Join Lee Lanier for an in-depth discussion in this video Recombining render passes in a composition, part of Maya: Rendering for After Effects Composites (2012).
At this stage of project 1 inside After Effects, we have imported the live action footage of actress and also all the render passes. The footage with the actress is shot1, and then we have all of the separate render passes brought in separately from the layered PSD files. We're in the same composition now, also called shot1. Now one great thing about all these separate render passes is we can turn those into separate layers and then adjust them individually--just transform them individually or apply separate effects. Each one could be adjusted different from the other.
Now one disadvantage of that is all these render passes are separate. So we do have all the separate layers, how are you going to move them together as a single unit? So one thing that often happens is you have to recombine the render passes and the composite, and the way you recombine them will affect the end result. So we need to do that with this project before we can move on to other steps, such as motion tracking. Now I'm not going to recombine these render passes in the shot1 composite. I'm going to make a brand-new composition. It will be easier to deal with them separately from the actual live action footage. So I am going to go to Composition > New Composition, and make a new composition that's identical to the first one.
Now what's interesting is After Effects will remember your previous settings and set these options for you. So as it happens, these are correct. I do want to HDTV 1080 with 24 frames per second, which is 1920x1080. I do want to 24 frames per second, once again, and the duration of 60 frames is correct. So in this case, the only thing that I might want to change is the name of the Composition, and I am going to call mine Render just so I can remember what that composition is for, and I'll click OK. So the new composition pops up as a new tab.
So now I can start to arrange my render passes in his composition to try to rebuild them. And the end goal here is to build them in such a way that they start to look like the Beauty render in Maya. So which ones do we pull in? The order does matter. I'm going to start with the diffuseMaterialColor. It's a common place to start. I'll pull that down to the composition, and there we have the diffuse render without any kind of shading or without any kind of shadows. Next one I want to grab is actually the Specular. I'll pull that down and place it on top. That's a specular component.
Now here you see our first essential problem. If I use the scroll wheel to zoom in and then middle mouse button to move around, I can see that the specular takes out the composition. In other words, it blocks the composition. I cannot see my diffuse thing any longer. In fact, if I click the eye I right here besides specular and turn that off, there's my diffuse. I turn the Specular back on, the Diffuse is missing. That's because the Specular render pass does not create a proper Alpha channel. Now I can take a look at that by double- clicking the Specular render right here in the Project panel and taking a look at it in a Footage Viewer.
I need to move my view around. There it is in RGB, but if switch the Show Channel menu right here from RGB to Alpha, I can take a look at that Alpha Channel, and it's completely solid white which means it's 100% opaque. Again, Alpha determines transparency, and in this case there is no indication where the object is. That's not going to work for us if we just simply place on top as is. So I'm going to go back to the Show Channel and change it back to RGB, and I am going to go back to the Composition view, and we'll deal with this.
So one current way to deal with this problem is to change the blending mode. Now each layer has a blending mode, and this similar to what you have in Photoshop and also what you have in the Render Layer editor inside Maya. In terms of the blending mode, it helps the program figure out what the color values of the pixels are, and you can buy in one layer with what's below it. So there's a Blending mode menu beside each layer here. Now if you don't see that under mode, what you can do is click this toggle switches button. So if you had this view where you don't see it, click that button again, and there is each of the Blending mode menus right here.
So for Specular, a common blending mode is called Screen. So if I click this menu and switch the screen that's going to work for us. So what does Screen do? Screen takes the brightest values between that layer and what's below it and places it on top. In other words it gives advantage to whatever pixels brightest regardless what's layer it's on. So if I pick Screen all the bright pixels when out from both layers. So what you have is a specular highlight, for instance, this hotspot right here on top of the diffuse color. So again, I'll go back to Normal here which you will get by default, and here's a specular by itself.
If I go back to Screen, here's the combined result. So blending modes are often very important. So now we have Specular working for us. Let's go to the next render pass. Next one we are going to pull down is Reflection. I'll place that on top. This is a similar problem to the specularity or specular layer. It takes over the composition, and I can't see what's below it. So in this case I can use a similar technique I'll go to that blending mode for that layer and switch that to Screen. So we now have a combination of the Reflection and the Specular on top of the Diffuse, and I have all three combined together and they're starting to build towards that beauty pass.
We're going to work with one more render pass right now, and that's the Shadow. I'll pull those shadowRaw down and place on top. Now shadowRaw produces a white shadow over a black field. Obviously, this is not going to work for us as is. Not only there is a block that's below it, but the shadow is white and not black. So in this case the first thing I need to do is invert this, flip the colors around. We're going to have to place of our first effect because of that to make this work. So with the shadowRaw layer selected, I'm going to go up to Effect > Channel > Invert and in Inverts affects the colors where black becomes white and vice-versa.
So if apply that the shadow becomes black, the field become white, and I potentially can use this. Obviously, this is not functional yet because it's blocking out everything below it, so I had to pick in another blending mode for this. Now because I want the dark areas to survive and get rather bright areas, what I can do is go to the blending mode and select Multiply. What Multiply does is it multiplies all values together, so what was dark is my top layer darkens everything below it, and anything that's white, it has no effect. So if I apply Multiply it places that darker shadow over what's basically a brighter spyglass.
So now we have arranged four of the render passes in this composition. I want to save the fifth one for later. But we have built this towards the Beauty render within Maya. It's going to look very similar at this point. Now we're ready to move on and use this composition, combine it with live action footage, and add motion tracking to get to follow the actress' hand.
- Working with image sequences
- Matching the 3D camera to video footage
- Lighting models in Maya
- Splitting a scene into multiple render passes
- Batch rendering
- Recombining render passes in an After Effects composition
- Setting up motion trackers
- Refining layers with rotoscoping
- Adding blur and effects
- Adjusting shadows and matte edges
- Using color correction
- Stabilizing shaky video