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So in this movie, we're going to talk about the concept of diffuse reflections. What is a diffuse reflection? Well, we have to think of it this way. All surfaces in the real world reflect light in one way or another. If they don't, then they're completely transparent. The light passes through them and they're essentially invisible to us. So when you're thinking about this kind of thing, you want to think about how smooth is the surface, because the type of reflection that is created is dependent on the smoothness of the surface. Let's take a look at this scene. We have two teapots here on this checkerboard surface.
I've created two very simple shaders to illustrate the point of diffuse reflections. So I'll do a quick render here and we can compare the result. So this teapot here on the left is highly reflective. The surface is a lot like a mirror. We can clearly see the checkerboards in the background reflected on the surface of the other teapot, and even other parts of the teapot reflected on the surface. This teapot on the right is also very reflective. However, you can see that the surface is somewhat rough.
What this means is that a smoother surface is going to reflect the light much like a mirror. A rougher surface is going to reflect the light kind of like - think about concrete on a sunny day. Concrete is very rough. So when the individual photons of light hit the surface, they're reflected back in all directions. What we end up with is we see the light reflected on the surface, but we don't actually see the other objects in the scene reflected on the surface. So I've created a dynamic simulation to illustrate this point a little bit better.
Imagine this surface, this plane, as being a smooth surface. At this point, we're so close to it that we can actually see the individual photons of light. So as I play the simulation, you'll see the photons of light come in and they bounce off the surface at about the same angle that they hit the surface. This is what a smooth or highly reflective surface would look like very close. Now if the surface starts to become rough, like concrete or something like that, you'll see that the photons, as they hit the surface, they're reflected back into the environment in all directions.
In other words, the photons of light are diffused back into the environment. Hence, the term diffused reflection. So as you can see from the way that I've set up this diagram, I have it gradually becoming rougher over time. Let's just illustrate the point that surfaces have a wide range of diffusion. So, as you think of your surface is going from perfectly smooth to very rough, you'll think about how that affects the individual photons of light. So we have a range of diffuse reflection, from perfectly smooth to very, very rough and everything in between.
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