# How to calculate subsurface scattering weights for fast skin shading

This question is in reference to the method described in ShaderX7 section 2.4 "Fast Skin Shading" by Hable et. al. The part I do not understand is how they derived the weights for the individual samples. They describe the process only very briefly like this:

"Since using a sum of Gaussian blurs is a good way to describe subsurface scattering, we describe the blur in this way. Then, in an offline process, we combine the sum of the blurs into a single blur, and then sample. This approach provides us with an intuitive way to tweak the blur for different skin types."

I assumed this means that they calculated the weight $$W$$ for a sample as

$$W = \sum_i w_iG(v_i, r)$$

but the result is completely off. So what is the correct way to calculate these?