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Questions tagged [physically-based]

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12 votes
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How correct is rendering in XYZ / linear RGB space?

I have a spectral power distribution (SPD, 5 nm steps) for all light sources in the scene and SPDs for the reflectance of all surfaces under any light / viewer angle in question. I'm going to ...
David Kuri's user avatar
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5 votes
0 answers
140 views

What is the potential equation in PBR?

I'am studying PBR and the book introduce the potential equation. They said the potential equation can describe shooting algorithms better, and $W(x, \theta)$ describes the fraction of the radiance $L(...
shashack's user avatar
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4 votes
0 answers
1k views

Better alternatives to the Lambert BRDF

After reading about the new Disney Diffuse BRDF, I have been wondering if this is currently the best Diffuse BRDF at the moment? How much more of a difference would this make compared to using a ...
Arjan Singh's user avatar
  • 2,511
4 votes
0 answers
186 views

How is glint rendering done in Ray Tracing?

How is glint rendering done with ray tracing in the photo below? Is it just a simple normal map? I found a paper online that describes the exact same method used in the photo above but I have no ...
Arjan Singh's user avatar
  • 2,511
3 votes
0 answers
49 views

Diffuse irradiance map : confusion about photometric vs radiometric units

I have spent the longest amount of time just taking the terminology for granted & have only just recently started studying or at least trying to understand the difference between radiometric and ...
Confusedius's user avatar
2 votes
0 answers
54 views

Chart swaps and path inversion in bidirectional path tracing

I've got a hard time to understand how we would implement the following in practice. I'd be great if someone could explain the details for the example below. Assume we're generating a path ${\rm x}=(\...
0xbadf00d's user avatar
  • 203
2 votes
0 answers
54 views

Would the surface of a large carbon-nanotupe structure look metalic?

CNT is a promising new material, which Wikipedia describes as such: Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. These cylindrical carbon molecules have unusual ...
Nikolaj's user avatar
  • 121
2 votes
0 answers
446 views

Is there a material table for the Cook Torrance BRDF?

Is there a material table that lists all the specific values to obtain a certain type of material (e.g: copper or asphalt) available? I found this table in the paper: A Reflectance Model for ...
Arjan Singh's user avatar
  • 2,511
1 vote
0 answers
56 views

Term confusion about volume scattering

We have two different terms, for example, let's talk about scattering only. Scattering coefficient Scattering cross-section These two terms are supposed to have different physical meaning. I read it ...
Enigmatisms's user avatar
1 vote
0 answers
91 views

Difficulty in understanding the interpretation of propagation of an exitant function from the book Advanced Global Illumination (2nd ed)

The book defines operator $\mathcal{T}$ for the propagation of an exitant function as: if I'm assuming that the position of the point $x$ is on the top-left surface, and that $\Psi$ is considered as ...
Domenico's user avatar
1 vote
0 answers
36 views

Image contribution function and reconstruction using filters

So I've been reading Physicall Based Rendering which in section 16.4.3 defines the "image contribution function" to be the following $$I_j = \int_\Omega h_j(X)L(X)d\Omega$$ where the variables are ...
Jake's user avatar
  • 205
1 vote
0 answers
129 views

Compute emitted importance of a pinhole camera

In section 16.1.1 of Physically Based Rendering the authors describe how we can check, if a given ray $r$ corresponds to one starting from the film area. They implement this check such that it works ...
0xbadf00d's user avatar
  • 203
1 vote
0 answers
527 views

Interpreting Cornell Box data for path tracer

So I want to path trace a Cornel Box scene, but I don't understand the values given here in section 2 and 3. Cornell Box Data | Cornell University Program of Computer Graphics No.2 Lists surface ...
gallickgunner's user avatar
1 vote
0 answers
114 views

How to validate whether a reflection model is implemented correctly?

I think this is one of the most important part when you write a physically-based renderer. The solution I came up with is to put a sphere to the scene with a constant background radiance. Solve the ...
Mustafa Işık's user avatar
1 vote
0 answers
85 views

Mitsuba Bidirectional Framework

I'm confused by the Mitsuba bidirectional framework for quite a while now, especially by the different eval and connect ...
demonFudgePies's user avatar
0 votes
0 answers
46 views

Understanding the BRDF Equation

I am studying the BRDF equation. From Wikipedia, the equation is as follows: I have one main question: Where does the $\cos{\theta_i}$ in the denominator come from? The denominator implies that $...
Christopher Miller's user avatar
0 votes
0 answers
17 views

Narrow-phase CCD in FEM topology query (finite element method)

I am implementing IPC from siggraph2020, and one of its step is about CCD line search, where CCD is applied each iteration in the descent method in a part of the algorithm. I have implemented CCD ...
Da1sy petals's user avatar
0 votes
0 answers
75 views

What's The Math Behind This Cloth Animation?

I progammed a simple cloth animation. Initially I tried to implement Hooke's law, but it wasn't numerically stable, presumably because I used explicit Euler. Anyway, I came up with something (WebGL2 ...
fweth's user avatar
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0 votes
0 answers
165 views

Ray casting and rasterization 101

Recently I've became an intern in company-name and my internship task is(for now) create rasterization using rays. I'm mostly interested in pure math, so basic ...
Pavel Snopov's user avatar
0 votes
0 answers
64 views

How is the image reconstruction filter on the path space defined in terms of the filter on the raster space?

Say we have a image reconstruction filter $h:R\to\mathbb R$ defined on the raster space $[0,w]\times[0,h]$, where $w,h\in\mathbb N$ define the width and height of the image plane in pixels, ...
0xbadf00d's user avatar
  • 203
0 votes
0 answers
94 views

Relation between camera sensor responsivity and image reconstruction filter associated with a pixel

Let $W_{\text e}$ denote the camera sensor responsivity (i.e. importance) and $h_j$ and $W_{\text e}^{(j)}$ denote the image reconstruction filter and sensor response associated with the $j$th pixel, ...
0xbadf00d's user avatar
  • 203
0 votes
0 answers
65 views

Is casting a shadow ray non-symmetric in pbrt?

According to the description in the book, Scene::IntersectP() "checks for the existence of intersections along the [passed] ray". This operatorion should be ...
0xbadf00d's user avatar
  • 203