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VFX Techniques introduces common yet critical visual effects techniques that are used in film and television shows on a regular basis. This installment shows how to simulate a large crowd by combining live-action footage of a small group of people, 3D renders, and Adobe Photoshop artwork—transforming an otherwise empty building into a rapt audience. Author Lee Lanier uses After Effects to set up image sequences, apply motion tracking to match the motion of the original camera, and key green-screen footage. Finally, you'll learn how to make all the elements cohesive with color correction and lighting techniques.
We are now ready to start working in After Effects. I have After Effects CS6 open right now. It's just an empty project, there is nothing in it. We can use this to import background footage and get started. As we discussed, image sequences are often used in visual effects work, and we are going to bring in our first image sequence. When we work with sequences, it is important to make sure we pay attention to the resolution, the frames per second, and the duration. We can get started by going up to File > Import > File. And even though image sequence is composed of many individual files, we could bring those in as a single unit in After Effects.
I want to navigate to my Footage folder and within that folder is a folder called WideSpeaker, in this sort of background, image sequence was converted from the original video. When you are working with the image sequence, all you have to do is to click on the very first frame of the sequence, in this case 000.png. Once you click on the very first one, you will see that in the lower left-hand corner of this window, there is a PNG Sequence check box, and this is checked automatically. This will be different based on the type of file you are working with, it could be TIFF or TARGA.
In this case, it is PNG. Now as long as this is checked, what we will do is bring in the entire image sequence as a single unit, which makes them much easier to work with. So that's checked, so I can go ahead and click Open. The image sequence comes in as a single piece. And then look up here at the top, in here you will see the resolution, the duration, and the frame rate, or the frames per second. In terms of duration, in this case it's read out in the frames, which is really good for working with visual effects. This is not a default setting for After Effects.
If you don't see this, there is a way to change that to make sure it reads frames. If it looks different, it might be in timecode. The way to check this or to fix this is to go up to File > Project Settings. In the very first option up here at the top is Time Display Style. By default, it's Timecode. We want to work in Frames, so if you don't see the Frames just click Frames, and then click OK. So we are looking at duration and frames, it's 200 frames, it also says 3 frames per second, and that is actually correct in this situation. The original video is shot 30 frames.
Now if this says something differently, or we are working on some different project, and you want to change its interpretation, you can, because again, image sequences do not carry a frame rate. You have to make sure that you interpret that frame rate. What you can do, though, in that situation is to go down to the footage itself, make sure it is highlighted, you can click on it if you need to, right-mouse key and go to Interpret Footage and then Main. In this Interpret Footage window, there is a Frame Rate option where you can force it to interpret the footage to a certain frame rate. For us, 30 frames per second is correct, so we are good here.
But if you need to, you can change it to something different, so I am just going to cancel out of this window. In terms of the resolution and the duration, that's correct. However, we do need to make sure that our first composition, where we are going to work in the timeline, matches that. There is a trick in After Effects for doing that, and that is to go ahead and click-drag the Footage, down to the empty timeline. We have timelines down here, but there is nothing in it. That is why we can't see anything up here in this Composition window. But if we click-drag this down into the timeline, and let go, they will appear in the timeline and what it does is it makes a brand-new composition that matches, and what's great about that trick is the composition will have the same exact resolution, and frame rate, and duration, as your footage.
There is a footage right here, and there is the composition. Now I can see that image sequence in the Composition Viewer. If you just choose a regular playback controls which are at the right here, it's not going to be real-time, it might be too slow or too fast based on your computer. What you can do, though, is use the RAM button at the very right here, RAM Preview, click that. What it does is the first time it plays back, it renders to disk, and that's why you see this green line appearing. Once the green line is there, it will play in real-time.
Now I have stopped it temporarily, but if you go back and click that button again, as it's playing, that will be real-time. We are now ready to move on and address some of the other issues in the image sequence. For one, we can remove some of the jitter by using some Stabilization tools. We are also ready to start constructing the crowd and start adding set dressing.
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