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Lecture 13: Global Illumination and Path Tracing (8)
Michael-hsiu

I wonder if the light reflected off of a ray follows a probability distribution: an obtuse angle of reflection might reduce the light entering the pixel, while a pixel directly facing the ray would maximize the light reflecting off the surface and thus entering the pixel (so we could use the cross product with the tangent to the pixel to determine radiance perhaps?).

youtuyy

we already have a cos factor and the bsdf rate for the irradiance of the light. I wonder what do you mean by an obtuse angle of reflection might reduce the light entering the pixel? Re you referring to the intensity or the radiance? I think we take intensity into account in the sum.

jchen12197

I'm not sure I'm understanding this image correctly. What does "into the ray's (reverse) direction" mean? Aren't the rays pointing towards the surface?

hershg

we can cast a ray from the viewpoint through the window and to the hit point on an object surface, and then find the irradiance (factoring in cos factors and all) to determine the lighting intensity for that pixel. The "into the ray's (reverse) direction" part refers to the fact that the radiance along the path from lightsource->surface->window pixel -> viewpoint == the radiance along the reverse path (which is what we're computing)

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