Questions tagged [pbr]

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USDZ File doesn't show PBR Texture in Quick Look

I have a USDZ file containing a picture in a 3D frame. The frame has a PBR wood grain texture, and when I browse the file in XCode (or import it into Reality Composer), the grain is visible and ...
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1 answer
40 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 $...
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Post-processing recommendations for PBR

I've implemented a PBR. It's good but I want it to look more realistic. Since I haven't applied any post-processing I feel like there's more room to improve in that direction. What kind of post-...
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51 views

What problem of my bsdf?

This is a image of microfacetdieletric. But i can not find the problem. My code is : ...
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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? ...
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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 ...
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1 vote
1 answer
103 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. ...
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1 vote
0 answers
43 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 ...
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1 answer
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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 ...
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1 vote
1 answer
78 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{\...
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2 votes
3 answers
287 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 ...
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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....
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2 answers
214 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 ...
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1 answer
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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 ...
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3 votes
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228 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 ...
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2 answers
250 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. ...
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1 answer
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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{...
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1 answer
278 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 ...
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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 (...
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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 ...
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2 votes
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149 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 ...
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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 ...
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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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1 answer
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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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164 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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1 vote
1 answer
475 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 ...
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1 vote
1 answer
373 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 ...
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5 votes
3 answers
403 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 ...
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3 votes
1 answer
226 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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2 votes
1 answer
112 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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2 votes
1 answer
248 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 ...
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1 vote
1 answer
157 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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1 vote
0 answers
74 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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1 vote
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541 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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0 votes
1 answer
373 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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2 votes
1 answer
141 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 ...
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0 votes
1 answer
169 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/...
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3 votes
1 answer
622 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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1 vote
0 answers
50 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?
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2 votes
1 answer
164 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 ...
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1 vote
1 answer
1k 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, ...
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3 votes
2 answers
586 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 ...
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6 votes
2 answers
394 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-...
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3 votes
1 answer
326 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 ...
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4 votes
1 answer
1k 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 ...
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4 votes
2 answers
351 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 ...
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3 votes
0 answers
80 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 the ...
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6 votes
1 answer
1k 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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1 vote
0 answers
94 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 ...
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4 votes
1 answer
431 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. ...
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