Questions tagged [pbr]
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56
questions
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16 views
Subpath connection in Bidirectional Path Tracing for subpaths consisting of a single vertex
Consider the PBRT implementation of the subpath connection in bidirectional path tracing for the strategy with a single camera vertex, as described here: http://www.pbr-book.org/3ed-2018/...
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36 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:
...
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0answers
23 views
Computing probabilties when connecting a camera subpath to a single light point
I'm struggling to understand how the connection step in bidirectional path tracing for the strategy with a single light vertex has to be implemented. The following code essentially shows the PBRT ...
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1answer
16 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, ...
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40 views
Implementation of the Primary Sample Space Sampler in the book Primary Sample Space Sampler
In the Multiplexed Metropolis Light Transport implementation of the book Physically Based Rendering, the proposal samples are generated by the Primary Sample Space Sampler ...
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62 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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1answer
60 views
Roughness Value of (Close to) Zero in Physically Based Rendering
In my Direct Light Physically Based Renderer, when I set the roughness too low (ie. 0.0 or close) the specular reflection doesn't show, not even at high resolutions and at perfect angle with the ...
1
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1answer
74 views
Understanding the irradiance map generation
I am trying to understand how the generation of irradiance maps works. I was reading LearnOpengGL tutorial and Codinglabs article. Reading those articles, I got a bit confused about how we use ...
5
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3answers
131 views
What is the purpose of the projected solid angle $dA^\perp$ term in the definition of Radiance?
In the definition of Radiance, which according to PBRT is defined as
flux per unit solid angle $d\omega$ per unit projected area $dA^\perp$
$$L_i=\frac{d\Phi}{d\omega\ dA^\perp}$$
My original ...
2
votes
1answer
82 views
Strange dark spot when lighting in deferred rendering PBR shaders
It's probably something obvious but there seems to be a strange issue with lighting in my pipeline. I'm trying to keep everything in world space at the moment for simplicity but cannot figure out what'...
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18 views
Specular error - wrong TBN transformations
I have a problem with TBN matrices due to their transformation in world space.
In .cpp I am trasforming my worldMatrix based on rotation:
...
2
votes
1answer
87 views
how many watts are in the SPD of the color white?
Please help. I'm trying to implement a ray tracer, going by the PBRT book and got stuck on an issue that I fail to find the answer to. My scenes are made from objects and light sources. From that, I ...
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24 views
Why need a $h$ parameter in the Geometry Function of a BRDF
Geometry Function in the specular BRDF term is defined as $G(l, v, h)$. Why need a $h$ since $h=\frac{l+v}2$.
$f_{spec}(l,v) = \frac{F(h,v)G_2(l,v,h)D(h)}{4|n\cdot l||n\cdot v|}$ from "Real Time ...
2
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1answer
79 views
Why is cos(𝜃) in the denominator in the reflectance equation and in the numerator in the shading equation?
Background: I'm reading https://learnopengl.com/PBR to learn about PBR. In the theory slide (https://learnopengl.com/PBR/Theory), the author has the reflectant equation as
The theta (the angle ...
1
vote
1answer
68 views
How to implement physically based unit in pbr renderer
According to this note, Frostbite use photometry unit in their calculation. I am trying to mimic this feature, but I am not sure what transformation need to be done. I will try to explain what I have ...
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0answers
54 views
Questions about BRDF parameterization
Hi I'm trying to get a better understanding of the BRDF modeling. I only implemented naive diffuse(lambert), specular and microfacet BRDF before, but I don't have much experience in mixed BRDFs and ...
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0answers
254 views
GGX BRDF is greater than 1?
I am implementing a GGX BRDF, this is the formula I used is from:https://schuttejoe.github.io/post/ggximportancesamplingpart1/
And this is my implementation:
...
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1answer
143 views
How Image Based Lighting is applied to indoor scene?
Now the mainstream engine's approach is to use image-based lighting to achieve approximate global illumination, but such a technique seems to be only applicable to outdoor scenes.What kind of ...
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1answer
115 views
Why can I see the diffuse lighting effect on a perfect mirror?
Currently I am learning PBR by Unity3D. I find that even I turn the smoothness to 1, I can still see the diffuse lighting effect, which does not make any sense to me.
Imagine I trace a ray from my ...
0
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1answer
101 views
Weirdly looking diffuse irradiance map
I have problem with creating diffuse irradiance map. As reference I am using https://learnopengl.com/PBR/IBL/Diffuse-irradiance and https://github.com/TheEvilBanana/PhysicallyBasedRendering/blob/...
3
votes
1answer
246 views
Iridescence/Thin-film interference integration as a layer
I'm trying to integrate the thin-film interference effect described in the paper "Belcour, L., & Barla, P. (2017). A practical extension to microfacet theory for the modeling of varying ...
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0answers
39 views
confused on isotropic BRDF
I am reading a paper and there is a part I don't understand:
I am wondering why the isotropic BRDF only depends on the view direction and roughness? Why is the light direction not related?
2
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1answer
75 views
Confused on reflection coeffcient of Fresnel equations
I am reading a paper about layered materials. However, I am confused on the implementation of this paper. The following picture describe the layered material.
r_ab is a complex reflection coeffcient ...
1
vote
1answer
225 views
Can't understand the Importance sampling GGX
I've read many articles relating to importance sampling of GGX. However, I still feel confused.
The formula of GGX is :
And many article says we should use this formula to sample:
In the formula, ...
3
votes
2answers
236 views
Luminance and Radiance in computer screen
I am currently building a graphics engine. I have a slight confusion on the imaging pipeline of computer screen. My question is how does computer transform the colour in the final frame buffer to ...
6
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2answers
247 views
PBR missing rim darkening on non metallic rough surfaces
If you have a dielectric (non metallic) sphere with a large roughness value (say, 0.95), and put it in a lighting environment that has a constant onmidirectional lighting value (such as 0.5) Cook-...
3
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1answer
172 views
Importance Sampling in Unreal Engine Formula Derivation (Irradiance term)
I am currently trying to understand IBL in Unreal Engine, and there are so much things that I don't understand about the formula. Unreal approximate the specular term of shading equation by doing ...
3
votes
1answer
488 views
BRDF normalization
I don't understand how to normalize the BRDF.
the constraint is that for each incoming ray, the exitant ray will be $1$ at most
ie integral of hemisphere of $f_r\cdot\cos(\theta)$ where $f_r$ is the ...
4
votes
2answers
231 views
Texture prefiltering for Linearly Transformed Cosines
I'm implementing Real-Time Polygonal-Light Shading with Linearly Transformed Cosines from Siggraph 2016.
I'm stuck on the texture prefiltering (section 5.3).
As I understand they use ...
4
votes
0answers
78 views
Predicting reflectance functions from complex surfaces
There are three principal ways to obtain a BRDF. We can
Derive an analytic formula using physical principles
Use simulation given an assumed or measured model of the surface
microgeometry
Measure ...
6
votes
1answer
801 views
Microfacet shading for diffuse materials
I recently replaced the Lambertian BRDF in my path-tracer with Oren-Nayar, under the assumption that I could adjust it to use the GGX distribution model with appropriate masking/shadowing.
PBR ...
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0answers
76 views
How to make Convolved Diffuse and Specular image in C#
I am trying to take either a HDR panoramic or HDR cubeMap and from that create a Lambert Irradiance environment map and a Cook-Torrence Specular environment map.
I am stuck at the proper ...
5
votes
1answer
204 views
Roughness Remapping
I have been recently exploring physically-based rendering (PBR), but there is one part that still confuses me. I don't quite get roughness remapping, as described in the PBR section on Learn OpenGL. ...
4
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0answers
792 views
Explanation of math of the Smith G1 term
In appendix A of the paper Microfacet Models for Refraction through Rough Surfaces there is a derivation provided for $\Lambda(w)$ but the mathematics is very confusing. Could somebody help me by ...
4
votes
1answer
242 views
Tasks of a professional graphics programmer?
Currently I'm 16 and in high school and I love graphics programming and I'm seriously considering it as a career path. I was wondering what a day as a graphics programmer looks like for offline ...
5
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2answers
2k views
How to calculate attenuation and radiance in PBR? (point and directional lights)
I would like implement physically based rendering, following this tutorial
I was able to find a list of light sources ordered by lumens, but I have no idea how to use it in the calculations.
...
6
votes
1answer
364 views
Dealing with blown-out highlights in PBR
I've been writing some custom shaders based around Unity's Standard BRDF, which is uses GGX distribution term and Smith visibility term. It looks great at either end of the smoothness scale (1 and 2 ...
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2answers
714 views
Why is the half vector not used in diffuse BRDF Fresnel calculations?
I am currently working with Earl Hammon Jr's Presentation PBR Diffuse Lighting for GGX+Smith Microsurfaces (now mentioned as [PBR, p.XYZ] and have read through (among others) Brent Burley's Physically-...
6
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1answer
118 views
Monte Carlo Integration
Let $I$ = the value of integration and $p$ = probability distribution.
The estimator is denoted as $\left\langle I \right >$ and is
$$\left\langle I \right >=\frac{1}{N}\sum_{i=1}^{N}\frac{f(...
6
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1answer
313 views
The reciprocity of BRDF
Many books describe that a BRDF has the following property (reciprocity):
$$f_r(x, \Theta \to \Psi ) = f_r(x, \Psi \to \Theta)$$
Why is the above equation correct?
I think the above equation ...
5
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0answers
135 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(...
13
votes
1answer
645 views
Confused with PBR implementations
I'm discovering the wonderful world of math and I'm hitting a huge wall with PBR and naming so I have a few questions:
As far as I understand BRDF describe how a material react to light (incoming ...
3
votes
0answers
289 views
Mathematics of Sub Surface Scattering
Can somebody help explain the mathematics of Sub Surface Scattering in a Path Tracer based on the Diffuse Approximation in A Practical Model for Subsurface Light Transport ?
I would like someone to ...
3
votes
0answers
98 views
How are fluid simulations handled in Computer Graphics?
How are fluid simulations handled in Computer Graphics? For a novice, there are hardly any novice friendly tutorials explaining how particles or fluids can be simulated.
Things like smoke, crown ...
5
votes
1answer
85 views
How is measured BRDF data recorded?
How is measured BRDF data recorded? Like the MERL BRDF Database.
What kind of equipment is used and what are the key values that need to be recorded?
I know one place this data was used was in the ...
1
vote
0answers
303 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 ...
7
votes
1answer
941 views
Why normalise Lambertian BRDF by 1/pi?
Why is a Lambertian BRDF normalised by dividing by $\pi$? Since the area of a unit sphere is $4 \pi$, and the area of the half sphere above the surface is $2 \pi$, shouldn't it rather be $1/(2\pi)$?
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3answers
311 views
How are Physically Based Rendering Methods Researched?
Recently a question that came to my mind was that How are Physically Based Rendering Techniques researched and developed? Do people just use current equations by physicists or do they create their own?...
5
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1answer
182 views
Error with tube lighting
I have recently been working on area lights for a small open source game engine called Urho3D but have run into an issues when rendering tube lights where the lights look the same as sphere lights ...
3
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1answer
291 views
Bug: Overly Sharp Highlights in PBR
I'm still working on my BRDF equations. Theoretically, all equations are correct, but the hilights are super sharp. I'm not sure if this is a result of me not using Image-Based Lighting (I currently ...
