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Ben Butterworth
on Mar 7, 2008 at 4:56:06 pm

Hi, I have a high contrast black and white piece of video in which a person is dancing.

I can create an image from this in which flames appear to make up her skin (video on one layer set as stencil luma - with layer of flames underneath - however what I would really like is for the hard outline of the video to be replaced with fire - as if it was licking the person's skin - very much like they are made of fire and it is escapgin ever so slightly from the edges.

Is this possible? If so, how?


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Burt Hazard
Re: Fire!
on Mar 10, 2008 at 3:18:30 pm

I love these tough questions. :)

It is doable, but as far as I can tell you're going to have to rotoscope your dancer using a mask and then applying that mask to a fire particle emitter's Shape Source well:

Shape Source>[drag in your animated mask/matte shape]

Now according to both the Motion 2 and 3 manuals you should be able to use an image/movie clip (with or without an alpha channel) to control the Emitter, but it does seem like a broken feature in Motion, since all it ever seems to do is use the media clip's outside rectangular edge.

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Ben Butterworth
Re: Fire!
on Mar 10, 2008 at 5:38:49 pm

Hi! THis is really helpful, however not 100% certain what you mean by rotoscoping the dancer? Do you mean drawing a mask around her on every frame? Or is there an auto-tace style function for tracing and creating a mask?



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Burt Hazard
Re: Fire!
on Mar 10, 2008 at 9:03:41 pm

[Ben Butterworth] "Or is there an auto-tace style function for tracing and creating a mask? "

If only things were that easy! (Actually there are other programs that can do auto-tracing type effects; Studio Artist is one of them but the roto effects it achieves are somewhat different.)

Actually, I do roto work in both Shake and Silhouette Roto, but you can do this type of stuff in Motion as well. Like Silhouette Roto, Motion offers both Bezier and B-Splines and like both Shake and Silhouette Roto you set keyframes at certain extremes in the subject's motion and the programs "tween," or interpolate the shapes in between the keyframes. You then go back and tweak the interpolation by setting further keyframes in between the ones you've already set (mostly trying to find the halfway point, but sometimes just where the roto-shapes are the most mis-aligned). And rotoing a person, for instance, you normally break up the person into several roto shapes just because it makes it much easier. In this case you might have to just use one shape just because you're trying to make an animated shape to drop into a particle emitters' shape well.

In Motion you would achieve this by creating your initial shape, then hitting the Record button, moving forward in the timeline and using the spline-tool to move the shape's points accordingly. The keyframes will show up under "shape animation" in the Keyframe editor. When you are done you would then deactivate the record button.

An easier alternative maybe would be to duplicate your footage, use a Color Correction>Contrast filter to really boost the contrast, apply a Stylize>Edges and a Blur>Gaussian Blur to create what is know as an "edge matte," then increase the scale slightly and use that to stencil luma (or whatever) fire clips or particle emitter fire "washes" to the exterior of your dancer.

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Burt Hazard
Re: Fire! followup
on Mar 13, 2008 at 9:51:19 pm

"Or is there an auto-trace style function for tracing and creating a mask?"

Actually I discovered that there might be, at least in Motion 3. Reading the MOTION 3 SUPPLEMENTAL DOCUMENTATION they do talk about the new Track Points behavior feature (p.54, 76, & 109) in which apparently you could set an initial shape, then go to Behaviors>Shape>Track Points:

Track Points Controls
The Track Points behavior allows you to link the control points of a shape or mask
(including paint strokes) to reference features on a source clip. This behavior also allows
you to apply existing tracking data that was recorded by the Analyze Motion, Match
Move, or Stabilize tracking behaviors to the control points of a shape or mask.
Parameters in the HUD
The Track Points HUD contains controls to load an animated object or tracking behavior
into the behavior (via the Source well or the tracking behaviors pop-up menu), to
specify how the destination object moves, to start the motion analysis (the Analyze
button), to reverse the direction of the track (the Reverse checkbox), and to offset the
track (the Offset Track checkbox).


To track a shape or mask using the Track Points behavior:
1 Select the shape or mask you want to track, click the Add Behavior icon in the Toolbar,
then choose Shapes > Track Points from the pop-up menu.
The behavior is added to the shape, and trackers appear for each control point on the
shape. The trackers are ordered in the same order that the shape was drawn: Control
Point 1 is Track 1, Control Point 2 is Track 2, and so on.

I have no idea how well this might work in practise, but it is definitely something you could play around with.

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