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May 7, 2007

lsgl: reverse engineering perspective

by sven at 11:50 pm

click on image to play clip (298 KB)

Another shot done: discovering the intergalactic distress beacon.

This one was damned tricky. Compositing the lavamen into a shot isn't too terrible if they're only moving from right to left... But if they're walking away from you, getting them to mesh with the environment is a real bear!

Here's the strategy that ultimately worked for me:

  1. choose just one actor to focus on
  2. review the original footage of the actor in our livingroom; take measurements in the actual space and make educated guesses about how far he was from the camera when he started and stopped walking
  3. set up the virtual camera and two lavamen stand-ins in LightWave; position them according to the real-world measurements -- one lavaman for the actor's starting position, and one for his end position
  4. if the movie frame was scaled down in AfterEffects, pull the virtual camera back so its view also looks "farther away"
  5. adjust the virtual camera's height and pitch to try to match the perspective of the DV footage
  6. adjust the virtual camera's position on the Z-axis and the "lens focal length" (which compresses and expands the apparent depth of space); this is the step where you're actually trying to sync up the virtual environment with the actor's apparent depth in space
  7. continue experimenting with steps 5 and 6 until you either get the shot right or your eyes bleed

And here's another Sneaky Pete I pulled while trying to create the illusion of depth...

In the real world, things that are in the far distance begin to get hazier due to atmosphere. It's not quite the same thing -- but with that principle in mind, I had the lavamen get darker as they recede into the distance. It's subtle -- but anything that can help glue the actors into this imaginary world is worth a try.

posted by sven | May 7, 2007 11:50 PM | categories: let sleeping gods lie