Hello 
I have a 3D scanner that produces models that sometimes need a bit of repair – a detail doesn’t resolve properly, or a thin surface swiss-cheeses. ZBrush seems like an obvious tool for this, but I’m struggling a bit with the workflow.
Firstly, I was expecting a tool that perhaps allows me to paint directly onto the texture through the model. But from what I’ve read, ZBrush doesn’t really support this, and instead the recommended path is to convert the model to PolyPaint, make the necessary edits, and then convert it back to a texture.
The model off the scanner has approximately 1M triangles and an 8192x8192 texture. When this loads into ZBrush, initially it collapses the texture down to vertex colours. Any high-detail area is completely destroyed. However, it is possible to import the texture in and then the model appears correctly. After doing this, though, any edit to the geometry immediately collapses it back down to PolyPaint. But, I can Divide the model first, and then when it converted to PolyPaint, it has more vertices to work with and not as much detail is lost.
When I click Divide, starting from 1M triangles, I end up with 3M quads, then 12M, then 48M. I can’t Divide past this point because of the hardcoded limit of 100M polygons, but this caps the geometry at quantitatively less than the number of texels. 48M isn’t that much lower than 67M, but it is unavoidable that I’ll be taking at least some loss in quality with this. Is there some way to subdivide further, so that instead of sticking to a rigid subdivision method, I can instead have approximately one vertex per texel?
Either way, I can make my edits and then reach a point where I need to get a texture-mapped model back out the other side. So the next step, after merging all subtools, is to Unwrap UV on the model. I made typical edits to a typical scan model earlier today and then clicked on Tool->UV Master->Unwrap, and the window has been frozen now for over an hour. Is this going to eventually finish successfully? Is there a better way to turn the edit results back into a texture-mapped model? The geometry has ~48M quads right now, but I can’t decimate the geometry while it is based on PolyPaint vertex colours, or I’ll lose my texture detail.
What to expect? What to do?