Zbrush to V-Ray for Houdini workflow--seams and facets in bump map?

[bentway23]

I'm trying to get something from ZBrush into Houdini (and use V-Ray) and keep getting inconsistent results and never what I'm looking for. The problem is definitely me--I find snippets of tips everywhere, but haven't found the one good workflow guide that I need. Basically, I'm dealing with a whole lot of super-remedial questions at once.

I think I have most everything beaten into some sort of submission, except that I'm getting seams and ridges when I apply my normal map (base diffuse color material --> BRDF Bump --> Output, alongside displacement which works okay once it's reined in to about a 0.05 scale). Attached are a screenshot of my simple bumpy ZBrush tongue and the Houdini version with displacement and bump applied.

I used both Smooth UV and Smooth Normals in ZBrush, as well as FlipG. I think I've tried all the combinations of those being on and off, but clearly not, otherwise they would be beautiful and perfect.

Thanks for any help!

ADDENDUM: This does seem to be a V-Ray in Houdini setting that is causing this faceting--using the same maps in Mantra I was able to get seamless bumps.

FURTHER ADDENDUM: The problem seems to lie in the BRDF Bump. When I do everything except the bump, running through a regular material, all is fine. Once I pump the material into the base_brdf of the bump material, everything gets faceted, whether or not I have a bump image going in to bump_tex_color--so clearly I have to tell it to do something I'm not telling it.

[chakarov]

Hello bentway23 , I'll need info about your OS, Houdini version and V-Ray build number. Also mesh file with textures will help a lot. You could send it to georgy.chakarov@chaosgroup.com or upload it here.

[bentway23]

I was able to figure this out, and hopefully this will help any other wayward souls who are lost as I once was--the normals that need to be exported from Zbrush should be object-space, not tangent-space. That clears up the seams.

[david.anastacio]

I was able to figure this out, and hopefully this will help any other wayward souls who are lost as I once was--the normals that need to be exported from Zbrush should be object-space, not tangent-space. That clears up the seams.

Hi bentway23,

I see you got your problem sorted, but just wanted to throw some more info your way that might be of value. Maybe you already know most of all of it.
The "bump" node has several modes, the default is for grayscale bump maps and then you have several normal modes, tangent, object, etc. In addition you can also use the "V-Ray Normal Map Flip" node to perform any flip or swap you might need.
For bump amounts, with the default mode "Bump" the amount is a real world amount, 1.0 is 1 meter of bump and 0.01 is 1cm.
And don't forget that sneaky little color space drop-down of srgb to linear, it's usually the culprit around here.

On the displacement, it's always important to use the "Amount" together with the "Shift" value. If you use a displacement map were your zero displacement is mid-gray (0.5) then when using an amount of 0.5, the shift should be -0.5

Best,
David.