Digital Modeling of Material Appearance

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Course Schedule and notes organization 1. ntroduction -10 mins Digital Modeling of the Appearance of Materials: Art or Science? 2. A Visual Tour of materials and their classification -20 mins 3.Really Brief Terminology and Mathematical Descriptions -10 mins 4. Models for reflectance -20 mins Empirical First Principles Measured 5. Spatial variations-15 mins 6. Processing of materials -30 mins 7. Additional materials DORSEY, J, AND HANRAHAN, P. Modeling and rendering of metallic patinas. In Proceedings of the 23rd annual conference on Computer graphics and interactive techniques(1996) ACM Press pp.387-396 DORSEY, J, PEDERSEN, H K, AND HANRAHAN, P Flow and changes in appearance. In Proceedings of the 23rd annual conference on Computer graphics and interactive techniques (1996), ACM Press, pp 411-420 DORSEY, J, EDELMAN, A, JENSEN, H.W., LEGAKIS, J, AND PEDERSEN, H K. Modeling and rendering of weathered stone. In Proceedings of the 26th annual conference on Computer graphics and interactive techniques(1999), ACM Press/Addison-Wesley Publishing Co., pp 25-234 8. References for further reading Slide 1 SIGGRAPH2005 Digital Modeling of the Appearance of Materials Julie Dorsey Holly Rushmeier ale University In these course notes we present basic principles of defining numerical models to be used in rendering realistic imagery of physical materials. Additional information on research in rendering and materials can be found at our group websiteathttp:/graphics.cs.yaleedul.Updatesorcorrectionstothesenotes will be posted at this site Slide 2 1INTRODUCTION Digital Modeling of the Appearance of Materials Art or science?? The materials here are rendered with models. artists conceived the shape and selected materials to construct such objects in the physical world. A purely artistic approach could be used to digitally paint the shades of light and dark on the digital shapes to give the illusion of translucent stone or shiny gold metal However, to generate these images material models are expressed numerically and rendered using lighting simulations. That is their appearance-the colors shades of light and dark, were computed, rather than being digitally painted on the model There are many ways in which compelling visual images can be generated of the world. Different approaches can be used to create images, all of which are valid in some set of circumstances To define our approach in this course we distinguish between the use of digital models to define materials, and the use of techniques. Broadly, by digital models we mean a scientific or engineering approach to rendering and by technique we mean an artistic or craft-oriented approach We are focused here on digital models of materials Slide 3 Digital Models: Predictable control parameters Consistent across view and lighting conditions Shinier We define a model as taking a physically measurable input and producing a predictive output that can be verified by physical measurement. A model of a material makes possible the reliable rendering of the appearance of that material in any geometric and lighting conditions. We define a technique as taking an input which is not necessarily measurable, and produces an output that may or may not reproduce the appearance of an object under arbitrary circumstances Human judgment is required to set the input of of a technique, and to evaluate its success Slide 4 Digital Models: Goal is to produce images that appear the same as seeing a scene or object in person Our goal is to make predictive images that give a view of a scene or object that is the same as if the person were viewing it directly. Material modeling is one aspect of this. We need to consider the object's shape, and the light incident on it. We also need to take into account how the incident light is perceived b humans. Perception is a complex phenomenon, but some simple understanding of it makes modeling easier. the complexity of human perception is what makes digital imaging even possible. It is a remarkable fact that vastly different arrays of incident light, if adjusted properly, give us the same visual impression Slide 5 Light leaving an object that reaches our eye is the physical stimulus that allows us to see it. The physics of light has been studied intensely for centuries. Our understanding of light has moved from the Greek's corpuscular theory, to Huygen's waves, to Einstein's theory of relativity and continues to expand. In modeling appearance our goal is not to incorporate the entire body of knowledge that has been accumulated. It is generally not appropriate or useful to use the most low level, detailed models of light that have been developed in physics What we want to do is extract from what is known about light the models that are relevant to the human process of seeing an object Most of the effects of light relevant to image synthesis are well modeled by geometric optics In geometric optiCS, in a typical scene, we model the way light travels as along straight paths between surfaces. The surfaces may either absorb or redirect the light into a new direction

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