About "pdf_weight"

[lijunnankman]

Hi,It's a nice work.
However,I have no idea about :https://github.com/NVlabs/nvdiffrecmc/blob/main/render/optixutils/c_src/envsampling/kernel.cu#L180.
Why the numerator of pdf_weight is params.cols.size(0) * params.cols.size(1)？
My understanding is that the function of pdf_weight is to convert the probability density function p(u,v) in the uv coordinate system into the probability density function p(w_i) in the spatial coordinate system.

[JHnvidia]

Hi @lijunnankman,

The pdf_weight ratio is normalization between the area of the 2D sampling domain [w,h] and the unit sphere + an additional term to account for latlong mapping area warp. Intuitively the nominator / denominator is flipped because you'll end up dividing by the pdf. The sampling code is inspired by: https://cs184.eecs.berkeley.edu/sp18/article/25

[lijunnankman]

Hi, @JHnvidia ,thanks for quick reply. I got it in https://cs184.eecs.berkeley.edu/sp18/article/25 step 4.
But ,I have another question about https://github.com/NVlabs/nvdiffrecmc/blob/b3089bba5fa52ece34ceac26965ebe744f4405f8/render/light.py#L50C41-L50C41 .
Why is the value of pdf obtained from max() on the base channels? In https://cs184.eecs.berkeley.edu/sp18/article/25 step 1, they just only use E to calculate pdf.(They did not explain how to deal with E)
Have you try another way to compute the pdf?