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In addition to painting masks by hand, ZBrush can generate masks based on the structure and detail of a model. Masking by cavity means that ZBrush identifies which vertices of a model are depressed inside creases and cracks, and masks them automatically. Masking by ambient occlusion is similar, but it masks off areas where the surface is close to other surfaces. It's like surrounding an object with lights and masking parts where the object cast shadows on itself. Let's open up the DemoRhino to have something to work with, and let's also make its color pure white, so that we can see the mask more clearly.
I also want to increase the subdivision levels a few times, so that we have more detail to work with. Just clicking it twice should be good enough. So let's go down to the Masking sub-palette. The first thing I want to talk about is masking by cavity. Let's zoom in on the rhino and identify what areas are actually cavities. A cavity is any area where there is like a depression or a crease where the model goes inwards. So you can see right here on the knee or the ankle, or whatever this is, there is a depression inwards.
Some cavities are more intense than others. This one right here at the shoulder is much deeper of a cavity, and you can control how ZBrush interprets the depth of cavities. You can experiment with Intensity to make the mask stronger or less intense. I'm going to leave it at 10 for now, but go ahead and experiment with that if you are having any issues with the masking process. One thing I want to open up is Cavity Profile. This is how you tell Zbrush how intense a cavity has to be before it's masked. I think by default ZBrush over-masks.
So what I want do is tell ZBrush to make only the more intense cavities masked, and the way you do this is you could just kind of drag up right here. By adjusting the curve like this, it's going to mean that a surface has to be even more in cavity before it will be masked. All right, let's click Mask By Cavity to see the result. So you see ZBrush went and looked inside any areas where there is a depression and masked it off. Now if we were to sculpt on this, those masked areas are going to be protected just like any other mask.
Let's undo that, and let's get rid of that mask as well by hitting Ctrl+Shift+A. Mask by Ambient Occlusion is similar. Now Ambient Occlusion is going to look at parts of the model and see if there is another surface of the model that is nearby. One area that it really likes to look at is like legs. Let's see if I can get a good view on this. These two legs are close to each other and would probably cast shadows on each other in real life. Ambient occlusion is going to look at that relationship and mask off the areas where one leg would cast a shadow on another.
I like to bump Occlusion Intensity up to about 2 or 2.5 to get a more intense result. Changing AO ScanDist, or Ambient Occlusion Scan Distance, can give you different results. I like to set it to something more like 0.5. This is basically looking at the distance between objects. So the greater the distance you'd set it to, the farther the ZBrush will look from one part of the model to the next to see if it's in shadow. So let's see what we get.
I'm going to hit Mask Ambient Occlusion now. Be aware that the more polygons you model, the longer ambient occlusion takes to calculate. You can usually experiment with the result on a lower subdivision level, and then when you like it, you can go up subdivision levels and mask again. You'll get a smoother result at higher subdivision levels, but it will take longer. On the lower levels, you can experiment more quickly. Now let's zoom out, Hit F, and see what it looks like. So it might not be entirely obvious what has been masked off. One way to get a sense of that is to unmask it and hit Ctrl+Shift+A to clear everything.
Then you can see by what changed, what is actually masked. To bring the mask back, simply undo. Hit Ctrl+Z. So as you can see, ZBrush has masked between different surfaces of the object. It sort of simulates how an object would cast shadows on itself. There are many reasons to mask by cavity and occlusion. You may want to use it to help paint darker colors and crevices to accentuate them. You may want to sculpt scratches on the surface of something, but keep recess areas protected from them like they would be in reality.
I'm sure there are many other creative uses for the style of masking that haven't even been thought of yet.
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