Controlling transparency with Transmission - Maya Tutorial

- [Instructor] Transparency is handled by the transmission attributes of the standard surface. In this version of the scene, I'm using an Arnold Skydome to provide illumination and a backdrop. I've also enabled a depth of field effect in the camera, in order to differentiate the foreground and background. We don't have time to cover those techniques in this course, but if you're interested, you can check out my other course, Maya Rendering with Arnold 6. I've got the sculpture selected. I'm displaying the standard surface attributes in the attribute editor. The Arnold RenderView is open and interactive production rendering is enabled. Once that's finished I'll create a snapshot so we can compare it to later versions. In the attribute editor, I'll open up the Transmission section and increase the transmission weight, from it's default of zero up to its maximum of one for a perfectly transparent surface. When that's finished, I'll create another snapshot. The default index of refractions is 1.5 and as we discussed earlier index of refraction determines the density of a material. A higher IOR will cause light rays to bend more as they enter or exit a solid transparent object. An index of refraction of 1.5 corresponds to ordinary glass, but if this were a crystal sculpture, it would probably be more dense then ordinary glass. I'll increase the IOR up to a value of 1.7. When that's finished once again, I'll create another snapshot. And I can stop the interactive production rendering and compare these two versions. This snapshot has an IOR of 1.7, and this one has an IOR of 1.5. We can see the differences if we switch back and forth between those two. Currently I've got a transmission weight of one. Notice that the base weight is grayed out. If transmission weight is equal to one, then the base color is disabled. You'll get no diffused reflections. The transmission weight does not affect the specular component. Also, if the transmission weight is set to any value other than zero, then Arnold will automatically disable the opaque attribute of the object's shape node. If I go into the Dancershade tab in the attribute editor and open up the Arnold section, we'll see a flag labeled Opaque. The opaque attribute optimizes retracing by determining if transmission rays are calculated for that shape. If opaque is on, then no transmission rays are calculated. But we can clearly see, that we've got transmission rays here. With a non zero transmission weight, Arnold automatically disables the opaque attribute. Allowing the transmission rays to be calculated. Transmission weight only affects the opaque attribute if opaque is enabled. If you disable opaque, then transmission rays will be calculated even if the transmission weight is zero. In that case, you'd be calculating transparency for an object that is actually opaque. That's not a good idea. It wouldn't lengthen render times unnecessarily. The smart move is to always leave opaque enabled. And anyway this attribute may be removed in a future version of Arnold. Since no solid material is perfectly transparent, you probably don't want to have a transmission weight of one. I'll go back to the standard surface and set the transmission weight down just a little bit to .98 or so and re-enable interactive production rendering. It's going to give us a little bit of diffuse reflection and since the base color is white, it's going to brighten the surface a bit. When that's finished, once again, I'll create another snapshot. Here's a version with a transmission weight of one. And here's a version with a transmission weight of .98. We brighten the surface a bit, by reducing the transmission weight to .98 and allowing a little bit of that base color to show through. That's the basics of the transmission attributes, for rendering a transparent refractive volume.