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Questions tagged [global-illumination]

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18 votes
1 answer
10k views

Progressive Path Tracing with Explicit Light Sampling

I understood the logic behind the importance sampling for the BRDF part. However, when it comes to sampling light sources explicitly, all becomes confusing. For example, if I have one point light ...
Mustafa Işık's user avatar
10 votes
2 answers
3k views

Rendering equation - why unsolvable directly?

Why is the rendering equation, introduced by Kajiya in 1986, not solvable directly/analytically?
Blongphong's user avatar
10 votes
1 answer
834 views

Using Monte carlo on Rayleigh scattering

Update I am editing and posting this question in a different way; this time from the point of view of Nishita paper. Sunlight gets scattered at P and attenuated before reaching Pv. Therefore ...
ali's user avatar
  • 740
9 votes
2 answers
5k views

A recent approach for subsurface scattering

I read "A Practical Model for Subsurface Light Transport" and "A Rapid Hierarchical Rendering Technique for Translucent Materials". If I understand correctly, the former does not consider the case ...
Mustafa Işık's user avatar
7 votes
1 answer
4k views

How does voxel cone tracing work?

Assume that we have voxelized a 3D scene into a regular 3D grid of cubes, storing the average (diffuse) radiance and some flag indicating whether or not a voxel is empty. Next, the finer levels of the ...
Matthias's user avatar
  • 1,074
7 votes
1 answer
1k views

Confused about prefiltering environment maps (Manson 16)

I'm working my way through this paper about GGX-filtering environment maps: http://www.ppsloan.org/publications/ggx_filtering.pdf I find myself stuck on the basics. In particular, I am confused by ...
user avatar
7 votes
2 answers
118 views

Global illumination leading to image variation

I have a 3D scene I use to generate some images which I then process in Matlab. I noticed that when global illumination (GI) is not enabled, rendering always generates exactly the same pixel-for-pixel ...
user3557985's user avatar
7 votes
2 answers
905 views

Selection of GI techniques working in real time

I'm considering topic of my thesis connected with computer graphics - I would compare some GI techniques which work completely in real time (no precomputation to lightmaps etc. and each frame ...
mdkdy's user avatar
  • 2,169
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
1k views

How to compensate low amount of rays reaching the light in a Path Tracer

I am trying to implement for research purposes a path tracer, but so far but results are not so good and I will explain you why. The general idea before getting to the code: I am working on paths ...
Tarta's user avatar
  • 355
6 votes
1 answer
680 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
5 votes
2 answers
797 views

Path tracer not rendering shadows

I am trying to implement for research purposes a gradient-domain path tracer. In order to achieve this step I first need a working Path tracer. I have been creating one so far but results are wrong ...
Tarta's user avatar
  • 355
5 votes
1 answer
106 views

The variance for the Monte Carlo estimator

I was wondering about the variance for Monte Carlo. The book (Advanced Global Illumination 2ed, p.60) writes the equation as follows: $\sigma^2 = \frac{1}{N} \int(\frac{f(x)}{p(x)} - I)^2p(x)dx$ $\...
shashack's user avatar
  • 523
5 votes
1 answer
748 views

Modern Screen Space Ambient Occlusion Techniques

Down the road, I'm planning to implement one or another GPU based ambient occlusion technique. My goal will be to approximate a physically based offline renderer, so I was pretty happy when Wikipedia ...
user avatar
4 votes
1 answer
86 views

Is there a material that contributes to GI, but isn't directly visible?

I am doing renders of the inside of a room. I would like to show a "bird's eye" view of the room, from above the ceiling (outside the room), but still see the interior of the room. An easy way of ...
aaaidan's user avatar
  • 143
4 votes
1 answer
1k views

Efficiently sampling specific surfaces using MIS in path tracing

Apologies for posting two questions in one post, but as they are relevant I kept them in one. Question 1 In the definition of multi sample estimator that Veach has defined, the integrand is the same ...
ali's user avatar
  • 740
4 votes
1 answer
491 views

How does Primary Sample Space Metropolis Light Transport work?

For simplicity, assume we're only dealing with surfaces which have either a Lambertian or perfectly specular material. Morever, assume that the only type of lights are area lights (i.e. surfaces with ...
0xbadf00d's user avatar
  • 203
4 votes
0 answers
139 views

Should I use nonsymmetric BSDF for refraction in BPT?

I'm implementing bidirectional path tracing. I want to simulate perfect refraction. I read in the Veach thesis that a perfect refraction BSDF is non-symmetric. Does it mean that I need to use ...
ciechowoj's user avatar
  • 203
3 votes
1 answer
170 views

Can a glass plate act like a lens?

I am trying to implement rough dielectrics on my renderer. I compared the results of my renderer and Mitsuba renderer. However, a thin glass plate which is a cube scaled by (0.4, 0.4, 0.01) magnifies ...
Mustafa Işık's user avatar
3 votes
2 answers
1k views

Generation of stratified cosine weighted samples on hemisphere

I have had luck with cosine weighted hemisphere samples, and I know how to generate stratified uniform samples, but I wanted to experiment with combining the two. However, how do I correctly stratify ...
Steven's user avatar
  • 315
3 votes
1 answer
573 views

Is there ongoing research on Markov Chain Monte Carlo algorithms (other than Metropolis-Hastings) for use in ray tracing?

Metropolis Light Transport is an application of the Metropolis-Hastings algorithm. Its variants differ only in the used "mutation strategy". Is there ongoing research on other Markov Chain Monte ...
0xbadf00d's user avatar
  • 203
3 votes
1 answer
218 views

What is a "light source" in global illumination?

In the context of global illumination and the scattering equation, do we need to understand "light sources" as surfaces with a "purely emissive" material on which no scattering is present? In ...
0xbadf00d's user avatar
  • 203
3 votes
1 answer
4k views

How does a path tracer with next-event estimation work?

I am trying to implement a simple path tracer with next-event estimation in Java. The general idea is to trace a ray through the scene as usual (using a cosine distribution to determine the next ...
Jeroen's user avatar
  • 125
3 votes
1 answer
392 views

Phong BRDF in Mitsuba, Tungsten and AGI

In the book AGI (Advanced Global Illumination), the Phong BRDF is $f_r(x,\Psi\leftrightarrow\Theta)=k_s\cfrac{(R\cdot\Theta)^n}{N\cdot\Psi}+k_d$ $k_d=\cfrac{albedo}\pi$ In Mitsuba and Tungsten, the ...
chaosink's user avatar
  • 591
3 votes
0 answers
120 views

Irradiance field approximation with black probes

I'm posting here after some time searching the Internet and reading presentations and papers, to find out the best options to solve the problem I have. I'm implementing irradiance field with ...
Alex's user avatar
  • 31
3 votes
0 answers
289 views

Beer's law in dielectric material

I am trying to implement Beer's law according to this page in dielectric material but I am not sure have done it correctly as the image does not suggest so. The formula is: I(s) = I(0) * pow(e, ln(A)*...
ali's user avatar
  • 740
2 votes
1 answer
1k views

Spectral path tracing - image color/brightness incorrect

I implemented a spectral path tracing using physically base BRDF models such as Oren-Nayar,Specular Reflection and Transmission, Lambertian. All calculation in the path tracer uses standard illuminant ...
Fabrizio Duroni's user avatar
2 votes
1 answer
1k views

Difference betwen Rendering Equation, Lighting model, Ray Tracing, Global Illumination and Shadows?

What is the difference between all these techniques? I know what a lightning model does, eg Phong, Flat, Gouraud. As far as I know both Ray Tracing and Global Illumination are just lighting models ...
KeyC0de's user avatar
  • 145
2 votes
1 answer
328 views

Comprehensive explanation of conservative rasterization algorithm

I am trying to implement conservative voxelization as part of real time GI in my hobby rendering engine. I find this article by NVIDIA. I am stuck at understanding the second algorithm. The problem ...
kevinyu's user avatar
  • 493
2 votes
1 answer
263 views

Real time image based lighting for arbitrary BRDFs coordinate alignment

I was trying to understand how real-time illumination happens with image-based lighting. I understood that importance of representing the Environment Map and BRDF in spherical harmonics. Because ...
Erdi İzgi's user avatar
2 votes
2 answers
255 views

Adding cos(θ) from rendering equation ruins the renderings

I'm following Ray Tracing The Rest of Your Life to implement a ray tracer, but the explains on math (mainly pdf part) got me confused so I followed Rendering Equation to understand the math behind. As ...
Rahn's user avatar
  • 183
2 votes
1 answer
316 views

light probe (for global illumination) placement techniques?

I'm learning light probes used for dynamic global illumination. I have a question regarding the placement of light probes, as based on most of the pictures I have seen, they seem to be placed ...
Bill Yan's user avatar
  • 121
2 votes
2 answers
246 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
1 answer
193 views

How do we approximate the integral of the measurement contribution function in Metropolis Light Transport?

In Metropolis Light Transport, we need to approximate the integral of the measurement contribution function. I've read that this can be done using a traditional approach like path tracing. However, ...
0xbadf00d's user avatar
  • 203
2 votes
0 answers
164 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 ...
0xbadf00d's user avatar
  • 203
2 votes
0 answers
98 views

Quantify the variance of pixel measurements

Say $E_j$ is an estimator of the value $$I_j=\int f_j\:{\rm d}\lambda$$ of the $j$th pixel given by the path space integral of the corresponding measurement contribution function $f_j$. $f_j$ is of ...
0xbadf00d's user avatar
  • 203
2 votes
0 answers
54 views

Chart swaps and path inversion in bidirectional path tracing

I've got a hard time to understand how we would implement the following in practice. I'd be great if someone could explain the details for the example below. Assume we're generating a path ${\rm x}=(\...
0xbadf00d's user avatar
  • 203
2 votes
0 answers
167 views

How does Voxel Cone Tracing solve the rendering equation? [duplicate]

so I am not new to interactive graphics programming, but I wanted to try out advanced techniques. Currently I am struggling to understand how the author of the 2011 paper "Interactive Indirect ...
DaOnlyOwner's user avatar
2 votes
0 answers
477 views

How to simulate specular reflection in Light Tracing?

I am implementing light tracing from this website. The right wall on the below image is perfect mirror(specular reflection). Its BRDF returns zero that's why it's been rendered black. But how is it ...
ali's user avatar
  • 740
2 votes
0 answers
161 views

Picking multiple light sources from a mixture densities

According to Peter Shirely paper, one pdf(probability density function) can be defined for the union of the light sources and pick only one using a random number from this density: $$p(x) = \alpha_1 ...
ali's user avatar
  • 740
2 votes
1 answer
124 views

Multiplication of SH coefficient sets representing occlusion and color

Currently I got interested in implementation of Precomputed Radiance Transfer. I decided that occlusion representation (which is not trivial to compute) would be precomputed as CPU raytracing and ...
mdkdy's user avatar
  • 2,169
1 vote
1 answer
528 views

Path tracer isn't converging

So I just completed a naive path tracer that uses explicit direct light sampling. Problem is the path tracer isn't converging. It's like a raytracer, showing a single image on each pass. More info on ...
gallickgunner's user avatar
1 vote
1 answer
249 views

Path tracing: how to deal with ray hitting an emitter

I am writing my first path tracer and kind of feeling confused by some mechanisms. For example, when I trace a ray and the ray hits a area emitter, then how to determine the radiance of this direct ...
Enigmatisms's user avatar
1 vote
1 answer
101 views

How to count the photons when Photon Mapping

I wrote a rather elegant and compact Photon Mapper in CUDA. But I treat all my photons they same, and ignore their colour. This simplicity has some nice properties: e.g. I can just count them with one ...
Bram's user avatar
  • 270
1 vote
1 answer
79 views

In bidirectional path tracing, is a camera subpath with $n$ vertices determined by a fixed number of random numbers?

In the Multiplexed Metropolis Light Transport implementation of the book Physically Based Rendering, the proposal samples are generated by the Primary Sample Space Sampler ...
0xbadf00d's user avatar
  • 203
1 vote
1 answer
141 views

Can anyone summarize in simple terms, how PSSMLT/MLT algorithms work?

I understand backwards path tracing and bidirectional path tracing (BDPT). However I'm failing to understand how Metrpolis Light Transport methods are even remotely feasible to run. My understanding ...
Chris Gnam's user avatar
1 vote
1 answer
197 views

Specular reflection with different viewing direction where reflection direction and viewing direction coincide

Suppose $P_1$ and $P_2$ two different points on surface. And let $l$: be the light source direction, $n$: normal vector $r$: specular reflection direction $v$: viewing direction . In case 1 (at $P_1$...
S. M.'s user avatar
  • 211
1 vote
1 answer
452 views

Understanding material .mtl files

I am reading this piece of documentation to understand mtl files So far I am stuck trying to understand the difference between ambient, diffuse and specular reflectivity (Ka, Kd, Ks). If I am ...
Makogan's user avatar
  • 1,726
1 vote
1 answer
814 views

Radiosity normal map light baking

I'm trying to implement radiosity normal maps from the old Valve paper: Half-Life® 2 / Valve Source™ Shading.pdf | valvesoftware.com I've tried generating the light maps using Vray and 3dStudio max, ...
Dusan Bosnjak 'pailhead''s user avatar
1 vote
1 answer
202 views

Light Falloff through a grid

I'm playing with a grid-based lighting system, where light is transported and accumulated through a grid. I initially tried attenuation based on ...
Anthony's user avatar
  • 11