Normal map with bold relief causes black artifacts with Glossy BSDF shader #51008

System Information
Windows 10 x64 home, Nvidia GTX 1070 with latest WHQL drivers.

Blender Version
2.78c

Short description of error
Some kind of normal maps - like folded foil or crumpled sheet of metal - produces black artifacts in their folds with "Glossy BSDF" shader node (no problems with
"Diffuse BSDF" though). That start to happen then "Strength" parameter of "Normal map" node is high enough - at low values (~"0.5" and lower) those black artifacts disappears.

Exact steps for others to reproduce the error

Open attached scene
Switch viewport to "Rendering" mode.

Example screenshot .
[Bugreports] Black artifacts on normal map.blend

Changed status to: 'Open'

Added subscriber: @Lex4art

Added subscriber: @LukasStockner

Changed status from 'Open' to: 'Archived'

This is the same problem as in #49921 - the normal mapping changes the surface normal, so the reflected ray would go inside the actual geometry, which isn't really possible.

In this case, the way to get around this problem is to use microdisplacement with a displacement map instead of normal maps.

Sorry for the non-answer, but this isn't really something we can fix.

Added subscriber: @MikiProxima

I also have struggled with this kind of artifacts and found a simple trick how to avoid them. Basically you can calculate a dot product between normal and incoming vector and attenuate the normal map where it could cause problems viz https://blenderartists.org/forum/showthread.php?382497-Black-material-artifacts-on-flat-angle-surface-areas

In #51008#424222, @MikiProxima wrote:
I also have struggled with this kind of artifacts and found a simple trick how to avoid them. Basically you can calculate a dot product between normal and incoming vector and attenuate the normal map where it could cause problems viz https://blenderartists.org/forum/showthread.php?382497-Black-material-artifacts-on-flat-angle-surface-areas

Thanks, that will do the job for me - smart solution ).

Added subscriber: @lsscpp

I found a weird shading bug for wide surfaces. The black reflections come back in this file: http://pasteall.org/blend/index.php?id=46239

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Normal map with bold relief causes black artifacts with Glossy BSDF shader #51008