Understanding and adapting to a Physically Based Rendering (PBR) workflow

So Physically Based Rendering (PBR) is here in a big way with Unreal Engine 4, Unity 5, Quixel Suite 2 and Marmoset Toolbag 2 but a few to name that now use this workflow as standard. It's quite a lot to take in, but not too hard to understand once you get going with it. Rather than try to explain what the differences are and what you need to do to adapt, I think it's more useful to just list the materials I found while learning this new workflow, as there's others out there that have already done that job.

Reading material

Physically Based Rendering Encyclopedia - https://docs.google.com/document/d/1Fb9_KgCo0noxROKN4iT8ntTbx913e-t4Wc2nMRWPzNk/edit

The above link covers most of the other materials I have read and listed below but it's also worth reading the rest as it may cover different tools and techniques in your own workflow.

Physically Based Rendering in Substance - https://www.youtube.com/watch?v=LP7HgIMv4Qo

Allegorithmic PBR Guide Playlist - https://www.youtube.com/watch?v=mnJ8NjLRmLk&list=PLB0wXHrWAmCwwpWr5aZ1lf0wY3IcWJAjE

Texture Maps Explained - PBR Workflow - https://www.youtube.com/watch?v=PjGCtnEDDeU

Physically Based Texturing - https://www.youtube.com/watch?v=Tt30zzBQb3w

Tutorial: Physically Based Rendering, And You Can Too! - http://www.marmoset.co/toolbag/learn/pbr-practice

Basic Theory of Physically-Based Rendering - https://www.marmoset.co/toolbag/learn/pbr-theory

Tutorial: PBR Texture Conversion - http://www.marmoset.co/toolbag/learn/pbr-conversion

Allegorithmic - The Comprehensive PBR Guide - https://www.allegorithmic.com/pbr-guide

Physically Based Materials (Unreal Engine 4 documentation) - https://docs.unrealengine.com/latest/INT/Engine/Rendering/Materials/PhysicallyBased/index.html

PBR Texturing Techniques - http://quixel.se/dev/issue03

Textures

gametextures.com
Offers a library of ready to use maps for use in a PBR workflow. Although not free, at the time of writing they do offer a 14 day free trial which includes 75 or 200 material downloads which is very generous and helps you get started with this new workflow and for $19 and $30 per month after that it seems like a fair deal.


Tools

gametextures.com workflow converter - https://www.gametextures.com/gametextures-to-metalness-a-new-tool-to-convert-workflows/

Allows you to take a set of maps from alternative workflows and convert for use in PBR. This is not just a plug everything in and hit convert process though. You will need to provide the required inputs to get good results and spend some time tweaking.

gametextures.com drag and drop Substance system - https://www.gametextures.com/how-to-import-gametextures-substances-into-ue4-and-unity-5/
The website now offers downloads of substances which can be quickly imported into Unreal Engine and Unity via drag and drop.

Need to create extra texture maps?
If you have a normal map then NDo has a built in feature to take a normal map and output a variety of different maps including AO, height, specular and cavity - http://quixel.se/usermanual/quixelsuite/doku.php?id=convertmenu

For the workflow converter you will also need a gloss map. These are easy enough to produce and this video shows the basic procedure - How to create a gloss map from a diffuse map https://www.youtube.com/watch?v=OKdUIm3i_jc


Workflow Tips

Albedo map creation

Manual process using Photoshop

How to Make an Albedo Texture from a Diffuse Texture - https://www.youtube.com/watch?v=KKQZN3eoKUo

Process steps:

1. open diffuse map
2. create a duplicate layer of the diffuse map. ensure the new layer is above the original
3. fully desaturate (CTRL + U or add an adjustment layer) the duplicated layer to create a cavity map
4. invert (CTRL + I) the duplicated layer, so that dark areas now show as light
5. change blending mode of the duplicated layer to Soft Light
6. make any changes to saturation etc of original map (if required)
7. using the luminosity values chart below select the value most appropriate to the type of material
8. open the histogram and ensure the expanded view is selected by clicking the arrow and four lines in the top right of the window and set Channel to Luminosity in the drop down
9. take note of the median value
10. adjust the levels (CTRL + L or add an adjustment layer) of the original map (or the overall new texture) so that the median level comes close to the luminosity value from the chart

Semi-automated process using ShaderMap

Creating an Albedo Map from a Photographic Texture - http://shadermaptutorials.com/tutorial/creating-an-albedo-map-from-a-photographic-texture/

Luminosity value guidelines

Material            Linear value  sRGB value  photoshop    source          
                                              median value
Brushed Metal       0.02          0.16                     [2]
Charcoal            0.04          0.22                     [1]
Fresh asphalt       0.04          0.22                     [1]
Rubber              0.04          0.23                     [2]
Black acrylic paint 0.05          0.25                     [3]
Coal                0.05          0.25                     [2]
Leaves              0.05          0.26                     [2]
Rust                0.06          0.27                     [2]
Plastic (glossy)    0.10          0.36                     [2]
Painted metal       0.12          0.38                     [2]
Rough steel         0.13          0.40                     [2]
Worn asphalt        0.12          0.38                     [1]
                    0.15          0.42                     [3]
African tanned skin 0.15          0.42                     [3]
Bare soil           0.17          0.44        112          [1]
Dirt                0.17          0.45        115          [2]
Plastic (rough)     0.19          0.48                     [2]
Brick/Concrete      0.23          0.51                     [2]
Dry clay soil       0.23          0.51                     [3]
Mud                 0.23          0.52                     [2]
Green grass         0.25          0.53                     [1][3]
Plaster             0.25          0.54                     [2]
Canvas              0.27          0.56                     [2]
Old concrete        0.30          0.57                     [3]
Wood                0.31          0.59                     [2]
Red clay tile       0.33          0.60                     [3]
Rock                0.33          0.61                     [2]
Desert sand         0.40          0.65                     [1][3]
Satin               0.43          0.69                     [2]
New concrete        0.50          0.72                     [3]
New concrete        0.55          0.76                     [1]
Clean cement        0.55          0.76                     [3]
Ceramic             0.57          0.78                     [2]
Ocean Ice           0.50–0.70     0.73-0.85                [1]
White cement        0.70          0.85                     [3]
White acrylic paint 0.80          0.90                     [3]
Fresh snow          0.80–0.90     0.90-0.95                [1][3]

Notes:
some values converted using https://docs.google.com/spreadsheets/d/1KcHvNFqQA8Y7xyjMTuuQgMTT3bB6lvNpTgpsU1MmDjs/edit#gid=0

Sources:
[1] https://seblagarde.wordpress.com/2011/08/17/feeding-a-physical-based-lighting-mode/
[2] http://www.marmoset.co/toolbag/learn/pbr-practice
[3] https://www.fxguide.com/featured/game-environments-parta-remember-me-rendering/