I’m using Vray to render a model with its displacement map generated by Zbrush. Everything is OK, except for the seams shown below. (When AA is off, there are additional small black pixels; When AA is on, most of them go way, but these seams remain still) The models’s UV was assigned using GUV function in Zbrush.
When I change GUV to AUV, the case is even worse, revealing the underlying topology structure. (The seams occur where the edges of the low-polygon lie.)
I find such deviations in the displacement map generated by Zbrush. (Although they just appear in the lower 1/4 area of the whole displacement map) Can these be the cause of the problem? Do you know how to solve it? Help, please! Thank you!
What’s the resolution of the displacement map? - Try exporting a displacement map from zBrush at the highest resolution (4096). I’ve found that lower resolutions produce seams.
Thank you for your suggestion. The displacement map was 2048x2048. I tried 1024x1024 too, but nothing changed. I don’t have got enough RAM to try 4096x4096 ones, but I assume resolution is not where the problem stems from.
OK, this is the picture with 4096x4096 displacement map (GUV). And seams seem a litte different, but still there. 
What version of Vray are you using? I’ve found that the 2d mapping method can generate black holes/specks like those seen in your first render above. Playing with the resolution setting in the Vray displacement modifier usually helps, but don’t go higher than the resolution of your actual map or it might crash Max. Try 3d mapping if 2d still gives you problems. Hopefully the modifier will work a lot better when Vray 1.5 comes out.
For the second render with AUV tiles, try increasing the mesh smooth amount in Max. I always convert to editable poly as well. The displacement and shift amounts might need some tweaking (you are using shift, right?). Try the fix seams button in Zbrush as well.
Thank you Zeddius for your suggestions. Here is something I’d like to clarify:
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My Vray version is 1.09A
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Change to 3D mode doesn’t help
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The resolution settings in the Vray modifier does little good.
(I never set it higher than the bitmap itself. The seams will not vanish until the value is as low as 32 or so. But then, gone are the details together.) -
Shift is used, and the blur amount is set to minimum.
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Fix seams doesn’t work.
And here is another question, fix seams can only be applied to materials, which means converting 16bit greyscale bitmap to a 24bit RGB one. Not acceptable for sure. So it’s impossible to use fix seams in displacement map generation?
The last stable official release of Vray was 1.09.03r I believe, so you should probably think about updating. 
Edit: Not 100% sure about fix seams, UV adjustment, check UV’s, and smooth UV’s, so I removed part of this post. Maybe Aurick or Pixolator will comment on this (I’m curious too).
You mean that FIX SEAMS function makes some change to the UV coordinate system rather than the texture bitmap? :eek: I’ll check it later. 
What are the settings that you used in the Displacement menu before generating the map?
Can you try testing the map with a different renderer? This will determine whether the problem lies with the map or with the renderer or render settings (which is actually the most likely case).
Also, you didn’t mention in your clarification whether or not you’re applying any iterations of mesh smoothing to your model at all. This does help sometimes with the exploding mesh problem (like the second image shows). And the first image still definitely looks like some of the problems I’ve encountered with Vray’s 2d mapping method in the past.
To Aurick:
Adaptive is on, SmooothUV is on, and DPResolution is set to 1024. I’ve tried to turn either and both of them off, but nothing changed.
To Zeddicus:
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I checked. The FIX SEAM Function just did some trick to the texture instead of the UV coordinate system, according to my test.
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Yes, I added a meshsmooth modifier, and the iteration level was set to 1. (I tried 2 or 3. Nothing helpful)
To Aurick:
I exported it again and tried it with both Vray and FinalRender(MTD). Although the image generated by finalrender is worse, but you can see clearly that the seam were always in the same place.
(And BTW, would you pleas tell me where I may put this model temporarily? I think it would be more easy to find out the bug with the file in your hand. Thank You)
The following picuture is generated by FR:
And the next one, by Vray:
I notices the same problem ate the UV seams when i apply a displacement map in Zbrush on a model. The problem is not visible in preview mode, until you aply the displacement map.
Can this problem be model-related? This model was exported from 3DSMAX as an .obj file and then imported into Zbrush. But not all the models from Zbrush bear this issue. :qu: :qu: :qu: :qu: :qu:
Is there any thing I shall not miss to get a displacement map that works correctly? (I think I’ve read the reference carefully.)
I have the same matter :mad:
If it´s impossible to fix ,how can I to avoid it?
Vray 1.5 …?
Although you haven’t shown a wireframe, it looks like the seams are probably due to triangles or diagonal discontinuity.
Displacement maps are very sensitive to changes that may appear at the UV borders!
There are several things that can be done to avoid visible seams. The fastest and easiest is to use a quad-based mesh with AUVTiles (at the default AUV ratio) or GUVTiles mapping.
If the mesh contains triangles, you may want to try the following:
- Go to subdivision level 2 (which is 100% quad-based).
- Press Tool>Geometry>Del Lower to make this the new subdivision level 1.
- If you wish to use a map size other than 1024x1024, create a texture of the size that you would like. ZBrush works best with a power of 2 (256x256, 512x512, 1024x1024, 2048x2048, or 4096x4096).
- Set the displacement map size to match the texture size, and create your displacement map.
- Export the displacement map and the mesh to the external renderer.
This approach will allow ZBrush’s SmartSeams routines to execute automatically.
Thank you very much Aurick, I´ll check all things you say(I´ve been changing a lot of things those days and I´m a bit confused).
Here is my mesh and especifications.
www.cgshopping.net/chuske/problema2.jpg
Maybe I´ve diagonals discontinuities…
:rolleyes:
Thank you Aurick for your suggestion. I tried it but the problem remained. But thank you all the same. I think I’ll try to find some way out myself, and I’ll post it here whenever I find the answer.