roll shots of the supporting characters in a ballroom  full of dancers were actually created using visual effects. When the  Line Producer asked the Director the minimum number of extras needed  for these shots during principal photography, the Director requested  50 extras. When only 7 extras showed up on the ballroom shoot days,  an alternate solution became necessary. The Visual Effects  Supervisor found takes which included empty sections of the  ballroom. Taking several high resolution stills from those takes, he  created 3 background plates. During a day of additional photography,  both the supporting characters who would appear in the foreground  and pairs of dancers who would appear in the middle ground were shot  against a greenscreen. The Visual Effects Supervisor then composited  up to a dozen elements to create shots which appear to contain the  bride, her bridesmaids and the young man and young woman characters  in the midst of a ballroom full of dancing couples.