Questions tagged [pbrt]
For questions related to techniques described in the book *Physically Based Rendering: From Theory to Implementation*
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How do you derive the integral equation of transfer in the PBRT book?
In the PBRT book section on the equation of transfer, they give the equation$\frac{\partial}{\partial t}L_o(p',\omega) = -\sigma_t(p',\omega)L_i(p',-\omega)+\sigma_t(p',\omega)L_s(p',\omega)$,and ...
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0answers
103views
How does PBRT rewrite the majorant transmittance integral over segments when sampling the majorant transmittance?
In the PBRT book section on Sampling the Majorant Transmittance, they take the equation:$\int_0^t \sigma_{maj}(p')T_{maj}(p \to p')f(p')dt'$,and using the multiplicative property of transmittance$...
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1answer
86views
How is this null-scattering transmittance equation in PBRT derived?
In the PBRT book section on null scattering, they define the null-scattering coefficient $\sigma_n$ and the constant majorant $\sigma_{maj}$, and define the equation:$\frac{dL_o(p, \omega)}{dt} = -(\...
1vote
2answers
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Issue with derivation of the Volterra integral formulation of volumetric transmittance on pbr-book.org
In the fourth edition of Physically Based Rendering, they take equation 11.9:$\int_0^d \frac{dL(p + t\omega)}{dt} \, dt = L(p') - L(p) = \int_0^d -\sigma_t(p + t\omega) \, L(p + t\omega) \, dt$,and ...
2votes
1answer
91views
The reciprocity of BSDF and equilibrium of rendered scene
in chapter 6 of Eric Veach's paper, Veach has proved general reciprocity of BSDF by Kirchhoff’s equilibrium radiance law and detailed balance$$\frac{f_s(w_i \rightarrow w_o)}{\eta_o^2} = \frac{f_s(...
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1vote
1answer
150views
PBRT - Transforming between Distributions (Section 2.4)
In the 4th edition of "Physically Based Rendering" here:pbrt book 4th ed Section 2.4in Section 2.4 "Transforming between Distributions", it is said "Suppose we are given a ...
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1answer
90views
How are these two projection matrices related?
I have two 3D perspective projection matrices $A,B$ with standard projection parameters $k=\cot(\theta/2)$, where $\theta$ is the field of view, $n$ is the $z$-near value, $f$ is the $z$-far value, ...
- 157
1vote
1answer
99views
Distance sampling with unbiased transmittance estimators
I'm currently trying some things with transmittance estimators in PBRT and I have implemented the following paper: Unbiased Ray-Marching Transmittance Estimator. This method assumes that two points $x$...
1vote
1answer
236views
Point light source radiance
I was reading Deriving radiance from irradiance and intensity and the last comment said that by dividing $r^2$ we convert radiant intensity to irradiance. What confuses me then is the fact that for ...
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1vote
1answer
118views
Confusion regarding incident direction in render equation
I am studying from pbrt-v3 and the rendering equation has just been introduced as$$\underbrace{L_\mathrm{o}(\mathrm{p},\omega_\mathrm{o})}_\text{Outgoing radiance }=\underbrace{L_\mathrm{e}(\mathrm{...
- 157
1vote
1answer
383views
Confusion about PDF defined in solid angle / area measure
When using MIS, we always want to express the PDF value in a unified measure in order not to render the ratio between them meaningless. Yet when I read through chapter 16 of PBR-book, I got confused ...
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0answers
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PBRT: requests sample dimensions in the same order
PBRT 7.2.2 illustrates an example onrequests sample dimensions in the same order:...
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0answers
159views
Sampling Quad Shape Light Using Spherical Rectangles in Local Space
The paper "An Area-Preserving Parametrization for Spherical Rectangles" describes an efficient approach for sampling solid angles for rectangle light sources.I am wondering ifThe light ...
- 750
1vote
1answer
217views
Conflicting definitions for the distribution of normals $D$ in microfacet BSDFs
Please do not confuse this question with this one. In Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs, Eric Heitz defines the distribution of normals as.There, the footnote. ...
2votes
1answer
540views
How is the maximum value for alpha (roughness == 1) decided for microfacet models?
Recently I have been looking at pbrt, and was looking at their remapping from roughness to $\alpha$ values:https://github.com/mmp/pbrt-v3/blob/master/src/core/microfacet.h#L86I understand that it is ...
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