Illumination engineering ppt

Global Illumination and Monte Carlo and ppt on illumination engineering
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Dr.ShaneMatts,United States,Teacher
Published Date:23-07-2017
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Global Illumination and Monte Carlo MIT EECS 6.837 Computer Graphics Wojciech Matusik with many slides from Fredo Durand and Jaakko Lehtinen © ACM. All rights reserved. This content is excluded from our Creative Commons 1 license. For more information, see http://ocw.mit.edu/help/faq-fair-use/.Today • Lots of randomness Dunbar & Humphreys 2 Today • Global Illumination – Rendering Equation – Path tracing • Monte Carlo integration • Better sampling – importance – stratification 3 © ACM. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 3 Global Illumination • So far, we've seen only direct lighting (red here) • We also want indirect lighting – Full integral of all directions (multiplied by BRDF) – In practice, send tons of random rays 4 Direct Illumination Courtesy of Henrik Wann Jensen. Used with permission. 5 Global Illumination (with Indirect) Courtesy of Henrik Wann Jensen. Used with permission. 6 Global Illumination • So far, we only used the BRDF for point lights – We just summed over all the point light sources • BRDF also describes how indirect illumination reflects off surfaces – Turns summation into integral over hemisphere – As if every direction had a light source 7 Reflectance Equation, Visually outgoing light to incident light the BRDF cosine term direction v from direction omega L in L in Sum (integrate) L in over every v direction on the hemisphere, L in modulate incident illumination by BRDF 8 The Reflectance Equation • Where does L come from? in x 9 The Reflectance Equation • Where does L come from? in – It is the light reflected towards x from the surface point in direction l == must compute similar integral there • Recursive x 10 The Rendering Equation • Where does L come from? in – It is the light reflected towards x from the surface point in direction l == must compute similar integral there • Recursive – AND if x happens to be a light source, we add its contribution directly x 11 The Rendering Equation • The rendering equation describes the appearance of the scene, including direct and indirect illumination – An “integral equation”, the unknown solution function L is both on the LHS and on the RHS inside the integral • Must either discretize or use Monte Carlo integration – Originally described by Kajiya and Immel et al. in 1986 – More on 6.839 • Also, see book references towards the end 12 The Rendering Equation • Analytic solution is usually impossible • Lots of ways to solve it approximately • Monte Carlo techniques use random samples for evaluating the integrals – We’ll look at some simple method in a bit... • Finite element methods discretize the solution using basis functions (again) – Radiosity, wavelets, precomputed radiance transfer, etc. 13 Questions? 14 How To Render Global Illumination? Lehtinen et al. 2008 © ACM. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 15 Ray Casting • Cast a ray from the eye through each pixel 16 Ray Tracing • Cast a ray from the eye through each pixel • Trace secondary rays (shadow, reflection, refraction) 17 “Monte-Carlo Ray Tracing” • Cast a ray from the eye through each pixel • Cast random rays from the hit point to evaluate hemispherical integral using random sampling 18 “Monte-Carlo Ray Tracing” • Cast a ray from the eye through each pixel • Cast random rays from the visible point • Recurse 19 “Monte-Carlo Ray Tracing” • Cast a ray from the eye through each pixel • Cast random rays from the visible point • Recurse 20

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