Questions tagged [pbr]
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78
questions
2
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"Charlie" Sheen BRDF's directional albedo integrates to values higher than 1 at low roughnesses. Does this mean it is not energy conserving?
I am implementing the BRDF from the 2017 paper "Production Friendly Microfacet Sheen BRDF". This BRDF is modelled as a coat layer stacked on top of a base specular. In order to do so in an ...
- 53
1
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1
answer
247
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Confusion over Microfacet-based BRDFs and Normal Distribution Functions
Through reading various sources online, I've become a bit confused. I'll briefly outline what I think I do understand:
My understanding is that microfacet-based BRDFs assume there is always a perfect ...
- 229
0
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0
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63
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Unable to compute fresnel reflections properly
I am implementing fresnel reflections for materials in my renderer.
According to this source, here the look I should obtain when rendering a sphere over a grey background:
I have two implementations. ...
- 103
0
votes
1
answer
168
views
Does fresnel reflection make sense for metals?
I am implementing fresnel reflections for materials in my renderer.
Does it make sense for metals?
Here my implementation:
...
- 103
0
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0
answers
179
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One-sample model Multiple Importance Sampling with balance heuristic
Recently I feel a bit confused about one-sample model MIS. One sample model MIS can be found here in Veach 1997. 9.2.4 The one-sample model, and this one-sample model is widely used in the opensource ...
- 1,112
1
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1
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101
views
Shading normal and geometric normal for refractive surface rendering
I got confused when implementing my own renderer. I read this from the PBR-book:
Fortunately, there is an elegant solution to these problems. When evaluating the BSDF, we can use the geometric normal ...
- 1,112
1
vote
0
answers
69
views
replace IBL with single color - the lighting equation
I want to avoid IBL (image based lighting), however my scenes are way too dark - especially close-to-mirror like surfaces, which get little contributions from other direct light sources in the scene.
...
- 41
1
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1
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175
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The purpose of NdotV in the directional-hemispherical reflectance equation in the book "Real-time rendering book"
I have been reading the book "real-time rendering 4th edition" and came across this Directional-hemispherical reflectance equation.
$$R(\mathbf{l}) = \int_{\mathbf{v}\in\Omega} f(\mathbf{l}, ...
1
vote
1
answer
66
views
Is the dichromatic model physically based?
lately I have been learning about photometry, and everywhere I look I see a BRDF written according to the "dichromatic model". Roughly speaking: $$\rho= \rho_D+\rho_S \cdot (...)$$
for some $...
- 113
1
vote
0
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94
views
Why my bsdf can not pass Chi2test?
I implemented a MicrofacetTransmission in nori. But it can not pass all Chi2test when alpha is large(>= 0.4 or ?),part of chi2test is passed.And I can not found the problem.Can someone help me?
...
- 31
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1
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127
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how can I compute a roughness map without any 3D softwares?
Recently, I want to use a roughness map to get better rendering results.
Most information on the internet is about the operation of 3D software.
So, how can I generate a roughness map of my own 3D ...
1
vote
1
answer
151
views
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. ...
1
vote
0
answers
136
views
Contour-line looking artifact on diffuse irradiance map
I tried implementing my own diffuse irradiance map maker after reading Learn OpenGL > PBR > IBL > Diffuse Irradiance.
It takes an HDR image and makes six HDR cube map.
But It keeps making ...
- 111
0
votes
1
answer
99
views
PBR pipeline with multiple HDR images?
I believe I already know the answer to this question, but I want to make sure I'm understanding this correctly. Within a physically based rendering pipeline, you calculate your indirect lighting from ...
- 105
3
votes
1
answer
208
views
Confusion of deriving the Jacobian of the reflection transformation in Walter et. al's 2007 paper
When deriving the Jacobian of the reflection transformation in Walter et. al's 2007 paper:
First we have a macrosurface BSDF which is:
$f_{s}(\mathbf{i}, \mathbf{o}, \mathbf{n})=\int\left|\frac{\...
- 31
2
votes
3
answers
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PBR : Understanding the right part of Split sum integration of specular IBL
This is the website I am learning from.
In the specular part of IBL this is the split sum approximation
Now the left part of the equation I have asked in This post and I have understood everything ...
- 179
0
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1
answer
125
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PBR : generating dynamic HDR maps
Most of the PBR tutorials out there use HDR maps loaded from disk. But in games these maps need to be generated by taking snapshots of the scene from the objects location which is where problems arise....
- 179
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2
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495
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PBR : Understanding importance sampling
I have read this article
On PBR and in it we have NDF function defined as follows
Then I have read this article on random vector generation
Here are what I feel are the important bits.
Now jump to ...
- 179
0
votes
1
answer
441
views
Path tracing: How to ensure we are sampling a direction vector within the visible hemisphere of a surface?
Given a surface Normal vector of an intersection point, how can one generate a random direction vector that is guaranteed to be in the visible hemisphere? The way I ...
- 241
3
votes
0
answers
653
views
Comparing different sampling methods for GGX IBL
I have made a demo that shades a sphere with an environment map. I wanted to compare 3 different ways of sampling the environment.
Uniform sampling.
Importance sampling with the NDF as suggested in ...
- 137
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votes
2
answers
499
views
Ray Tracing, why does the GGX make my rendering result darker and darker for each frame?
I am trying to add GGX and PBR textures to my GPU ray tracer. The result is very strange, it's getting darker for each frame.
...
- 131
0
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1
answer
322
views
BRDF for point lights should not return values over 1
This is standard Cook-Torrance BRDF in formulation for a single point light. No intergrals over a hemisphere, just a single direction to a source of incoming energy.
$$
L_o = { \bigg ( (1-F) \frac{...
- 193
0
votes
1
answer
538
views
What is wrong with my metallic PBR shader?
I feel like my light conservation math isn't correct, but I am not sure which part is wrong.
Is reflected light supposed to influence the diffuse light?
Does metalness only affect the reflected ...
- 153
1
vote
0
answers
70
views
How to handle negative reflection directions in raytracing?
I got a function that generates samples from a GGX visible normal distribution function. When I use it to calculate reflection directions obviously some of these intersect with the surface agin (...
- 11
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0
answers
86
views
Considering a path generated by bidirectional path tracing under a different strategy
Say I have constructed a path, using bidirectional path tracing (BDPT), consisting of a light subpath $y$ with $s=2$ vertices and a camera subpath $z$ with $t=3$ camera vertices.
Now I want to ...
- 203
2
votes
0
answers
164
views
Scaling of the final image in Metropolis Light Transport
I don't understand why the PBR implementation of Metorpolis Light Transport scales the final image by b / mutationsPerPixel.
The authors write:
Each Metropolis ...
- 203
0
votes
0
answers
66
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 ...
- 203
0
votes
0
answers
53
views
Distribution of the first vertex on a camera subpath in bidirectional path tracing
Suppose we are sampling camera rays of a perspective camera with a finite aperture. The PBRT implementation of the sampling scheme looks like this:
...
- 203
0
votes
1
answer
598
views
Standard ways to create xml scenes for research purposes
I am a newbie in computer graphics and just started working on physically based rendering engines such as Mitsuba.
I found it difficult to create my own scenes, that are xml files. To create one, ...
- 147
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votes
0
answers
212
views
Multiple Importance Sampling in Bidirectional Path Tracing
I'm trying to understand the computation of the path density described in the book Physically Based Rendering. They assume that a path $$x=(x_0,\ldots,x_{n-1})=(q_0,\ldots,q_{s-1},p_{t-1},\ldots,p_0)$$...
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