PBR material reflectance / IOR / fresnel database? + question about sRGB and Linear interpretations
polycounter lvl 5
Hello artists,
I'm reading the book "The PBR Guide" by Wes McDermott.
In the book, Wes explains the importance of finding the right physically accurate values for settings such as reflectance/specularity, IOR and Fresnel.
Is there a good resource or image that might list various materials (metals to dielectrics) and their corresponding values to the variables listed above?
Also, I'm struggling to understand some interpretations that are discussed. These are:
1. sRGB for base colour or albedo
2. 'linear' for roughness and metallic
3. AO, Height and Normal- as these aren't colour values are these also 'linear' interpretations? What does linear mean?
Loving the book and learning Substance Painter/Designer at the moment and am enthusiastic about learning these fundamentals inside and out.
Many thanks,
Kieran
I'm reading the book "The PBR Guide" by Wes McDermott.
In the book, Wes explains the importance of finding the right physically accurate values for settings such as reflectance/specularity, IOR and Fresnel.
Is there a good resource or image that might list various materials (metals to dielectrics) and their corresponding values to the variables listed above?
Also, I'm struggling to understand some interpretations that are discussed. These are:
1. sRGB for base colour or albedo
2. 'linear' for roughness and metallic
3. AO, Height and Normal- as these aren't colour values are these also 'linear' interpretations? What does linear mean?
Loving the book and learning Substance Painter/Designer at the moment and am enthusiastic about learning these fundamentals inside and out.
Many thanks,
Kieran
Replies
Linear for roughness, metallic, height, normal and ambient occlusion should be linear because linear color space is more interested in preserving "data" and giving each color value equal space and weight. Something sRGB does not do.
Linear color is just that. .25 linear greyscale is .25 of the way from white to black .25 sRGB greyscale is not .25 of the way from white to black, its weighted in such a way that gives you more color that your eyes are sensitive to at the cost of accurate, linear data.
Any channel that's representing a number rather than a colour (roughness, normal etc) will be linear, anything that's perceptual (basecolor, emissive etc) will usually be sRGB
sRGB channels are converted to linear space in the Shader so all the maths can be done nicely,
if you read Sebastien Legarde's PBR papers you'll find links to a library of properly measured materials (the bulk of which are useless outside of a lab) and some code you can use to convert them to colour values.
Honestly - you've got pretty much everything you need in the supplied substance reflectance node (open up the pbr base material and you'll find it.
Also if you're not using the specular level channel with your metal/rough workflow then it's all moot anyway because everything will be treated as plastic (not many people do).
Thank you very much for your explanations! You've both really cleared that up. I also got a reply on twitter from Wes McDermott himself regarding a list of material values and he came back with this IOR list:
https://pixelandpoly.com/ior.html
I hope you find this useful. Many thanks and kind regards.