General PBR info
Physically based rendering (PBR) is a subset of computer-generated imagery that aims at production of pictures while making use of physically based shading.
There's a lot of info about this theme written already, so I wouldn't copy-paste it all, there are some links
And here's a nice video from SIGGRAPH and this real good quick explanation from Cubetutorials.
Maps:
- Albedo - Base colors with no lighting/shading data. Most albedo values exist within the midtones. (sRGB)
- Normal - High-res surface detail used for faking the lighting of bumps and dents. (RGB)
- Roughness - Defines reflective surface properties. (Grayscale)
- Metallic - Determines if a material is a metal or dielectric. (Grayscale)
- Ambient Occlusion (AO) - used to calculate how exposed each point in a scene is to ambient lighting. (Grayscale)
- Cavity - Micro-ambient occlusion. (Grayscale)
- Height - Surface elevation information. (Grayscale)
- Opacity - Transparency. (Grayscale)
The distribution of the deviated rays which are important for the reflection can be represented by a cone around the ideal mirror direction. The roughness texture controls the aperture of the cone and thus the blurriness of the reflection. The rougher the surface, the larger the cone. The roughness is the inverse of the glossiness. Sometimes glossiness and roughness are referred to as the microsurface value
Dielectrics have a 0 metallness value and do not require a metallic map. If they are part of an asset that needs one, the non-metal portions should be black. Metallic map properties should represent the top layer of the material, like painted metal, which would not be metallic in this case. Most metals have a value of 1, and the metallic map is multiplied against the base color texture.
Color space conversions
This math section is only to show how it actually works.
Here are formulas to convert between color spaces:
sRGB = ((Linear RGB / 255) ^ 0.4545) * 255 Linear RGB = ((sRGB / 255) ^ 2.2) * 255
Here's some explanation, where are the values coming from:
- 2.2 # this is gamma
- 0.4545 = 1 / 2.2 # this is an inverse of gamma
- X / 255 # this means normalizing the value (convert from 0-255 range to 0-1)
To check the albedo of your texture (in sRGB space):
Albedo = ((R/255)^2.2 + (G/255)^2.2 + (B/255)^2.2) / 3
For example, color-pick:
And check by calculation, for this example we have 0.27 albedo value:
To avoid doing any calculations, you can check the value in Photoshop and Substance Designer.
How to check albedo value in Substance Designer
Add Convert to Linear node and Grayscale Conversion node with standard settings.
Pointing at color with cursor in 2D view you can see it's value in float. On the example below, it's 0.270588.
How to check albedo value in Photoshop
Add Exposure correction layer with Gamma Correction set to 0.4545
Then, add Channel Mixer layer, check the Monochrome box and set all channels to 33%
With color picker you can see the albedo value, which in this case is 26% for our example above:
Albedo values
Gathered from all around the web, they might be not 100% accurate, but more or less close.
For dielectric, the darkest albedo carbon has with 0.04 value, the lightest ones are the white paint and fresh snow with values around 0.8.
Values are in Linear RGB (float).
Dielectric values
Ground, sand, rock
- Carbon (Coal, forged iron) 0.04
- Black soil, wet 0.08
- Black soil, dry 0.15
- Bare soil 0.17
- Grey soil, wet 0.10 – 0.12
- Grey soil, dry 0.25 – 0.30
- Dry silt loam soil 0.23 – 0.28
- Dry clay soil 0.15 – 0.35
- Dry sandy soil 0.25 – 0.45
- Dry salt cover 0.5
- Wet sand 0.23
- Dry sand 0.4
- Yellow clay 0.16
- Rock 0.3 – 0.4
Vegetation
- Conifer Forest 0.08 – 0.12
- Deciduous trees 0.15 – 0.18
- Tall wild grass 0.16 – 0.18
- Short green grass 0.20 – 0.25
- Grain crops 0.10 – 0.25
- Corn field 0.16 – 0.17
- Tea bushes 0.16 – 0.18
- Summer foliage 0.09 – 0.12
- Autumn foliage 0.15 – 0.3
- Tundra 0.2
Snow, ice, water
- Melting snow (clean) 0.6 – 0.62
- Ice 0.5 – 0.7
- Ice, sea 0.3 – 0.45
- Ice, glacier 0.2 – 0.4
- Fresh snow 0.7 – 0.9
- Water, sun near zenith 0.05
- Water, sun near horizon 0.5-0.8
Asphalt
- New asphalt 0.04 – 0.05
- Aged asphalt 0.1 – 0.18
- Wet asphalt 0.06 – 0.08
- Gravel 0.13
Roofs
- Tar & gravel 0.33
- Corrugated roof 0.1 – 0.15
- Red/Brown roof tiles 0.1 – 0.35
- White asphalt shingle 0.2
Concrete
- Aged concrete 0.2 – 0.3
- New concrete (traditional) 0.4 – 0.55
- Polished concrete 0.55
- New concrete with white portland cement 0.7 – 0.8
Wood
- Batten (fresh wood) 0.35 – 0.42
- Batten (old, weathered) 0.12 – 0.16
- Varnished wood 0.13
Tiles, bricks, finishings, etc
- Terracotta tile 0.28
- Brick 0.2 – 0.4
- Sandstone 0.18
- Plaster 0.4 – 0.45
- Magnesium oxide 0.96
- White gypsum 0.85
- Alabaster 0.92
- Granite gray 0.35 – 0.40
Paint
- Black acrylic paint 0.05
- White acrylic paint 0.8
- Colored paint 0.15 – 0.35
Misc
- Forged Iron 0.04
- Natural silk fabric 0.35 – 0.55
- Skin 0.25 – 0.35
- White paper sheet 0.6 – 0.7
Metallic values
sRGB values are for reference, may vary a little bit.
Metals have black diffuse albedo value and colored specular albedo. In metalness-roughness workflow, for metals (pixels set to white in the metalness map) the specular color and intensity is taken from the albedo map. Metals albedo values are between 0.5 and 0.98. Lower values are for matte, higher are for polished metal.
Iron = c4c7c7 (198, 198, 200)
Brass = d6b97b (214, 185, 123)
Copper = fad0c0 (250, 208, 192)
Gold = ffe29b (255, 226, 155)
Aluminum = f5f6f6 (245, 246, 246)
Chrome = c4c5c5 (196, 197, 197)
Silver = fcfaf5 (252, 250, 245)
Cobalt = d3d2cf (211, 210, 207)
Titanium = c1bab1 (195, 186, 177)
Platinum = d5d0c8 (213, 208, 200)
Nickel = d3cbbe (211, 203, 190)
Zinc = d5eaed (213, 234, 237)
Mercury = e5e4e4 (229, 228, 228)
Palladium = ded9d3 (222, 217, 211)