Setting up render passes

One of the great benefits of using render layers is that we can now render unique passes associated with the selected render layer. This gives us a lot of flexibility in our composite, where we can make adjustments to a single pass. Let's take a look at how we can create these render passes. Here in Nuke, I'm going to show you what these passes actually look like separated out. So here's our car render layer that we rendered out, and here is our ambient occlusion which I call AO. I'm simply hitting the number 1 button, so our viewer is now viewing that node.

I can also just grab the Viewer node, and move it to a different node. So now we're looking at our Indirect pass, Specular, Reflection, and Refraction. If we were to add all these up using the Merge add node, we would end up with the same render that we started with. Let's go back to Maya, and see how I output these render passes. Here in Maya, I have to make sure, first and foremost, that my Car render layer is selected. That way, when I go into my Passes tab, any associated passes I add will be added to my Car render layer.

Let's go back into our Render Settings, and Create new render pass. Now we have this big list that comes up. Let's go ahead and find those passes that I rendered out. First one is Ambient Occlusion, and now let's scroll down; we can use this side scrollbar here. Holding down the Control button, I'm adding a selection; in this case, Diffuse. Let's go ahead and add Indirect. Let's continue down. Let's go ahead and add Reflection, Refraction, and finally, Specular.

And we can say Create and Close. Since these Render Passes are up in here in the scene selection, we still have to associate them with the render layer. So let's select this button right here, which associates the selected render passes to that render layer. Next, let's go back to our Common tab. Right now we're only rendering out images, car.tif. If we want to render out separate render passes, we simply right-click; go down to our render pass name, let's insert a forward slash, and hit Enter.

Now we're rendering to Concept_Car/images, to a directory called Car; within that directory, we're going to be getting our associated render passes. Let's go ahead and open up our Hypershade window. Go to Window > Rendering Editors > Hypershade. Notice that each of these shaders is a mia_material_x_passes shader. This is very important. If these materials don't have the x passes truncated on to the end, then when we render out our render passes, these passes will not render.

So we select mental ray, we scroll down, and notice several of the shaders have passes associated to them. In this particular case, we're using the mia_material_x_passes. Now we know that our passes will be rendered out when anything is assigned to that object with that shader. To properly composite these passes, we must make sure they have the highest bit depth available, so let's examine how to make these passes 32-bit.