Hi

I'm wondering why do we need to take the pdf of primary ray into account and ignore primary ray pdf in traditional path tracing.

In a bidirectional path tracing algorithm, the connected segment won't take pdf from any point to the other because those two points are generated from more earlier points. My take on it is that it is pretty similar to light tracing by connecting light sample and camera eye point. (I didn't consider anything about finite size aperture with DOF effect, maybe it is relevant.)

Appreciate for any tips.

Thanks

Jerry