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In this movie, we are going to talk about making sense of some of the mental ray shaders that come with Maya. Some of these shaders can be quite complex and especially when you are first learning mental ray they can be difficult to use. They are good for simulating a variety of materials but they can give you a lot of headaches. So, my goal for this movie is to help you eliminate some of those headaches. I am going to talk about how these shaders work and also some alternatives that can make your life a bit easier. In this rendering here I have three teapots and each one has a different mental ray shader apply to it.
Up here, in the far left I have a DGS shader applied to this teapot. That's the Diffuse, Glossy, Specular shader. In the center, I have the dielectric shader applied and this is meant to simulate glass or liquid. You see it has very nice refractive qualities to it. Then down here on the lower right I have an MIB network applied to this shader. The MIB stands for Mental Images Base shader. So, let's take a look at what's going on in this scene. I am going to store this image in the Render View and minimize the Render View.
I am going to start with the DGS shader. So, I am going to select this object, open the Hypershade by choosing Windows > Rendering Editors > Hypershade. In the work area of the Hypershade, I am going to right-click and choose Graph Materials on Selected Objects. And here we see the dgs_material1. So, I'll select this material and open up the Attribute Editor. Let's just take a quick look at it. The material here it doesn't have too many settings.
The main settings are the Diffuse, Glossy and Specular channel and then below this we have additional settings that allow you to adjust the Transparency, Index of Refraction as well as the quality of the Specular highlight. Now, the Diffuse channel is fairly straightforward. This is where you determine the color of the objects. So, if I click on there. I can choose a color so I'll just choose green for this. But,what's confusing where the shaders we have a Glossy channel and a Specular channel and both of these have different ways of controlling the reflective qualities of the material and it's slightly redundant.
So, for example if I set these both to black the Glossy channel controls the specular highlight, the color of it and it's overall brightness, but it also controls some of the reflective qualities of the shaders as well. So, if I hide the lower two parts, I am just going to select them and press Ctrl+H to hide them and zoom in and I'll do a quick rendering. You can see that we have reflection and we also have specular highlight.
But if I select this material and turn the Glossy to black and turn up the Specular aspect of it and then do another render, now we see a nice reflection but no specular highlight. So, where this gets confusing is that the Glossy channel controls both the specular highlight and the reflectivity and the Specular channel controls just reflectivity. So, which one do you use? How do you get the proper reflection out of your material? It gets a little bit confusing and can spend a lot of time doodling with this and not get way the results you want.
On top of this you have a Shiny setting which controls the blurriness of the reflections. So, it's an okay material but I don't use it very much in my own work because I find it very non-intuitive. So, I am going to select the dielectric_pot here in the outliner and choose Display > Show Selection and I'll select the dgs_pot and do Ctrl+H to hide it. Let's take a look at this material. I am going to do another quick render here. To the most pot of this material does a good job of simulating glass but you'll notice that the shadow cast by the object is opaque.
This can drive you a little bit crazy because you have to jump through a number of hoops in order to get a transparent shadow going that's effective. So, if I select the dielectric_pot object in the outliner, right-click in the Hypershade, and choose Graph Materials on Selected Objects. I can select the material and open up the attribute editor. There are several channels to control the color of the object. You have Color and Outside Object and Outside Color. You also have two settings for Index of Refraction and the idea is that material is meant to accurately simulate light as it passage through multiple surfaces.
So, for example the Index of Refraction here would control the index of refraction for the glass. Outside Index of Refraction would control say the index of refraction of the air. So, if I set this to 1 that will be the index of refraction for the air. Then the Phong Coefficient controls the specular highlight. What makes this material particularly difficult to use is in order to get that transparent shadow you have to either create some workflow that involves render passes or render layers. So, one render layer would have the dielectric material and no shadows cast and another render layer would have an object that has a transparent material applied but the object is hidden and then you could composite the shadow.
You can see it starts to get more and more complicated. The other alternative would be to select the dielectric_material shading group node and connects the dielectric_ material Photonic node to the photon shaders slide down here in the shading group node. Again, very complicated and on top of this you have to start messing with caustics. It becomes a pain in the neck. So, again not a material that I use very often. Then finally I'm going to display the MIB_pot.
I'll select it, right-click in the Hypershade, and choose Graph Materials on selection. You can see for this material this shader has actually created of a network of two other materials. We have the mib cook_torrance which determines the diffuse quality as well as the specular highlight but does not have any settings for the reflection. Reflection is controlled by the mib_glossy_reflection node. So, in order to set this up I need to connect the mib cook_torrance to the Base material of the glossy_reflection_node.
You'll notice if I select in the Hypershade under Materials that there are a number of MIB nodes. We have a Blinn, Cook-Torrance, Lambert, Phong, Ward and so on and so forth. All of these shaders control the diffuse quality and the specular highlight but they need to be connected to an mib_ glossy_reflection node or to indicate a transparent material you need to connect it to a mib_glossy_refraction node. Then to get the look that you want you need to basically adjust the settings on both nodes.
So, there's a lot of jumping back and forth and adjusting these settings until you get what you want. Again, it can be a kind of a headache especially if you are just hasn't come up with something fairly simple. So, what is the alternative? Well, these shaders are from an older version of mental ray that has been integrated into Maya. The reason they still exist is largely to provide legacy support for people using older shaders or older workflows. There is an alternative to using these shaders that can make your life a lot easier. So, I am going to show these objects again and I am going to set Diffuse back to dark gray color for the dgs node.
I am going to select the mia_pot 1, 2 and 3 objects in the Outliner and I'm going to choose Display Show Selection. So, what I've done in this scene is I've created three alternate pots here in the back behind these in the front. These pots all have different variations of the mia_material applied to them. So, again if I open up the Hypershade the mia_materials found under mental ray > Materials and it's this material right here, mia_material.
I use the mia_x_passes material most of the time. This material is an awful lot of settings but at the same time these settings allow you to simulate just pretty much anything you want to without the headaches of the other more complex shader networks. So, if I do a render here you'll see that what I've done is I've quickly used mia_materials to imitate the same look that I created with the other mental ray shaders. I'm just trying to drive home the point here that for the most part you don't need to use the DGS, the Dielectric or the MIB shading networks to create good-looking materials.
You can skip those altogether and just start working with the mia_materials. You can see like for instance this transparent glass shader that I've created using mia_material. It looks extremely as similar to the Dielectric shader. I think it's a bit more physically accurate we don't have these over bright reds here. This to me looks more realistic than this does and you'll also notice nice transparent shadow has already been created and it's part of the material. I don't need to jump through any extra hoops to create a transparent shadow for this shader.
Diffuse glossy shader, I've imitated very quickly using an mia_network and same with the MIB-based network. Again, I think this shader to me looks more realistic than what I've created with the MIB Base material. So, the bottom line as an academic exercise it's a good idea to learn about how these materials work. But if you really want to get some work done and you what to create a good-looking render which I'm assuming is your actual goal, then skip these shaders, go straight to the mia_material and master that maternal.
You'll be able to simulate pretty much anything you can think of. mia_ stands for Mental Images Architectural shading node and the purpose behind it is for simulating hard surface objects. But I've actually used it to simulate a wide variety of shading types. I've used it for insects. I've used it for translucent plastic. I've used it for special effects for things like you know scanning electron, microscope shaders. Pretty much anything you can think of with the exception maybe of human skin the mia_material is perfect for it.
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