Questions tagged [pathtracing]
For questions about the path tracing Monte Carlo algorithm for physically accurate global illumination, or its variants.
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Path tracing: how to ensure the new direction vector is a valid direction vector with respect to a BSDF?
Given the BSDF function and the Normal vector of the intersection point in world space, how can I generate a new direction vector ...
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1answer
34 views
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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1answer
32 views
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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1answer
45 views
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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1answer
41 views
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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33 views
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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1answer
37 views
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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68 views
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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22 views
How to update large step probability when exchanging states in Metropolis Sampler?
I want to implement good path guiding for photons for my Vertex Merging integrator.
After reading through this 2 papers:
Hachisuka T., Jensen H. W.: https://www.ci.i.u-tokyo.ac.jp/~hachisuka/...
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1answer
137 views
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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1answer
73 views
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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1answer
70 views
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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1answer
66 views
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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1answer
73 views
“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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1answer
170 views
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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1answer
94 views
Path tracing - cannot converge diffuse sampling + oversaturation
I'm in process of creating progressive path tracer using DX12 + DXR. I managed to create working raytracing code + pathtracing code with multiple bounces but I'm experiencing problems stated below (...
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1answer
68 views
Path Integral Form with Path Tracing
The description is going to be long and detailed, thanks in advance for your patience!
I am learning the path integral form of light transport equation(LTE) to be able to follow recent rendering ...
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1answer
75 views
What should I do when a new sampled direction is below a normal oriented hemisphere?
I generate random directions from the pdf of D term in GGX BRDF. On the picture, white dots are new directions and the cross is the light direction, with roughness = 1. What should I do with the ...
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2answers
80 views
issue with importance sampling
I was trying to do importance sampling on lambertian surface.At first I uniformly choose direction from unit sphere.
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2answers
281 views
Why is eye-based ray tracing preferred over light-based ray tracing?
It seems that virtually all path tracers use eye-based or view-based path tracing. That is, the light rays originate from the camera rather than the light source. The reason given for this everywhere ...
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1answer
61 views
Probability density for explicit light sampling
When implementing explicit light sampling, I am separating the monte-carlo approximation to two parts
$$\frac{1}{N+M}(\sum^N \text{direct} + \sum^M \text{indirect})$$
$$\text{direct} = \frac{\text{...
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2answers
118 views
BRDF that interpolates between diffuse, glossy and reflective?
Is there a way to obtain a parametrized BRDF that smoothly interpolates between diffuse, glossy and mirror? For example, $\lambda = 0$ would be perfectly diffuse, $\lambda=0.5$ glossy and $\lambda = 1$...
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63 views
Implementing monte carlo path traced refractions problem
I am writing a forward monte carlo path tracer with the added feature of specular refractions for transparent materials, I have managed to come this far but something is not quite right and I am ...
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1answer
108 views
How do I make sure my cosine-weighted sampling works fine?
I'm working on a pathtracer and while it's working mostly fine, I'm getting different outputs with cosine-weighted sampling and uniform sampling :
Uniform sampling is on the left, cosine-weighted is ...
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98 views
How to properly combine diffuse and rough specular BRDFs in a path tracer
Looking around here on various sources (including related questions on this site), if my understanding is correct, when implementing a path tracer with a material which has both a diffuse term and a ...
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29 views
Birectional path tracing - connection of paths
I have a few questions about setting up a bidirectional path tracer described by Veach here.
I have created both an eye path and a light path. Both are using BRDF for calculating how much light can ...
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1answer
101 views
BRDF sampling and evaluation of diffuse vs specular component
When I am sampling diffuse BRDF I am using cosine-weighted distribution and when I want to sample specular BRDF I use sampling by GGX distribution. I can decide how much light is reflected and how ...
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3answers
164 views
Correct way to think about Fresnel effect
I am using Schlick approximation to calculate the value of the Fresnel effect I found here
When I try to find corner cases for the formula I get the value of 1 when the angle between normal and ...
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2answers
115 views
Understanding of Microfacet monte-carlo path tracing
I am trying to implement BRDF microfacet path tracing and I think I need a little push.
I will explain what I understand so that you can correct my mistakes.
I start with simple rendering equation:
...
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0answers
148 views
Understanding BRDF sampling
I'm trying to understand BRDF importance sampling following the exemples of the lambertian/diffuse model and the reciprocal Phong model.
I would like to be able to extend the principle to other ...
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29 views
Wrong calculation of the balance heuristic weights in PBRT
Please consider section 16.3.4 of the PBR book, where the authors describe how the balance heuristic weights for the multiple importance sampling estimator in bidrectional path tracing can be computed....
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104 views
Visualize the variance of an image
Let $h_j$ denote the image reconstruction filter of pixel $j$.
I'm estimating the color value $$I_j=\int h_jf\:{\rm d}\mu$$ of the $j$th pixel (see [Veach, Section 8.2]) by an asymptotically ...
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59 views
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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92 views
How to achieve higher FPS for my GPU pathtracer?
So I've written a GPU based pathtracer using OpenCL-GL interoperability. The system uses the Mega-Kernel Approach instead of a wavefront one as I was aiming it as an educational software for other ...
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46 views
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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1answer
88 views
BDPT - How to handle deterministic ray PDF?
I'm trying to implement a simple BDPT without MIS as described in Lafortune's paper. I've used the weighting scheme defined in the paper in which they suggest that the weight be based on the surface ...
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39 views
Terminology Question: Temporal Stability
I am reading the paper Blockwise Multi-Order Feature Regression for Real-Time Path Tracing
Reconstruction and the authors use a term several times which I am not sure what it means. This is in the ...
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38 views
How do I fix skipping ray-triangle intersections on concave edges/cavities of model?
I'm writing a path tracer and I have a problem with ray-triangle intersection tests. The problem happens most frequently with materials that implement random scattering of the ray. Here's a function ...
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1answer
193 views
Sampling the light vs. sampling the BRDF: difference in intensity
(possible duplicate)
I'm trying to implement multiple importance sampling, as described in the PBRT book (no bouncing yet, I want to make MIS work first).
What my problem is, that while the BRDF ...
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47 views
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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47 views
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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1answer
58 views
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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1answer
72 views
Intrepret path/light tracing by rewriting light transport equation
Given the rendering equation:
$$
L_o(x, \theta_o) = L_e(x, \theta_o) + \int_{\Omega} \! f(x,\theta_i,\theta_o) L_i(x,\theta_i) \cos(\theta_i, \theta_o) \, \mathrm{d} \theta_i.
$$
Rewriting it using ...
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1answer
157 views
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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1answer
52 views
Trouble making path tracer multithreaded, read access violation
I'm trying to make the path tracer shown in the Ray Tracing in One Weekend series multithreaded.
Here's the starting of my main function:
...
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2answers
202 views
Should ray throughput always decrease when bouncing?
In the accepted answer for the question What is Importance Sampling?, in the example code there is this line:
...
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0answers
105 views
Importance Sampling path tracer, Different pdfs result in different luminance?
I'm having a lot of trouble implementing Importance Sampling path tracer.
If I understand it correctly, what I need to evaluate for a path tracer is this:
$\int_\Omega L_{in}(L) * fr(L, V) * \cos(\...
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1answer
239 views
Why is Russian Roulette used in ray tracing?
Why should we use Russian Roulette? Does it reduce ray tracing artifacts?
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1answer
181 views
Multiple samples per pixel and texture blurring
As far as I know path tracers (or super-sampling antialiasing) typically calculate the final color of a single pixel by averaging the result of all samples taken inside that pixel. This gives a nice ...
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99 views
Path tracing: How to do tone mapping and gamma correction?
I am not sure what is the correct way to do tone mapping and gamma correction in a Monte-Carlo Path Tracer. Should I apply tone mapping before or after averaging the samples?
