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In this course, professional animator and director Lee Lanier shows how to create render passes in Autodesk Maya, recombine the passes in Adobe After Effects, and motion track the passes to live-action video footage that contains a moving camera or a moving character. The course covers both the Render Layer Editor and mental ray contribution pass systems. Additionally, 1- and 2-point motion tracking and match moving, stabilization, and 4-point corner pin tracking are discussed.
Each time you have to match a 3D model to a piece of live-action footage, the challenges are slightly different. Now you still have to place the camera, perhaps bring in the image plane for reference, also create lights, and adjust those lights, but no two steps are going to be the same. For example, this is the start of the second project where we're going to integrate this 3D spaceship with the footage of this actress looking up at the sky. So, some of the work's already been done here, but we will use some of the steps that we have talked about in previous movies. Image plane has been brought in, the image sequence is functioning, so all the frames are viewable in the timeline, the camera has been positioned, and the goal of camera positioning is to create the illusion that the spaceship is in the sky above this building.
Now, the camera is positioned for the first frame. There is no animation on it. So, the concern is not replicating the exact movement of the camera, but only to rough in the perspective. The actual fine motion is going to be added in the After Effects Composite later on. The other thing that's been done at this point is that the lights have been added. A similar problem-solving technique where you look at the footage and figure out where lights are coming from and how you might recreate those. In this case, the light is coming from the sun high above on the right side of the frame.
So the key light is the directional light placed in a similar position. There is also a fill light coming from the opposite direction from the ground that represents bounced light, as if light from the sun bounced off the concrete. There are only two lights in this situation though. Now, one new thing that we do with this particular project is deal with shadows on this building. Also, we can figure out a way to cut the spaceship out so it looks like it's actually behind the building and not over the top of it. If I go to this view and maximize it, right now it's in the X-ray mode, but if I turn off the X-ray mode, you can see it's solid, and it's going to eventually appear as if it's on top.
What we can do, though, is create a piece of primitive geometry and assign it a special material called a Use Background to capture the shadow, which we can use in compositing to put it over this building, and also cut out the spaceship so it looks like it's sitting behind the edge of the building, like it's high up in the air. So let's do that. So I am going to create a primitive plane. A primitive plane is going to fit the front of the building quite well. So I am going to go to Create, you can use the NURBS Primitive or a Polygon. One thing I am going to do, though, is turn off the Interactive Creation. I actually want to create this at 0, 0, 0. So, I am going to turn this off, go back to Create, and then grab a NURBS plane, and it comes in right there at 0, 0, 0.
I am going to rotate it in the X direction by 90 degrees to make it stand up on its end and then scale it. It's definitely too small at this point. The goal here is to scale it in such a way that it covers the front of this building, as if it's a front wall. So I am just going to make it nice and skinny and long like that. Now, in order to see through this, to see through the image plane, I'll go back to the X-ray mode, and here is the X-ray button right here. So now I can see through it. So I want to loosely fit this plane to the building, just under the edge, not too tight to the edge, maybe like this, actually underneath these little castle indentations here.
Now, the perspective is working quite well on this. The reality is, though, if you were to set this shot yourself, or you had some different footage, you might have to spend more time working with the position rotation of this geometry and also the position rotation of the camera. For instance, if I was to move the camera to a different position, you can see that obviously the plane does not match perspective any longer. The choice here would be to rotate and position the plane to get to a fit or to go and work on the camera some more to get into a better position, and you might have to go back and forth, camera to plane, camera to plane 'til you work it out.
It's not instantaneous. Now, since I did some work on this already, I can just back up to my previous view and go from there. So I did some of the hard work in advance to get this to look like it's in the correct place. Now, we can assign it to that special material. So I am going to go to the Hypershade, and inside to Use Background, which is the last regular material right here. So, I am going to click that Use Background, get the new material, select the plane, and then right-mouse marking menu, and choose Assign Material To Selection. It's going to turn a slight greenish color to indicate it's using Use Background.
But the way Use Background works is it captures the color whatever is behind it. If you have an image plane there, it actually uses the image plane as its color. Now, if I was to get rid of the image plane, it's going to use the empty background color, and that actually works much better. So I am going to go to the Image Plane Attributes, Image Plane > Image Plane Attributes, and turn the Alpha Gain to 0. And again, that will hide that image plane from this view. Now, if I render this out and then take a look at the Alpha or the RGB, you will see how it's different from the regular material. Now, I am looking at the Alpha right now, and this is the Alpha button right here.
Whatever is white is opaque, wherever is black is transparent. You can see how the primitive plane with the Use Background cuts a hole into that spaceship. If I go to the RGB, you will see the same result, spaceship is cut roughly where the edge of the building is. So, because there's an image plane behind this, Use Background surface, you get this result. Now, another thing this Use Background material does is actually capture shadows. If I was to move to layer frame sequence, say, frame 90 and re-render, you will see that the shadow cast by the key light which is already set up is going to appear right here in the Alpha Channel on this plane. So I will re-render this.
Now, RGB is not very exiting. The ship has not been cut out. However, if I go to the Alpha channel, you will see the shadow cast by the key directional light is right here. Now, it's just in the Alpha Channel while the RGB is black. But what we can do in the composite later on is pull this out and place it back over the footage to make it look like a slightly darker shadow area, which will help with the realism. So you can use the Use Background material as an Alpha matte, basically the color holding something, and/or to capture shadows. So this is a really good trick to have realism later on.
Now, one last point about this, now again the camera has been pre-positioned, but if I turn back on the Image Plane, you will see a potential issue. I will turn it off again back to 1, and I will maximize this once again. If I scrub through the footage, you will see that the building plane is not really following the building in the footage. That's not really a concern at this point. Our primary concern is the perspective is roughly the same. However, I am not worried if it breaks a little bit. What we're going to do is apply motion tracking in the After Effects to solve that fine motion.
So, I just worry about the perspective at this point, since the camera is already set up, we're good to go there. Now, one last thing I can do is maybe take into account these little notches in the building, and you want to cut it out of the ship to get those little notches. So, what I can do with this big plane is make a copy of it and scale those copies down to fit that kind of castle-like top. So I can do a Ctrl+D, or Command+D, to copy this right here, that copy is right there. I can go ahead and scale it, make it skinnier, and move it up a little bit and create those little castle cut-outs. I will go ahead and do Ctrl+D again, make a few more of those.
I don't want it to be too tight. It's a little bit loose, so I want to hit the edge too perfectly, because we're going to fine-tune that later on in the composite. So I made four copies of that main plane to make those castle-like protrusions, because our copies are still using these backgrounds. So since we have our camera, our lights, and also our special plane to capture our shadows and do the Alpha matte, we're ready to go on to the next step where we'll create render passes to render out that spaceship in different layers so we can recombine those in the composite.
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