Displacement on corners and edges

[evanerichards]

Ok. So I'm going to preface this by saying this probably isn't a vray quesion. But I suppose it might be and I just don't know.

Here is my problem. I'm modeling in zbrush. I have a rectangle piece of geometry and I sculpt on one side.
When I export the displacement map for it all the corners and edges are white which means they are all poking out.
I read in an online forum the following explanation:
That is technically correct. It is generally assumed that you will take your low res geometry and subdivide it a few times before displacement. When the box is subdivided it's going to ball up around the corners, hence the edges should be white because they need to be pushed back out to a point.

If this is true, is there a way to make this work in vray or do I have to paint out those white parts in the displacement map in photoshop?

Below is an image that shows what I am talking about. Take note of the displacement map on the bottom and how white the corners are and how it affects the vray render (upper left hand) and causes the corners to poke out.


This is a problem that has been plaguing me for days and days now. Any help would be hugely appreciated.

[Morbid Angel]

I think the issue you have is because its a box like object the search radius in the corners is too great and it creates this white artifact. If you apply this same displacement map back to zbrush cube, what happens?

[evanerichards]

Well it looks the same if I apply the displacement in zbrush.
But I feel like it isn't necessarily a zbrush problem because the displacements I create in mudbox exhibit the same problems.

For instance. This:

Is a displacement I export from a rectangle polygon object in mudbox. I have done no sculpting whatsoever. The way I understand it, this should be a solid 50% gray color. But that is obviously not what it is. So it seems as though perhaps I don't understand who these programs generate their displacement maps. Because everything I've gotten so far is unusable in vray (I haven't tried any other renderers).

[Morbid Angel]

if you use raycasting method you will get that, however in mudbox if you use subdivision method, you may get better result.

[vlado]

Did you try what it says in the ZBrush help (i.e. subdividing the geometry a few times)?

Best regards,
Vlado

[evanerichards]

Yeah. I have tried a ton of different settings, subdivisions, etc, but still haven't been able to get a clean displacement map on a hard surface model. It always puffs out areas around edges/corners.
I did figure it out in mudbox (there was just a setting I had to toggle off and it stopped softening my edges) but haven't figured it out in zbrush yet.

I have literally been trying to solve this problem for the better part of a week. I have posted 20+ posts to 6 or 7 different forums and still haven't had a response that helped. Frustrating!

[evanerichards]

I'll post this here just to show one of my tests.





So I've got a basic rectangle with some sculpting on one single face. It has 11 different subdivision levels. At level one the map is so faint as to be worthless. But if you look on the thin edges at the left you can still see a white line will run through the edges poking out and making a very visible seam. And I assure you that seam is not in the sculpting. As I move up in displacement levels (creating the displacement from subdivision levels higher than 1) You can see that seam starts to widen and move out to the corners. By subdivision level 10 there is hardly any artifacting at all, but by that point my shape is a million+ polys which sort of defeats the purpose of a displacement pat in the first place.

I have also tried the base mesh being a higher resolution (more subdivisions) but still get the same results.

[vlado]

I meant subdividing the mesh in Maya, through a Maya mesh smooth operator; not smoothing it in zbrush.

Best regards,
Vlado

[evanerichards]

I did. Sorry I was unclear.

That's what I meant at the end when I said "I have also tried the base mesh being a higher resolution (more subdivisions) but still get the same results."
I meant I created a base mesh with many more polys, sent that to zbrush and sculpted on it.

I also took the initial shape in Maya, applied a mesh smooth operator to it and then applied the displacement map to what I had created in zbrush (if that is what you mean). Either way, I get roughly the same results.

[Morbid Angel]

I just tried a simple cube and zbrush totally flipped on me... did you post on zbrush forums about it?

[evanerichards]

I know right?? Try doing a sphere!! You've never seen a more messed up displacement map.

I did post on zbrush's forums but only got a single reply that didn't answer my question. It's not like v-rays forums. As far as I'm concerned the forums here are next to none. I've always gotten extremely quick and helpful replies. And to have someone like Vlado who is actually developing the software answering questions and taking suggestions? I can't think of a better situation than that.

But here's the deal. I finally got an answer by submitting a support ticket and someone from the zbrush team got back to me. Apparently zbrush automatically smooths between every hard corner and edge on your model. And if you create a displacement map, it will show up there. However, in the geometry tab of zbrush there is a sub-section called "crease". If you clikc the "crease all" button before you create the displacement maps it should create them without softening all the edges and corners. Try it and see if that works for you. It worked for me.

Zbrush has now become a usable tool for me. I'm excited by the possibilities!