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- 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
Skill Level Intermediate
We'll take a moment to talk about image sequences. Now if you have already worked with image sequences, this might be familiar information, if you haven't, this will be good to know. Now there are two ways to work with live-action footage inside compositing program like After Effects. One is to bring in a movie like a QuickTime or AVI file, and the other is to work with the image sequence. Now traditionally, Visual Effects work uses image sequences, but what is an image sequence? An image sequence is a series of still images that are numbered in such a way that they can be imported in the correct order.
Compared to a movie, a movie is a single file where all the frames are stuffed into a single file, like a QuickTime. Well, why do we use image sequences? Well, for instance, motion pictures are often shot on motion picture film. In other words features are shot on actual film. That film has to be converted to some digital format to do the effects, therefore they run through a scanner. The scanner converts individual film frames into individual still images. Another reason is because of quality.
Often if you need to work with footage, and you're using a movie, there are compression issues. For instance, a QuickTime or AVI will be compressed. Another reason is the fact that Visual Effects often involve using CG. If you render out CG from a program like Maya, you tend to pick image sequences. Now it is possible to render a QuickTime or AVI in a program like Maya. The problem is management, let's say you start to render, and you need to cancel a render. If you cancel a render, while you're rendering a movie that movie is broken, you can't use it.
However, if you break a render, and you're rendering an image sequence, the frames that rendered up to that point are perfectly fine. So let's say you render frames 1 to 100, and you cancel a render, you can then start the render later at frame 100 and go forward. So it's great for management, it's much more efficient to use an image sequence. The problems does arise with digital video, if you shoot digital video, digital video cameras store that footage as some type of movie. It might be MPEG4, it might be a QuickTime, it might be AVI, or some other formats.
If you want to use that to composite with, you have to think about whether you want to convert that into an image sequence. Now if you do, it's really not that hard, in fact, we'll demonstrate it right here in After Effects. Let's give it a try, and I have prepared a QuickTime we can use as a test, so File > Import > File, this is in the Footage folder, and it is called test.mov, for movie. This is HD, and it happens to be 72 frames long. Let's say we want to turn this into an image sequence, but only use some of the frames, we can do that.
First thing I'll do is make a new composition, Composition > New Composition, make sure they are the correct size, correct frame rate. Again, let's say we only want to export a piece of this movie, your movie might be much longer if you shoot yourself. Just for now though, I'm going to enter 48 frames for the duration. The movie is 72, but we're going to only export 48, then I'll click OK. I want to double-click the movie to take a look at it, and I will come up in the footage viewer. What you can do is find the section you want to export by using the time slider, let's say I'll look through the footage, and I want to actually start at frame 10.
I can go to frame 10 here, and click this button which is the Set IN point button that basically chops off the front, it's going to start this clip right here. Now since I want 48 frames, I'm going to go forward to frame 58, you can see the frame read out right here. Once I get to frame 58, then I can click this button, which is the Set OUT point, so this starts as a simple editing tool. Once I have that section selected, and I have my composition ready, I can click this button which, is the Overlay Edit.
That will pull this section down and place on the timeline, and there it is, there is that little section. Now I can render it. Of course, you can adjust this at this point, I can add effects to this, adjust the color and so on, but you can also just export as is. That's what I'll do here. So with this composition selected, I'm going to go to Composition > Add to Render Queue. Now once you see the Render Queue tab, there are two things you need to check before you actually render. One is the Output Module, so just click on the word Lossless.
This way you select the Format you're going to render to. Now you can't render it to a movie, in fact, this is AVI by default, or you can render to things like QuickTime or MPEG4. Now any of these options that say sequence, that's an image sequence, that will be a series of individual frames. So, for example, we can select Targa Sequence and render out a series of Targa images. Occasionally, you have to deal with the format options, but for Targa Sequence, you're basically done here. I can just go ahead and click OK. Now with the image sequence I am not worried about sound, an image sequence does not carry sound because it's a series of images.
Next thing you have to check here is the Output To, so I'm going to click the Comp 1 word right here, this is given to you by default. This way you pick where you're going to write the image sequence to, and what the name of that sequence will be. So the image sequence is generally good to put it in its own folder. Now in my case, I have a folder set up already, but you might need to make a new one yourself. Now the browser has a new folder button, and this will vary in location based on Windows versus Mac, but you can make a new folder. Once you have the new folder, try and go into that folder, then pick a name, so I am going to call mine test.
It's generally a good idea to use the same name and format, and that's name dot bracket, these pound signs bracket dot and the extension. Now these brackets and the pound signs represent the numeric placeholders, which will turn into numbering for the sequence. So what this means is bracket three pounds signs bracket is I'll have three placeholders, so it will be test.000.tga, test.001.tga, and so on. You can change the number of pound signs if you want to change the number of numeric placeholders, but in this situation, this is perfectly fine.
So once you have the name set up, click Save. So I have checked the Output Module and the Output To, I'm ready to hit the Render button at this point. So Render, render through the sequence, with this example it goes pretty fast, so now I can go outside After Effects and look at that sequence. So here is my test folder and here is the image sequence. First frame is named test.000.tga, all the way up to 47, this is the 48 frame sequence, but I started with frame 000, so therefore, it ends with 047.
Let's get back to After Effects. So at any point if we want to bring this in again, I could that. I can go back to my composition, I can go up to File > Import > File, go to that folder, for me it's on my Desktop, grab the first frame, make sure it has Sequence down here, make sure that's checked. And I'll bring in the entire sequence as a single unit, and there we go, there's our footage. So we discussed why image sequences are used in the Visual Effects industry, what their advantages are, and also how to create your own, if you have your own piece of video footage that's stored as a movie.
After Effects is not the only program you can do this in, pretty much any major compositing package has this ability to convert a movie into an image sequence. So image sequences are good to work with, and we will be working with them throughout this series of videos.