Lambertian vs. Ashikhmin-Shirley

This is a recreation of an image found in the paper An Anisotropic Phong BRDF Model by Michael Ashikhmin and Peter Shirley.

The left sphere uses a Lambertian BRDF. The right sphere uses the Ashikhmin-Shirley BRDF with Shininess U and Shininess V set to 5 and the Glossy Reflectance set to 0. Note the presence of highlights on the right sphere (along with strong edge darkening, which is a known problem of this BRDF model).

The white square on the left is actually a red light; the one on the right is a green light. They appear white because they are too bright to be represented in a low dynamic range image. The strong aliasing around the lights is also a consequence of their brightness. Both problems can be solved with proper tone mapping, a feature that appleseed doesn't support yet (as of version 1.1.0 alpha-9).