How-to: Lightsaber - working with CG props

Download animation (AVI)

I wanted to have a lightsaber floating through the air.  I would then grasp it and turn it on.  This would involve designing and building the lightsaber in Lightwave.  I then had to animate it and somehow match the saber movement to my hand movement.  Matching the light would also be a topic.
 

I realized that I needed some physical object to grab and hold in the live footage.  This would make sure that my fingers and hand was in a suitable position, and it would also give me something to track.  I found a piece of a vacuum cleaner that had the right thickness.  The item was black.  I marked it with white tape and hung it vertically in two thin threads from the ceiling.

.

The saber should be flying in from the left rotating.  At some point I would make it line up with the live object, and this was when I would grab it.  When I grabbed the object, the threads would snap, and I would be able to move it.

I modeled and textured a lightsaber in Lightwave.  I made sure the diameter would match the real stand-in object.

The next task was to animate the saber.  It should have a rotating movement in the beginning of the shot.  From the point where it lined up with the stand-in, I would track it to the stand-in object.  I found that using two null objects made the tracking easier.  I made two nulls in Lightwave that I tracked to the two marks on the stand-in.  I parented the front null (NULL2) to the one nearest my hand (NULL1).  I also made the NULL2 point at NULL1.  Then I animated the two nulls so that they always were in the center of the two white markers. 

Because I had NULL2 pointing at NULL1, NULL2 actually had both movement and rotation quite right, so I was able to parent the saber to NULL2 and get a good match.  I did this parenting using the Parent plugin from the Polk collection by Worely.  This plugin let me dynamically parent the saber from the point where the tracking began leave it unparented before that time.  Then it was just a matter of animating a rotating movement up to the line-up.

The saber would be reflecting.  I built a room with walls, ceiling, floor and the end of the bookshelf and gave the surfaces the right colors so that the saber would reflect the environment.  The saber is not a mirror, so it is not necessary to build or texture this environment in any detail.

My hands needed to cast shadows on the saber.  I built some crude hands that I animated more or less the way my hands moved in the footage.  These hands were set 'Invisible to camera' so that they did not show up in the rendering, but their shadow s did.  The environment was also invisible.

 

The finished rendering looked like this.  I rendered the saber, the saber alpha channel and the shadows separately.

I then brought everything into combustion.

The tasks inside combustion would include 

• Final tracking
• Removing the stand-in object where it was visible
• Masking to make my fingers go in front of the saber in the right places

I then needed to remove the stand-in object from the beginning of the shot, before the saber covers it.  I did this by using fram 102 of the footage as a separat layer.  In this image, the stand-in has been moved from its initial position so that the background is visible.  I then made a mask so that the only visible portion of this layer was where the stand-in had been.  This image shows the effect of this layer before it was mad 'invisible' by color correcting it and feathering the mask.

The last thing to do was to mask out the saber object where my fingers should be visible.  The image below shows the first mask dealing with the tumb.  The points on the masks were animated to follow the movement of the hand during the shot.  This masking process (especially the animation bit of it) took some time to get right.

The flare from the red light was done using a flare effect in combustion which was tracked to the light on the object.