Metal materials study

Texture artist Jarrod Hasenjager posted a page of various metal materials study: aluminum, brass, bronze, chrome, copper, gold, iron, lead and steel, and rusted steel and iron. According to the description, the renders are done in Houdini, and the look is driven by artistic taste and personal experience rather than from physical values.

Toward physically based rendering, screenshot after screenshot

Here are the screenshots I made for the talk I previously mentioned. They show how the rendering evolves through the choice of shading. The setup consist of a close yellowish punctual light on the up right, and a distant red-ish punctual light on the back left, as well as a dim blue ambient. The objects only differ by the specular exponent, which jumps by a times two factor from one object to the next one, left to right.

One light, Lambert diffuse only.

Two lights, Lambert diffuse only, with variance shadow map.

Two lights, Lambert diffuse only, with albedo.

Two lights, diffuse and Phong specular. Notice the color on the left.

One light, Phong specular only. Notice the discontinuity on the left.

Two lights, diffuse and Blinn-Phong specular.

One light, Blinn-Phong specular only. Notice the absence of discontinuity.

Two lights, diffuse and normalized Phong specular. Notice the highlight intensity.

Two lights, diffuse and normalized Blinn-Phong specular.

Two lights, diffuse and normalized Blinn-Phong specular, Fresnel term with Schlick

Two lights, Heidrich-Seidel anisotropic specular.

Next steps: getting used to the Fresnel version, experimenting with the exponent as a texture lookup, and normalizing the Heidrich-Seibel specular.

Talking about light at Revision

Over the last months I have been reading various resources on light shading, and shared the most relevant ones on this blog. Along the way I became more and more thrilled by how light interacts with materials and how we can model it to get more convincing rendering.

I found some insights to be really enlightening and very worth sharing. Therefore as a way of challenging my own understanding of this matter and as an opportunity to practice talk, I decided to speak about real-time lighting during a seminar at Revision.

Revision is a big demoparty that will be held during four days over the Easter weekend in Saarbrücken, Germany. If you are coming (which I recommend) and want to hear about shading, specular and Fresnel, come and see me!

Update: the talk is scheduled for Saturday April 7th, 14h – 15h.

“Introduction to light shading for real-time rendering”

Update: see this post for the material.

Readings on physically based rendering

Physically based rendering (PBR) seems to be the hot thing recently in game as well as film industries. Last year at SIGGRAPH Naty Hoffman led a course on physically based shading. The first talk in particular gives some excellent insights on the physics behind lighting.

This year, at SIGGRAPH again, the physically based lighting used in Call of Duty: Black Ops was one of the topics of the course Advances in Real-Time Rendering in 3D Graphics and Games. Keith Judge wrote an article to sum up the ideas presented in this talk in shading language. Sébastien Largarde also has some insights on the shift to physically based shading from a production point of view.

On a narrower topic Rory Driscoll briefly explained the problem of energy conservation, a first but important step toward PBR, in a convincing and straight to the point manner. In articles mentioning normalization factors the origin is not always clear, especially when authors take shortcuts to avoid digressing from their topic. Fortunately Fabian Giesen wrote a demonstration of the normalization factor for the Phong and Blinn-Phong models and Chris­t­ian Schüler gathered various of the normalization terms we can see in publications, with proper references.

There are many other sources to read, but I will stop there for now. Just follow the links and you have plenty of reading already. ;)

Addendum: Sébastien pointed out this article on energy conservation for wrapped diffuse lighting and this one on physically plausible microfacet BRDF, which includes a WebGL demo to play with.

Update: Tri-Ace has made a couple of presentations on the matter over the last years, which you can find on their research page.

Update: this article, Basic Theory of Physically-Based Rendering, presents the ideas of PBR in a very easy to read manner and works well as an introduction.