CS 655 – Computer Graphics Global Illumination

BRDF Measurments FYI: Cornell has done BRDF measurements and made them available at: http://www.graphics.cornell.edu/online/measurements/

Global Illumination How do we accurately simulate all light interactions between objects? Diffuse to Diffuse Specular to Diffuse Diffuse to Specular Specular to Specular Which are handled by Ray tracing? Which by Radiosity?

Global Illumination An accurate method must handle all four types Radiosity – very good at diffuse-diffuse. A two pass algorithm can include specular to diffuse. Radiosity is view independent, specularity is not. Ray tracing – specular to specular handled well. Diffuse to specular handled somewhat. Specular to diffuse can be included using a two-pass method or by backwards ray tracing.

Global Illumination Putting light interactions in regular expression form, with E = eye L = light D = Diffuse reflection or transmission G = Glossy reflection or transmission S = Specular reflection or refraction How well do the various algorithms do? Appel ray casting Whitted recursive ray tracing Kajiya path tracing Goral radiosity: E(D|G)L E[S*](D|G)L E[(D|G|S)+(D|G)]L ED*L

Combining Rendering Algorithms Can we get the diffuse interactions of radiosity and also the specular interactions of ray-tracing? Several approaches to doing this Each of them use two passes

Combining Radiosity and Ray Tracing A two pass approach Pass 1: enhanced radiosity to account for diffuse to diffuse and specular to diffuse. Pass 2: diffuse to specular and specular to specular using enhanced ray tracing. Why two passes? A view-independent diffuse computation followed by a view-dependent specular computation is doable.