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Lecture 13: Global Illumination and Path Tracing (19)
joannejqi

What is the purpose of the cosine term in the denominator? Professor Ng mentioned it in lecture briefly but I wasn't able to catch it.

letrangg

The Cosine term is from Lambert's geometric law https://en.wikipedia.org/wiki/Lambert%27s_cosine_law From lecture: with the same amount of light coming in, at a larger angle, there's going to be less light reflected

GitMerlin

What's the point of w_i pointing away from the surface? Do we need to flip signs for that or something?

gprechter

@GitMerlin The way I've thought of the ray of w_i pointing away from a surface is really only convention. I believe all that you need to do is switch the signs for the direction, but overall, I think that the reason they both point out of the hit point is because the hit point is the only coordinate we have readily available, and we need some origin for our rays; and since we don't know where the the ray is going to intersect, we use the hit point.

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