Questions tagged [pbr]

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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 ...
avilapa's user avatar
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1 answer
162 views

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 ...
Chris Gnam's user avatar
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0 answers
63 views

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. ...
StudenteChamp's user avatar
0 votes
1 answer
138 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: ...
StudenteChamp's user avatar
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0 answers
127 views

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 ...
Enigmatisms's user avatar
1 vote
1 answer
75 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 ...
Enigmatisms's user avatar
1 vote
0 answers
62 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. ...
Tomas's user avatar
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1 vote
1 answer
158 views

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}, ...
Mohamed Hashem's user avatar
1 vote
1 answer
65 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 $...
Lilla's user avatar
  • 113
1 vote
0 answers
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? ...
bin guo's user avatar
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1 answer
120 views

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 ...
jack tsang's user avatar
1 vote
1 answer
144 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. ...
GroundGlassUnknown's user avatar
1 vote
0 answers
116 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 ...
Ingun전인건's user avatar
0 votes
1 answer
90 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 ...
commanderZiltoid's user avatar
3 votes
1 answer
205 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{\...
user10546666's user avatar
2 votes
3 answers
1k views

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 ...
Sync it's user avatar
  • 179
0 votes
1 answer
123 views

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....
Sync it's user avatar
  • 179
0 votes
2 answers
465 views

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 ...
Sync it's user avatar
  • 179
0 votes
1 answer
382 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 ...
Amir's user avatar
  • 241
3 votes
0 answers
623 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 ...
user1754322's user avatar
0 votes
2 answers
468 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. ...
iaomw's user avatar
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1 answer
313 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{...
Emil Kabirov's user avatar
0 votes
1 answer
501 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 ...
zoran404's user avatar
  • 153
1 vote
0 answers
66 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 (...
noName's user avatar
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0 answers
85 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 ...
0xbadf00d's user avatar
  • 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 ...
0xbadf00d's user avatar
  • 203
0 votes
0 answers
64 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
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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: ...
0xbadf00d's user avatar
  • 203
0 votes
1 answer
543 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, ...
WDC's user avatar
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0 answers
211 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 $$x=(x_0,\ldots,x_{n-1})=(q_0,\ldots,q_{s-1},p_{t-1},\ldots,p_0)$$...
0xbadf00d's user avatar
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1 vote
1 answer
989 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 ...
Daniel Marques's user avatar
1 vote
1 answer
881 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 ...
Riki's user avatar
  • 111
5 votes
3 answers
735 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 ...
eclmist's user avatar
  • 222
3 votes
1 answer
358 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'...
user1117065's user avatar
2 votes
1 answer
128 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 ...
egor's user avatar
  • 23
2 votes
1 answer
354 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 ...
Harry Kane's user avatar
1 vote
1 answer
218 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 ...
kevinyu's user avatar
  • 493
1 vote
0 answers
83 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 ...
AccM's user avatar
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1 vote
0 answers
850 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: ...
TIANLUN ZHU's user avatar
0 votes
1 answer
569 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 ...
jacksparowll's user avatar
2 votes
1 answer
181 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 ...
TIANLUN ZHU's user avatar
0 votes
1 answer
322 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/...
DirectX_Programmer's user avatar
3 votes
1 answer
794 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 ...
avilapa's user avatar
  • 43
1 vote
0 answers
85 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?
TIANLUN ZHU's user avatar
2 votes
1 answer
258 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 ...
TIANLUN ZHU's user avatar
1 vote
1 answer
2k 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, ...
TIANLUN ZHU's user avatar
3 votes
2 answers
958 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 ...
kevinyu's user avatar
  • 493
6 votes
2 answers
474 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-...
Alan Wolfe's user avatar
  • 7,801
3 votes
1 answer
458 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 ...
kevinyu's user avatar
  • 493
5 votes
1 answer
2k 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 ...
kalonymus's user avatar