# Questions tagged [lighting]

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### Distance to arbitrary set of line segments acceleration structure?

Background: I'm trying to render lightning within a volumetrically rendered cloud. I'm currently using a series of line-segments to represent lightning. At first I used a distance field rendered into ...
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### physics/math of lighting gradient of a 3D object

Consider a monochrome ball. The colours of the pixels is a function of the point height, the light intensity, the light angle, and the surface material (reflection). What is the simplest formula ...
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### Using the Preetham/Shirley/Smits daylight model to get practical (s)RGB values

I have implemented Preetham, Shirley, and Smits’s daylight model using Aubrey Jaffer’s Scheme implementation as a reference and confirmed that my implementation produces the same results in the xyY ...
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### 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 ...
1 vote
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### 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, ...
1 vote
61 views

### Are virtual point lights in many-light global illumination the same light probes?

There are several papers like this one here that refer to a concept called many-light global illumination using Virtual Point Lights (VPL). That is, the problem of global illumination is reduced to a ...
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### 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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1 vote
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### OpenGL old-style diffuse shading producing unexpected effects

Question: What is going wrong with the shape of the contours of constant illumination in the below picture ? Detail: Although Lambertian shading might be ill-regarded because it exposes the hard edges ...
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### Specular reflection with different viewing direction where reflection direction and viewing direction coincide

Suppose $P_1$ and $P_2$ two different points on surface. And let $l$: be the light source direction, $n$: normal vector $r$: specular reflection direction $v$: viewing direction . In case 1 (at $P_1$...
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### [Subsurface Scattering]What's the meaning of diffuse coefficient Rd in bssrdf

Recently, i am reading the papaer A Practical Model for Subsurface Light Transport . I have understand the radiative transport equation : and the approximation of the diffusion equation: . In BRDF ...
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### [Subsurface Scattering]Reflection from Layered Surfaces due to Subsurface Scattering

Recently, I am doing some research about subsurface scattering. i am a little confused about the backscattered radiance mentioned in this paper Reflection from Layered Surfaces due to Subsurface ...
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I am writing a raytracer which is meant to support shadows. Previously, I have naively implemented hard shadows by casting a shadow ray towards the light (+ offset) and seeing if it hits anything ...
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### 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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### Trying to understand how to render a volumetric point light

My goal is to render a volumetric point light as explained in this book's chapter 10: FGED Rendering The book explains the math pretty well, but I'm not sure I understand what is the required setup ...
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### 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 ...
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### Techniques to implement a glow that encompasses a volume

I have an old renderer from years ago written with OpenGL immediate mode. I've decided to learn Vulkan and I'm converting my old project as a way to learn the new concepts. One of the things my old ...
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1 vote
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### Area-light approximation in 2D

I’m trying to render a 2D image something like this: …where an arbitrary shape has its border illuminated by a line in a relatively physically accurate way, i.e. with less illumination reaching the ...
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1 vote
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### Ray tracing Bug with Diffuse material

I am trying to do ray tracing in python (following the tutorial given in Ray Tracing in a weekend). Basically I am shooting rays from eye and the recursively bounce around, each time they hit ...
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1 vote
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### Is spectral response curve and spectral power distribution the same thing?

I'm reading section 5.2 of pbrt 3rd edition and came across the part where they explain the concept of RGB colors. When we display an RGB color on a display, the spectrum that is actually displayed ...
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### Why do materials have both an ambient color and a diffuse color?

One of the first things I learned about computer graphics lighting (and light in general) is that when a ray of light hits a surface, the surface absorbs certain colors and the light retains the rest. ...
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### How's this laser cutting effect with backlight achieved?

Sorry for the general question, I don't even know how to tag it: https://www.youtube.com/watch?v=61UkkpsASwQ In this video, the effect is such as if there were a laser cutting a shape with a light ...
1 vote
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### 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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### What effects are used to light this scene?

I am interested how that image on the right of the slider (just albedo) can produce such a realistic looking scene as the scene on the left. What effects (at a minimum) does this scene seem to be ...
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### "whiteness" in center of bright colored lights - what is it called?

When a source of colored light is very bright, it's center appears white. What is the term I need to look for so I can implement this in my shader? I have added an image which is an example of what I ...
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### I am trying to find a clip about the art of old computer graphics

I have saw a clip where a guy talked about the art of squeezing some nice graphics into a very small space that was available on old computers. Come to think of it, it sounded something like today's ...
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### IBL looks too dark with uniform sampling

I'm making a program that illuminates a sphere using an environment map. For each fragment in the sphere, I compute a many random directions in the hemisphere along the surface normal (no importance ...
• 117
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### Problem sampling uniformly envmap with GGX

I have made a program that samples uniformly an environment map and computes the lighting using the GGX BRDF. I have made a small example that reproduces the issue I'm having. You can check it out ...
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According to Phong's reflection model, there are different reflection constants (k) and different intensities of the light source (i) for ambient, diffuse, and specular terms: $I_p=k_ai_a+\sum_{m \in ... 2 votes 2 answers 304 views ### OpenGL - Recreate position in viewspace from depth values Current state: I belive the reconstructed positions are correct. However, I still have the same problem as all the time. When I rotate around my single pointlight appears to be moving around also. I ... • 126 1 vote 1 answer 115 views ### Raytracer help - Background color writing over some colors? I'm implementing Peter Shirley's "Raytracer in a Weekend: The next week" and I'm having some trouble with rendering a scene with a light. I'm not sure if the issue is the background color or ... • 13 6 votes 1 answer 1k views ### What is a vertex normal used for? I'm new to the graphics area, and when it comes to the light part, the concept of vertex normals confuses me a lot. First, I cannot imagine how a vertex could have a normal, and second, when ... • 163 1 vote 1 answer 123 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 ... • 111 0 votes 1 answer 279 views ### What is wrong with my metallic PBR shader? I feel like my light conservation math isn't correct, but I am not sure which part is wrong. Is reflected light supposed to influence the diffuse light? Does metalness only affect the reflected ... • 143 0 votes 0 answers 167 views ### Pdf division in BRDF sampling While following scratchapixel's tutorial on indirect diffuse implementation in path tracing, the samples gets divided by the pdf, which in case of a uniform pdf results in$1/2\pi$so we have that the ... • 135 0 votes 1 answer 127 views ### Confusion about light PDF I have a doubt regarding shape lights pdfs, specifically various sources point at the fact that the pdf is a constant: $$lightpdf = 1/A$$ Where$A$is the area of the light surface. Expressed in ... • 135 0 votes 0 answers 26 views ### Adding specular reflections to a ripple simulation I am following the algorithm shown in this code here. Essentially there is a simple simulation of heights and then the difference in heights on the x and y axis respectively (sampling adjacent points) ... • 143 2 votes 2 answers 79 views ### Techniques for making tesselated shapes appear smoother? What are some common techniques for making the edges on a tesselated shape less apparent without increasing the amount of tesselation which is actually carried out? As an example, I followed along ... • 153 0 votes 0 answers 61 views ### Formula for non area light BRDFs I'm reading a graphics book and it talks about BRDFs being the ratio between differential outgoing radiance and differential irradiance. The formula it gives is f(l, v) = dL(v)/dE(l) Where l is the ... 1 vote 0 answers 291 views ### Why does Schlick's approximation contain a \$(1-\cos\theta)^5\\$ term?

The approximation writes the reflection coefficient as$$R(\theta)=R_0+(1-R_0)(1-\cos\theta)^5,\,R_0=\left(\frac{n_1-n_2}{n_1+n_2}\right)^2.$$Why is the exponent 5? Schlick 1994 introduces this ...
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### Rendering equation for spherical lights

I am currently implementing spherical lights in my DirectX game engine. I decided to build the shading formula from the classical rendering equation. Here is what I get: The simplifications show that ...
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### Irradiance field approximation with black probes

I'm posting here after some time searching the Internet and reading presentations and papers, to find out the best options to solve the problem I have. I'm implementing irradiance field with ...
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### Difference betwen Rendering Equation, Lighting model, Ray Tracing, Global Illumination and Shadows?

What is the difference between all these techniques? I know what a lightning model does, eg Phong, Flat, Gouraud. As far as I know both Ray Tracing and Global Illumination are just lighting models ...
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### Color shading and light calculation for ray tracing

I am currently building a ray tracer and I came across a problem and confusion regarding the light calculations. For lighting, I am using the following mathematical model: Where ...
1 vote
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### 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
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### Do I need a normal matrix if I calculate lighting in an objects space?

As a quick reminder, here is what normal matrix is and why do we need it. Now the question - if I take the light position and transform it into an object space than I don't need the normal matrix at ...
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### Pseudo rounded cube in OpenGL

If I have a cube in OpenGL, how can I have it appear like rounded? I think it's too complicated to really have the cube rounded so is there any "light trick" to have something like this: The cubes ...
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I am trying to simulate the actual response of a camera given some object that is reflecting light. I've written a ray tracer, and have a BRDF that I need to use, and I have a camera sensitivity in ...
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### Clarification about Phong lighting model

I've read some tutorials about Phong and Blinn lighting models and tried to implement a rendered myself. To my knowledge, the basic approach consists of the following steps: calculate the vector from ...
1 vote
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### 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 ...
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