14
votes
Accepted
What is the accepted method of converting shininess to roughness, and vice versa?
As you already note, there is no clear cut interpretation/conversion for these values. I think it is even much worse: Depending on your BRDF and internal limitations (like having defined exponents ...
- 843
14
votes
Accepted
How to properly combine the diffuse and specular terms?
Using two Fresnel terms is correct in the sense that any given diffuse path will pass through the surface twice. If you're solving diffusion by tracing a path through the medium until it bounces out ...
- 330
11
votes
Confused with PBR implementations
DFG pops up in the family of microfacet based BRDFs. It is simply the product of three terms:
D : The microfacet distribution.
F : The fresnel coefficient.
G : The geometric attenuation between ...
- 1,585
11
votes
Accepted
Why normalise Lambertian BRDF by 1/pi?
I think I got it!
Because $cos(\theta)$ integrates to $\pi$ over the hemisphere (and not $2\pi$). And the incoming light is multiplied by $cos(\theta)$ (and the BRDF).
- 480
10
votes
Accepted
In a physically based BRDF, what vector should be used to compute the Fresnel coefficient?
In Schlick's 1994 paper, "An Inexpensive Model for Physically-Based Rendering", where they derive the approximation, the formula is:
$$F_{\lambda}(u) = f_{\lambda} + (1 - f_{\lambda})(1 - u)^...
- 3,652
10
votes
Accepted
Rendering in radiometric units or photometric?
It's fine to use photometric units as an overall scale for setting light brightnesses. However, there's a technical subtlety you should be aware of. I'll quote from a blog post I wrote on the subject ...
- 24.3k
9
votes
Accepted
16bit half-float linear HDR images as (diffuse/albedo) textures?
In film production, we almost never use 8-bit textures for color/albedo, because of banding, etc. (JPEG is especially problematic since by spec, it's sRGB rather than linear values.) We either use '...
- 206
8
votes
In a physically based BRDF, what vector should be used to compute the Fresnel coefficient?
The Fresnel coefficient should be evaluated using $H$, not $N$.
You wrote,
I have trouble seeing why we can still use that formula in a BRDF, which is supposed to approximate the integral over all ...
- 24.3k
8
votes
How to properly combine the diffuse and specular terms?
While browsing to properly write my question, I actually found the answer, which happens to be very simple.
Another Fresnel term is also going to weight in as the photons make their way out of the ...
- 4,340
8
votes
16bit half-float linear HDR images as (diffuse/albedo) textures?
Yes, it's possible in some extreme cases for HDR lighting and tonemapping to expose banding issues in color textures. In those cases, having a higher bit depth for the textures could be useful. ...
- 24.3k
7
votes
Accepted
Correct form of the GGX geometry term
TL;DR: Your $G1$ formula is wrong.
Just to avoid confusion, I am assuming the isotropic version of the BRDF, the Smith microfacet model (as opposed to the V-cavity model), and the GGX microfacet ...
- 1,414
7
votes
Dealing with blown-out highlights in PBR
Using physically based BRDFs only makes sense if your entire pipeline is built for physical units - the extreme range of values can't be displayed properly without some form of tone mapping. You didn'...
- 706
7
votes
Accepted
Why is the half vector not used in diffuse BRDF Fresnel calculations?
I finally figured out a flaw in my argumentation to use the half vector for the diffuse part.
tl;dr version:
$\alpha_{hi}$ and $\alpha_{ho}$ are not equal, this assumption only works for the specular ...
- 1,477
6
votes
Accepted
Tasks of a professional graphics programmer?
I don't know if this is exactly what you're looking for. I work tangentially in the film and TV industry. I don't work for a studio, but I work on the software that studios use for their productions. ...
- 3,371
6
votes
Accepted
Microfacet shading for diffuse materials
You can combine Oren-Nayar with GGX, if your normalize the result. A BRDF is defined by two properties: Helmholtz reciprocity and energy conservation.
$f(l_i, l,_o) = f(l_o, l_i)$
$f(l_i, l_o) \leq ...
- 1,477
6
votes
Accepted
The reciprocity of BRDF
You probably know that the BRDF is to calculate the reflected light, from a light source to a camera (In examples a light source and a camera is used, but it does not need to be just that).
The ...
- 1,595
6
votes
Accepted
What is the purpose of the projected solid angle $dA^\perp$ term in the definition of Radiance?
Your main idea is more or less correct. The cosine hidden in the projected area measure $dA^\perp = dA\cos(θ)$ compensates the weakening of irradiance due to incident angle (the Lambert's cosine law). ...
- 1,414
6
votes
Accepted
Roughness Value of (Close to) Zero in Physically Based Rendering
Yes, I think it's expected that setting roughness = 0, combined with using point lights for illumination, leads to no visible specular highlight. The size of the highlight is infinitesimally small, so ...
- 24.3k
5
votes
16bit half-float linear HDR images as (diffuse/albedo) textures?
I'd like to invite readers to read this article about Quake 2 engine rasterization technology explained in details, if they have the time.
If TLDR, please pay attention to this image:
What we see is ...
- 623
5
votes
Accepted
The purpose of NdotV in the directional-hemispherical reflectance equation in the book "Real-time rendering book"
First, you are not exactly capturing "reflected light from view direction". What you mean is called importance, and it is transported exactly the same way in the scene as radiance (Helmholtz ...
- 166
4
votes
Accepted
Error with tube lighting
Found the solution, it turns out the lightVec is not the vector of light from the tube but rather the direction the tube will point. Therefore i will need to pass it a light rotation value to be used ...
- 91
4
votes
Accepted
How are Physically Based Rendering Methods Researched?
I think you need to split your question into real-time and offline PBR research.
For real-time PBR it's mostly about finding fast approximations for path traced equivalent. For example we know how to ...
- 3,586
4
votes
How are Physically Based Rendering Methods Researched?
I guess physicists, and before that term was used philosophers, have always been thinking about the nature of light, color and shadow. Knowledge about those matters is not purely rooted in people ...
- 231
3
votes
How are Physically Based Rendering Methods Researched?
The most straightforward method of researching physically based lighting is to grab a light and a camera and start taking pictures of an object from all angles when lit from all angles at varying ...
- 5,830
3
votes
Bug: Overly Sharp Highlights in PBR
Just to comment on the 0.16*Specular^2 term that was mentioned in the comments by Karim:
Frostbite only remaps the specularity for their internal purpose so that they can pack gemstones specularity ...
3
votes
Accepted
Monte Carlo Integration
In Monte Carlo integration, the samples $x_1, x_2, \ldots x_N$ are independent, identically-distributed random variables. This implies they all have the same expectation value. The derived quantities $...
- 24.3k
3
votes
Accepted
Importance Sampling in Unreal Engine Formula Derivation (Irradiance term)
I just read notes on moving frostbite to pbr and I found the derivation of the method above. So I will just show the derivation here and quote some of the explanation.
One can notice an extra〈n·l〉...
- 483
3
votes
PBR missing rim darkening on non metallic rough surfaces
The problem is in the diffuse term, which can be seen by making the specular portion of IBL not be added into the result. The diffuse only render will not have the darkening, and of course, the ...
- 7,711
3
votes
Accepted
Iridescence/Thin-film interference integration as a layer
Unfortunately, the iridescence model is not made to be applied to a diffuse term. Pascal and I made it for microfacet models only (that is the specular term).
One way to understand how to include it ...
3
votes
Accepted
Why can I see the diffuse lighting effect on a perfect mirror?
Dielectric materials (which is what you get when metalness is 0) don't exhibit a mirror-like effect. Think of a sheet of smooth, non-transparent plastic. Real-life mirrors are panes of glass or ...
- 872
Only top scored, non community-wiki answers of a minimum length are eligible