GLB/ GLTF NormalMap Issue

Questions
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1

Hi,
I have a problem with my NormalMaps that I just can’t solve…
The NormalMap was created in Houdini, baked from highpoly to lowpoly mesh. The texture looks clean. Normal is displayed correctly in Blender:

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Exported as GLB or GLTF the model looks like this:
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Very strong, faceted artifacts become visible in the NormalMap. I loaded the model in modelviewer and https://gltf-viewer.donmccurdy.com/ - same result.
When i reimport the GLB into blender, extract the normal texture and adjust the levels, I can see the artifacts in the texture:
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So i thought this is some kind of compression of the GLB. I tried exporting GLTF with external (uncompressed png) normal texture - but the result is the same when I upload this model in the viewer.
As a comparison, I exported a NormalMap from a GLB Example Asset and placed both NormalMaps on a plane. I can clearly see that my custom NormalMap has strong artifacts while the example NormalMap looks pretty clean.
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image1092×626 58.8 KB

I’m kind of at a loss here…

2

As is often the case: as soon as I posted the problem, I stumbled upon the solution: My NormalMap comes from Houdini as a 16bit texture and is probably converted to 8bit during the GLB export - which creates the artifacts. If I convert the NormalMap to 8Bit before exporting it looks correct.
Here you can finde more information about this:
https://cgcookie.com/posts/bit-depth-how-compression-affects-normal-maps

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3

This is how our Universe works.

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