Questions tagged [global-illumination]

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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 ...
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27 views

Confused on GPU Voxelization

I am learning how to voxelize a scene using GPU. In OpenGL Insights, there is a algorithm doing this on page 6. However, I am confused on the last step: Convert 2D fragment to 3d voxel. In the book, ...
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1answer
56 views

Factor of 2 converting radiance to irradiance

For a Lambertian surface, the radiance at a point is $$L = \frac{\alpha}{\pi}\cos\theta_i E_0$$ If we have an infinite flat surface, albedo = 1, illuminated directly normal, then we get $$L = \...
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96 views

How Image Based Lighting is applied to indoor scene?

Now the mainstream engine's approach is to use image-based lighting to achieve approximate global illumination, but such a technique seems to be only applicable to outdoor scenes.What kind of ...
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1answer
124 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 ...
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0answers
95 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 ...
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171 views

Understanding bad shadows with voxel ray tracing

I have a voxel raytracer that is generating some weird shadows and I want to understand what is the source of the problem. The image is voxelized, resulting in: I then generate Hard shadows from the ...
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1answer
82 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, ...
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1answer
160 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 ...
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1answer
174 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 ...
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1answer
233 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 ...
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1answer
649 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 ...
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90 views

Hard edges appearing in voxel cone tracing (how to remove them?)

I am generating shadows using a voxel pyramid (commonly called voxel cone, although I hate that term). Some of my shadows come as expected, however some are very strange. For example in this image: ...
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88 views

Voxel cone tracing artifacts (what causes them and how to solve them)?

I am trying to generate soft shadows using voxel cone tracing. Which gives me the next images: In the first image you can see an artifact of a sequence of horizontal shadows alternating with ...
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208 views

How exactly do soft shadows get generated using a voxel cone tracing rendering technique?

Let's assume we have voxelized a scene, and all of our materials have an opacity level of 1. The reuslt would then look like: If we raytraced the final volume that gets generated after rasterization. ...
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1answer
87 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 ...
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0answers
97 views

How to validate whether a reflection model is implemented correctly?

I think this is one of the most important part when you write a physically-based renderer. The solution I came up with is to put a sphere to the scene with a constant background radiance. Solve the ...
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1answer
126 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 ...
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1answer
304 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, ...
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113 views

What is voxel based global illumination in a nutshell?

As title says. What are the broad, general ideas of voxel based global illumination and what exactly makes it efficient enough to produce real time dynamic shadows with so much photorealism?
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1answer
103 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 ...
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0answers
194 views

Octahedral mapping for Spherical functions

I guess most of you are familiar with environment maps, they represent distant lighting distribution, and are used to render objects given their BRDF or SVBRDF distribution. Many papers map the ...
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51 views

Intensity of pixel area light in reflective shadow map?

In reflective shadow map, there is definition about intensity of pixel area light: $$ I_p(\omega) = \Phi_p \max\{0, \langle n_p | \omega \rangle\} $$ where $ \langle | \rangle $ is the dot product, $...
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1answer
57 views

Natural Environment Illumination in Augmented Reality

I've basically 0-knowledge about augmented reality. For academic purposes I've to study this paper http://ieeexplore.ieee.org/document/8007317/?reload=true I'm struggling trying to understand some ...
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1answer
575 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 ...
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0answers
270 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 ...
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373 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 ...
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1answer
240 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 ...
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203 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)*...
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1answer
90 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: $\sigma^2 = \frac{1}{N} \int(\frac{f(x)}{p(x)} - I)^2p(x)dx$ $\...
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2answers
2k 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 ...
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1answer
4k 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 ...
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1answer
558 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 ...
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1answer
541 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 ...
6
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1answer
393 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 ...
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0answers
147 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 ...
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2answers
713 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 ...
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1answer
93 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 ...
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2answers
766 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 ...
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1answer
70 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 ...
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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'...
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100 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 ...
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1answer
211 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 ...
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2answers
1k views

Rendering equation - why unsolvable directly?

Why is the rendering equation, introduced by Kajiya in 1986, not solvable directly/analytically?
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2answers
106 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 ...
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1answer
572 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 ...
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2answers
540 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 ...
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1answer
693 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 ...
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1answer
587 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 ...