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Decimating a flat surface ruins the texture

ZBrush Usage Questions
#1

I have a similar problem to that asked here in this thread http://www.zbrushcentral.com/showthread.php?163453-Help-PolyPaint-to-Texture-workflow-Answered&highlight=decimation+poly+paint

However, although I was already using this workflow sucessfully with previous models I now find myself with a problem. I have a sculpt that is essentially a thick flag shape. Onto this I have painted a detailed flag using Spotlight. Now wishing to 3D Print this I have to export a model with fewer polygons. My normal workflow as shown in the previous thread does not work on this scuplt because upon decimating it both sides of the flag get some crazy shaped polys MUCH larger than all others. When exporting the model the texture becomes all warped and twisted on those two faces (which can be seen immediatly upon decimation). I should point out that other parts of the scuplt that are rounded and organic shaped decimate just fine and the texture is good.

I have tried masking the faces prior to decimating but this does nothing at all, as if the masking wasn’t even there.

Has anyone had similar issues with decimating large, flat surfaces? Know of a workaround?

I CAN work round this by projecting the high-poly tool onto a sub-tool that is at the max size for printing without using any decimating but this is not an ideal solution and the texture is not as nice.

Glenn

#2

I am assuming you are using polypaint and not a texture.

you need to unwrap your model and generate a texture
when you decimate tell it to keep your UVs
after you decimate apply the texture.

If you must have polypaint/vertex color information for your 3D printer then you can’t decimate that section because it doesn’t doesn’t have the poly density to support your texture. You get one or the other on flat surfaces, either good polypaint, or low tricount.

#3

Thanks for replying, but no, I do have UV’s and texture saved before decimating. The only thing I’m not quite clear on is when you say “After you decimate apply the texture”. Normally, once I’ve decimated my next step is to export the model as a WRL which of course includes the previously saved texture. It is absolutely the weird poly’s that are affecting the texture…

So, are you saying that there is something I should be doing to apply the texture AFTER decimating but BEFORE exporting?

When I get home this evening I will try and upload a screenshot to show people what this looks like. In the meantime anyone can do a simple test if they’d like: Create a thin rectangular solid and Divide it three or four times. (I actually Dyanamesh it once at 128 and then Divide it). Now Decimate it at 50% about two times and turn on the poly’s to look at them. You should see the front and back faces have large and distorted poly’s in them. Doesn’t affect the modeling in the least, but it does affect a texture if you have one on it.

Glenn

#4

You sir, are correct.

It appears Keep UVs is also getting effected by the same math that decides what to remove during decimation.

Images showing off the error you’re talking about.
https://www.dropbox.com/sh/55ecp7wzy1mt16v/i-mjc678Lm

Hmm…Which version of Zbrush are you using?

#5

Well, thanks for doing that so I know I’m not going mad! Below is my own screenshot test verifying this. Those large blank areas are polys. You can see on the edges that the polys are fine…

I’m using version 4R4

screenshot.jpg

#6

Have you submitted a support ticket?

#7

No, I haven’t. I figured it would be something they’d be aware of… maybe not.

In the meantime I have been experimenting with Go Z, something I’d not used before, and so far it seems wonderful. Can get some great detail on a low poly model. Haven’t worked entire way thru to end, but it looks promising.

#8

Under Preferences: Decimation Master, is an option to ‘Use and keep polypaint’ (or similar wording). This decimates the mesh in a way that it would preserve the verts required to preserve the polypaint data.

What I would do, even if this was a texture, is convert the result to polypaint and decimate it with that option. Afterwards you could create a new set of UVs and transfer the result back to the texture before exporting.

Similarly, you could manually retopologize the plane or use something like dynamesh/zremesh/etc to create a new plane, and transfer the results that way.

#9

Cyrid, thanks for the reply and sorry for late response. I did manage to use a workaround in the end but I will take a look at what you advised. Maybe it was something as simple as checking off “Use and Keep Polypaint” (or whatever it is).