Friday, November 11, 2011

Russian Roulette, RGB Version

What I did this week was to do correct photon absorption and power adjustment. This is done through a randomized method called Russian Roulette. Here's a quick summary: when a photon hits a surface, given the surface is not a 100% reflective (mirror), the photon will bounce off with less power. Instead of casting a photon with decreased power, Russian Roulette method casts the photon with a probability equivalent to the reflectivity of the surface. When integrating (averaging) photon powers to get the reflected radiance, the results are the same. This is an optimization since less photons will have to be cast total, and thus less would have to be integrated.

I implemented this in my photon scattering code on the Javascript side, and visualized it using WebGL, with colored lines representing the photon color (respective RGB power) and the incident direction.

At the moment I have the basic photon scattering and tracing down. The next step would be to do photon gathering or the radiance estimate. I am planning to implement this on the shader, per pixel; however, Norm mentioned that I should be doing this on the Javascript side as well since radiance estimate is also view-independent. I'm not too sure about this and will need to look into it further.

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