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Importing footage with an alpha channel

From: After Effects CS5 Essential Training

Video: Importing footage with an alpha channel

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.

Importing footage with an alpha channel

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.

Show transcript

This video is part of

Image for After Effects CS5 Essential Training
After Effects CS5 Essential Training

111 video lessons · 67458 viewers

Chad Perkins
Author

 
Expand all | Collapse all
  1. 5m 40s
    1. Introduction
      1m 30s
    2. What is After Effects?
      3m 12s
    3. How to use the exercise files
      58s
  2. 28m 14s
    1. After Effects workflow overview
      2m 18s
    2. Bringing elements into After Effects
      2m 23s
    3. Adding elements to the Timeline
      1m 57s
    4. Working with layers
      3m 45s
    5. Creating animation with presets
      3m 24s
    6. Applying effects
      3m 34s
    7. Creating animation without presets
      5m 38s
    8. Previewing your work
      2m 46s
    9. Exporting content as a movie file
      2m 29s
  3. 27m 20s
    1. Touring the interface
      6m 2s
    2. How After Effects projects work
      4m 47s
    3. What is a composition?
      4m 52s
    4. Tips for adding content to compositions
      2m 49s
    5. Understanding the properties of video
      8m 50s
  4. 57m 8s
    1. Importing an Illustrator file
      4m 57s
    2. Animation basics
      7m 12s
    3. Animating opacity
      6m 40s
    4. Understanding anchor points
      4m 57s
    5. Animating position
      6m 8s
    6. Animating rotation
      4m 41s
    7. Animating scale
      7m 19s
    8. Using the Puppet tool
      7m 13s
    9. Copying and pasting keyframes
      3m 4s
    10. Animation shortcuts
      4m 57s
  5. 9m 42s
    1. Understanding precomposing
      6m 51s
    2. Navigating through compositions quickly
      2m 51s
  6. 1h 12m
    1. A showcase of effects
      2m 34s
    2. Creating a layer for effects
      3m 1s
    3. Applying effects
      4m 54s
    4. Animating effect properties
      4m 29s
    5. Using Glow
      5m 34s
    6. Creating patterns and textures
      6m 57s
    7. Creating a fireball
      7m 9s
    8. Using the Cycore effects
      5m 58s
    9. Adding blur
      5m 45s
    10. Creating a galaxy scene from scratch
      8m 38s
    11. Distorting objects with effects
      4m 7s
    12. Creating and using lens flares
      4m 21s
    13. Creating lightning bolts
      4m 3s
    14. Viewing random variations with Brainstorm
      4m 39s
  7. 30m 52s
    1. Shortening the duration of layers
      4m 23s
    2. Trimming in the Footage panel
      4m 14s
    3. Slowing and accelerating video speed
      7m 9s
    4. Applying video transitions between clips
      6m 7s
    5. Working with image sequences
      4m 47s
    6. Importing footage with an alpha channel
      4m 12s
  8. 36m 11s
    1. Brightening dark footage
      9m 12s
    2. Changing colors in footage
      6m 34s
    3. Creating cinematic color treatments
      8m 17s
    4. Creating a quick vignette
      3m 42s
    5. Colorizing black-and-white objects
      4m 50s
    6. Using adjustment layers
      3m 36s
  9. 21m 9s
    1. Creating and editing text
      7m 39s
    2. Applying text animation presets
      4m 41s
    3. Animating text manually
      4m 43s
    4. Applying layer styles to text
      4m 6s
  10. 28m 58s
    1. Let's get better
      37s
    2. Using work areas
      3m 37s
    3. Creating markers
      6m 17s
    4. Replacing layers
      2m 35s
    5. Mastering Timeline navigation
      3m 18s
    6. Aligning and distributing layers
      3m 4s
    7. Selecting layers quickly
      1m 56s
    8. Cropping layers
      3m 43s
    9. Adjusting comp resolution
      3m 51s
  11. 23m 53s
    1. Using the paint tools
      9m 35s
    2. Using the Roto Brush tool
      9m 25s
    3. Animating growing vines
      4m 53s
  12. 40m 29s
    1. Creating and using masks
      6m 42s
    2. Exploring mask options
      7m 57s
    3. Creating masks with Auto-trace
      6m 51s
    4. Masking objects with other objects
      5m 33s
    5. Making shape layers
      3m 43s
    6. Modifying shape layers
      9m 43s
  13. 30m 44s
    1. Turning 2D layers into 3D layers
      9m 22s
    2. Creating lights and cameras
      6m 14s
    3. Creating shadows
      4m 23s
    4. Using depth of field
      4m 42s
    5. Working with 3D effects
      6m 3s
  14. 18m 10s
    1. Removing a green screen background
      4m 37s
    2. Refining the matte
      4m 48s
    3. Compositing with color adjustments
      4m 50s
    4. Compositing with blend modes
      3m 55s
  15. 25m 44s
    1. Understanding spatial interpolation
      2m 5s
    2. Creating and adjusting motion paths
      3m 55s
    3. Orienting moving objects along a path
      1m 29s
    4. Drawing motion with Motion Sketch
      2m 51s
    5. Creating pauses in animation
      3m 6s
    6. Understanding temporal interpolation
      1m 56s
    7. Easing keyframes
      5m 57s
    8. About the Graph Editor
      4m 25s
  16. 12m 13s
    1. Stabilizing shaky footage
      7m 46s
    2. Tracking the motion in footage
      4m 27s
  17. 24m 58s
    1. Setting up parent layers
      5m 49s
    2. Working with null objects
      2m 31s
    3. What are expressions?
      7m 17s
    4. Modifying simple expressions
      2m 20s
    5. Using the wiggle expression
      7m 1s
  18. 6m 52s
    1. Understanding audio in motion graphics
      1m 22s
    2. Previewing and mixing audio
      3m 55s
    3. Enhancing audio tracks with effects
      1m 35s
  19. 11m 36s
    1. Adding comps to the Render Queue
      2m 30s
    2. Exploring key Render Queue settings
      4m 11s
    3. How should I export my video?
      4m 55s
  20. 7m 16s
    1. Using Photoshop with After Effects
      2m 10s
    2. Using Illustrator with After Effects
      3m 2s
    3. Using Flash with After Effects
      2m 4s
  21. 11s
    1. Goodbye
      11s

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