-aware textures

Individually visible scratches, also called isolated scratches, are very common in real world surfaces. Although their microgeometry is not visible, they are individually perceptible by the human eye, lying into a representation scale between BRDF and texture. In order to simulate this kind of scratches in synthetic images we need to know their position over the surface (texture scale), so we can determine where to use the specific scratch BRDF instead of the ordinary surface BRDF. Computing the BRDF of a scratch is difficult because it depends on the scratch’s invisible microgeometry. In this paper, we propose a new physically based model to derive this microgeometry by simulating the formation process of scratches. We allow specifying intuitively the parameters involved in the process such as the scratching tool, the penetration forces, and the material properties of the object. From these parameters, we derive the microgeometries of the scratches by taking into account the real behaviour of the process. This behaviour has been determined by analysing existing models in the field of materials engineering and some “scratch tests” that we performed on metals. Our method has the advantages of easily simulating scratches with a wide range of microgeometries and taking into account the variability of their microgeometry along the scratch path. Another contribution is related to the location of the scratches over the surface. Instead of using an image of the paths as in previous work, we present a new representation based on curves defining the paths. This offers an independence on the image resolution or the distance from the observer and accurately provides the scratch direction in order to compute scratch BRDFs.

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A Physically-Based Model for Rendering Realistic Scratches

Fracture modeling in computer graphics

The simulation of weathered appearance is essential in the realistic modeling of urban environments. A representative and particularly difficult effect to produce on a large scale is the effect of fluid flow. Changes in appearance due to flow are the result of both the global effect of large-scale shape, and local effects, such as the detailed roughness of a surface. With digital photography and Internet image collections, visual examples of flow effects are readily available. These images, however, mix the appearance of flows with the specific local context. We present a methodology to extract parameters and detail maps from existing imagery in a form that allows new target-specific flow effects to be produced, with natural variations in the effects as they are applied in different locations in a new scene. In this article, we focus on producing a library of parameters and detail maps for generating flow patterns; and this methodology can be used to extend the library with additional image exemplars. To illustrate our methodology, we show a rich collection of patterns applied to urban models.

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Image-guided weathering: A new approach applied to flow phenomena

A common weathering effect is the appearance of cracks due to material fractures. Previous exemplar-based aging and weathering methods have either reused images or sought to replicate observed patterns exactly. We introduce a new approach to exemplar-based modeling that creates weathered patterns on synthetic objects by matching the statistics of fracture patterns in a photograph. We present a user study to determine which statistics are correlated to visual similarity and how they are perceived by the user. We then describe a revised physically-based fracture model capable of producing a wide range of crack patterns at interactive rates. We demonstrate how a Bayesian optimization method can determine the parameters of this model so it can produce a pattern with the same key statistics as an exemplar. Finally, we present results using our approach and various exemplars to produce a variety of fracture effects in synthetic renderings of complex environments. The speed of the fracture simulation allows interactive previews of the fractured results and its application on large scale environments. © 2012 Wiley Periodicals, Inc.

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Carles Bosch

Papers

A Physically-Based Model for Rendering Realistic Scratches

Fracture modeling in computer graphics

Image-guided weathering: A new approach applied to flow phenomena

Example-Based Fractured Appearance

Statistical Analysis of