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Texturing: Bump offset causing visible seam


I have an issue where using a bump offset causes a visible seam where I cut my UV map, as seen in the picture below: alt text

When I disconnect the bump offset, the item does not display visible seams, but of course loses the effect I am trying to achieve, as seen in the next picture: alt text

Now, the first thing you might be thinking is that there's an issue with the actual texture images themselves. However, the normal map as seen in the picture is created from the bump map, not the diffuse map. As such, if the bump map had an issue, so would the normal map. But it doesn't (tested extensively in MudBox where I made it)

Anyone have any idea how to fix this?

Product Version: UE 4.21
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asked Jan 11 '19 at 11:58 AM in Blueprint Scripting

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Crowley Caine
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Using bump offset with non tiling textures is very difficult since at its core the technique relies on sampling outside the areas the UVs originally lied. In your case the gray "background" part of the image slides in because that's what's visible when you look at the texture from sideways. (You look "under" the surface.)
You could mitigate the issue a little bit by adding more data to the texture, around the area which is covered by your untouched UVs. Essentially making the important part on the picture "fatter" so the UV island has some wiggle room to move before touching the gray area. Your milage may vary, how far you can push this depends a lot on the art assets you work with.
For a more robust fix you might want to use more complex materials where multiple tiling textures are used to define the different surfaces and you blend between them using masks which are non-tilable like the one texture in your example. It will need some tricks (like scaling down bump offset height near a mask's edge) but generally provide a better result.

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answered Jan 11 '19 at 01:05 PM

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avatar image Crowley Caine Jan 11 '19 at 01:44 PM

Yeah I tried this out too, the issue is that I am texturing in Mudbox, using layers to create the colors and effects. Adjusting it there is a bit more difficult without getting bad distortion, especially for smaller items like this where detail is supposed to be possible to inspect up close.

One option would be to reduce the size of the UV in my 3d modelling software, but that would offset details that needed to placed at specific points on the asset.

What did work for me was adjusting the BumpOffset node, I tried first with height ratios (lowering), which did work but kinda ruined the effect I was going for. What did work was simply adjusting the reference plane value. I didn't really lose any detail and it now covers the entire model at any range or angle.

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