Working with reflectivity
Working with reflectivity
The shiny highlights of an Arch and Design material are controlled by its reflectivity parameters. We'll use those to improve the look of the leather on the wrist band. I've got the last rendered image stored in my Rendered Frame window. This is the result that we get from the Leather preset in Arch and Design with default reflectivity parameters. And it looks kind of dull, and it's kind of diffuse in character. What I'd like to see is much sharper, shinier highlights that are smaller and more focused.
Let's go into the Material editor. I'm going to close the Material Map browser tool here, because we're not going to be using that right now. And double-click on the Leather Arch and Design material. And up at the top, we've got Reflection and Reflectivity. But before we go into that, I actually had decided that I want to knock the diffuse color down to solid black so that we'll get a really rich, dark leather look. I'm going to that color for the Diffuse channel. And I'll mention in passing that you'll notice that very small numerical changes at the bottom end of the value range here will be very large changes on the screen.
In other words the difference between 0.01 and let's say 0.05 is a very noticeable change. That's 0.01 here and that's 0.05. And we're getting a nonlinear response here in the value range. And that's because Gamma is enabled. But Gamma has to be enabled in order to work with Exposure control. So there's no work around for this. You just have to get used to the fact that extremely tiny changes at the low end here will make huge changes in the actual value.
And changes in the upper range will have very little effect. In other words, the difference between 0.95 and 0.9 is not very much. So a lot of difference down here in the dark low end, and not very much difference here in the high end. And again there's no workaround for that. Anyway I'm going to set this down to exactly zero. And then click OK. And now I'll get a very rich, dark black on the screen. Now the reflectivity parameters are here. And the most important one I'd like to point out is this Highlights Plus FG Only check box.
And if that's on, then we will not get any reflection on the surface of the object. Reflection Mapping is disabled, and we do want to have Reflection Mapping because we've got a nice cloud pattern and we want to see some of that in this surface. So we want to disable that switch so that we'll get true Reflection Mapping. Then we have the amount of reflectivity and the glossiness. Glossiness controls the spread of the highlight. And with a low glossiness here of 0.25 we're getting highlights spreading across almost the whole surface.
I'm going to turn the Glossiness all the way up to a value of One, and do another rendering. With the Diffuse color set to Black, the Glossiness turned up to One and Highlights Plus FG Only disabled, we're getting shinier highlights. And they're spreading out quite a bit actually here because of the final gather and the environment that we've built. What I'm going to do is I'm actually going to reduce the overall Reflectivity, and then I'm going to play around with some of the other attributes in order to make that Reflectivity more focused here in the areas that are facing towards the camera.
First I'll reduce the overall Reflectivity down to 0.5. Which seems like a very low number, but that's going to make sure that we don't get very much reflection in these broad areas. And we'll get reflections in these areas that are facing towards us. Scrolling down a little bit we have anisotropy. Anisotropy means that the highlights can be streaked. And if we break down the word anisotropy, isotropy means the same in all directions, or round.
And anisotropy means not the same in all directions, or not round. With a value of one, the highlights are going to be round, but I actually want to have streaked highlights. Not extremely streaked, but a little bit streaked, and I'll set anisotropy down to 0.5. Now, we come to BRDF, and that's a mouth full. It stands for the Bidirectional Reflectance Distribution Function. And it has to do with the way reflective surfaces work in the real world.
Generally, things are more reflective on the edges, and not as reflective on the front surface. And that's what this lets us control. Zero degree reflection is the amount of reflectivity that we get when the surface is pointed directly toward the camera. In other words, these surfaces that are sort of flat on to the camera. That's the Zero Degree Reflection amount. And 90 Degree Reflection is the amount of reflection for surfaces that are at right angles to the camera or that their normal is facing kind of sideways.
And normally for materials like glass and so on, you want a low zero degree reflection and a high 90 degree reflection. In this case, I want the reflectivity to be just constant across the entire surface, and when it's set to zero degree and 90 degree reflections both to a value of one. Now, lets do another test render. Okay, now we're getting somewhere. We've got some nice shiny highlights here, that are facing directly towards the camera. And also some shiny highlights here on the edges. And we're getting a nice, rich black here on the main surface.
But I want to actually crank up the Reflectivity so that we're getting really bright highlights. And I could do that by going into Reflectivity here. But if I did increase it there, we would get some shiny highlights in areas that we don't want them. But there's an interesting trick that we can do. I'm going to scroll down and go into Advanced Rendering Options. Open that up. And there is a parameter here called Relative Intensity of Highlights. And this controls the balance between Reflection Mapping and the highlights from the actual lights in the scene.
And by default it's set to one. And if I give this a value of zero for example that would mean I'm only getting Reflection Mapping and no standard highlights from the lights. In this case, what I want to do is increase the relative intensity of highlights, which means that the highlights coming from the lights are going to contribute to the brightness of the reflectivity much more than the Reflection Mapping. I'm going to set that to a value of five, and then do another render.
All right, cool, that's much better. Now I'm getting a nice shiny highlight here, and no highlights here, and it's pretty much exactly what I wanted. As we go forward we can adjust those parameters and fine tune that a little bit more, now that we understand how all those different parameters interact.
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