Join Aaron F. Ross for an in-depth discussion in this video Using IOR to control reflectance, part of 3ds Max: Advanced Materials.
- [Instructor] You probably know that index of refraction, or IOR, controls how light bends through a transparent medium. It's the density of the material. In the physical material in 3ds Max, we see in the reflections section, there's an IOR parameter. That should be an indicator that index of refraction also affects reflections, and it's easiest to see if we turn the metalness down to 0, although it will work in any mode. I'll set metalness to 0, and we have an IOR at the default of 1.52, which is about the same as standard glass.
We can increase or decrease the strength of the highlights by playing with this IOR parameter, and that in turn will affect this Advanced Reflectance Parameters section, which is defaulted to accept a value by IOR. So as we change the IOR value, we will change the intensity of highlights either on a facing angle, meaning a polygon that's directly facing the camera, or on edge, which are polygons that are facing 90 degrees away from the camera.
I'll increase the IOR to a value of 2, and that immediately increased the strength of the highlights overall. We can see here now that we're getting a reflection on the facing angle, where previously we were getting very little. Turn this up a bit more to a value of 3, and now we have very strong, unrealistic highlights there, but it does serve to illustrate the point. Let's bring IOR down to its lowest real value that's possible, a value of 1, and now we have no reflections at all.
No specular reflections. We're getting a diffuse color here, and nothing else. All right, cool. So that's how IOR works with no metalness, now let's look at it with metalness enabled. The graph in the Advanced Reflectance Parameters controls the amount of reflection color that's added to the shader. We always get the base color at full strength, but when we increase the IOR up from 1 to 2, we start to see a paler look and some additional reflections appearing on the sides.
That's because we're adding the reflection color of white with white lights in this scene. If we bring IOR back down to 1, then we effectively turn off the reflection color. If the IOR goes below 1, we will get weird effects, which in some cases might be useful, but in our case it really does look a bit too blasted out. We're getting a solarized effect here, and that's not desirable, and it's simply because we're blasting out with a very low IOR.
We'll bring this back to a value of 1. Let's split the difference here, and we'll give it an IOR value of 1.2. That then gives us a little bit more realism than the extreme low value of 1.0.
- Streamlining material editor workflow
- Managing XREFs and materials
- Laying out a scene for material testing
- Using the Physical Material
- Controlling highlights with Roughness
- Directing reflections and refractions
- Simulating translucency and scattering
- Building a shading network
- Combining and color correcting maps
- Baking maps such as ambient occlusion
- Procedural mapping with Substance
- Using relief maps: bump, normal, and displacement