8 votes
Accepted

Compensation for energy loss in single-scattering microfacet BSDF models

To my knowledge, there is no easy and analytic way of recovering the energy lost in single-scattering models. The previous techniques precompute the energy loss and reinject it in the BRDF as a ...
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7 votes
Accepted

How does Smith multiple scattering interact with diffuse subsurface scattering?

The goal of Heitz et al.'s model is pretty much the opposite of subsurface scattering: They only consider surface scattering, i.e. the ray can never enter the material. Because microfacets are ...
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5 votes
Accepted

Correct form of the GGX geometry term

TL;DR: Your $G1$ formula is wrong. Just to avoid confusion, I am assuming the isotropic version of the BRDF, the Smith microfacet model (as opposed to the V-cavity model), and the GGX microfacet ...
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  • 1,377
3 votes
Accepted

Relationship between roughness and BRDF

Most normal distribution functions (NDFs) are parametrized by some variable (tipically $m$ or $\alpha$) that determines the "roughness" or "spikiness" of the NDF (this is often meant to be the rms ...
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3 votes
Accepted

Why can I see the diffuse lighting effect on a perfect mirror?

Dielectric materials (which is what you get when metalness is 0) don't exhibit a mirror-like effect. Think of a sheet of smooth, non-transparent plastic. Real-life mirrors are panes of glass or ...
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2 votes

Can microfacet BRDF (including ggx) represent perfect mirror?

If this was correct, $\frac{D(H)G(L,V,H)}{4|N⋅V|}$ should be a dirac delta function. But I don't think so. Actually, you're close to your answer - you just are trying to find out, what the assumption ...
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  • 1,437
2 votes
Accepted

Can't understand the Importance sampling GGX

In microfacet BRDFs, the half-vector is the same as the microfacet normal. The half-vector is exactly the required normal for a microfacet to reflect light from the incident ray to the outgoing ray, ...
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  • 23.6k
2 votes

Relationship between roughness and BRDF

for each point $p$ in theory we have a 3D function that tells us the orientation in a given direction You have missunderstood this. $D$ is a Normal Distribution Function (or short NDF), so it doesn't ...
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  • 1,437
2 votes

Implementing the example of Walter et al. (2007) paper

Initially and still I'm not so sure how to get the color of the object behind the glass into the formulas. Normal, this was written with path / ray tracers in mind where that part is easy. Your idea ...
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  • 1,575
2 votes

Conflicting definitions for the distribution of normals $D$ in microfacet BSDFs

The units of the NDF are tricky. For whatever it's worth, Heitz's convention of defining it relative to a 1 m² reference geometric surface is unusual, and although I can see why he would want to ...
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  • 23.6k
1 vote
Accepted

How is the distribution of normals constructed from the distribution of slopes in 'Understanding the masking-shadowing function' paper?

The "slope space" is a coordinate system that describes unit vectors in the upper hemisphere using their $x$ and $y$ slopes, i.e. $-x/z$ and $-y/z$. It's related to the usual polar ...
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  • 23.6k
1 vote
Accepted

How is the maximum value for alpha (roughness == 1) decided for microfacet models?

In truth, there is no mathematical maximum value for $\alpha$. As you noted, microfacet slope is unbounded, so in principle you could have arbitrarily large slope values and hence arbitrarily large $\...
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  • 23.6k
1 vote
Accepted

Microfacet BRDF artifacts

It turns out that the ring was happening from a negative divided by a negative, so adding nom = max(nom, 0.0); fixed the problem. The new highlight, amplified:
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  • 188

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