Questions tagged [pathtracing]
For questions about the path tracing Monte Carlo algorithm for physically accurate global illumination, or its variants.
171
questions
3
votes
0answers
31 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
34 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
44 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
57 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
64 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
257 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 ...
0
votes
1answer
56 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
99 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
52 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
73 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
46 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 ...
1
vote
0answers
33 views
How to find the BRDF of a rough specular surface
So I know that the BRDF for a diffuse material is `albedo/Ļ', and I know that the BRDF for a perfectly specular surface is only non-zero on the reflected direction. How would I find the BRDF for a ...
0
votes
0answers
21 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
89 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
126 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
95 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
136 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
28 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....
1
vote
0answers
85 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
53 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
82 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
45 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
77 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
35 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 ...
0
votes
0answers
42 views
Case where ray hits corner of box
I am writing a path tracer and when wrting method for returning the normal for the plane that was hit, I am not quite sure what to do when the ray hits box in a corner, placing the intersection point ...
1
vote
0answers
37 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
172 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
48 views
Subpath connection in Bidirectional Path Tracing for subpaths consisting of a single vertex
Consider the PBRT implementation of the subpath connection in bidirectional path tracing for the strategy with a single camera vertex, as described here: http://www.pbr-book.org/3ed-2018/...
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:
...
0
votes
0answers
34 views
Computing probabilties when connecting a camera subpath to a single light point
I'm struggling to understand how the connection step in bidirectional path tracing for the strategy with a single light vertex has to be implemented. The following code essentially shows the PBRT ...
2
votes
0answers
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}=(\...
0
votes
0answers
35 views
Inverse path sampling in (bidirectional) path tracing
In Section 4.1 of the paper Fusing State Spaces for Markov Chain Monte Carlo Rendering, it is described that the CDF $P$ of the distribution of paths of length $k\in\mathbb N$ may be factored into a ...
0
votes
0answers
24 views
Computing inverses in Reversible-Jump Metropolis Light Transport
Say we are sampling a path $\rm x=(\rm x_0,\ldots,\rm x_{n-1})$ of length $n-1$ using bidirectional path tracing. Let $p_s$ denote the area product density corresponding to the used connection ...
1
vote
1answer
54 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
67 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
147 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
0answers
50 views
Implementation of the Primary Sample Space Sampler in the book Primary Sample Space Sampler
In the Multiplexed Metropolis Light Transport implementation of the book Physically Based Rendering, the proposal samples are generated by the Primary Sample Space Sampler ...
0
votes
1answer
51 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:
...
0
votes
1answer
146 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
78 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(\...
2
votes
1answer
165 views
Why is Russian Roulette used in ray tracing?
Why should we use Russian Roulette? Does it reduce ray tracing artifacts?
1
vote
1answer
127 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 ...
1
vote
0answers
79 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?
0
votes
0answers
38 views
Questions in Veach path-space formulation
http://graphics.stanford.edu/papers/veach_thesis/chapter8.ps
In chapter 8 of his thesis which he talks about the three-point form of the transport equations, equation (8.1) in particular, it seems ...
0
votes
0answers
36 views
Factorize probability densities in Bidirectional Path Tracing
Say we have fixed a length $k$ for paths we want to sample using bidirectional path tracing as described in the Physically Based Rendering book. Let $q_{s,\:t}$ denote the probability density of ...
1
vote
0answers
100 views
Why does the reflected component in Lambertian path tracing get multiplied by a factor of 2?
I would like to intuitively understand the Path Tracing equation/formula/pseudocode, but I'm not fully getting the last return statement.
As per Wikipedia page:
<...
2
votes
1answer
98 views
Strange artifacts while rendering a dielectric material
I am trying to render a dielectric sphere inside the Cornell Box. Some circles are generated on the sphere. Here is the photo generated by path tracer:
And below is my main function:
...
1
vote
0answers
25 views
Report standard deviation in Rendering results
I noticed that a common metrics for image quality assessment (Monte Carlo path tracing) is MSE between the generated image and a reference one. My question is: why isn't the standard deviation ever ...
0
votes
0answers
81 views
Multiple Importance Sampling in Bidirectional Path Tracing
I'm trying to understand the computation of the path density described in the book Physically Based Rendering. They assume that a path $$x=(x_0,\ldots,x_{n-1})=(q_0,\ldots,q_{s-1},p_{t-1},\ldots,p_0)$$...
1
vote
0answers
27 views
Image contribution function and reconstruction using filters
So I've been reading Physicall Based Rendering which in section 16.4.3 defines the "image contribution function" to be the following
$$I_j = \int_\Omega h_j(X)L(X)d\Omega$$
where the variables are ...
