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Thread: Specular Channel BSDF

  1. #1
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    Specular Channel BSDF

    Hi everyone, having some difficulty using the spec. channel in the PBSDF Attributes panel. It's behaving as an "all or nothing" switch. 0% gives me just that... 0% specularity. Anything above 0% brightness gives me 100% intensity no matter what the setting is. .0001% is the same intensity as 100%. May be doing something wrong but what?
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  2. #2
    You're half right.

    If you set it to 0, that disables it. If you set it to 0.0001 or above it enables it. Now it should not be at 100%, unless your roughness is 0, and you are viewing it at a glancing angle. Pbsdf has a Fresnel falloff, so the facing amount is driven by the specular amount (and will be 0-8%), but the glancing angle amount will be 100%. As you increase the roughness the glancing amount drops off, because as roughness increases the percentage of microfacets facing the camera increases.

    In some situations you can get a nuclear spec hit, because you're using double spec (see my YouTube tutorial on the env light), or your normals are all screwed up, confusing the Fresnel falloff...

  3. #3
    Goes bump in the night RebelHill's Avatar
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    Specular in principled has built in fresnel, and anything with even the slightest amount of reflectivity, will have a strong effect at glancing angles (depending on roughness). There are a few things to get used to and keep in mind about the new shading system... you'll find a lot to start with here...

    https://www.youtube.com/playlist?lis...MnKF7-4W84I5Tz
    LSR Surface and Rendering Tuts.
    RHiggit Rigging and Animation Tools
    RHA Animation Tutorials
    RHR Rigging Tutorials
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  4. #4
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    Thanks for the advice. The material in question is concrete. I've noticed that concrete can become somewhat reflective as perspective nears the glancing angle but falls off rather quickly as it shifts away from it. Is the fresnel effect 'locked' or can that curve be tweaked or shifted for various materials?

    - - - Updated - - -

    Checking out the material you directed me to BTW.
    Mac Pro Dual Quad Core, 6 GB RAM, NVIDIA QuadroFX 2000 2GB Ram, 2 TB HardDrive LW 2019

    I Wished My Brain Came With A Manual... I could look up everything I've learned sorted by topic...

  5. #5
    The amount is tied to roughness. Even polished concrete will have quite a high roughness, so increase roughness, and your glancing reflection amount will decrease a lot.

  6. #6
    Goes bump in the night RebelHill's Avatar
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    Polished concrete can be kinda shiny... but most of the time, its going to be quite rough, and you'll likely find that using true spec with high roughness unnecessary for such a surface. Instead, try killing the spec and turning up the sheen setting (possibly very high... like 300%+)
    LSR Surface and Rendering Tuts.
    RHiggit Rigging and Animation Tools
    RHA Animation Tutorials
    RHR Rigging Tutorials
    RHN Nodal Tutorials
    YT Vids Tuts for all

  7. #7
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    Thanks for the tip Rebelhill, I'll give that a go and I'm going to purchase the tutorial series the moment I can swing it.
    Mac Pro Dual Quad Core, 6 GB RAM, NVIDIA QuadroFX 2000 2GB Ram, 2 TB HardDrive LW 2019

    I Wished My Brain Came With A Manual... I could look up everything I've learned sorted by topic...

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