Start learning with our library of video tutorials taught by experts. Get started

After Effects Apprentice 09: Expressions
Illustration by John Hersey

Simple math


From:

After Effects Apprentice 09: Expressions

with Chris Meyer and Trish Meyer

Video: Simple math

In the previous movie, I showed you where you could accidentally screw up an expression by adding some undesired text onto the end of it. Just some garbage characters, Enter, and I get this error message. I'll undo. However, there are times when you do want to edit an expression. For example, you may want to perform some very simple math, like make something go faster, slower, bigger, or smaller. Let's start with rotation. Let's say that I want the red pulley to rotate twice as fast as the blue pulley is.

Watch this entire course now—plus get access to every course in the library. Each course includes high-quality videos taught by expert instructors.

Become a member
please wait ...
After Effects Apprentice 09: Expressions
1h 37m Intermediate Jul 27, 2011 Updated Nov 29, 2012

Viewers: in countries Watching now:

Expressions are one of the most powerful but underused features in After Effects. They can be used to animate layer properties with code, as compared to explicitly keyframing every value in the Timeline, and have multiple parameters and layers that follow the lead of a master layer or controller effect, making it much easier to coordinate complex animations and quickly accommodate client changes. In this introduction, Chris Meyer shows how to let After Effects do most of the work by creating simple but very useful expressions that can be put to work on a wide variety of jobs.

The After Effects Apprentice videos on lynda.com were created by Trish and Chris Meyer and are designed to be used on their own and as a companion to their book After Effects Apprentice. We are honored to host these tutorials in the lynda.com Online Training Library®.

Topics include:
  • Creating and managing expressions
  • Linking together different parameters
  • Randomizing a layer's movement
  • Looping an animation
  • Controlling multiple layers from a single source
Subjects:
Video Motion Graphics Visual Effects
Software:
After Effects
Authors:
Chris Meyer Trish Meyer

Simple math

In the previous movie, I showed you where you could accidentally screw up an expression by adding some undesired text onto the end of it. Just some garbage characters, Enter, and I get this error message. I'll undo. However, there are times when you do want to edit an expression. For example, you may want to perform some very simple math, like make something go faster, slower, bigger, or smaller. Let's start with rotation. Let's say that I want the red pulley to rotate twice as fast as the blue pulley is.

I will press the asterisk key to signify multiply. Yes, you kind of have to use computer math, not real calculator math here, and then 2 for times 2. Press Enter and you can already see that where the first layer is at 2.6 degrees, my expressed layer is twice of that, 5.2 degrees. I will RAM preview and now that red pulley is indeed spinning twice as fast. Let's say that instead you want the pulley to go half as fast. Well, that's simple.

Rather than asterisk, or times 2, you do a slash or divided by 2. Enter, RAM preview, and now it's doing the same animation, just only half as much. And again, you make any changes you want to the layer that you are following, the master, and the express layer will automatically be updated to follow along. Expressions are live; you don't need to copy and paste all of your changes. I will move this keyframe back later in time.

What if you want the red pulley to rotate in the opposite direction? That's simple enough. I will do *-1. Enter, RAM preview, and now you see that they are now rotating in opposite directions. So this is all very simple. You can do the same thing with the Scale property. Let's say you want the red pulley to be half of the size of blue pulley. You can do divided by 2, /2. Now it's just half the size, but otherwise performing the same animation.

Let's say instead you want it to be 90% of the size, almost as big, but not quite of the same size. Again, very simple, asterisk for times, 0.9 for 90%, and you will see where the first layer is 100%, our expressed layer is now 90%. Preview. Similar sizes but just slightly different, and it goes on and on. I have shown you multiplying and dividing. You can also do simple things like adding. For example, maybe you want the red pulley to have the same rotation, but just to be offset very slightly, say 30 degrees, so that their spokes are not exactly lined up.

Preview, same rotation, just slightly offset to create some appearance of irregularity in the animation. Now, the really nice thing about expressions is that they can be combined with keyframes or the original value applied to a layer. For example, instead of saying +30, I can say +value. Value says add this expression's contribution to whatever the underlying value or keyframed value of this layer happens to be.

I will press Enter to accept, turn off expression for a second. My Rotation value is 0 so it's not very interesting, but if I made it something like, say, 25 degrees, turn the expression on, now you see this pulley is offset by 25 degrees. The really cool thing is that this is even live. You can scrub the value. It will temporarily switch back to showing you the underlying value of this layer. Maybe I'll go negative. Release and now you will see the result of the expression, following the blue pulley, then adding the underlying value of the layer.

And the same would hold true if I was to keyframe this layer, rather than just set a constant value for it. It triggers your memory to tack on "+ value" to the end of most expressions.

Find answers to the most frequently asked questions about After Effects Apprentice 09: Expressions.


Expand all | Collapse all
please wait ...
Q: This course was updated on 11/29/2012. What changed?
A: We have added exercise files designed for After Effects CS6. We also added a movie that shows our premium subscribers how to use the exercise files.
 
Share a link to this course

What are exercise files?

Exercise files are the same files the author uses in the course. Save time by downloading the author's files instead of setting up your own files, and learn by following along with the instructor.

Can I take this course without the exercise files?

Yes! If you decide you would like the exercise files later, you can upgrade to a premium account any time.

Become a member Download sample files See plans and pricing

Please wait... please wait ...
Upgrade to get access to exercise files.

Exercise files video

How to use exercise files.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.
Upgrade now


Exercise files

Exercise files video

How to use exercise files.

For additional information on downloading and using exercise files, watch our instructional video or read the instructions in the FAQ.

This course includes free exercise files, so you can practice while you watch the course. To access all the exercise files in our library, become a Premium Member.

join now Upgrade now

Are you sure you want to mark all the videos in this course as unwatched?

This will not affect your course history, your reports, or your certificates of completion for this course.


Mark all as unwatched Cancel

Congratulations

You have completed After Effects Apprentice 09: Expressions.

Return to your organization's learning portal to continue training, or close this page.


OK
Become a member to add this course to a playlist

Join today and get unlimited access to the entire library of video courses—and create as many playlists as you like.

Get started

Already a member?

Become a member to like this course.

Join today and get unlimited access to the entire library of video courses.

Get started

Already a member?

Exercise files

Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships. Learn more

Get started

Already a Premium member?

Exercise files video

How to use exercise files.

Ask a question

Thanks for contacting us.
You’ll hear from our Customer Service team within 24 hours.

Please enter the text shown below:

The classic layout automatically defaults to the latest Flash Player.

To choose a different player, hold the cursor over your name at the top right of any lynda.com page and choose Site preferencesfrom the dropdown menu.

Continue to classic layout Stay on new layout
Exercise files

Access exercise files from a button right under the course name.

Mark videos as unwatched

Remove icons showing you already watched videos if you want to start over.

Control your viewing experience

Make the video wide, narrow, full-screen, or pop the player out of the page into its own window.

Interactive transcripts

Click on text in the transcript to jump to that spot in the video. As the video plays, the relevant spot in the transcript will be highlighted.

Are you sure you want to delete this note?

No

Notes cannot be added for locked videos.

Thanks for signing up.

We’ll send you a confirmation email shortly.


Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

Keep up with news, tips, and latest courses with emails from lynda.com.

Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

   
submit Lightbox submit clicked
Terms and conditions of use

We've updated our terms and conditions (now called terms of service).Go
Review and accept our updated terms of service.