Telecine

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Telecine (pronounced "tel-e-Sin-ee" or "tel-e-Sin-a" as 'cine' is the same root as in 'cinema') is the process of transferring motion picture film into electronic form, or the machine used in this process. Telecine enables a motion picture, captured originally on film, to be viewed with standard video equipment, such as televisions, video cassette decks or computers. This allows producers and distributors working in film to release their products on video and allows producers to use video production equipment to complete their film projects.

[edit] Basic principle

The telecine was invented to transfer motion picture film images into video signals. In all forms of telecine, some kind of light is projected through the film (whether negative or positive image) onto some sort of pick-up device that translates the image into an electronic (or digital) video signal. This also allows the electronic (or digital) video signal to be processed and altered. See color grading for more information.

[edit] History of telecine

With the advent of popular television, broadcasters soon realized 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 before television in addition to originating television programming on film that could be aired at different times in different time zones. Broadcasters needed to find a way to transfer record a live broadcast on film to re-broadcast later. The kinescope was the early tool for this.^[1] With the advent of color television, the film-chain tool, quite literally a film projector hooked to a video camera came onto the scene. In the United States, this film-chain was a film projector attached to a video camera with three vidicon image tubes. The image from the projector was separated via prism into the three primary colors, each directed at a vidicon tube. The three signals were then recombined to form the color video image.^[2] In Great Britain, Rank Precision Industries was experimenting with the flying-spot scanner, which inverted the cathode ray tube (CRT) concept of a television screen. The CRT emits a pixel-sized electron beam, which is converted to a photon beam through the phosphors coating the envelope, which then passes through the film into a pickup device. The modern telecine was born.

[edit] Flying spot scanner

The parts of a flying-spot scanner: (A)The CRT (B)photon beam (C)&(D)dichroic mirrors (E),(F)&(G)red, green and blue photomultipliers.

In a flying-spot scanner (FSS) or CRT telecine, a pixel-sized light beam is projected through exposed and developed motion picture film (either negative or positive) at a phosphor-coated envelope. This beam of light "scans" across the film image from left to right to record the vertical frame information. Horizontal scanning of the frame was then accomplished by moving the film past the CRT beam. This beam passes through the film image, projecting it pixel-by-pixel onto the pickup (phosphor-coated envelope). The light from the CRT passes through the film and is separated by dichroic mirrors and filters into red, green and blue wavelengths. Photomultiplier tubes or avalanche photodiodes convert the light into separate red, green & blue electrical signals for further electronic processing. This can be accomplished in "real time", 24 frames a second (or in some cases faster). Rank Precision introduced the "Mark" series of FSS telecines, culminating in the MkIII.

The problem with Flying Spots was the difference in frequencies between television field rates and film frame rates. This was solved first by the Mk1 Polygonal Prism system, then the Mk II Twin Lens and finally the Mk III Hopping Patch (jump scan). The Mk III series progressed from the orignal "jump scan" interlace scan to the MK IIIB which used a progressive scan and included a digital scan converter (Digiscan) to output interlaced video. The Mk IIIC was the most popular of the series and used a next generation Digiscan plus other improvements. The Mk I was remarkable in that the film could be run at any speed, and was optically sychronised to the television frame rate by the rotating prism. That series was then replaced by the Ursa, the first in their line of telecines capable of outputting digital information in 4:2:2 color space. The Ursa Gold stepped this up to 4:4:4 and then the Ursa Diamond, which incorporated many third-party improvements on the Ursa system.^[3]

[edit] CCD

The parts of a CCD scanner: (A)Xenon bulb (B)film plane (C)&(D)prism and/or dichroic mirrors (E),(F)&(G)red, green and blue sensitive CCDs.

While Rank Precision Industries (which became Cintel International) introduced their MkIII telecine, the Robert Bosch company, which later became Philips Digital Video Systems and is now part of Thomson Grass Valley, was working on a CCD telecine, the FDL-60.

In a charge-coupled device (CCD) telecine, a "white" light is shone through the exposed film image into a prism, which separates out the image into the three primary colors, red, green and blue — each beam of colored light is then projected at a CCD (one for each color). The CCD converts the light into electrical impulses which the telecine electronics modulate into a video signal which can then be recorded onto video tape, or broadcast.

Philips eventually evolved the FDL-60 into the Spirit DataCine, which was capable of scanning the film image at resolutions up to 2K. This device opened the door to the technology of digital intermediates wherein telecine coloring tools were not just for video outputs, but could be used for high-resolution data that would later be recorded back out to film.^[3]The Spirit 4k replaces the Spirit Datacine and uses both 2K and 4k line array CCDs.

[edit] Frame rate differences

Main article: Frame rate

The most complex part of telecine is the synchronization 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.

In countries that use the PAL or SECAM 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 frame/s are simply sped up by 4% to 25 frame/s. This causes a 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 precedes an alternative method of telecine for 25 frames/s formats.

Although the 4% speed increase has been standard since the early days of PAL and SECAM television, another slightly more complex method which exploits interlacing has recently gained popularity. It involves devoting every individual frame of film to one frame (two fields) of video, except that every 12th frame of film is repeated for one additional field of video (see 2:2:2:2:2:2:2:2:2:2:2:3 pulldown below). The result is 24 frames of film fitting neatly into a full 25 frames (50 fields) of video per second, with the speed and pitch of the telecined presentation being identical to that of the original film. Undoubtedly this method was born out of a frustration with the faster, higher pitched soundtracks that traditionally accompanied films telecined for PAL and SECAM audiences. More motion pictures are beginning to be telecined this way.

In the United States and other countries that use the NTSC television standard, film is generally photographed at 24 frame/s. Color NTSC video is broadcast at 29.97 frame/s. For the film's motion to be accurately rendered on the video signal, an NTSC telecine must use a technique called the 3:2 pulldown to convert from 24 to 29.97 frame/s.

Similar techniques must be used for films shot at "silent speeds" of less than 24 frame/s, which include most silent movies themselves as well as many home movies.

[edit] Common pulldown patterns

[edit] 3:2 pulldown (technically, 2:3 pulldown)

The process of converting 24 frame/s material to 29.97 frame/s is known as 3:2 pulldown. The term "pulldown" comes from the mechanical process of "pulling" the film down to advance it from one frame to the next at a repetitive rate (nominally 24 fps). This is accomplished in two steps. The first step is to slow down the film motion by 0.1%. This speed change is unnoticeable to the viewer, and makes the film travel at 23.976 frame/s.

The second step of the 3:2 pulldown is the 3:2 (or 2:3, see below) step. At 23.976 frame/s, there are 4 frames of film for every 5 frames of NTSC video:

These four frames are "stretched" into five by exploiting the interlaced nature of NTSC video. For every NTSC frame, there are actually two complete images or "fields," one for the odd-numbered lines of the image, and one for the even-numbered lines. There are, therefore, ten fields for every 4 film frames, and the telecine alternately places one film frame across two fields, the next across three, the next across two, and so on. The cycle repeats itself completely after four film frames have been exposed, and in the telecine cycle these are called the "A," "B," "C," and "D" frames, thus:

Note that the pattern in this example is actually 2-3, 2-3. A 3-2 pattern is identical to this, only shifted by one frame. For instance, starting with film frame B, followed by frame C, yields a 3-2 pattern (B-B-B-C-C). In other words, there is no difference between the two - its only a matter of reference.

[edit] 2:2:2:2:2:2:2:2:2:2:2:3 pulldown

This pulldown method^[4] is sometimes used in order to convert 24 frame/s material to 25 frame/s. Usually, this involves a film to PAL transfer without the aforementioned 4% speedup. For film at 24 frame/s, there are 24 frames of film for every 25 frames of PAL video. In order to accommodate this mismatch in frame rate, 24 frames of film have to be distributed over 50 PAL fields. This can be accomplished by inserting a pulldown field every 12 frames, thus effectively spreading 12 frames of film over 25 fields (or "12.5 frames") of PAL video.

[edit] Telecine judder

The "3:2 pulldown" telecine process creates a slight error in the video signal compared to the original film frames that can be seen in the above image. This is one reason why NTSC films viewed on typical home equipment may not appear as smooth as when viewed in a cinema. The phenomenon is particularly apparent during slow, steady camera movements which appear slightly jerky when telecined. This process is commonly referred to as telecine judder. Reversing the 2-3 pulldown telecine is discussed below.

PAL material in which 2:2:2:2:2:2:2:2:2:2:2:3 pulldown has been applied, suffers from a similar lack of smoothness, though this effect is not usually called "telecine judder". Effectively, every 12th film frame is displayed for the duration of 3 PAL fields (60 milliseconds), whereas the other 11 frames are all displayed for the duration of 2 PAL fields (40 milliseconds). This causes a slight "hiccup" in the video about twice a second.

[edit] Reverse telecine (a.k.a. IVTC/inverse telecine)

Some DVD players, line doublers, and personal video recorders are designed to detect and remove 2-3 pulldown from interlaced video sources, thereby reconstructing the original 24 frame/s film frames. This technique is known as "reverse" or "inverse" telecine. Benefits of reverse telecine include high-quality non-interlaced display on compatible display devices and the elimination of redundant data for compression purposes.

Reverse telecine is crucial when acquiring film material into a digital non-linear editing system such as an Avid or Final Cut Pro, since these machines produce negative cut lists which refer to specific frames in the original film material. When video from a telecine is ingested into these systems, the operator usually has available a "telecine trace," in the form of a text file, which gives the correspondence between the video material and film original. Alternatively, the video transfer may include telecine sequence markers "burned in" to the video image along with other identifying information such as time code.

It is also possible, but more difficult, to perform reverse telecine without prior knowledge of where each field of video lies in the 2-3 pulldown pattern. This is the task faced by most consumer equipment such as line doublers and personal video recorders. Ideally, only a single field needs to be identified, the rest following the pattern in lock-step. However, the 2-3 pulldown pattern does not necessarily remain consistent throughout an entire program. Edits performed on film material after it undergoes 2-3 pulldown can introduce "jumps" in the pattern if care is not taken to preserve the original frame sequence (this often happens during the editing of television shows and commercials in NTSC format). Most reverse telecine algorithms attempt to follow the 2-3 pattern using image analysis techniques, e.g. by searching for repeated fields.

Algorithms that perform 2-3 pulldown removal, also usually perform the task of deinterlacing. It is possible to algorithmically determine whether video contains a 2-3 pulldown pattern or not, and selectively do either reverse telecine (in the case of film-sourced video) or deinterlacing (in the case of native video sources).

Some product sheets refer to reverse telecine as "reverse 3:2 pulldown."

[edit] Digital television, and high definition

Digital television and high definition standards provide several methods for encoding film material. 50 field/s formats such as 576i50 and 1080i50 can accommodate film content using a 4% speed-up like PAL. 59.94 field/s interlaced formats such as 480i60 and 1080i60 use the same 2-3 pulldown technique as NTSC. In 59.94 frame/s progressive formats such as 480p60 and 720p60, entire frames (rather than fields) are repeated in a 2-3 pattern, accomplishing the frame rate conversion without interlacing and its associated artifacts. Other formats such as 1080p24 can decode film material at its native rate of 24 or 23.976 frame/s.

All of these coding methods are in use to some extent. In PAL countries, 25 frame/s formats remain the norm. In NTSC countries, most digital broadcasts of 24 frame/s material, both standard and high definition, continue to use interlaced formats with 2-3 pulldown. Native 24 and 23.976 frame/s formats offer the greatest image quality and coding efficiency, and are widely used in motion picture and high definition video production. However, most consumer video devices do not support these formats.

[edit] DVDs

On DVDs, telecined material may be either hard telecined, or soft telecined. In the hard-telecined case, video is stored on the DVD at the playback framerate (29.97 frames/sec for NTSC, 25 frames/sec for PAL), using the telecined frames as shown above. In the soft-telecined case, the material is stored on the DVD at the film rate (24 or 23.976 frames/s) in the original progressive format, with special flags inserted into the MPEG-2 video stream that instruct the DVD player to repeat certain fields so as to accomplish the required pulldown during playback. Progressive scan DVD players additionally offer output at 480p by using these flags to duplicate frames rather than fields.

NTSC DVDs are often soft telecined, although lower-quality hard-telecined DVDs exist. In the case of PAL DVDs using 2:2 pulldown, the difference between soft and hard telecine vanishes, and the two may be regarded as equal. In the case of PAL DVDs using 2:3 pulldown, either soft or hard telecining may be applied.

[edit] IVTC with regard to piracy

The term telecine is sometimes used to refer to a less common form of pirated releases of films created by using a telecine machine, as opposed to recording the projected image with a video camera (the video camera method with a direct line or dts audio source is called a telesync). Since this process requires not only a print of the movie on film, which cannot be obtained legally by an individual, but also extremely expensive equipment ^{[citation needed]}, telecine-format movies are less common than cams are. The studios have integrated security features, like CAP to discourage, track and prosecute pirates.

[edit] References

1. ^ Pincus, Edward and Ascher, Steven. (1984). The Filmmaker's Handbook. Plume. p. 368-9 ISBN 0-452-25526-0
2. ^ Kallenberger, Richard H., Cvjetnicanin, George D. (1994). Film into Video: A Guide to Merging the Technologies. Focal Press. ISBN 0-240-80215-2
3. ^ ^{a b} Holben, Jay (May 1999). "From Film to Tape" American Cinematographer Magazine, pp. 108-122.
4. ^ http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-dvd-mpeg4.html

[edit] External links

• IVTC Explained (brief)
• Explanation of telecine methods
• EBU I42 2004: Telecines for broadcasters — Techical information
• The Big Picture — 3:2 Pulldown and Inverse Telecine — In-depth explanation of interlaced and progressive frames, and the telecine process
• Tutorial Regarding Methods of Inverse Telecining

Hardware Products:

• Cintel: manufacturer of CRT and CCD based telecines and scanners
• Thomson: manufacturer of CCD based telecines and scanners
• Moviestuff: manufacturer of 16mm and 8mm film telecine units for home transfers
• Motion picture film scanning system for virtual telecine
• Frame rate test video files