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Lighting and Rendering with mental ray in Maya with Eric Keller shows how to master practical mental ray techniques for rendering models created in Maya. This course walks through the most efficient and innovative mental ray techniques, including direct versus indirect lighting methods, creating different types of shadows, using the new ShadowMap camera, and reusing shadow and final gathering maps. A chapter on optimizing render times and enhancing render quality is also included. Exercise files are included with the course.
Maya uses render layer overrides to separate different scene elements from one render layer to the next so that when you render using render layers, one render layer - an object such as the room geometry - can appear different than it does on another render layer. So, for example, in this scene I have my room geometry, and it is textured and lit. That's the way that it appears here on the roomLit_RL layer. And then on another render layer, such as the volumeLight_RL - I am going to turn on Shading > Wireframe on Shaded, so you can see the geometry is actually here, on this layer, I have applied a black surface shader to the geometry, and that's a type of render layer override.
It's a material override. In other words, the material on the geometry of the room is different on the volumeLight_RL render layer than it is on the roomLit_RL render layer. That's just one example of a type of override. Same with Color Mask. I have a red surface shader applied and to the room geometry, blue surface shader applied to the lampshade. If I turn off Wireframe on Shaded, you can see I have green material applied to the globes of the chandelier. So these are all material overrides.
In some cases, overrides are applied automatically to render layers when you change something. For example, if I select the room geometry on this render layer and press Ctrl+H, it's going to hide the room geometry on this render layer. But it will be visible on another one such as roomLit_RL. So that's a type override, as well. I am going to switch back to the colorMask_RL, select the roomGeometry in the Outliner and press Shift+H to unhide it again. I will show an example of another type of render layer.
For instance, on the colorMask_RL, I don't actually need mental ray to render this; it's kind of overkill. I could render it with Maya Software. So I can create a type of override that says, render this layer with Maya software and render the other ones with mental ray. So to do this, I'll select the colorMask_ RL in the Render Layer Editor, and I'll click in this little Clapboard icon, and this pulls up the Render Settings. And as you can see in the Render Settings, I have a Render Layer menu, which lists all the different render layers. And I could switch from one render layer to another in the Render Settings just by choosing one of these.
But I'll stick on colorMask. So to create an override, I'll just right-click over Render Using and choose Create Layer Override. And you'll see that this lettering turns orange, indicating that a render layer override has been applied to this attribute for this render layer. So I'll set this to Maya Software. So now this render layer, colorMask_RL, is set to Maya Software. So if I switch to another one, such as the roomLit_RL render layer, see there is no override here, and it's set to mental ray.
When I created the AO_RL render layer, the Ambient Occlusion render layer I used a preset. And when I did that, it automatically set a override to use mental ray. The other layers are already using mental ray, but this is just an automatic feature of using a preset. If I switch to Quality, I could create an override so that the quality on one render layer is different than another. And an example of this is when I applied the Ambient Occlusion Render Layer preset to this layer, it did in fact do that. You can see these letters in orange here.
These indicate that an override has been applied to those attributes. So I'll show you another quick example. I am going to go to the roomLit_RL render layer. And when I originally rendered this, if I pull up my Render view, and I'll scroll to - you can see right here this is the roomLit_RL render layer. This is the render that it's created. One thing about this render that this is a little strange is that the fact that it's dark outside here, but you can clearly see light is pooling up on the ground.
So I could create a quick render layer override to fix that, and I could apply that to the camera. So I'll select a renderCam camera and open its Attribute Editor, and I'm going to scroll down here to the Environment tab. I am going to right-click over this Background Color and choose Create Layer Override. This turns orange, indicating an override has been applied, and now I'll just move this up to maybe a very light gray.
And now when I - I'll store this image, create a render - you'll see that that background color has been applied to the camera in the render layer to create a light color outside, but not to anything else. And of course, it would help if I rendered from the right camera. Let me escape there and do a Render > renderCam. There we go. By default, if you don't do that it will render from the Perspective view, so you'll get something strange. As this is rendering, you can see now I have a light gray color outside the room. And it starts to look a little bit more natural.
All right, so we can see our render here. Now that I have applied that render layer override, we have a nice background color here. It's starting to look more like a scene of a room in an overcast day. So we can see the light coming through here and reflected on the floor as well. So it's starting to look a little more realistic. I'll store that. So what can you apply render layer overrides to? Almost anything that affects the rendering of the image. In other words, you can't apply it to something like the way a character is animated from one layer to another, but certainly the way that character looks, things like the intensity of a light, the reflectivity of a particular shader.
If I select, for instance, this table and go to the tableShader tab, if I wanted to change the Eccentricity of this Specular Highlight on one render layer and have it different from another, all I need to do is create a render layer override, so this turns orange, and change its value, and now it will appear differently on this render layer than another. So that makes it convenient because then you can create variations of your different objects form one render layer to another. And you'll also notice that in some cases if you create a render layer and start to adjust an attribute or turn something on or off, in particular something like visibility, so if I select for instance the room here, and I can get rid of some of these tabs by deleting history on this, Delete by Type > History.
So now we have fewer tabs to deal with. For instance, sometimes overrides will be applied automatically. If I am on a render layer, so currently I am on the roomLit_RL render layer, if I switch to the Attribute Editor and start to change these, you are going to see that it's just turning orange. So in this case, Maya is just assuming I want an override for these attributes. So in some cases you'll see those things turn on automatically. But most anything can be turned into a render layer override. You can see that's one of the most powerful aspects of using render layers is the ability to create variation, to turn things on and off, to create different versions for render layers, or to separate for easy compositing.
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