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In After Effects CS5 Essential Training, author Chad Perkins discusses the basic tools, effects, and need-to-know techniques in Adobe After Effects CS5, the professional standard for motion graphics, compositing, and visual effects for video. The course provides an overview of the entire workflow, from import to export, as well as detailed coverage of each stage, including animating text and artwork, adding effects to compositions, working in 3D, and rendering and compressing footage. Exercise files are included with the course.
You may have noticed in the last movie when we imported the robot files, which we can do right now, actually. Go in the Project panel. Double-click. Go back to the robot render folder, inside of the Images folder. I believe it's called Images. And that's inside the Media folder of the Exercise Files folder. Go ahead and click on the first eddie technology Targa file with Targa Sequence checked and click Open there. You might have noticed this little dialog box, which is largely important, and what this says, this "item has an unlabeled Alpha Channel." Alpha Channels are a huge component when working with After Effects, whether you're working with motion graphics, like files brought in from Photoshop and Illustrator, or whether you are working with files brought in from a 3D program, maybe for compositing, whether you're working with green screen footage or what have you.
This is largely importantly. Basically, what an Alpha Channel is, it's a component of a file that tells it about transparency information. Now, what I'm going to do is I'm going to, in the Alpha Channel area, I'm going to click Ignore. This will basically make it as if there were no Alpha Channels, just regular old files. We're going to ignore that. Click OK. And then what I'm going to do is I'm going to drag this footage to my Composition here. Now you'll notice, if I click this Eye icon for this layer and turn this layer off and on, we could see that there was a background here, and we wanted to put our robot on top of that background. Instead, we get the robot and the black background, which we don't want.
What we really want to do is bring in this robot with the Alpha Channel, so there's transparency here, so we could see the background around the robot. There are some ways to remove this black background, but that's a huge step. It's tedious, and it doesn't always work that great, especially on footage like this that it's not intended to be used on. So, what I'm going to do is, instead of re-importing this, which is one option, what we could do is select this footage and then come down here to the bottom left-hand corner of the Project panel. And there's this little icon right here that says Interpret Footage.
So, if we click that, this gives us a bunch of options for how to interpret our footage. So, if there's problems with interlacing and some other video issues, the frame rate or whatever, we could go in here and choose to change how After Effects views this footage. In this case, we're going to change the alpha. So, by default, it's set to Ignore. We're going to change this to Straight - Unmatted. By the way, by just clicking that, you could see now that we have our robot, and our black background is gone. It is exactly what we wanted. We could also Invert the alpha, which basically makes a hole where our robot was, but we don't want that.
I'm just going to uncheck that here. You might be wondering what the difference is between Straight - Unmatted and Premultiplied. Here's the difference. It's a little complex, a little technical, but for those of you that are interested here we've go. A premultiplied Alpha Channel has semi-transparent edges. This is so if you're rendering something from one program with an Alpha Channel, and you know the background that it's going to be on, like eventually - let's say, for example, we know this guy is going to be on this bluish type gray background. So, what we could have done is if we had him on this background in a 3D program, we could have made him with a premultiplied Alpha Channel, which would put some semi-transparent edges around his edge mixed with this blue-gray color.
That would make it so that when we blend him in onto this background now, that it blends in a little bit smoother, because in reality, having a soft edge like that or a slightly soft edge like that, aids in the look of compositing. But for simplicity's sake, you might want to choose Straight - Unmatted if you have a choice. That means that everywhere where you see transparency, it's completely transparent Everywhere where you see opacity or an object, then there is a more defined line there. If from your source program, you create a Premultiplied Alpha Channel, you'll need to know what color it's matted with and choose that here.
If you're going to create Alpha Channels from Photoshop, which is another subject entirely, but if you know how to do that, you can choose Straight - Unmatted. That's the kind of Alpha Channels that Photoshop creates for you, and this file is created with a Straight - Unmatted Alpha Channel. So, there you have it. We have a nicely composited robot here because we used the Alpha Channel. It saves you a lot of headache, and it will come in handy later on when we talk about compositing.
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