"Gone Nuts 3D" Takeaway #4: Roll, Baby, Roll

4. Roll, Baby, Roll

The Day the Alignment Grid Became My New BFF

Grass is fun to roll in, but grass is not fun to roll to properly align the left and right clips of your stereosequence sequences.  Gone Nuts 3D was shot entirely outdoors, affording us a beautiful autumn film shoot.  This also meant that grass was in the background of almost every shot.  

Grass,

and more grass

    

       grass, 

I soon learned that when adjusting the degree of rotation of a video clip to align two homologous points, it helped if the video clips included strong lines and patterns.  These strong lines clearly display when two points are or are not aligned.  In contrast, grass is not a symmetrical and I could not anticipate which direction a given blade of grass should point.  This made it tough to know whether the left side and right sides of both video clips matched when one clip screened the other. 

After this project, our instructor Chris Eller introduced the alignment grid to our filming procedure.  The alignment grid is held within sight of both cameras for a few seconds after the slate.  This alignment grid provides the strong lines to align the homologous points of the left and right clips.  Example A below shows the left and right video clips screened in their stereosequence before any other alignment adjustments were made.  

Example A:
Alignment grid before adjustments

Example B:
Alignment grid after adjustments

The alignment grid introduced an easier way to align the images.  My strategy to fix roll is to adjust the rotation of one of the clips so that the diagonal lines of the alignment grid are parallel to each other.  (See Example B)  The diagonal lines of the two images may line up perfectly depending upon how you adjust the horizontal image translation (HIT).  The alignment grid is useful fixing more than just roll, but the alignment grid significantly speeds the alignment process.  Now whenever I am on a shoot, I monitor to ensure we always begin with the slate and alignment grid.  I am thankful for editing without the alignment grid because I more deeply understand and appreciate its handiness.   

LESSONS LEARNED

1.  Use an alignment chart to speed up manual stereoscopic adjustments like roll, VIT, etc.

2.  Stay current on tips from other stereographers 

3.  Take your instructors' advice.  Groups not consistently using the alignment grid regretted it!