 The New York Transit Authority denied permission to film even  background shots on its property, but the filmmakers shot them  anyway. Cinematographer Gerald Hirschfeld (qv) and an assistant  rode the subway with a hidden camera, and when its sound was  noticed, they stopped and came back later to finish the job.  Hirschfeld said in an interview that he filmed in black and white in  order to get "the most realistic style of photography possible";  test shots were taken in muted color but they were deemed to  distract from the desired "somber" effect.