PBR VS Photorealistic Images

Hassan

Hello guys, I'd like to know what is the difference between a PBR material, and a photorealistic material? is their any difference between them or I can use PBR materials to produce photorealisitc images like an architecture project?? 

Eric Chadwick

Yes, you can use PBR to make photo-real materials. 

Most modern archviz renderers use physically based rendering. 

I use V-Ray at work. It uses a slightly different paradigm than typical game PBR, Chaos Group have added specific surfacing and rendering optimizations that go beyond straight PBR. 

We add shading effects like extra Fresnel for fabrics, or complex Blends for antiqued furniture, or fiber rendering for rugs... effects that aren't strictly physically-based, not energy-conserving. But we end up with surfaces being photo-real while also saving a lot of creation & rendering time.

We go quite a bit beyond what's usable in a game engine, because for our needs, image fidelity is more important than rendering speed.

TTools

I would go as far as to say you "should" use PBR to make photo-real materials, up until the point where the utilization or creation of a physically accurate material becomes so tasking to the renderer or production creation time that settling for ad-hoc (or in other words, faked) shading techniques are more reasonable and sufficient to achieve the desired look.

@Eric Chadwick  gives a great example with fabrics, fibers, etc.  Snow is another great example.  A physically accurate shader for snow, even in offline rendering vs real-time rendering, is massively difficult to compute, which is why more often than not, ad-hoc methods are implemented that can look just as believable.

PBR serves as a foundation to start with that is based on the physical properties of light and surface types.  Metal vs non-metal, or electric vs dielectric.  Starting out with anything other than PBR for a photo real render seems to me to be setting one up for a lot more work, and a less believable render.  The foundation of a physically accurate workflow is to put all of our materials and lighting in parity with each other based on scientifically garnered values.  That means less guesswork, or "eye work" to try and get things to look photo real.

This is just an opinion, and perhaps I am even misunderstanding the question of PBR vs photoreal shader.  I would assume, perhaps incorrectly, that if a shader is classified as type: "photoreal" by it's definition, it would be PBR.  If it's not PBR, then it seems a bit strange to me to 'classify' it as photo-real at all.  Take my comments  with a grain of salt

TL;DR: Go physically based until it is no longer feasible to do so.

Hassan

Thanks guys for your help I appreciate it a lot I was confused ....but excuse me I have another question please, does this technique "the PBR technique" is being taught in architectural schools or this is just for games ?? 

thanks in advance 

Eric Chadwick

It's universal. Used also in movie FX, animation houses like Pixar/Disney/DreamWorks, etc.

SeveredScion

"PBR" is more of a concept than a specific technique. Different software and engines implement PBR differently. The *term* is used more commonly in games/realtime applications, simply because for so long, creating something physically accurate in realtime wasn't feasible due to tech hardware limitations. But software for games as well as architecture can both use materials and lights that are physically accurate.

@Hassan I think maybe the difference you're thinking of is realtime (game engines like Unity or Unreal) vs. offline rendering (V-Ray, Corona, Mental Ray, etc.). Traditionally architectural visualization has not been realtime. So perhaps in schools that teach arch viz they refer to it as "photoreal" due to more realistic lighting.

The following is usually the case (but not an absolute). Hopefully helps clarify:
Lighting - realtime engines - not as photoreal or accurate as offline renderers (although recently realtime has caught up tremendously).
Materials - realtime engines - usually lock the settings down to force physical accuracy - special effects require different shaders.
Lighting - offline renderers - very realistic light bounces, global illumination, refraction, etc.
Materials - offline renderers - physically-accurate starting point but allow you to edit settings until materials are no longer physically accurate. End result still looks fairly photoreal because the lighting and general quality is so high.

Here are some good explanations, with additional more technical reference links at the end. Personally I would say the two most important concepts to physically-based rendering are 1) energy conservation and 2) the fresnel effect. They are explained below.
https://www.marmoset.co/posts/basic-theory-of-physically-based-rendering/
https://www.marmoset.co/posts/physically-based-rendering-and-you-can-too/