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Now when you use bump mapping, it basically is a render effect. It creates the illusion of a bumpy surface. It doesn't actually change the geometry of an object. To do that, we require displacement mapping. Now let's take a quick look at bump mapping again, just to see how it works. So I have this cube and if I do a quick render of it, you see that, well, it's got this black-and-white texture on, which we can use as a bump map or a displacement map.
So if we go over to our Texture panel here, so we can see under Influence, it's influencing the color of the object. And you can see that here in the preview. Now, if I turn this off for color and go over to Geometry here, under Influence, and turn on Norm, you can see how I can create a normal map, or bump map, that has that cross effect. So if I do a quick render, you can see how yeah, I do get those lines embossed on that surface.
But if we scroll in, you can see that well it's not really affecting the geometry of the object. To do that we need a displacement map. So I am going to turn off the Norm and turn on Displacement. Now, this particular cube doesn't have a lot of detail. If I look at it in Edit mode here, you will see that I only have a few subdivisions on each side. And this is actually going to be a problem when it comes to actually displacing this object.
That's because it doesn't have enough detail to displace. Now remember, displacement mapping actually changes the structure of the object. It actually displaces the geometry. So in order to displace geometry, I need more geometry. Now I can do that in one of two ways. I can simply make my mesh more complex, which is really going to bog down my scene, but probably the more efficient way is just to add a subdivision surface to my object. So I am going to go select my object, go over to Modifiers here, and add in a subdivision surface. I can probably keep my Render settings at two, and let's just see what happens.
This is the default. And you can see that, okay, so now that displacement really works. If I turn up my Render settings to, say, 3 or 4 and hit Render, you can really see how this works. The displacement map actually changes the structure of the geometry to match that image map. So this is a very efficient way of creating additional geometry.
Now if I go over here, you can see I have a Displacement option here, and this is actually a physical displacement. Actually, it's an actual measured value, so if I want to, I can make it a bigger number, or I can go negative to turn those bumps into divots. In other words it becomes a channel rather than a bump. So the one downside to displacement mapping is that you do need more geometry, but Subdivision Surfaces can help you add this without too much overload.
So remember bump mapping is a surface effect; it does not change the underlying geometry. Displacement mapping, however, does, although you do need enough geometry to displace. So go ahead and use these as you want. I would tend to opt for bump mapping first and if that doesn't work, then going to displacement mapping.
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