Skip to main content

Questions tagged [physically-based]

The tag has no usage guidance.

Filter by
Sorted by
Tagged with
36 votes
2 answers
7k views

How physically-based is the diffuse and specular distinction?

The classical way of shading surfaces in real-time computer graphics is a combination of a (Lambertian) diffuse term and a specular term, most likely Phong or Blinn-Phong. Now with the trend going ...
David Kuri's user avatar
  • 2,293
19 votes
3 answers
14k views

What are Spherical Harmonics & Light Probes?

What are Spherical Harmonics & Light Probes? How useful are they in computer graphics? What exactly do they do? I've heard the word spherical harmonics & Light Probes everywhere, from siggraph ...
Arjan Singh's user avatar
  • 2,511
18 votes
3 answers
9k views

Physically based shading - ambient/indirect lighting

I implemented a physically based path tracer after studying PBRT by M. Pharr and G. Humphreys. Now I'm trying to apply physically based rendering to real time graphics using OpenGL ES (in an iPhone ...
Fabrizio Duroni's user avatar
15 votes
4 answers
7k views

For shader math, why should linear RGB keep the gamut of sRGB?

sRGB is often contrasted with "linear RGB." Images are stored on disk and passed to displays in sRGB, which is approximately perceptually uniform in intensity. Shader math is done in linear RGB, ...
Maxpm's user avatar
  • 295
15 votes
2 answers
2k views

How to build a decent lens/camera objective model for path tracing?

I have written a small path-tracer after learning and experimenting on smallpt. The only thing that I did not write (and understood) myself is how the initial rays are computed and fired from the ...
teh internets is made of catz's user avatar
14 votes
3 answers
5k views

Correct Specular Term of the Cook-Torrance / Torrance-Sparrow Model

For a while I have been doing some research on the topic of Physically Based Rendering. One reflection model that is mentioned over and over is the Cook-Torrance / Torrance-Sparrow model. It seems ...
Thordal's user avatar
  • 141
12 votes
1 answer
358 views

Polarising reflection and refraction for a wrap around water surface

I want to render realistic images of water in an orbiting space habitat. The image does not need to be generated in real time, although I wouldn't want it to take weeks either. I'm looking for an ...
trichoplax is on Codidact now's user avatar
12 votes
0 answers
864 views

How correct is rendering in XYZ / linear RGB space?

I have a spectral power distribution (SPD, 5 nm steps) for all light sources in the scene and SPDs for the reflectance of all surfaces under any light / viewer angle in question. I'm going to ...
David Kuri's user avatar
  • 2,293
11 votes
3 answers
2k 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 ...
Kristoffer Helander's user avatar
11 votes
1 answer
5k views

Area Lights in Path Tracing

I have been following the scratchapixel ray tracing tutorials online which have been great at explaining the theory behind everything & how to implement it. However, I reached the point where I ...
Arjan Singh's user avatar
  • 2,511
11 votes
1 answer
911 views

Compensation for energy loss in single-scattering microfacet BSDF models

Single-scattering microfacet-based surface models like the original Torrance-Sparrow BRDF or derived models like the BSDF for rough dielectric surfaces by Walter et al. neglect inter-reflection of ...
ivokabel's user avatar
  • 1,464
11 votes
1 answer
813 views

Ocean Wave Rendering

How could I generate the waves for a water body with whitecaps & foam and variable intensity of the waves? Is the surface a mesh with a normal map? Is there a formula for generating that? Is there ...
Arjan Singh's user avatar
  • 2,511
10 votes
1 answer
941 views

Modelling Young's double slit experiment

Young's double slit experiment is very simple to set up and simple to explain, but it is an example of both diffraction and interference, neither of which are modelled by conventional raytracing. It ...
trichoplax is on Codidact now's user avatar
10 votes
2 answers
889 views

Total emitted power of diffuse area light

I am reading the book Physically Based Rendering (Pharr, Humphreys). In the chapter on lights, they talk about approximating the total emitted power of different kinds of lights. For example, a point ...
Rasmus Rønn Nielsen's user avatar
9 votes
1 answer
4k views

Does PBR incur a performance penalty by design?

I am wondering if the various PBR models used in modern game engines for real time are heavier in terms of computation, that more classic approaches to rendering. Worded differently, is PBR just a ...
teh internets is made of catz's user avatar
7 votes
2 answers
4k views

Physically Based Area Lights

So after reading https://www.guerrilla-games.com/read/killzone-shadow-fall-creating-art-tools-for-a-new-generation (a guerilla games presentation on PBR) I noticed the Area lights as opposed to the ...
Arjan Singh's user avatar
  • 2,511
7 votes
2 answers
3k views

Better Shadow Mapping Techniques

Currently I have basic shadow mapping setup in my engine. I am currently trying to implement something more realistic like PCSS (percentage closer soft shadows), to get a more physically accurate ...
Arjan Singh's user avatar
  • 2,511
7 votes
1 answer
1k views

Resulting Probabilty Density in Path Tracer for paths using Next Event Estimation

I am trying to implement my own Gradient Domain Path Tracer by following the code of this guy who already implemented it: https://gist.github.com/BachiLi/4f5c6e5a4fef5773dab1 I already managed to ...
Tarta's user avatar
  • 355
7 votes
1 answer
618 views

What is the most physically accurate model of surface materials possible in computer graphics?

I am looking for theoretical and implemented models to represent surface materials in software that strives for physical accuracy. Is BRDF really the best model? What alternatives are better? Why? ...
Mr. Developerdude's user avatar
7 votes
1 answer
3k views

What is Radiosity?

After reading a wikipedia article about Global Illumination It mentions a variety of techniques like Ray Tracing, Path Tracing and Ambient Occlusion. One technique it mentions is Radiosity which I don'...
Arjan Singh's user avatar
  • 2,511
6 votes
1 answer
817 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 ...
shashack's user avatar
  • 523
6 votes
1 answer
3k views

Depth of Field in Path Tracing: What do I do with the secondary ray?

How can I implement Depth of Field in my Path Tracer? I have read this article which explains the theory behind everything & I already have a good understanding of what this effect needs to ...
Arjan Singh's user avatar
  • 2,511
6 votes
2 answers
4k 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. ...
Iter Ator's user avatar
  • 278
6 votes
1 answer
135 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(...
shashack's user avatar
  • 523
6 votes
1 answer
688 views

How Sunlight is added in Bidirectional Path tracing?

How is distant directional light source(like sun) added in BDPT? If this is an indoor scene that gets sunlight through windows, how is this handled in BDPT(other than to consider Sun as a big disc far ...
ali's user avatar
  • 740
6 votes
1 answer
4k views

What's the difference between irradiance and fluence/radiant exposure?

A paper$^1$ I'm reading says fluence measures the incoming radiance from all directions and that fluence is similar to irradiance. It's defined by $\phi(x) = \int_{4 \pi} L(x, \vec{\omega'}) d\omega' $...
maogenc's user avatar
  • 235
5 votes
2 answers
6k views

What are the current open problems in Computer Graphics?

I did a quick investigation about the topic but there doesn't seem a decent resource to find related problems without digging into latest CG papers (unlike CS problems you can easily find a Wikipedia ...
concept3d's user avatar
  • 243
5 votes
2 answers
3k views

Books to learn Ray Tracing [closed]

Recently I have developed and interest in Ray Tracing and like most computer graphics tutorials online there is nothing regarding implementation for a beginner like myself. So far I have only done ...
Arjan Singh's user avatar
  • 2,511
5 votes
1 answer
2k views

Alternatives to Ambient Occlusion

Recently I wanted to improve the lighting in my game engine, naturally I looked towards Ambient Occlusion. I was considering SSAO but are there any better techniques? Maybe some that are Physically ...
Arjan Singh's user avatar
  • 2,511
5 votes
2 answers
276 views

Rendering Hypercentric Perspective

I came across some Non-Euclidean Games which involve Hyperbolic Spaces, Spherical Spaces, Portals, etc. And, I noticed that they give quite deep feel of what Non-Euclidean Spaces feel like. So, I was ...
Monster196883's user avatar
5 votes
1 answer
148 views

Trying to understand environmental cubemaps

I am trying to implement a physically based renderer, in OpenGL. I was planning to implement the Cook-Torrance BRDF. I read about radiance cubemaps (for reflections), like the one discussed here, for ...
MKII's user avatar
  • 153
5 votes
1 answer
223 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 ...
Josh Nuttall's user avatar
5 votes
1 answer
239 views

Questions about Preconditioning Conjugate Gradient method in Baraff & Witkin 98?

I encountered some problems when implementing the cloth simulation algorithm from Baraff & Witkin 98's Large Steps in Cloth Simulation. Baraff & Witkin 98 Consider the cloth as a particle ...
stanleyerror's user avatar
5 votes
0 answers
140 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(...
shashack's user avatar
  • 523
4 votes
2 answers
994 views

Why is eye-based ray tracing preferred over light-based ray tracing?

It seems that virtually all path tracers use eye-based or view-based path tracing. That is, the light rays originate from the camera rather than the light source. The reason given for this everywhere ...
jheindel's user avatar
  • 163
4 votes
1 answer
327 views

Material Layering

So after reading this Unreal Engine 4 Documentation page: https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/LayeredMaterials/ (Which describes how to use material layering in UE4) ...
Arjan Singh's user avatar
  • 2,511
4 votes
0 answers
1k views

Better alternatives to the Lambert BRDF

After reading about the new Disney Diffuse BRDF, I have been wondering if this is currently the best Diffuse BRDF at the moment? How much more of a difference would this make compared to using a ...
Arjan Singh's user avatar
  • 2,511
4 votes
0 answers
189 views

How is glint rendering done in Ray Tracing?

How is glint rendering done with ray tracing in the photo below? Is it just a simple normal map? I found a paper online that describes the exact same method used in the photo above but I have no ...
Arjan Singh's user avatar
  • 2,511
3 votes
1 answer
109 views

Intrepret path/light tracing by rewriting light transport equation

Given the rendering equation: $$ L_o(x, \theta_o) = L_e(x, \theta_o) + \int_{\Omega} \! f(x,\theta_i,\theta_o) L_i(x,\theta_i) \cos(\theta_i, \theta_o) \, \mathrm{d} \theta_i. $$ Rewriting it using ...
WDC's user avatar
  • 147
3 votes
2 answers
639 views

How to determine RGB values given a display spectral response curve?

I am reading Physically Based Rendering section 2.2.2 on RGB color. I am trying to understand how, given a display spectral response curves for rgb intensities, we can choose the intensities so that ...
Elad Maimoni's user avatar
3 votes
1 answer
3k views

Ray tracing: transforming ray to object's local space for intersection test

Im writting a raytracer, for which I want to be able to test intersections with implicit surfaces (in my case spheres). Without applying any transformation it works great, but I would like to upgrade ...
Nadir's user avatar
  • 267
3 votes
1 answer
370 views

How is Iridescence handled in a Path Tracer?

I have little knowledge of this topic but from what I gather in a Ray Tracer each ray is given its own wavelength as opposed to an RGB value. This automatically simulates Dispersion and Fluorescence. ...
Arjan Singh's user avatar
  • 2,511
3 votes
0 answers
51 views

Diffuse irradiance map : confusion about photometric vs radiometric units

I have spent the longest amount of time just taking the terminology for granted & have only just recently started studying or at least trying to understand the difference between radiometric and ...
Confusedius's user avatar
2 votes
2 answers
137 views

Why is the approximation valid, in the formula provided by Brian Karis?

I'm sorry I'm bringing this topic up again, but I need to expound some of the topics. With reference to this question, I was wondering if someone can help me out in expanding some of the details. In ...
user8469759's user avatar
2 votes
1 answer
1k views

PBR - How to handle multiple BSDFs and material type

So I am in the midst of writing my own path traced renderer and right now I have only implemented the old Blinn-Phong models where we separately calculated the diffuse and specular components of the ...
gallickgunner's user avatar
2 votes
1 answer
581 views

What is the physical interpretation of Normal, Roughness, Albedo and Metalness map?

In PBS context what is the metalness map? Are my interpretation of Normal, Roughness and Albedo map correct? I know almost for sure that: Normal map : Models the normals per differential region in ...
user8469759's user avatar
2 votes
1 answer
304 views

Rendering equation integration variable change

I'm watching the TU Wien rendering lectures in the course we were presented with a rendering equation (first one on the screenshot) and then another, which results from a change of variables (if I ...
analysis1's user avatar
2 votes
2 answers
247 views

Properties of the image reconstruction filter in rendering

Let $f$ denote the measurement contribution function for paths of length $k\in\mathbb N$, i.e. $$f(x)=g(x_0\leftrightarrow x_1)W_{\text e}(x_1\to x_0)t_k(x_0,\ldots,x_k)L_{\text e}(x_k\to x_{k-1}),$$ ...
0xbadf00d's user avatar
  • 203
2 votes
2 answers
351 views

Physically Based Shading for Diffuse surfaces

So I am currently in the process of implementing Physically based Shading in my pathtracer using microfacet models and I'm quite stuck at comprehending light interaction with diffuse surfaces. First ...
gallickgunner's user avatar
2 votes
1 answer
309 views

Rendering Equation for photons carrying flux

I am trying to understand the mathematical/physical foundations of photon mapping better. In the forward photon tracing step it is established, that the rays are carrying portions of total power (...
CygnusX1's user avatar
  • 121