Normal/bump maps and sharp shadow terminator

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Hi,

I feel I'm going crazy. It seems to me that bump/height and normal maps are rendering "wrong" in Houdini, revealing a very sharp shadow terminator whenever the bump intensity is more than minimal.

The images below illustrate the issue. The scene is a simple sphere with polar UVs, and the new 20.5 quicksurfacematerial lop applying the standard Houdini bricks001_height.rat as a bump map.







I have tried with normal maps and bump maps, from various sources and through built-in methods (height to normal), in Mantra and Karma, with and on two different computers with Houdini 20.5 and 19.5. I've tried building the node networks myself - yes, the normal map texture is brought in as Vec3 and fed through a mtlxnormalmap node. Everywhere it's the same.





Turning off shadows on the light, or increasing the light's size/radius/angle makes it clear it is the cast shadow that is causing the sharp line. But in, for instance, Maya and rendering with Arnold, things render just as expected and normal/bump maps can be overcranked like crazy:




I get that bump/normals are supposed to be a subtle effect... but this seems to be quite limiting. What am I doing wrong?

Attachments:
bump-tests.hipnc (1.1 MB)
bump-scale-shows-shadow-terminator.png (214.7 KB)
bump-maya.png (174.0 KB)
bump-geo-setup.png (64.8 KB)
bump-material-setup.png (102.9 KB)
bump-scene-setup.png (271.5 KB)
bump-mtlx-setup.png (210.9 KB)

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Arnold is doing something non-standard here. A harsh terminator is what I would expect from a small/directional light source.
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You may try Bump Shadow Terminator [www.sidefx.com] (a H20.5 Karma CPU(only) feature) in Render Geometry Settings to soften the hard shadow line.
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