Questions tagged [physically-based]

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Why is the indirect illumination (using IBL) in my PBR shader overpowering everything?

I'm trying to implement a basic form of physically based rendering (PBR) and I am using the PBR tutorial from learnopengl dot com as a reference. The PBR I am implementing consists of two parts, ...
3 votes
2 answers
589 views

How to determine RGB values given a display spectral response curve?

I am reading Physically Based Rendering section 2.2.2 on RGB color. I am trying to understand how, given a display spectral response curves for rgb intensities, we can choose the intensities so that ...
0 votes
1 answer
68 views

Point light source radiance

I was reading Deriving radiance from irradiance and intensity and the last comment said that by dividing $r^2$ we convert radiant intensity to irradiance. What confuses me then is the fact that for ...
0 votes
0 answers
43 views

Understanding the BRDF Equation

I am studying the BRDF equation. From Wikipedia, the equation is as follows: I have one main question: Where does the $\cos{\theta_i}$ in the denominator come from? The denominator implies that $...
15 votes
4 answers
6k views

For shader math, why should linear RGB keep the gamut of sRGB?

sRGB is often contrasted with "linear RGB." Images are stored on disk and passed to displays in sRGB, which is approximately perceptually uniform in intensity. Shader math is done in linear RGB, ...
0 votes
0 answers
17 views

Narrow-phase CCD in FEM topology query (finite element method)

I am implementing IPC from siggraph2020, and one of its step is about CCD line search, where CCD is applied each iteration in the descent method in a part of the algorithm. I have implemented CCD ...
2 votes
2 answers
245 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. $$f(x)=g(x_0\leftrightarrow x_1)W_{\text e}(x_1\to x_0)t_k(x_0,\ldots,x_k)L_{\text e}(x_k\to x_{k-1}),$$ ...
1 vote
0 answers
56 views

Term confusion about volume scattering

We have two different terms, for example, let's talk about scattering only. Scattering coefficient Scattering cross-section These two terms are supposed to have different physical meaning. I read it ...
1 vote
1 answer
327 views

Cosine in Rendering Equation and BRDF cancel out: Why cosine at all?

I am somewhat confused with the following issue reading about the rendering equation and BRDFs. That is, the BRDF is usually defined as surface radiance $Lr(ω_r)$ over irradiance $L_i(ω_i)cosθ_i$ for ...
2 votes
1 answer
201 views

Rendering equation integration variable change

I'm watching the TU Wien rendering lectures in the course we were presented with a rendering equation (first one on the screenshot) and then another, which results from a change of variables (if I ...
1 vote
0 answers
90 views

Difficulty in understanding the interpretation of propagation of an exitant function from the book Advanced Global Illumination (2nd ed)

The book defines operator $\mathcal{T}$ for the propagation of an exitant function as: if I'm assuming that the position of the point $x$ is on the top-left surface, and that $\Psi$ is considered as ...
1 vote
1 answer
73 views

How is the distribution of normals constructed from the distribution of slopes in 'Understanding the masking-shadowing function' paper?

Recently I'm reading Eric Heitz's paper 'Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs', in section 5, 5.2, the paper defines the distribution of slopes and then says the ...
1 vote
1 answer
65 views

Is the dichromatic model physically based?

lately I have been learning about photometry, and everywhere I look I see a BRDF written according to the "dichromatic model". Roughly speaking: $$\rho= \rho_D+\rho_S \cdot (...)$$ for some $...
3 votes
0 answers
46 views

Diffuse irradiance map : confusion about photometric vs radiometric units

I have spent the longest amount of time just taking the terminology for granted & have only just recently started studying or at least trying to understand the difference between radiometric and ...
1 vote
1 answer
58 views

How is the beam transmittance calculated in PBRT V3?

In pbrt v3, the book gives this description of beam transmittance, but I don't know how to solve the differential equation like it says to get Tr , can someone please tell me how to solve the ...
0 votes
0 answers
75 views

What's The Math Behind This Cloth Animation?

I progammed a simple cloth animation. Initially I tried to implement Hooke's law, but it wasn't numerically stable, presumably because I used explicit Euler. Anyway, I came up with something (WebGL2 ...
5 votes
2 answers
264 views

Rendering Hypercentric Perspective

I came across some Non-Euclidean Games which involve Hyperbolic Spaces, Spherical Spaces, Portals, etc. And, I noticed that they give quite deep feel of what Non-Euclidean Spaces feel like. So, I was ...
0 votes
1 answer
84 views

Motivation behind tesselation

This question is NOT about the hardware difficulties and shortcomings of tesselation shaders I am trying to understand the motivation behind tesselation shaders. Why/when/where tesselation is a good ...
0 votes
1 answer
90 views

PBR pipeline with multiple HDR images?

I believe I already know the answer to this question, but I want to make sure I'm understanding this correctly. Within a physically based rendering pipeline, you calculate your indirect lighting from ...
0 votes
1 answer
167 views

State of the art in real-time global illumination algorithms [closed]

What is the state of the art in global illumination algorithms in real time applications? Which algorithms or categories of algorithms are actually used in the wild and what are their characteristics (...
1 vote
1 answer
446 views

How to change a RGB value using a radiance value?

I am new to this awesome community, I am currently writing a ray tracer but I hit a problem... Let's say I have a surface(material doesn't matter) of colour [1, 0, 0] in RGB, and the radiance reaching ...
0 votes
0 answers
164 views

Ray casting and rasterization 101

Recently I've became an intern in company-name and my internship task is(for now) create rasterization using rays. I'm mostly interested in pure math, so basic ...
7 votes
2 answers
4k views

Physically Based Area Lights

So after reading https://www.guerrilla-games.com/read/killzone-shadow-fall-creating-art-tools-for-a-new-generation (a guerilla games presentation on PBR) I noticed the Area lights as opposed to the ...
1 vote
1 answer
128 views

Prove radiance contributions of deeper paths fade away

When ray tracing, I find it intuitively clear that deeper paths have a lower contribution to the overal picture than shorter paths. This is the main reason why it is generally okay to render a picture ...
4 votes
2 answers
889 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 ...
7 votes
2 answers
3k views

Better Shadow Mapping Techniques

Currently I have basic shadow mapping setup in my engine. I am currently trying to implement something more realistic like PCSS (percentage closer soft shadows), to get a more physically accurate ...
12 votes
0 answers
859 views

How correct is rendering in XYZ / linear RGB space?

I have a spectral power distribution (SPD, 5 nm steps) for all light sources in the scene and SPDs for the reflectance of all surfaces under any light / viewer angle in question. I'm going to ...
1 vote
2 answers
220 views

Understanding lighting for physically based rendering

i wanted to ask if you know the best books or resources to understand light physics. I have heard that Subrahmanyan Chandrasekhar's book "Radiance Transfer" is very good. Any other books or ...
5 votes
2 answers
5k views

What are the current open problems in Computer Graphics?

I did a quick investigation about the topic but there doesn't seem a decent resource to find related problems without digging into latest CG papers (unlike CS problems you can easily find a Wikipedia ...
0 votes
0 answers
64 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, ...
0 votes
0 answers
94 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, ...
0 votes
0 answers
64 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 ...
2 votes
0 answers
54 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}=(\...
36 votes
2 answers
7k views

How physically-based is the diffuse and specular distinction?

The classical way of shading surfaces in real-time computer graphics is a combination of a (Lambertian) diffuse term and a specular term, most likely Phong or Blinn-Phong. Now with the trend going ...
3 votes
1 answer
107 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 ...
1 vote
1 answer
989 views

Roughness Value of (Close to) Zero in Physically Based Rendering

In my Direct Light Physically Based Renderer, when I set the roughness too low (ie. 0.0 or close) the specular reflection doesn't show, not even at high resolutions and at perfect angle with the ...
1 vote
0 answers
36 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 ...
1 vote
1 answer
456 views

Tone Mapping in a physically based rendering ray tracer

I'm implementing a pbr ray tracer. Let's say that I'm at the end of the process: for each pixel pi, I accumulated the radiance value in vector pi = (radR, radG, radB). At this point, these values are ...
0 votes
1 answer
207 views

total internal reflection implementation in pbrt-v3

I've been implementing a path tracer, referring pbrt-v3. However, I'm a bit confused about its implementation. Code is here. It seems when we sample to do transmission, it tests if it meets a total ...
2 votes
1 answer
1k views

PBR and Specular Aliasing

I have been following LearnOpenGL.com's tutorials on PBR. Everything makes sense and I wrote up a shader for my physically based renderer. I noticed that the results look great, however all of my ...
0 votes
1 answer
85 views

kinematics and dynamics of a sphere in a spring mass system?

I am attempting to code a simple spring mass system simulation in which a sphere pendulus hangs from a string (a spring) by the top and then another sphere (controlled by the user) can move and ...
1 vote
2 answers
2k views

How to set equivalent PDFs for cosine-weighted and uniform-sampled hemispheres?

I'm trying to add BRDFs to a very basic path tracer. Starting out, I'd like to convert just the Lambertian material, with two different sampling methods, to ensure that everything is working right. ...
2 votes
2 answers
323 views

Physically Based Shading for Diffuse surfaces

So I am currently in the process of implementing Physically based Shading in my pathtracer using microfacet models and I'm quite stuck at comprehending light interaction with diffuse surfaces. First ...
2 votes
1 answer
290 views

Rendering Equation for photons carrying flux

I am trying to understand the mathematical/physical foundations of photon mapping better. In the forward photon tracing step it is established, that the rays are carrying portions of total power (...
1 vote
0 answers
129 views

Compute emitted importance of a pinhole camera

In section 16.1.1 of Physically Based Rendering the authors describe how we can check, if a given ray $r$ corresponds to one starting from the film area. They implement this check such that it works ...
11 votes
1 answer
778 views

Ocean Wave Rendering

How could I generate the waves for a water body with whitecaps & foam and variable intensity of the waves? Is the surface a mesh with a normal map? Is there a formula for generating that? Is there ...
2 votes
1 answer
957 views

PBR - How to handle multiple BSDFs and material type

So I am in the midst of writing my own path traced renderer and right now I have only implemented the old Blinn-Phong models where we separately calculated the diffuse and specular components of the ...
3 votes
1 answer
361 views

How is Iridescence handled in a Path Tracer?

I have little knowledge of this topic but from what I gather in a Ray Tracer each ray is given its own wavelength as opposed to an RGB value. This automatically simulates Dispersion and Fluorescence. ...
1 vote
0 answers
526 views

Interpreting Cornell Box data for path tracer

So I want to path trace a Cornel Box scene, but I don't understand the values given here in section 2 and 3. Cornell Box Data | Cornell University Program of Computer Graphics No.2 Lists surface ...
3 votes
1 answer
3k views

Ray tracing: transforming ray to object's local space for intersection test

Im writting a raytracer, for which I want to be able to test intersections with implicit surfaces (in my case spheres). Without applying any transformation it works great, but I would like to upgrade ...