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3 votes
Accepted

Plotting pbrt-v3 Gaussian filter

You probably want to set sigma to be a fraction of the radius, rather than a fixed value. Sigma controls the actual shape of the filter, while radius just controls how far out the filter gets cut off (...
Nathan Reed's user avatar
3 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 ...
Nathan Reed's user avatar
2 votes
Accepted

How to change a RGB value using a radiance value?

What you're looking for is called tone mapping, which is the process of mapping from HDR color values generated by a physically based renderer, to LDR color values suitable for display on a screen. It ...
Nathan Reed's user avatar
2 votes
Accepted

Confusion about PDF defined in solid angle / area measure

Actually,shape->Sample(ref, u, pdf) returns the pdf in solid angle measure.The sample function in sample is actually this. ...
袁军平's user avatar
1 vote

Confusion regarding incident direction in render equation

$L_i(p,\omega_i) = L_o(p+t\omega_i,-\omega_i)$ where t is some distance to another point, so $\omega_i$ is "positive" (-) when evaluating $L_o$ but "negative" (+) for $L_i$. So if $...
Mathis's user avatar
  • 139
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 $\...
Nathan Reed's user avatar
1 vote
Accepted

Is spectral response curve and spectral power distribution the same thing?

The book distinguishes a spectral power distribution from a spectral response curve because they are not the same, they are adjoint. The thing about adjoints that makes them a little tricky to wrap ...
Pseudonym's user avatar
  • 771
1 vote
Accepted

How can I account for specular interactions in shadow rays?

Shadow rays that hit a glass surface or similar are stopped because there's no direct path from the light source to the shading point—there's a piece of glass in the way. for perfectly specular ...
Nathan Reed's user avatar
1 vote
Accepted

How to decide which child of BVH to visit based on sign of ray's direction vector?

In your example of a BVH cell partitioned along the x axis, if the ray is going left to right (increasing x), then the cell with the lower x comes first; but if it's going right to left (decreasing x),...
Nathan Reed's user avatar
1 vote
Accepted

How to calculate the PDF of a multi-lobe BSDF

The summation doesn't include the BxDF that was picked for sampling. Look again at this line: if (bxdfs[i] != bxdf && bxdfs[i]->MatchesFlags(type)) ...
Nathan Reed's user avatar

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