# Questions tagged [global-illumination]

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### 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....
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 ...
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, ...
76 views

### Relation between camera sensor responsivity and image reconstruction filter associated with a pixel

Let $W_{\text e}$ denote the camera sensor responsivity (i.e. importance) and $h_j$ and $W_{\text e}^{(j)}$ denote the image reconstruction filter and sensor response associated with the $j$th pixel, ...
112 views

### Properties of the image reconstruction filter in rendering

Let $f$ denote the measurement contribution function for paths of length $k\in\mathbb N$, i.e. $$f(x)=g(x_0\leftrightarrow x_1)W_{\text e}(x_1\to x_0)t_k(x_0,\ldots,x_k)L_{\text e}(x_k\to x_{k-1}),$$ ...
134 views

### Scaling of the final image in Metropolis Light Transport

I don't understand why the PBR implementation of Metorpolis Light Transport scales the final image by b / mutationsPerPixel. The authors write: Each Metropolis ...
30 views

### Quantify the variance of pixel measurements

Say $E_j$ is an estimator of the value $$I_j=\int f_j\:{\rm d}\lambda$$ of the $j$th pixel given by the path space integral of the corresponding measurement contribution function $f_j$. $f_j$ is of ...
36 views

### Is casting a shadow ray non-symmetric in pbrt?

According to the description in the book, Scene::IntersectP() "checks for the existence of intersections along the [passed] ray". This operatorion should be ...
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/...
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: ...
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 ...
47 views

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### Natural Environment Illumination in Augmented Reality

I've basically 0-knowledge about augmented reality. For academic purposes I've to study this paper http://ieeexplore.ieee.org/document/8007317/?reload=true I'm struggling trying to understand some ...
2k views

### How does voxel cone tracing work?

Assume that we have voxelized a 3D scene into a regular 3D grid of cubes, storing the average (diffuse) radiance and some flag indicating whether or not a voxel is empty. Next, the finer levels of the ...
333 views

### How to simulate specular reflection in Light Tracing?

I am implementing light tracing from this website. The right wall on the below image is perfect mirror(specular reflection). Its BRDF returns zero that's why it's been rendered black. But how is it ...
502 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 ...
296 views

### Phong BRDF in Mitsuba, Tungsten and AGI

In the book AGI (Advanced Global Illumination), the Phong BRDF is $f_r(x,\Psi\leftrightarrow\Theta)=k_s\cfrac{(R\cdot\Theta)^n}{N\cdot\Psi}+k_d$ $k_d=\cfrac{albedo}\pi$ In Mitsuba and Tungsten, the ...
222 views

### Beer's law in dielectric material

I am trying to implement Beer's law according to this page in dielectric material but I am not sure have done it correctly as the image does not suggest so. The formula is: I(s) = I(0) * pow(e, ln(A)*...
92 views

### The variance for the Monte Carlo estimator

I was wondering about the variance for Monte Carlo. The book (Advanced Global Illumination 2ed, p.60) writes the equation as follows: $\sigma^2 = \frac{1}{N} \int(\frac{f(x)}{p(x)} - I)^2p(x)dx$ \$\...
3k views

### A recent approach for subsurface scattering

I read "A Practical Model for Subsurface Light Transport" and "A Rapid Hierarchical Rendering Technique for Translucent Materials". If I understand correctly, the former does not consider the case ...
6k views

### Progressive Path Tracing with Explicit Light Sampling

I understood the logic behind the importance sampling for the BRDF part. However, when it comes to sampling light sources explicitly, all becomes confusing. For example, if I have one point light ...