The original videotape prints of 1960s-era episodes no longer exist. As a result, all later broadcasts of these episodes (PBS, Sci-Fi Channel, BBC) have used film and kinescope transfers. When these early episodes began to be issued on DVD in the early-2000s, computer technology was used to restore the video look to these episodes. In addition, other restorations and corrections to the original broadcasts were made. (For example, the sound mix is altered to remove background noise and accidental sounds like coughs in the studio, in one episode a boom shadow was digitially removed). These restorations are particularly apparent in the box sets Lost in Time and The Beginning which compile surviving episodes from the early years of the series.
