Bidirectional Path Tracing using Nvidia Optix , Part 10 (Importance sampling)

Up until the last post , i have been using a very naive importance sampling. I found the several combinations of paths for each pixel , the color of which was finally the average value of the light gathered from the various paths. This had the problem that a very probable path e.g. a path with 3 hops from the eye hitting the light , had the same weight in the total light gathering with a very long path which was a lot less probable to happen.

I have changed the weights of the paths in a manner that the more probable the paths are, the more is the contribution of that path into the final gathering.

So i used , a weighted average such as this : 

In this figure the w(x) is the weight of the path x , and p(x) is the probability of this path actually happening

So i had these results with the exact same materials and scene : 

Without Importance Sampling (1/N)

With weighted importance sampling

NEXT POST : I have also implemented the specular gloss material ,as described by Phong model, and i am implementing the Schlick metallness coefficient right now