With the advent of popular television, broadcasters realised they needed more than live programming. By turning to film-originated material, they would have access to the wealth of films made for the cinema, in addition to recorded television programming on film that could be aired at different times. However, the difference in frame rates between film (generally

A Telecine island or Film Chain
A Telecine island or Film Chain
24 frames) and television (25 frames in South Africa) meant that simply playing a film into a television camera would result in flickering when the film frame was changed in mid-field of the TV frame.

Originally, the kinescope was used to record the image off of a television display to film, synchronised to the TV scan rate. This could then be re-played directly into a video camera for re-display. Non-live programming could also be filmed using the same cameras, edited mechanically as normal, and then played back for TV. As the film was run at the same speed as the television, the flickering was eliminated. Various displays, including projectors for these "video rate films", slide projectors and movie cameras were often combined into a "Film Chain", allowing the broadcaster to cue up various forms of media and switch between them by moving a mirror or prism. Colour was supported by using a multi-tube video camera and prisms to separate the original colour signal and feed the red, green and blue to separate tubes.

However, this still left film shot at cinema rates as a problem. The obvious solution is to simply speed up the film to match the television frame rates, but

Flying Spot Telecine
Flying Spot Telecine
this, at least in the case of the American system known as NTSC, is rather obvious to the eye and ear. The problem is not difficult to fix, however; the solution being to periodically play a selected frame twice. For NTSC, the difference in frame rates can be corrected by showing every 4th frame of film twice, although this does require the sound to be handled separately to avoid "skipping" effects. A more convincing technique is to use "2:3 pulldown", which turns every other frame of the film into three fields of video, which results in a much smoother display. PAL uses a similar system, "2:2 pulldown". These projectors could be included into existing film chain systems, allowing cinematic films to be played directly to television. With the introduction of videotape into television processing in the 1950s, it became practical to record telecined movies to videotape for later playback. This eliminated the need for the special projectors and cameras in the broadcast studio.

Since that time, telecine has primarily been a film-to-videotape process, as opposed to film-to-air. Changes since the 1950s have primarily been in terms of equipment and physical formats, the basic concept remaining the same. Home videotapes of movies used this technique, and it is not uncommon to find telecined DVDs when the source was originally recorded to videotape. The same is not true for modern DVDs of cinematic movies, which are generally recorded in their original frame rate in these cases the DVD player itself applies telecining as required to match the capabilities of the television.

The most complex part of telecine is the synchronisation of the mechanical film motion and the electronic video signal. Every time the video part of the telecine samples the light electronically, the film part of the telecine must have a frame in perfect registration and ready to photograph. This is relatively easy when the film is photographed at the same frame rate as the video camera will sample, but when this is not true, a sophisticated procedure is required to change frame rate.

To avoid the synchronisation issues, higher end establishments now use a scanning system rather than just a telecine system. This allows them to scan a distinct frame of digital video for each frame of film, providing higher quality than a telecine system would be able to achieve. Normally, best results are then achieved by using a smoothing (interpolating algorithm) rather than a frame duplication algorithm (such as 3:2 pulldown, etc) to adjust for speed differences between the film and video frame rate.

In countries that use the PAL (South Africa) or SECAM (France and parts of the Soviet Union) video standards, film destined for television is photographed at 25 frames per second. The PAL video standard broadcasts at 25 frames per second, so the transfer from film to video is simple; for every film frame, one video frame is captured.

Theatrical features originally photographed at 24 frames are simply sped up by 4% to 25 frames. While this is usually not noticed in the picture it causes a slightly noticeable increase in audio pitch by about one semitone, which is sometimes corrected using a pitch shifter, though pitch shifting is a recent innovation and supersedes an alternative method of telecine for 25 frame/s formats. However, a difference between the two is rarely noticed unless the original audio is compared side by side with the pitched audio.

The pulldown process in a Telecine which is used to correct these differences in frame rates is complex and we will not get into detail here, however in the next newsletter we will progress to the Flying Spot Telecine (no - not a dog with wings!) and Charged Coupled Device (CCD) telecines and their impact on the broadcast and post production market.

Remember: Any production, be it a feature film, commercial or music video shot on film WILL go through the telecine process before it goes on air or to DVD.