<p>From the ray tracing wikipedia page <a href="https://en.wikipedia.org/wiki/Ray_tracing_(graphics)" rel="noreferrer">https://en.wikipedia.org/wiki/Ray_tracing_(graphics)</a>:</p>
<p>&quot;Path tracing is a form of ray tracing that can produce soft shadows, depth of field, motion blur, caustics, ambient occlusion, and indirect lighting.&quot;</p>
<p>So a path tracer is a ray tracer, but not all ray tracers are path tracers.</p>

CC BY-SA 4.0
2021-06-16T05:51:07.643Z
It's also worth noting that (pre-Whitted) ray tracing was originally invented as a hidden surface algorithm, something that we now usually call "ray casting". But it's still a kind of ray tracing.
Pseudonym
CC BY-SA 4.0
2021-06-15T19:44:55.067Z
2021-06-15T19:44:55.067Z
Peter
<p>This question is the result of the modern era using the blanket word ray-tracing to denote every similar technique as it's based off of it. Just wanted to give a more historical answer if anybody is interested.</p>
<p>As lightxbulb said, historically, Turner Whitted was the first person to come up with the raytracing technique but it only had a limited number of rays. Reflection/Refraction and these secondary rays got terminated when they hit a diffuse surface since no GI rays were shot.</p>
<p>The problem of Global Illumination is recursive and as you might've guessed it requires many many rays. The math wasn't that complex and sophisticated in pure raytracing. Then later on, <a href="https://en.wikipedia.org/wiki/Radiosity_(computer_graphics)" rel="nofollow noreferrer">Radiosity</a> method was introduced by Goral which accounted for GI but only for diffuse surfaces using the Finite element method. This was a major step ahead and helped in laying the foundation for pathtracing.</p>
<p>After that Pathtracing got introduced by Kajiya which accounted for all types of surfaces, He used Monte-Carlo Integration to solve the recursive integral related to the GI problem.</p>
<p>As time went by, the word raytracing somehow overshadowed the other words in this field. And recently, with NVIDIA dishing out their RTX technology pretty much sealed the fact. So raytracing in today's era doesn't necessarily mean whitted-style raytracing which was the original raytracing.</p>

CC BY-SA 4.0
2021-06-16T09:10:35.700Z
I would refrain from attributing ray-tracing to Whitted. Appel's paper is from 1968 for example, and the idea is much older. Ray-tracing is called this way because you trace rays. In fact in the production of lenses they also use ray-tracing, but not in the context of Whitted-style ray-tracing or path tracing. This is the reason it is an umbrella term - because it simply describes processes that use the tracing of rays, regardless of the framework on top. If one wants to be truly precise, then path tracing is just numerical integration for the series arising from the rendering equation.
lightxbulb
CC BY-SA 4.0
2021-06-16T13:58:37.230Z
I know that, used to be called ray casting way back then, but didn't want it to become a wikipedia historical article so I've dumbed down the answer. The original raytracing used to produce all these photorealistic images was infact given by Turner Whitted so no harm attributing the technique to him.
gallickgunner
CC BY-SA 4.0
2021-06-16T14:06:44.710Z
Dumbing down the answer in a manner that makes it incorrect is not recommended. Whitted-style ray-tracing can be attributed to Whitted, ray-tracing in general cannot be. The usage of the term ray-tracing in literature is for any process that involves the tracing of rays. If one wants to be specific about the technique, they can be (i.e. Whitted, Kajiya, Cook, etc.). Then again, Kajiya's work subsumes Cook's work, which subsumes Whitted's work. From a scientific perspective both Cook's and Whiited's work are trivial, and wouldn't even be worth mentioning in most other fields.
lightxbulb
CC BY-SA 4.0
2021-06-16T14:13:31.507Z
Like I said, the you are referring to the core idea of casting rays which was known as ray-casting when Appel used it. Ray-tracing got popular because of the whole algorithm of Turner whitted to produce photorealistic images. So when you say ray-tracing, you aren't talking about just casting rays generally. It was named Whitted-Style afterwards when the same technique started to be used in many other similar algorithms to differentiate it. Nevertheless, you don't like the answer just downvote it? don't wanna argue with you in the comments anymore, too troublesome.
gallickgunner
CC BY-SA 4.0
2021-06-16T14:19:56.643Z
I don't plan to argue with you either, your opinion simply disagrees with the usual usage in literature. I will also leave this here: 
https://en.wikipedia.org/wiki/Ray_casting 
https://en.wikipedia.org/wiki/Ray_tracing_(graphics) 
"The idea of ray tracing comes from as early as the 16th century when it was described by Albrecht Dürer, who is credited for its invention.[6]"
lightxbulb
CC BY-SA 4.0
2021-06-16T05:54:25.103Z
2021-06-16T05:54:25.103Z
gallickgunner
<p>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.
Here's an example of what I mean (timestamp linked):
<a href="https://youtu.be/LAsnQoBUG4Q?t=320" rel="nofollow noreferrer">https://youtu.be/LAsnQoBUG4Q?t=320</a></p>
<p>If the rays in Raytracing still bounces, why does it not create Global Illumination like Pathtracing does?</p>

CC BY-SA 4.0
2021-06-15T20:29:36.967Z
The person in the video is talking about Whitted-style ray-tracing, which is limited to bounce rays only off ideal specular surfaces (reflection/refraction) and considers only Dirac delta light sources. Whether you choose to simulate the remaining bounces is up to you, and the process still uses ray-tracing.
lightxbulb
<raytracing><pathtracing><global-illumination>
Can someone explain why raytracing isn't able to make Global Illumination?
LinguiniThePasta
# Can someone explain why raytracing isn't able to make Global Illumination?

(Asked by: username_0 on 2021-06-15)

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.
Here's an example of what I mean (timestamp linked):
<https://youtu.be/LAsnQoBUG4Q?t=320>

If the rays in Raytracing still bounces, why does it not create Global Illumination like Pathtracing does?

**Tags:** raytracing, pathtracing, global-illumination

> **Comments:**
> **username_1**: The person in the video is talking about Whitted-style ray-tracing, which is limited to bounce rays only off ideal specular surfaces (reflection/refraction) and considers only Dirac delta light sources. Whether you choose to simulate the remaining bounces is up to you, and the process still uses ray-tracing.  

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## 2 answers

### Answer by username_2 on 2021-06-15. Score: 5

From the ray tracing wikipedia page <https://en.wikipedia.org/wiki/Ray_tracing_(graphics)>:

"Path tracing is a form of ray tracing that can produce soft shadows, depth of field, motion blur, caustics, ambient occlusion, and indirect lighting."

So a path tracer is a ray tracer, but not all ray tracers are path tracers.

> **Comments:**
> **username_3**: It's also worth noting that (pre-Whitted) ray tracing was originally invented as a hidden surface algorithm, something that we now usually call "ray casting". But it's still a kind of ray tracing.  

---

### Answer by username_4 on 2021-06-16. Score: 2

This question is the result of the modern era using the blanket word ray-tracing to denote every similar technique as it's based off of it. Just wanted to give a more historical answer if anybody is interested.

As username_1 said, historically, Turner Whitted was the first person to come up with the raytracing technique but it only had a limited number of rays. Reflection/Refraction and these secondary rays got terminated when they hit a diffuse surface since no GI rays were shot.

The problem of Global Illumination is recursive and as you might've guessed it requires many many rays. The math wasn't that complex and sophisticated in pure raytracing. Then later on, [Radiosity](https://en.wikipedia.org/wiki/Radiosity_(computer_graphics)) method was introduced by Goral which accounted for GI but only for diffuse surfaces using the Finite element method. This was a major step ahead and helped in laying the foundation for pathtracing.

After that Pathtracing got introduced by Kajiya which accounted for all types of surfaces, He used Monte-Carlo Integration to solve the recursive integral related to the GI problem.

As time went by, the word raytracing somehow overshadowed the other words in this field. And recently, with NVIDIA dishing out their RTX technology pretty much sealed the fact. So raytracing in today's era doesn't necessarily mean whitted-style raytracing which was the original raytracing.

> **Comments:**
> **username_1**: I would refrain from attributing ray-tracing to Whitted. Appel's paper is from 1968 for example, and the idea is much older. Ray-tracing is called this way because you trace rays. In fact in the production of lenses they also use ray-tracing, but not in the context of Whitted-style ray-tracing or path tracing. This is the reason it is an umbrella term - because it simply describes processes that use the tracing of rays, regardless of the framework on top. If one wants to be truly precise, then path tracing is just numerical integration for the series arising from the rendering equation.  
> **username_4**: I know that, used to be called ray casting way back then, but didn't want it to become a wikipedia historical article so I've dumbed down the answer. The original raytracing used to produce all these photorealistic images was infact given by Turner Whitted so no harm attributing the technique to him.  
> **username_1**: Dumbing down the answer in a manner that makes it incorrect is not recommended. Whitted-style ray-tracing can be attributed to Whitted, ray-tracing in general cannot be. The usage of the term ray-tracing in literature is for any process that involves the tracing of rays. If one wants to be specific about the technique, they can be (i.e. Whitted, Kajiya, Cook, etc.). Then again, Kajiya's work subsumes Cook's work, which subsumes Whitted's work. From a scientific perspective both Cook's and Whiited's work are trivial, and wouldn't even be worth mentioning in most other fields.  
> **username_4**: Like I said, the you are referring to the core idea of casting rays which was known as ray-casting when Appel used it. Ray-tracing got popular because of the whole algorithm of Turner whitted to produce photorealistic images. So when you say ray-tracing, you aren't talking about just casting rays generally. It was named Whitted-Style afterwards when the same technique started to be used in many other similar algorithms to differentiate it. Nevertheless, you don't like the answer just downvote it? don't wanna argue with you in the comments anymore, too troublesome.  
> **username_1**: I don't plan to argue with you either, your opinion simply disagrees with the usual usage in literature. I will also leave this here:  https://en.wikipedia.org/wiki/Ray_casting  https://en.wikipedia.org/wiki/Ray_tracing_(graphics)  "The idea of ray tracing comes from as early as the 16th century when it was described by Albrecht Dürer, who is credited for its invention.[6]"  

---

