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What are expressions?


After Effects CS5 Essential Training

with Chad Perkins

Video: What are expressions?

Expressions are just another way to control properties of layers in After Effects. Now they look like a programming language and they are kind of our programming language, but they are not that challenging. So, a lot of new users are intimidated by expressions. You need not be. So, let's go ahead and open up this Left Wheel layer properties. Go ahead and press T for Opacity. The way we set expressions is by holding down the Option key on the Mac or the Alt key on the PC when we click the stopwatch. Then we get this field that allows us to input information.
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  1. 5m 40s
    1. Introduction
      1m 30s
    2. What is After Effects?
      3m 12s
    3. How to use the exercise files
  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
    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

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Watch the Online Video Course After Effects CS5 Essential Training
8h 39m Beginner Apr 30, 2010

Viewers: in countries Watching now:

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.

Topics include:
  • Understanding the After Effects workflow
  • Precomposing footage
  • Explaining the basics and beyond of animating
  • Creating glows, patterns, textures, and more with effects
  • Color correcting footage
  • Working with text
  • Manipulating video playback speed
  • Masking objects and shape layers
  • Removing backgrounds with keying
  • Compositing multiple pieces of footage
  • Integrating After Effects with the rest of the Creative Suite
After Effects
Chad Perkins

What are expressions?

Expressions are just another way to control properties of layers in After Effects. Now they look like a programming language and they are kind of our programming language, but they are not that challenging. So, a lot of new users are intimidated by expressions. You need not be. So, let's go ahead and open up this Left Wheel layer properties. Go ahead and press T for Opacity. The way we set expressions is by holding down the Option key on the Mac or the Alt key on the PC when we click the stopwatch. Then we get this field that allows us to input information.

So, it's just looking for a number here. That's basically all expressions are. I could type in 75 and if I press Enter on the numeric keypad or simply click outside of this field to accept that value, then that's what happens. It just turns the Opacity to 75%. So, as you could see here, Opacity, the value turns red and the red indicates that the value here is being received or calculated based on the expression. So, I might say 50+20, and I click away.

And that's 70, as you could see here. It did the math for me. Your Opacity value is 70. So, really, expressions are not that challenging. Of course, they get much more robust in this and if you know JavaScript, which is kind of what expressions are based on, then you can actually do some programming here, but at their very basic level, they don't need to be that complicated. I am actually going to remove this expression by holding the Option key again, or the Alt key, and clicking the stopwatch one more time. Now, we have talked about the parent relationship. Let's say I want both of these wheels to rotate simultaneously in the same way.

Well, if we take the Right Wheel, for example, make this the child of the Left Wheel and if we select the Left Wheel and hit R for rotation, when we rotate the Left Wheel, you would think that they would both rotate in the same way. But they don't because you use the parent's Anchor Point. So if we rotate the child by itself, if I press R and rotate the child, the child still rotates on its own. But when the parent rotates, the child rotates around it, it rotates around the parent's Anchor Point. So, actually what I can do here is remove the parent relationship by going to this dropdown and choosing None, and then I am going to actually zero out these Rotation values and what we can do here is create an expression.

Now actually I am going to undo this a few time. We just notice that our Right Wheel here is up in the air. Once you take away the parent-child relationship, then you got to be careful of where you're at, at that time, because that is how the objects will stay in that condition. So, I am actually going to zero out Rotation, then remove the parenting relationship. Sorry about that. I had to undo a few times. But I want to create an expression now that will connect these, basically making it so that the Right Wheel will get its value from the Left Wheel's Rotation.

So, they are not really connected on a layer basis like parenting. Just these two properties will be connected. So, I'll go to the Right Wheel. I'll Option+Click or Alt+Click the stopwatch here for Rotation. Instead of putting in a number here manually, I'm going to take this pick whip again. I am going to click and drag to the Rotation property of the Left Wheel layer. That will basically say that in this composition there was a layer called Left Wheel and in that layer Left Wheel, there is a transform called Rotation.

So, basically make this value whatever this Rotation value is. So, I click outside of that and now if I rotate the Left Wheel, the Right Wheel goes along with it. So, if I drag out here, let's say, to 79 degrees. You'll notice as soon I let go off the mouse that the Right Wheel, its Rotation is 79 degrees as well. So, really then, instead of just typing 79, it's getting a live update from this layer's Rotation value. So, as you could see, again, expressions do not need to be overly difficult and complex to be very useful.

Let's look at another example of how we can make expressions work for us. Now we've been looking at this Bike girl throughout the entire training series and in the beginning I went ahead and did this for you. I connected her feet to these pedals using expressions, because I knew that later on, right now in the training series we'd be talking about how to do this manually. So, as you could see now the Top Pedal and the Bottom Pedal are no longer connected to the feet. So, as I move in time, there is no connection between the pedals and the feet. So, what we're going to do is we're going to connect these pedals to the feet.

Now the feet don't really have a point or anything to them, like if you have a certain layer, there is not like the back of the layer with the left side of the layer. It's just a layer. However, I did-- if we select the Biker Body layer and press U two times-- you'll see that we did add the Puppet tool to this. So, what we can do is link the position of the pedal to one of the Puppet control points and that will get us in the ballpark of having linked the pedals to the feet.

So, what I am going to do is find this point right here, which is actually Puppet Pin 1. So, if I scroll down right here, you'll see that it is now selected here in the Composition panel and also here in the Timeline panel. So, what I want to do is I want to control the Top Pedal's position by the Puppet Pin 1. So, I am going to select P for position with the Top Pedal selected. I am going to Option+Click or Alt+Click the stopwatch to get an expression and I am going to pick whip to the Puppet Pin 1 position and let go.

Now I could accept that by clicking away from the layer. And we see now that as we move in time this pedal has been connected to the foot. So, we're seeing it right below there. It's a little bit pixilated because we're zoomed in above 100%, but you can still see that there is the pedal underneath that foot. We could do the same thing with the other pedal, but the Bottom Pedal is actually connected to the Biker Right Leg. So, we can go ahead and press U to reveal all of the keyframes for the Biker Right Leg, and we might want to select one of these pins, and actually if I click this one, we could see that it's Puppet Pin 1 on the Biker Right Leg.

That's the pin we want to connect to. That's the foot pin. So, we could go to the Bottom Pedal layer. Press P for Position. Again, we'll create another expression. Alt+Click or Option+Click the Stopwatch, and then drag the pick whip to Puppet Pin 1 on the Biker Right Leg layer to that Position property and click away to accept it. And now as we move around here, we could see that our pedals are connected to the feet pretty much, and that gives you illusion that she is actually riding this bike.

We'll talk more about expressions in the next couple of movies, but basically, what I want to convey to you about expressions now in this movie are two things. Number one is that, really expressions are just trying to get to a value. They are just trying to come up with a number in a creative way. And it's basically a way to control a property of a layer. And number two, I wanted you to be able to see how to connect different properties using this pick whip.

Find answers to the most frequently asked questions about After Effects CS5 Essential Training .

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Q: In the "Creating a fireball" movie in Chapter 6, the author showed how to make a fireball. Unfortunately, it all centered around a blob layer that he made without showing how to make a blob layer. How does one go about creating a blob layer like the one used in the video?
A: To create a blob layer, make a shape layer using the Pen tool. Animate the anchor points over time to make it move. These concepts are reviewed in depth in Chapter 4, "Learning to Animate."
Q: In the Chapter 5 video "Understanding precomposing," the exercise file provided does not seem to match up with the file the instructor uses. My file does not include a "Biker Body" layer. Is there an error in the exercise file?
A: Unfortunately, the exercise file originally distributed for this chapter was incorrect. A new file was issued in February 2011. If you downloaded the exercise files prior to then, you can download the corrected file on the Exercise Files tab of the course page.
Q: How do I transition from one piece of animated type to another in After Effects?
A: There isn't an effect that can create these types of transitions. It's really a matter of animating the type and camera, using basic keyframing and positioning.
If you understand the basics of moving the anchor point of a type layer, animating the parameters of that layer (Scale, Rotation, Position, etc.) and then separately animating the camera around the type layers, you can achieve different types of transitions.  Check out the following videos for more information:

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