Questions tagged [pathtracing]
For questions about the path tracing Monte Carlo algorithm for physically accurate global illumination, or its variants.
209
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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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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 ...
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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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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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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 ...
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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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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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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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Naive path tracer - correct results?
I'm trying to implement the most basic Monte Carlo path tracer based on this equation:
So far I've got the following implementation:
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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 ...
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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 ...
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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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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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Problem about Metropolis light transport?
This problem is about the bidirectional mutation strategy in Veach's thesis(page 345).
The bidirectional mutation strategy is as follows:
current path is $\bar x=x_0x_1...x_k$
delete edges between $...
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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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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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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 ...
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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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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.
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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 ...
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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 ...
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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) ...
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485
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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 ...
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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, ...
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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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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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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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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 ...
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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 ...
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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 ...
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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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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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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 ...
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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 ...
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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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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 ...
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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 ...
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How to link Intel Open Image Denoise in Qt Creator and use it to denoise noisy Monte Carlo path tracing renderings?
I've been trying to link my the Intel Open Image Denoise libraries for about a week and still have no luck as of now. This could partly be because I am also novice in C++ stuff. So I need some help in ...
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Transforming a ray from camera space to world space
I am writing a Raytracer and generating rays from the camera. I have a working program but slightly confused about the linear algebra concepts involved in transforming the ray from camera space to ...
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Does film filter introduce bias in path tracing?
Does using box or gaussian filter introduce bias to the image when reconstructing the pixel?
Bias does not seem to be talked in the Chapter 7.8 of PBRT
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How to use IES Light Profile with an area light source?
I want to use IES profile with an area light. My understanding is that the IES file assume the source to be a point light. That is in case of (large)area light the measurements are taken at a distance(...
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How can I account for specular interactions in shadow rays?
I've been working through PBRT, implementing my own version of it in Rust. Right now I'm working on shadow rays, and it looks like pbrt doesn't do anything to account for specular behavior, and treats ...
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Hero wavelength multiple importance sampling
I want to add spectral rendering and dispersion to my pathtracer. I found the Hero Wavelength paper but I have trouble implementing this. This is how I understand the process and where I am stuck:
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Energy redistribution sample re-integration
I'm implementing ERPT-style energy redistribution of primary samples within a pathtracer. Specifically, to improve the sampling of defocused areas.
The core algorithm does two things:
If sample ...
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Pathtracing - many bounces reduce shadows
I'm creating DXR PathTracer highly influence by Matt Pettineo's one - https://github.com/TheRealMJP/DXRPathTracer ; Relevant HLSL code below:
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430
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Importance sampling GGX NDF - fireflies and bright final result
https://schuttejoe.github.io/post/ggximportancesamplingpart1/ - I have problem implementing this method. Somebody asked question about this before ( Can't understand the Importance sampling GGX ) ...
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Deriving radiance from irradiance and intensity
I'm reading PBRT and am stuck in chapter 5.4 about radiometry. In particular:
We define the irradiance as the average density flux arriving at a surface with units $\frac{W}{m^2}$. So for a point ...
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"Importance Sampling of Many Lights with Adaptive Tree Splitting" - paper: participating media
I'm reading and implementing a paper about Importance Sampling of Many Lights with Adaptive Tree Splitting. In section 5.2 on cluster importance for participating media, there is a part that I don't ...
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Why does my image has a square pattern in cuda path tracer?
I am writting a path tracer in cuda following the Shirley's book. I am having a square pattern as an output.
The size of the block change if I change the block dimensions. For this image, the block ...
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