Tutorial: Page (1) of 2 - 02/09/04 Email this story to a friend. email article Print this page (Article printing at MyDmn.com).print page facebook

After Effects Spline Tricks, Part 3

Animated splines and Auto-trace By Ko Maruyama
In Spline Tricks Parts 1 and 2, we looked at an overview of Auto-trace (an easy way to create splines for masks) and how to use some of those splines as positional data. While there are some advantages to using Auto-trace in some instances, other uses may not be so "press and play." So, in this latest installment in our Spline Tricks series, we'll examine some of the obvious and not so obvious issues and explain some fixes that may help you to work around the problems.

If you haven't read the first two parts regarding Auto-trace, check out the earlier scribblings here:

Although Auto-trace can be a fun, and sometimes productive tool to use, it is still hampered by the limitations of After Effects' pixel searching and tracking abilities. I don't mean to say the tool is defective in any way, but in some cases, pixel data is too slim to define. Other times, Auto-trace cannot anticipate whether or not more pixels will be added, requiring pre-roll or post-roll spline data. Auto-trace does a pretty good job with the data it sees, creating multiple mask shapes--hundreds if necessary (I've successfully created 295 separate mask shapes on a single layer)--but it does trip and fall occasionally.

Here is are some examples of how it works well, and not so well.

Animated Auto-trace does work
The first animated clip to be traced is a 3D render that came directly out of Maxon's Cinema 4D, a simple animation with a corresponding alpha channel. The logo spins around the Y-axis in the center of frame.

In this QuickTime movie, you can see the vertices jumping around the edges of the alpha channel as After Effects creates new keyframes for the curves of the changing shape. The settings for Auto-trace are rather loose, but do an excellent job clinging to the alpha shape.

Sometimes Auto-trace doesn't work so well
However, the same is not true with our second image. This is the alpha channel from a simple 3D prerender made with Zaxwerks Invigorator Classic. Note that even in frame 1, the masks are off. This isn't a big deal, as I can go into the opacity keyframes of this mask and turn it off. However, Auto-trace doesn't handle the masks at the end of the sequence so well.

Frame 1 looks like this:

As for the animated Auto-trace at the end of the sequence, note the color of the masks. I've stroked each mask with a different color in order to make it more obvious. Auto-trace uses Difference Masks in order to calculate the cutout it renders. Regardless of the method it uses to produce the alpha, the problem it creates is the juggling of mask names. Watch how mask numbers 2, 3 and 4 flip flop at the end of the animation through frames 38-41.

This "juggling" of names, regardless of how well it produces a mask for the image, eliminates the potential of using this generated mask as a reference for a simple effect reference.

Creating a more defined Auto-trace area doesn't remedy this name jockeying. Instead, it merely produces a cleaner spline, with more vertices bouncing from object to object.

Page: 1 2 Next Page

Related Keywords:After Effects Spline Tricks, Part 3 Animated splines and Auto-trace, visual effects

Content-type: text/html  Rss  Add to Google Reader or
Homepage    Add to My AOL  Add to Excite MIX  Subscribe in
NewsGator Online 
Real-Time - what users are saying - Right Now!

Our Privacy Policy --- @ Copyright, 2015 Digital Media Online, All Rights Reserved