Questions tagged [global-illumination]
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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 ...
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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 ...
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Directly Sampling an Area Light
So in my path tracer I sample both some bounce ray given an importance function for the current BRDF, and if applicable (reflection is non-specular) I directly sample all light sources (for my ...
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Question about reconstruction filter in ray tracing?
Suppose we have an 512x512 image, then the value of pixel j should be $I_j = \int_{0}^{512} \int_{0}^{512} h_j(u,v)L(u,v) \,dudv$, where $h_j(u,v)$ is the filter function for pixel j, $L(u,v)$ is the ...
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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 ...
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Are virtual point lights in many-light global illumination the same light probes?
There are several papers like this one here that refer to a concept called many-light global illumination using Virtual Point Lights (VPL). That is, the problem of global illumination is reduced to a ...
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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 $P_1$...
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The attenuation function in SSDO
When using Screen Space Direction Occlusion(SSGO) related techniques, such as Screen Space Global Illumination(SSGI), what is the commonly used attenuation function? I read from some materials that ...
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State of the art in real-time global illumination algorithms [closed]
What is the state of the art in global illumination algorithms in real time applications?
Which algorithms or categories of algorithms are actually used in the wild and what are their characteristics (...
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Can someone explain why raytracing isn't able to make Global Illumination?
I've watched a few videos about raytracing vs pathtracing, and one thing that consistently pops up is the idea that pathtracing seems to be able to do global illumination, whilst raytracing is not.
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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 ...
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Considering a path generated by bidirectional path tracing under a different strategy
Say I have constructed a path, using bidirectional path tracing (BDPT), consisting of a light subpath $y$ with $s=2$ vertices and a camera subpath $z$ with $t=3$ camera vertices.
Now I want to ...
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How is the image reconstruction filter on the path space defined in terms of the filter on the raster space?
Say we have a image reconstruction filter $h:R\to\mathbb R$ defined on the raster space $[0,w]\times[0,h]$, where $w,h\in\mathbb N$ define the width and height of the image plane in pixels, ...
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Relation between camera sensor responsivity and image reconstruction filter associated with a pixel
Let $W_{\text e}$ denote the camera sensor responsivity (i.e. importance) and $h_j$ and $W_{\text e}^{(j)}$ denote the image reconstruction filter and sensor response associated with the $j$th pixel, ...
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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. $$f(x)=g(x_0\leftrightarrow x_1)W_{\text e}(x_1\to x_0)t_k(x_0,\ldots,x_k)L_{\text e}(x_k\to x_{k-1}),$$ ...
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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 ...
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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 ...
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Is casting a shadow ray non-symmetric in pbrt?
According to the description in the book, Scene::IntersectP() "checks for the existence of intersections along the [passed] ray". This operatorion should be ...
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Distribution of the first vertex on a camera subpath in bidirectional path tracing
Suppose we are sampling camera rays of a perspective camera with a finite aperture. The PBRT implementation of the sampling scheme looks like this:
...
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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}=(\...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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