Questions tagged [pathtracing]

For questions about the path tracing Monte Carlo algorithm for physically accurate global illumination, or its variants.

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59 views

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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79 views

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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1answer
60 views

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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68 views

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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43 views

What problem of my bsdf?

This is a image of microfacetdieletric. But i can not find the problem. My code is : ...
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1answer
3k views

Anti-aliasing / Filtering in Ray Tracing

In ray tracing / path tracing, one of the simplest way to anti-alias the image is to supersample the pixel values and average the results. IE. instead of shooting every sample through the center of ...
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51 views

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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1answer
100 views

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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1answer
149 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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40 views

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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43 views

Reorder mesh triangles

Good Morning! My problem is: I need to get the vertices of a mesh and send them to a shader. Inside the shader I will reassemble the mesh from its vertices. So far so good, I send the information and ...
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1answer
37 views

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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29 views

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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27 views

How to calculate MIS weight for indirect light path?

I am trying to add MIS into my render. So, looking into some shadertoy examples. https://www.shadertoy.com/view/MsXfz4 https://www.shadertoy.com/view/4sSXWt Here comes the problem. All of them are ...
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23 views

Double sided area light produces much more fireflies than single sided, how to fix it?

I am testing area light with my render. I prefer double sided light, because it produces some glow around the light. But it produces much more fireflies which is annoying. While the single sided light ...
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2answers
112 views

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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1answer
80 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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1answer
275 views

Should I expect differences with explicit light sampling other that the noise?

I am trying to understand why my explicit light sampling implemetation does not produce the same results as my naive path tracer. Here are my results : Naive Version : Explicit light sampling ...
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145 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 ...
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38 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 ...
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1answer
631 views

Using Monte carlo on Rayleigh scattering

Update I am editing and posting this question in a different way; this time from the point of view of Nishita paper. Sunlight gets scattered at P and attenuated before reaching Pv. Therefore ...
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1answer
956 views

Path Tracing With Multiple Lights

I've got my path tracer working great for a single light, but I'm having trouble coming up with a solution for scenes with multiple lights. My first thought was to just send a ray to each light and ...
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52 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 ...
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1answer
78 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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1answer
81 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
284 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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49 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 ...
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1answer
60 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
1k views

More accurate Fresnel approximation for a RGB-based Path Tracer

I'm writing a path tracer and, for the moment, spectra related data (spectral power distributions and spectral reflectance curves) are stored as RGB tuples. In the Cook-Torrance specular BRDF I am ...
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46 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
55 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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136 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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1answer
187 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
140 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
167 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
88 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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2answers
231 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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1answer
186 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
99 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
165 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
139 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
88 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
121 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
332 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
82 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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1answer
174 views

Light Falloff through a grid

I'm playing with a grid-based lighting system, where light is transported and accumulated through a grid. I initially tried attenuation based on ...
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2answers
236 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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1answer
185 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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0answers
73 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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0answers
245 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 ...