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Human Torch Effect in Apple Motion

Check out this Apple Motion tutorial on how to create a human torch.

In Motion, creating the base layer for a basic "Human Torch" effect from a subject shot on green screen is fairly straightforward – plus, it illustrates several core concepts of compositing.  There are a lot of steps in this tutorial, but each one calls on several principles that are useful on their own.

We go over the first parts of this tutorial in the video tutorial above -- if you're interested in using this approach to the effect, I suggest taking a look at the rest of this article for more ideas and suggestions.

In plain English, this is what needs to happen:
  1. First, we'll cut out the subject from the green screen by using a key (Primatte RT, since it's built in to Motion).
  2. Then, we'll bring some stock footage of fire into the project, and use it to make our "torched" version of the subject.
  3. Finally, we'll animate a mask to "reveal" the torched version of the subject.
Step By Step
Part 1
  1. Bring your green screen footage into your Motion project.
  2. Apply the Primatte RT key to the footage layer (Add Filter --> Keying --> Primatte RT).  Tweak the three sliders (Noise Removal, Matte Density, and Spill Suppression) until you're happy with the key.
  3. If there's extraneous material in your shot -- like the "off-set" parts of the shot I'm using -- you might want to use a Mask to exclude them from the shot now.
Part 2
  1. Bring in your layer of stock fire footage.  You can find footage like this online or in any number of stock libraries, and it's well worth having around for this and other Motion projects. 
  2. Use the keyed copy of your subject to "cut out" the fire layer, so that it takes the outline of your subject.  With the fire layer selected, select Object --> Add Image Mask, then drag the keyed copy of your subject into the "Mask Source" well in your Image Mask Inspector.
  3. To make the fire footage take on the texture of your subject, you'll probably want to use a Bump Map or Displace filter.  These two filters are both in the Distortion category of filters, and they have a similar effect: namely, they shift the pixels of the target layer depending on how bright the source layer is at that point.  In other words, they use the brightness of the source layer to create "bumps" in the target layer.  With your fire layer selected, click Add Filter --> Distortion --> Bump Map (or Displace, at your preference).
  4. Tweak the filter controls until you like the bump map that you see.
--This is where the video tutorial leaves off--

Part 3
  1. In order to have the "real" version of your subject reveal the torched version, first make sure that your layers are stacked properly.  The layer with the keyed footage should be on top of the layer with the flame footage.
  2. Now, you'll want to selectively reveal the flame layer with a Bezier mask that you animate over time.  Be sure your keyed footage layer is selected, and use the Create Bezier Mask tool to outline the subject.
  3. Click the Record Button to turn on automatic keyframing, then scrub forward and reshape the mask to reveal part of the flame layer.  Continue like this until you're happy with the reveal action.
  4. You'll probably want to use the Feather control in the Mask Inspector to make the boundary between the natural subject and the flame layer less obvious.

There are any number of ways to tweak this project to make it more realistic or more visually compelling.  Some suggestions:
  • Blend the flamey subject back with the original footage of the subject.  You might consider desaturating the natural footage of the subject, or applying some type of color remapping filter (Gradient Map?) to castthe natural footage into a flame-like range of reds/yellows/oranges/blues/blacks.
  • Attach extra "flares" of flame to the subject, perhaps at points like her hand or her shoulder.  This would likely involve either a luma key or blend mode to separate the flares' light from their dark background, and keyframing or motion trackers to attach the flares at various points on the subject's body.
  • Add a "trail" of flames as the subject moves.  This could involve many different approaches: the most Motion-specific would probably be a particle system of flames that emit from the contour of the subject.
  • Refine the edge between the natural subject and the flamed subject – perhaps to provide a bright, liquid-fire-like edge; or a to add the illusion of depth with a shadow or highlight.  This could involve making multiple copies of your flame layer and the keyframed mask that reveals the flame layer, and selectively isolating the edge of the mask using some combination of Mask Feather and Mask Blend Modes.  In a simpler approach, you might consider converting a copy of the reveal mask to a simple shape, then using the Outline controls for that shape.
  • Accentuate the subject's features by using detail layers that rely on different properties of the subject's image.  Both the Bump Map and the Displace filters rely on the subject's brightness – perhaps you could add additional layers of flamey footage, and constrain them based on utility layers like a copy of the subject with an Edge Detect filter on.

Feel free to contribute your own ideas in the comments, and remember that we lay the foundation for the techniques in this tutorial in our 2- and 3-day Motion classes!


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