25 votes
Accepted

Progressive Path Tracing with Explicit Light Sampling

There are multiple areas in path tracing that can be importance sampled. In addition, each of those areas can also use Multiple Importance Sampling, first proposed in Veach and Guibas's 1995 paper. To ...
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  • 3,512
15 votes

Rendering equation - why unsolvable directly?

I'm sadly not able to add a comment to the answer above (not enough reputation), so I will do it like this. I'd like to point out that what Dragonseel describes is simply an integral equation (...
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  • 304
13 votes

Rendering equation - why unsolvable directly?

The rendering equation is as follows: Now, the integral is over the sphere around the point $x$. You integrate over some attenuated light, incoming from every direction. But how much light comes in? ...
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  • 1,750
10 votes
Accepted

A recent approach for subsurface scattering

As mentioned in the comments, I would highly suggest starting with Full Volumetric Scattering. This is two fold: Since you are doing path tracing, adding volumetrics isn't super difficult. Fully ...
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  • 3,512
8 votes
Accepted

Can a glass plate act like a lens?

The box.obj file has no vertex normals, and by default Mitsuba will generate smooth normals for OBJ files that don't specify their own normals. This creates the ...
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  • 23.6k
7 votes
Accepted

Confused about prefiltering environment maps (Manson 16)

Your first quote is referring to "Split-sum approximation" presented in "Real Shading in Unreal Engine 4" by Brian Karis, and also referred in the paper [Kar13]: $$\frac{1}{N}\sum_{k=1}^N \frac{L_i(...
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  • 3,556
7 votes

Spectral path tracing - image color/brightness incorrect

The problem lies mainly in CIE1931XYZ::tristimulusValues() function, where you normalize the resulting color to the luminance of your illuminant which causes that ...
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  • 1,377
6 votes
Accepted

Path tracer not rendering shadows

The problem appears to be unintentionally transparent surfaces Although the image is grainy, it is sufficiently clear to estimate that all of the darker regions are due to surfaces facing away from ...
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  • 5,882
6 votes
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Difference betwen Rendering Equation, Lighting model, Ray Tracing, Global Illumination and Shadows?

The rendering equation aims to describe what the light distribution for a specific scene is, under several assumptions. The most important assumption is that we are working in a geometrical optics ...
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  • 1,838
5 votes

Path tracer not rendering shadows

is it correct having such a big light? I don't see any problem with having a big area light. That said, it also depends on the scale of your scene. If the light is large compared to it, shadows will ...
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5 votes
Accepted

Modern Screen Space Ambient Occlusion Techniques

This bachelor thesis briefly reviews six SSAO techniques. It could be a good start. CryEngine 2 AO StarCraft II AO HBAO Volumetric Obscurance Alchemy AO Unreal Engine 4 AO http://frederikaalund.com/...
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5 votes

Global illumination leading to image variation

If you can make your samples deterministic (the same from run to run - don't base random sample points on time or any other non deterministic value), it will be a stable rendering that you get every ...
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  • 7,341
5 votes

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

A note first From the look of your screen capture, I suspect there might still be a bug in your code. Noise is to be expected with only 16 spp, but your picture still looks surprisingly dark to me. ...
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5 votes

Generation of stratified cosine weighted samples on hemisphere

The classic method is to uniformly sample the disc at the base of your hemisphere and to project your samples upwards on the hemisphere (eg. compute z from x and y). This yields a cosine weighted ...
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  • 1,575
5 votes
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Is there a material that contributes to GI, but isn't directly visible?

You can use single sided triangles for the ceiling so that they are pointing towards the room. This way the ceiling influences the GI in the room but you can see through it when observing from outside
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  • 3,556
5 votes
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How does voxel cone tracing work?

Illumination components If our scenes only contain point lights (e.g., omni lights, spotlights, etc.) and emissive surfaces, the illumination contributions at a surface position, $x$, are computed as ...
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  • 1,024
5 votes

A recent approach for subsurface scattering

For cases where the diffusion approximation is preferred over full volumetric path tracing, the method published by Solid Angle is fairly efficient: https://www.solidangle.com/research/...
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5 votes

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

Overview Here is a short overview of the most used space representations, MLT variants and mutation strategies for these MLT variants. As you can see, there are quite some papers dating back to 2017 (...
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  • 1,024
5 votes
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Comprehensive explanation of conservative rasterization algorithm

I'm not sure what exactly you mean by how to visualize a plane that use w value as one of this coordinates but here's a sketch that will, hopefully, clarify this sentence: a line through each ...
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  • 66
5 votes

Can someone explain why raytracing isn't able to make Global Illumination?

From the ray tracing wikipedia page https://en.wikipedia.org/wiki/Ray_tracing_(graphics): "Path tracing is a form of ray tracing that can produce soft shadows, depth of field, motion blur, ...
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  • 479
4 votes
Accepted

The variance for the Monte Carlo estimator

I don't have that book to check the context of this, but from the equations you posted, yes, it looks like you're right. The $1/N$ factor should be applied to both terms. That agrees with the formula ...
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  • 23.6k
3 votes
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Phong BRDF in Mitsuba, Tungsten and AGI

It's the normalization factor to make sure the BRDF always reflects the same amount of energy regardless of the value of the specular exponent n. Without that factor, changing the specular exponent ...
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3 votes
Accepted

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

I noticed three potential problems. First, this bit of code looks suspicious: ...
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  • 23.6k
3 votes
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What is Radiosity?

Radiosity is a way to calculate diffuse GI, i.e. every surface is assumed to be Lambertian surface without specular component. In the radiosity algorithm you split surfaces into small patches and ...
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  • 3,556
3 votes
Accepted

Real time image based lighting for arbitrary BRDFs coordinate alignment

The surface reflectance of a BRDF function doesn't depend on orientation or position of the surface in the world space (except for the view vector) but is defined relatively to the surface normal (or ...
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  • 3,556
3 votes

Selection of GI techniques working in real time

In this vein a bit, Killzone renders one bounce reflections, but uses temporal anti aliasing to combine the last frame with the current frame. In practice, this means you get MANY bounce reflections, ...
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  • 7,341
3 votes
Accepted

How Sunlight is added in Bidirectional Path tracing?

This can be done in two ways - either use a sky with a sun in it as an cubemap-type light source outside your building, or use the windows as light sources. With BDPT, you could sort of do both, and ...
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  • 188
3 votes
Accepted

Path tracer isn't converging

I can find two possible reasons for the image not converging. #1. Every sample is the same For every sample, you generate random rays. You do that when you shoot the ray through a pixel (for anti-...
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  • 1,565
3 votes

How Image Based Lighting is applied to indoor scene?

There's two main things it seems like you've not understood correctly. IBL is for indoor scenes and outdoor scenes In the early days when IBL was hot, the Uffizi light-probe was probably the most ...
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  • 6,450

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