Questions tagged [pbr]
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3
votes
1answer
127 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 ...
1
vote
0answers
35 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?
1
vote
1answer
42 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
73 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
129 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
votes
2answers
176 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-...
2
votes
1answer
115 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 ...
2
votes
1answer
218 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
163 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
74 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 ...
5
votes
1answer
511 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 ...
1
vote
0answers
56 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
141 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. ...
2
votes
0answers
572 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 ...
5
votes
1answer
217 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
votes
2answers
1k 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
263 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 ...
7
votes
1answer
473 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
votes
1answer
95 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
$$\left\langle I \right >=\frac{1}{N}\sum_{i=1}^{N}\frac{f(...
6
votes
1answer
200 views
The reciprocity of BRDF
Many books describe that a BRDF has the following property (reciprocity):
$$f_r(x, \Theta \to \Psi ) = f_r(x, \Psi \to \Theta)$$
Why is the above equation correct?
I think the above equation ...
5
votes
0answers
120 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(...
12
votes
1answer
465 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 ...
4
votes
0answers
235 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 ...
4
votes
0answers
93 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 ...
6
votes
1answer
77 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
218 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 ...
8
votes
1answer
648 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 $1/(2\pi)$?
1
vote
3answers
293 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
votes
1answer
166 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
votes
1answer
252 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 ...
8
votes
2answers
952 views
In a physically based BRDF, what vector should be used to compute the Fresnel coefficient?
The well known Schlick approximation of the Fresnel coefficient gives the equation:
$F=F_0+(1 - F_0)(1 - cos(\theta))^5$
And $cos(\theta)$ is equal to the dot product of the surface normal vector ...
9
votes
1answer
2k views
Correct form of the GGX geometry term
I'm trying to implement a microfacet BRDF in my raytracer but I'm running into some issues. A lot of the papers and articles I've read define the partial geometry term as a function of the view and ...
10
votes
3answers
831 views
16bit half-float linear HDR images as (diffuse/albedo) textures?
So I been thinking about this for a while and tried to google for an answer but without any success.
If all your textures are 8bit LDR images, like JPEGs, couldn't that potentially cause conflicts ...
17
votes
2answers
4k views
How to properly combine the diffuse and specular terms?
As far as I understand, in a BRDF the Fresnel term is telling us the probability for a photon to be reflected or refracted when it hits a surface.
The reflected photons will contribute to the ...
9
votes
1answer
321 views
Rendering in radiometric units or photometric?
In traditional rendering, it is typical to do all the calculations with radiometric units, either as full spectral rendering, or component-wise (XYZ, RGB, etc).
However, as modern rendering adds more ...
11
votes
1answer
2k views
What is the accepted method of converting shininess to roughness, and vice versa?
Most modern renderers use physically-based materials and their models are often parameterized over roughness. Since this wasn't always the case with renderers, conventional assets often don't have a ...
