ZBrushCentral

mask by ambient occlusion

ZBrush Usage Questions
#1

Is there some sort of trick to masking by ambient occlusion? how long should masking by ambient occlusion take? My model has about 13 million polys at the highest level. I don’t know exactly how long it took because I ended up going to bed and let it run, but I know it at least took a couple of hours just to generate the ao mask. Is this something that should be done at the lowest level like when creating a displacement or normal map? I wouldn’t think so but not sure. Also, after finally generating the map, I clicked the create alpha button and then zbrush crashed saying I didn’t have enough memory. it just seems that something like this shouldn’t be so resource heavy, but I don’t know.

My system specs are below.

Windows Vista x64
Intel Core 2 Quad 3.0Ghz
8gb of RAM
1gb 9800 GT Nvidia

#2

Depending on the complexity of your model it can take a very long time at high polygon counts. This is why the documentation explains that it’s best to use the lowest subdivision level that gives decent results. Remember that you can always blur the mask after you’ve gone back up in levels again.

Every point in the model needs to have its masking evaluated, which I believe is done by casting multiple rays from that point to see if it hits anything. At 13 million polys, that’s a LOT of rays.

Another trick you can do is run your masking tests at low levels, then only switch to a higher level for the final masking calculation when you are satisfied with the settings. This won’t speed up the calculation, but it will speed up all of the tests while you’re finding the values you want.

#3

thanks aurick, that makes sense.