Archives for: July 2009, 20


Permalink 09:17:11 pm, by Olliebrown Email , 433 words, 3858 views   English (US)
Categories: GSoC 2009

Baseline / Test Cases

Here are some test cases I'm working with to debug and develop the global illumination changes. They are small tests that display important effects of globally lighting very clearly and have appeared in the literature describing various algorithms for such.

Cornell Box:

The scene for the cornell box already exists in the 'data' directory of the main development branch but the materials describing the different colors are broken. I instead uses a scene of the Cornell Box for Blender. First I generated a ground truth image using the radiosity system in Blender, then I exported the geometry and fixed up the color materials inside the world file to make sure we can achieve the same result in lighter2. Here are some images to show the differences. I will use images of this scene to show progress through each milestone.

Cornell box rendered using the radiosity system in BlenderCornell box rendered using direct lighting only in Lighter2
The Classical Cornell Box: (Top) Goal/Ground Truth image - radiosity simulation for the classical Cornell Box scene generated by the built-in radiosity solver in Blender. (Bottom) lighter2 results for direct illumination (no global illumination at all)


  • Area light has been approximated by point lights
  • Milestone 1: we will look for brightening in the shadow areas
  • Milestone 2: we will look for the color bleeding from the walls to the boxes

Construction in Wood:

One very interesting test case for radiosity is a sculpture in the Hirshhorn Museum in Washington D.C. by John Ferren, entitled "Construction in Wood, A Daylight Experiment". It was discovered by some of the early radiosity researchers (particular credit goes to Cindy Gorn who first modeled the sculptured and presented it in her thesis) and used it to show how important diffuse-to-diffuse light interaction can be. All of the color visible on the viewing side of this sculpture comes from light bouncing off the surfaces on the back of the sculpture diffusely (not specularly). The result is a structure that looks completely white and boring when naïvely ray-traced or directly lit but vibrantly colorful when a global lighting solution is computed. I will also use this scene to evaluate and demonstrate progress on this project.

The Ferren Sculpture rendered with the radiosity simulator in BlenderFerren Sculpture - direct light onlhy
John Ferren Sculpture: (Top) Goal/Ground Truth image - radiosity simulation for the Ferren sculpture generated by the built-in radiosity solver in Blender. (Bottom) lighter2 results with only direct illumination showing almost nothing (except some very nice shadows) as expected.


  • I'm still working on getting the materials in CS for this model. I've let it go for now and will try again later.
  • We will look for the same effects in this example for each milestone but they should be easier to discern


Info about progress on my Google Summer of Code 2009 project on Advanced Lighting & Shading in CrystalSpace.

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