PDA

View Full Version : Exact Meaning of PBR



Farhad_azer
11-17-2015, 01:55 AM
What is it?

Instead of surfing web I thought it is a better idea to learn it from you fellas and have a detailed discussion on this.

I know that Lights don't bounce off of the surfaces in 3d environment which is contrary to real (physical) world. so isn't GI kind of PBR? if it is then why are people so excited to see new PBR?

hrgiger
11-17-2015, 02:08 AM
https://www.youtube.com/watch?v=7NjGETJMZvY

DrStrik9
11-17-2015, 03:36 AM
I've been looking around for the same info. That's a good video. The old buzz-term, "energy conservation" (an object can not reflect more light than it receives) is apparently being handled by the software, which takes a load off the artist. PBR, then, is apparently three main things: Diffuse Map (Albedo), Gloss (Normal) Map, and sometimes a Specular map, if there is both metal and wood in the same surface.

At least that's what I got from that video, and some other reading.

PBR = "Physically Based Rendering"

pinkmouse
11-17-2015, 04:18 AM
He waffles, but it's a good overview:

https://www.youtube.com/watch?v=LNwMJeWFr0U

Kaptive
11-17-2015, 06:11 AM
I am no expert... in fact, quite the opposite, but I get the feeling that it seems to be the following having scanned the vids:-

Currently we create the estimation of an objects surface by projecting it out from the model, faking the look and feel of surfaces. Where as, with PBR it is the viewpoint (camera) combined with how light reflects off a surface that defines how something looks.

To put it another way via example:-
When we see a plant as being green, what we are actually witnessing is the sun shining white light and the red spectrum being absorbed by the leaves, and the yellow blue spectrum being reflected back into our eyes. Not that I expect PBR to be quite this complex (though maybe I am wrong) but I think the basic concept applies. It's kind of an inversion. But it does sound like it will be less work from an artistic point of view.

Like I say, this is just me trying to figure it out too. Would love to hear from someone who actually knows!

Good vids chaps. Re: Pinkmouses video... At 20m 20 seconds in he does a swift recap of everything he says, so it saves a fair bit of waffling. The vid below should start at that point.


https://youtu.be/LNwMJeWFr0U?t=20m16s

Schwyhart
11-17-2015, 07:59 AM
Good information!
I've watched and read a lot about PBR, but I still don't grasp it. Probably because I don't have any software that utilizes it yet.

tcoursey
11-17-2015, 08:37 AM
I can say moving from LW Native render to Octane (which is PBR) my surfacing has become much easier/efficent/better. I use to have to fake surfacing for different lighting conditions that I had setup...so assets wouldn't look the same from scene to scene. Now that is completely gone and I can trust the "look" I get from scene to scene with different lighting setups, knowing "thats" what it would look like in these conditions...

I am excited to see what PBR looks like in the next LW but am afraid if it's not GPU enabled...I will not become a fan! Octane is incredibly amazing!

Kaptive
11-17-2015, 10:09 AM
If you have a fair bit of time (or can have something on in the background) I'd highly recommend the following talk by John Carmack about "The physics of Light and Rendering". Extremely insightful regarding the history of CG rendering and the modern approaches regarding PBR.


https://www.youtube.com/watch?v=P6UKhR0T6cs

rcallicotte
11-17-2015, 01:49 PM
Here's a useful guide from brilliant experts in this field. I love this team!

https://www.allegorithmic.com/pbr-guide

rcallicotte
11-17-2015, 01:52 PM
Another couple of very good explanations of PBR:

http://www.marmoset.co/toolbag/learn/pbr-practice

https://docs.google.com/document/d/1Fb9_KgCo0noxROKN4iT8ntTbx913e-t4Wc2nMRWPzNk/edit

Luc_Feri
11-18-2015, 07:44 AM
I can say moving from LW Native render to Octane (which is PBR) my surfacing has become much easier/efficent/better. I use to have to fake surfacing for different lighting conditions that I had setup...so assets wouldn't look the same from scene to scene. Now that is completely gone and I can trust the "look" I get from scene to scene with different lighting setups, knowing "thats" what it would look like in these conditions...

I am excited to see what PBR looks like in the next LW but am afraid if it's not GPU enabled...I will not become a fan! Octane is incredibly amazing!

Forget the science bit Farhad, everyone still has different interpretations of the same principles :D

As tcoursey says.

This is the main thing to take from PBR and Substance Designer PBR workflows, less hacks/fakes with textures and more consistent looks with your assets across different lighting setups. It is much more consistent.

jeric_synergy
11-18-2015, 09:39 AM
131072

Dan Ritchie
11-18-2015, 11:31 AM
My simplest explanation of physically based rendering is that "the color of a point on screen is the accumulation of all reflected light in a scene."

Biased rendering does no ray-casting. A point is an approximation. Its the cosine of the angle between the surface normal and the light normal.

Raytracing uses biased rendering and adds a ray cast to calculate a shadow if the ray is occluded somewhere between the surface spot and the light.

PBR does away with approximations and it just sums the result of a large number of ray casts. The raycast returns the color of a light if it hits one, or the reflected light from a surface, if it hits one. That's about it.

As an addendum, reflection happens naturally as a result of PBR. "Diffuse" is really just a reflection, but the normals on the surface have been jittered accordingly. Specular also happens naturally, except it is not an approximation. It is a true reflection of a light object. In fact, a lot of surface properties that we are accustomed to thinking of as part of a surface just happen naturally, and surface properties become more of just a matter of how and in what direction rays are sent out away from the surface.

As another addendum, on specular reflection. The reflection of the light source is a true reflection, but that does not mean a surface is completely reflective. Even if normals are very diffuse (shot out randomly) there is still a latent reflection of a light source, due to the high dynamic range of the light being enough to still allow a accurate latent image to resolve. Caustics and other reflections happen in a similar manner automatically.

Farhad_azer
11-20-2015, 01:17 AM
Thank you fellas, the answer by Dan Ritchie was the type of answer I was looking for,

I should read it a couple of times and think alittle to totally absorb it,

Sorry I haven't had time to view those lectures,