Questions tagged [physically-based]

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34
votes
2answers
4k 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 ...
15
votes
3answers
7k 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 ...
13
votes
2answers
1k 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 ...
13
votes
3answers
2k 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 ...
12
votes
4answers
643 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, ...
12
votes
1answer
270 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 ...
11
votes
1answer
541 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 ...
11
votes
1answer
349 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 ...
10
votes
3answers
5k 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 ...
10
votes
3answers
957 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 ...
10
votes
0answers
441 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 ...
9
votes
1answer
480 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 ...
9
votes
2answers
374 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 ...
7
votes
1answer
2k 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 ...
7
votes
1answer
2k 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 ...
7
votes
1answer
370 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? ...
7
votes
1answer
787 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 ...
6
votes
2answers
2k 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 ...
6
votes
1answer
246 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 ...
6
votes
1answer
2k 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 ...
6
votes
1answer
110 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
389 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 ...
6
votes
1answer
2k 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' $...
5
votes
2answers
2k 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 ...
5
votes
1answer
1k 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 ...
5
votes
1answer
2k 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 ...
5
votes
1answer
107 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 ...
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. ...
5
votes
1answer
171 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 ...
5
votes
1answer
2k 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'...
5
votes
1answer
146 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 ...
5
votes
0answers
133 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(...
4
votes
1answer
223 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) ...
4
votes
1answer
2k 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 ...
4
votes
0answers
124 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 ...
3
votes
2answers
96 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 ...
3
votes
1answer
787 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 ...
3
votes
1answer
171 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. ...
3
votes
0answers
699 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 ...
2
votes
1answer
148 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 ...
2
votes
2answers
169 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 ...
2
votes
1answer
92 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 (...
2
votes
1answer
251 views

PBR and Specular Aliasing

I have been following LearnOpenGL.com's tutorials on PBR. Everything makes sense and I wrote up a shader for my physically based renderer. I noticed that the results look great, however all of my ...
2
votes
1answer
217 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 ...
2
votes
0answers
44 views

Would the surface of a large carbon-nanotupe structure look metalic?

CNT is a promising new material, which Wikipedia describes as such: Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure. These cylindrical carbon molecules have ...
1
vote
3answers
304 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?...
1
vote
1answer
708 views

What are some new Real-Time Graphics Rendering Techniques to get closer to real life? [closed]

So recently after implementing PBR in my engine, I was wondering what are some new & old Rendering Techniques that people are implementing and researching to get Real Time Graphics closer to what ...
1
vote
1answer
82 views

Tone Mapping in a physically based rendering ray tracer

I'm implementing a pbr ray tracer. Let's say that I'm at the end of the process: for each pixel pi, I accumulated the radiance value in vector pi = (radR, radG, radB). At this point, these values are ...
1
vote
1answer
118 views

total internal reflection implementation in pbrt-v3

I've been implementing a path tracer, referring pbrt-v3. However, I'm a bit confused about its implementation. Code is here. It seems when we sample to do transmission, it tests if it meets a total ...
1
vote
1answer
65 views

kinematics and dynamics of a sphere in a spring mass system?

I am attempting to code a simple spring mass system simulation in which a sphere pendulus hangs from a string (a spring) by the top and then another sphere (controlled by the user) can move and ...