Table of Contents (WIP)

PHYSICALLY BASED RENDERING ENCYCLOPEDIA

v. 0.95 (july 17, 2014) Compiled by: Brian Yu (3py0n)

There is no one way to accomplish a task, more specifically in texturing. The below is a guideline of the most common and effective routes currently and is by no-means the only way to texture for PBR. Final name of this document is in consideration. ENJOY!

Introduction

An emporium/bible of sorts wherein I will try to encompass all there is to know about creating physically based materials for the next-gen. I am still new to PBR texturing and am learning as I make this bible. The reason for me making this is to have a central database for artists and developers to look at to help them with their workflow. It’s also a great way for people who are new to PBR to learn more. Please note that this is just a general guide/bible and is not the end-all-be-all. That is to say, there is typically not only 1 way of doing things. Before I finish, this document is also for people who have prior knowledge in texturing and making 3D art in general.I would like to take this opportunity to thank all the wonderfully talented and innovative people who I sourced from for their work on this subject matter. :)

Copyright

I do not pretend to own all of what I am stating in this document. Some parts will be from my personal experience/knowledge while other parts will be excerpts taken from sources (credit will be identified at the beginning of a section).

Terms and Services of Use

Please refrain from copying and pasting elsewhere as I am compiling it and would like to ensure the accuracy of the document before sharing everywhere. If there is anything that is incorrect, needs adjusting, or you would like to add to the bible, please email me with the information and source/credit and I will add it to the corresponding category. As well, if you must post this somewhere, please give credit where and when it is due. That is all for now.

Table of Contents (WIP)

Light Interaction & Really Sciency Stuff

PBR: The Definition & More

Guidelines & Basics: The How-To Guide

Material Reference Values

Tips & Techniques

Examples

Additional Readings & References

FAQ

Glossary & Terms

Tools & Programs

Light Interaction & Really Sciencey Stuff

I won’t be going through or compiling scientific formulas on how light is perceived and bounces off X material, etc. There are many other sites for that online. Instead I’ll just be compiling some basic rules of how light interactions with types of materials. This will offer a better understanding when texturing in order to achieve more realistic results!

Diffuse and Specular Reflectance(source)

When light hits a surface, it splits into two directions: some part of it is reflected immediately while the rest gets refracted and enters the surface. The refracted light can be absorbed or can be scattered around underneath the surface and exit again at a slightly different location.

Light that gets reflected directly from the surface is handled as specularreflectance in a shading model. The light that is refracted and undergoes subsurface scattering is handled as diffusereflectance.

The amount of light that is reflected versus refracted depends on the surface substance and the angle at which the light hits the surface. At a grazing angle, the amount of light that gets reflected directly (specular) gets higher, until it reaches 100% at an extreme angle. This behavior is described by the Fresneleffect.

Material Types(source)

There are only two categories of substances which are relevant for rendering: metals(conductors like iron, gold, copper, etc.) andnon-metals (dielectric materials like plastic, stone, wood, skin, glass, etc.). Both have special characteristics regarding diffuse and specular reflectance.

Metal has no diffuse reflection. This means that metalshould have ablack diffuse color. All visible light is reflected directly from the surface (specular reflectance). The different types of metalhave characteristic specular colors.

Metal actually neither refracts nor absorbs ANY light, metals are so dense that light can't actually enter the surface, which is why all of the light is reflected. (source)

In contrast to metal, non-metal has diffuse reflection, however the specular reflection is a lot weaker and less varied than for metal. Specular reflectance for non-metal is monochromatic (no color, just gray). Most non-metals reflect only a small fraction of the light as specular, for most materials between 2% and 5%.

Energy Conservation(source)

Reflection and diffusion are mutually exclusive. This is because, in order for light to be diffused, light must first penetrate the surface (that is, fail to reflect). This is known in shading parlance as an example of “energy conservation”, which just means that the light leaving a surface is never any brighter than that which fell upon it originally.

This is easy to enforce in a shading system: one simply subtracts reflected light before allowing the diffuse shading to occur. This means highly reflective objects will show little to no diffuse light, simply because little to no light penetrates the surface, having been mostly reflected. The converse is also true: if an object has bright diffusion, it cannot be especially reflective.

Energy conservation of this sort is an important aspect of physically-based shading. It allows the artist to work with reflectivity and albedo values for a material without accidentally violating the laws of physics (which tends to look bad). While enforcing these constraints in code isn’t strictly necessary to producing good looking art, it does serve a useful role as a kind of “nanny physicist” that will prevent artwork from bending the rules too far or becoming inconsistent under different lighting conditions.

When the equations are properly balanced, a renderer should display rough surfaces as having larger reflection highlights which appear dimmer than the smaller, sharper highlights of a smooth surface. It is this apparent difference in brightness that is key: both materials are reflecting the same amount of light, but the rougher surface is spreading it out in different directions, whereas the smoother surface is reflecting a more concentrated “beam”:

Here we have a second form of energy conservation that must be maintained, in addition to the diffusion/reflection balance described earlier. Getting this right is one of the more important points required for any renderer aspiring to be “physically-based”.

Linear-Space Lighting & Gamma(source)

Some more sciency information for those who are curiousity-inclined. I read it. Great read! Here is the shortened version of the shortened version. the TL:DR if you will. I’m almost making a note here incase the site goes down. It is a little dated.

The gamma colour space is 0 - 255. The neutral gray/50% is 187, not 127(128).

As of the original writing, standard monitor gamma is about 2.2, with some exceptions.

A more indepth explanation of gamma and how it affects displays (monitor, cameras, LCD on camera, etc) is given in the article. For the sake of lessening the amount of diagrams, etc I’ve omitted it.

Date: 2015-12-24; view: 1115