Lecture 007

Conductor vs. Dielectrics

Conductor vs. Dielectrics

BRDF History:

Three Levels of Detail

Three Levels of Detail

Non-Physics-Based Model

Phong Model: just diffused reflection

Phong BRDFA

Phong BRDFA

Blinn-Phong BRDF: says that the normal isn't just surface normal. instead, the normal of a point depends on your viewing angle (due to microfacet)

Blinn-Phong BRDF

Blinn-Phong BRDF

Phong vs Blinn-Phong: Blinn-Phong produce correct specular highlight

Phong vs Blinn-Phong: Blinn-Phong produce correct specular highlight

Ward Model: Gaussian blur distribution over half vector slopes (Original version had issues with energy conservation and singularities; several modified variants exist)

Limitations:

Physically-Based Model

Torrance-Sparrow Model: originally used by physicist until Cook, Torrance, Blinn adapted for graphics. Assumes surface is composed of many micro-grooves, each of which is a perfect mirror.

Microfacet Model

Microfacet Model

There are many microfacet distributions:

Beckmann Distribution

Beckmann Distribution

Beckmann vs GGX Distribution

Beckmann vs GGX Distribution

Beckmann vs GGX Image

Beckmann vs GGX Image

Beckmann Shadowing

Beckmann Shadowing

Torrance-Sparrow (Blinn) Shadowing

Torrance-Sparrow (Blinn) Shadowing

Microfacets does not account for second bounce within microfacets itself, so there is energy loss with large angle.

Increase roughness lead to great energy loss. But there is a paper try to solve it, with huge computational cost.

Increase roughness lead to great energy loss. But there is a paper try to solve it, with huge computational cost.

The Oren-Nayar Model: assumes facets are diffuse, instead of perfect mirror.

Top: Actual Moon. Down: Moon simulated by Original Microfacets model that assumes mirror reflection

Top: Actual Moon. Down: Moon simulated by Original Microfacets model that assumes mirror reflection

Oren-Nayar Model

Oren-Nayar Model

Layered Material Coating

Layered Material Coating

Smooth Plastic

Smooth Plastic

Now, people use all sorts of equipments to get data-driven BRDFs

Spherical Gantry

Spherical Gantry

And they created MERL Database 2003

Sections 5.A-5.C of Eric Veach's thesis have a detailed discussion of the issues we discussed in today's recitation regarding measures, Dirac deltas, and the various ways to write out specular BSDFs. If you are interested, I encourage you to take a read: https://www.proquest.com/docview/304456010?pq-origsite=gscholar&fromopenview=true

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