Questions tagged [pathtracing]
For questions about the path tracing Monte Carlo algorithm for physically accurate global illumination, or its variants.
180
questions
2
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59 views
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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0answers
29 views
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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0answers
52 views
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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0answers
44 views
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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0answers
36 views
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 ...
0
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1answer
47 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 ...
0
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1answer
44 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 ...
0
votes
1answer
103 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 ...
1
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1answer
69 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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40 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(...
1
vote
1answer
40 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 ...
2
votes
0answers
76 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:
...
0
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0answers
23 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/...
1
vote
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 ...
0
votes
1answer
76 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:
...
0
votes
1answer
94 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 ) ...
4
votes
1answer
77 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 ...
1
vote
1answer
81 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 ...
3
votes
1answer
175 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 ...
1
vote
1answer
109 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 (...
2
votes
1answer
87 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 ...
5
votes
1answer
76 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 ...
1
vote
2answers
87 views
issue with importance sampling
I was trying to do importance sampling on lambertian surface.At first I uniformly choose direction from unit sphere.
...
2
votes
2answers
284 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 ...
1
vote
1answer
68 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{...
3
votes
2answers
142 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$...
2
votes
0answers
65 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 ...
3
votes
1answer
113 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 ...
1
vote
0answers
118 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 ...
0
votes
0answers
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 ...
1
vote
1answer
115 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 ...
0
votes
3answers
221 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 ...
0
votes
2answers
128 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:
...
3
votes
0answers
153 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 ...
0
votes
0answers
118 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 ...
0
votes
0answers
60 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 ...
0
votes
0answers
97 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 ...
0
votes
0answers
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, ...
1
vote
1answer
91 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 ...
1
vote
0answers
40 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 ...
1
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0answers
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 ...
2
votes
1answer
222 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 ...
0
votes
0answers
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:
...
2
votes
0answers
48 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}=(\...
1
vote
1answer
59 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 ...
3
votes
1answer
73 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 ...
4
votes
1answer
158 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 ...
0
votes
1answer
54 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:
...
1
vote
2answers
209 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:
...
2
votes
0answers
126 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(\...
