Questions tagged [pathtracing]
For questions about the path tracing Monte Carlo algorithm for physically accurate global illumination, or its variants.
221
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Multiple importance sampling with Next Event Estimation gathers less energy compared to One-sample-model
I'm developing a webgpu pathtracer using multiple importance sampling with two similiar techniques, next event estimation and one-sample model.
For some reason, next event estimation seems to gather ...
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1
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61
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Point light source radiance
I was reading Deriving radiance from irradiance and intensity and the last comment said that by dividing $r^2$ we convert radiant intensity to irradiance. What confuses me then is the fact that for ...
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Measure (or Jacobian) conversion for direction sampling
If in the path tracing use case, I have some sampling strategies to sample a scattering direction in a 2D space ($\theta, \phi$). Of course, I need to convert it to a 3D direction vector (with length ...
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Forward path tracing versus backward path tracing. How may I achieve realistic shading in forward path tracing?
I have a forward path tracer. Essentially, it looks flat:
This is the backward path tracer in comparison:
My question is: How do I get pseudorandom lighting like with the backward path tracer, when ...
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39
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Understanding the BRDF Equation
I am studying the BRDF equation. From Wikipedia, the equation is as follows:
I have one main question:
Where does the $\cos{\theta_i}$ in the denominator come from?
The denominator implies that $...
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1
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109
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Evaluating the Rendering Equation by hand (simple case)
I'm trying to make intuitive sense of the rendering equation and so I'm trying to work out a trivial example by hand, though ultimately I'm just trying to understand how monte carlo importance ...
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1
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113
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How does a path tracer capture light falloff if it deals exclusively with radiance?
My understanding is that path tracers deal with radiance because radiance is constant along a ray. You simply go through and evaluate the light transport equation:
$$
L_o(p, \omega_o) = L_e(p,\...
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Vulkan (Hardware) Path Tracing Formulation
I've been implementing a path tracer in Vulkan using the VK_ray_tracing extension and am a bit confused on how to set up the pipeline. Currently I've been following the style of the Reference Path ...
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62
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What performance to expect from an optimised pathtracer?
I am currently writing a fairly basic pathtracer as a compute shader in C++/CUDA, which has been running on a GTX 1080, and I have noticed that when logging some statistics, I get around ~1 billion ...
2
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1
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90
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How to approach implementing Cook-Torrence microfacet brdf?
Trying to implement the Cook-Torrance BRDF for my path tracer. Confused about how to do it though. I've seen two approaches:
1: Sample the NDF, evaluate diffuse and specular components and add them ...
0
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0
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31
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Combining Path Tracing and Photon Mapping
I'm trying to implementing the paper "Deep Kernel Density Estimation for Photon Mapping". One part that has me confused is when the authors describe their rendering algorithm as hybrid ...
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Confusion about different sampling strategies in Monte Carlo Path Tracing
I am studying Monte Carlo Path Tracing from different sources. However, I have some confusion about the sampling part and dare to post here for experts' ...
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1
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58
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Fixing bias in Specular lobe
Im currently making some modifications for a path tracer for Minecraft, specifically adding glossy refractions. The program currently uses for specular reflections this method, linear interpolation ...
2
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1
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169
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Cosine weighted hemisphere sampling is a little bit darker and arguably noisier than reference
I'm writing a small path tracer that currently:
Samples a random light source at each bounce (direct lighting)
Bounces rays around multiple times (indirect lighting)
The scene only contains ...
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1
answer
287
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Importance sampling of the blinn-phong brdf in pathtracing
tl;dr:
How do you importance sample the blinn-phong-brdf?
Recipe for importance sampling of the phong brdf as far as i understood it (pseudo-code):
...
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1
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154
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Importance sampling in a path tracer
So, I'm attempting to implement a monte carlo path tracer that uses the ggx brdf model. However, I'm rather confused about how to sample the light direction.
I know that theta and phi can be sampled ...
0
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1
answer
35
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Theoretical speedup from sample number in path tracing algorithm
Suppose, in a Kajiya style path tracing algorithm, I have 100x100 pixels, and I am using 32 samples per pixel. So, the total ...
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0
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Bright results when importance sampling GGX NDF
I've been trying to importance sample the GGX NDF of my Cook-Torrance BRDF for some time now but I can't get it right.
I've been following this article.
Here's my code for the importance sampling part....
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1
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87
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Importance sampling microfacet BRDF and coordinate frame
I'm trying to importance sample the Cook Torrance BRDF for my path tracer but I'm not sure about the part where you have to change the sample from one coordinate frame to another.
This resource states ...
2
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1
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164
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How to properly use the BRDF from glTF 2.0 specification in path tracing while using metallic/roughness materials?
I've built a renderer which should render glTF materials, as they are defined in their specification. So I should be able to render satisfying (similar to Cycles and Ospray) results just from the base ...
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1
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166
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Confusion about PDF defined in solid angle / area measure
When using MIS, we always want to express the PDF value in a unified measure in order not to render the ratio between them meaningless. Yet when I read through chapter 16 of PBR-book, I got confused ...
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1
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127
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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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1
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228
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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 ...
4
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1
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145
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Why do I need to remove the positive charactaristic function for the pdf of the outgoing direction to integrate to 1 with GGX?
Context: I am attempting to implement Trowbridge–Reitz (GGX) based on Microfacet Models for Refraction through Rough Surfaces in a pathtracer. I use numerical integration to check if the pdfs ...
2
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1
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181
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Rendering equation integration variable change
I'm watching the TU Wien rendering lectures in the course we were presented with a rendering equation (first one on the screenshot) and then another, which results from a change of variables (if I ...
0
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0
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88
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Trouble getting a raytracer camera representation for different aspect ratios
I am trying to make my camera representation work for images whose aspect ratio isn't 1 (640x480, 1920x1080...), but I am having some trouble getting it to work.
The camera model is pretty simple, as ...
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1
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82
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Path tracing - colors/shadows sharper than they should be
Problem description
When comparing Cornell Box image generated by my path tracer I noticed that colors are much more sharp/saturated (don't know specific term) than they should be. Comparison (on the ...
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0
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64
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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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140
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Why does cos sampling directions over hemisphere use cos theta distribution instead of cos theta / pi distribution?
When choosing a probability density function for Monte Carlo evaluation of rendering integrals, I get how importance sampling suggests choosing e.g. $cos(\theta)$ for $p(x)$, and then, over say the ...
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54
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How do I convert pathtraced distance to value that is usable by OpenGL's depthbuffer?
I was hoping someone could check my understanding.
I've got a pipeline that does some path tracing, and then draws some debugging rays using standard rasterization. I'm trying to get depth to work ...
3
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1
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157
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(Lorenz-)Mie phase function instead of Henyey-Greenstein?
Is it practical to implement the Lorenz-Mie(LM) phase function in a renderer ?
$p(\cos\theta)=\frac{|S_1(\theta)|^2+|S_2(\theta)|^2}{4\pi\sum_{n=1}^\infty (2n+1)(|a_n|^2+|b_n|^2)}$
I'll spare you the ...
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0
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153
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Applying Monte-Carlo methods in path tracing
I've noticed that I consistently get worse results in path-tracing when I try to do monte-carlo correctly compared to when I don't, and I think this might be because of a fundamental misunderstanding.
...
0
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1
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84
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What is the rendering cost of photo realistic video today?
I can only find online infomation such as some scene need days to render a single frame, but I'm not sure what is the hardware based on, it may be based on CPU rendering farms in the 2000s. There is ...
2
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1
answer
85
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What does 'free-path' mean?
I've seen some phrases like 'free-path', 'free-path distributions', 'mean free path' in some computer graphics resources, but none of them explains what does these phrases mean, does anyone have an ...
2
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1
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199
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importance sampling rectangular light
I have been struggling very much to wrap my head around this part of Peter Shirley's book. There is no explanation what the angle Alpha represents and to make things worse in the code the cos(Alpha) ...
2
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1
answer
719
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Rendering equation - brdf / pdf > 1?
I am creating a path tracer and I got some strange results when calculating the strength of light.
I am using a rendering equation inspired by this diagram:
When I use the cosine everything gets ...
2
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0
answers
302
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How are point and pure directional lights sampled in an unbiased path tracer?
To perform importance sampling on a light source, a probability density function must be provided for the sampling distribution. For most light sources, a valid probability distribution can be found, ...
3
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1
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323
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Next Event Estimation for Triangle-based Light Sources
I have a question regarding the NEE for light sources that are composed from triangles. I implemented the next event estimation (explicit light source sampling) for spherical light sources but after ...
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0
answers
94
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Why my bsdf can not pass Chi2test?
I implemented a MicrofacetTransmission in nori. But it can not pass all Chi2test when alpha is large(>= 0.4 or ?),part of chi2test is passed.And I can not found the problem.Can someone help me?
...
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775
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What is meant by ‘NEE’ in computer graphics?
I am reading this paper [Practical Path Guiding for Efficient Light-Transport Simulation, Müller et al, 2017] and it contains the following sentence:
In practice, however, we recommend combining path-...
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1
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337
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PDF for sampling emissive meshes for NEE/MIS
I'm writing a Monte Carlo path tracer, and I'm trying to allow any mesh to be an emitter, but I'm not entirely sure about the probabilities to use when I sample them.
Right now, my algorithm for light ...
3
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0
answers
53
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How much information should intersection routines return in a path tracer?
When designing/coding/"architecting" some geometry-ray intersection routines for a path tracer, there seems to be a spectrum of potential designs, with these two extremes:
Return the ...
0
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1
answer
116
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HalfEdge: How to get list of all faces from one face
I need to, starting from one face, iterate over the rest of the faces until I reach the first facet. For this I can use twin, start, end or other info of halfedges, faces, vertex. That is, I need to ...
0
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0
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115
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Unity crashes when running path tracing
I'm studying path tracing, at the moment I created a compute shader that aims to calculate the intersection of rays with meshes.
However, when I run the code the unity crashes, displaying a graphics ...
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2
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354
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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.
...
3
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503
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Path tracing : fireflies/hot pixels when directly sampling lights
I am implementing a pathtracer with both indirect and direct light sampling at each intersection (I believe the "direct light sampling" part is also referred to as "next event ...
0
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0
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76
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Unity path tracing makes the pc crash
Good Morning. I'm testing Path Tracing techniques with unity, following this tutorial.
http://three-eyed-games.com/2019/03/18/gpu-path-tracing-in-unity-part-3/
But I'm in trouble.
Whenever I try to ...
0
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1
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111
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Magic number meaning in smallpt's camera ray calculation
In smallpt's source at line 90 the direction is multiplied by 140 and I was wondering where that number is coming from. I was hoping for it to be explained in the ...
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64
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What denoising filter gives highest quality for indirect light image?
Some background of my scenario: I have two images of indirect radiance, both are from an animation. I will reproject an pixel from the previous frame to current frame, and I want to do comparisons ...
0
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370
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Path tracing: How to ensure we are sampling a direction vector within the visible hemisphere of a surface?
Given a surface Normal vector of an intersection point, how can one generate a random direction vector that is guaranteed to be in the visible hemisphere? The way I ...