70mm films on laserDisc. Part #2 |
This article first appeared in |
| Written by: Ole Alstrup | Issue 41 - October 1995 |
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Part 1 of this
article was an introduction to LaserDisc, the increasingly popular 12-inch
consumer video disc system among film collectors, which offers a wide
selection of the great 70mm screen epics in the superior picture and audio
quality, transferred from original archive elements in widescreen aspect
ratio, thereby preserving the original cinematography. This Part 2 is an
attempt to explain basics of film-to-video transfers, a delicate process
which is unknown to most of those who collect films on video, often regarded
as mysterious or unimportant. Part 3, published in a future issue, will deal specifically about technology that have made it possible to transfer directly from 65mm or 70mm film elements, surpassing the best quality of the conventional 35mm transfers. |
Further in 70mm reading:
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Film and video |
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Before we take a look at how the technology of the film transfers have
evolved over the years, it is very important also to define the different
kinds of laboratory pre-print film elements that is used to make the final
release prints used in theatres, whether they are 35mm or 70mm, as these
elements used for state-of-the-art video transfers. In general, most prints shown in cinemas are fourth generation copies. The first generation is the original camera negative (OCN), assembled or cut together from all the different rolls of film negatives used in the camera to shoot a film. The second generation is a positive protection copy, made on extremely fine grain film stock, directly from the OCN. The copy is called the interpositive (IP). From this element a dupe negative is struck, usually referred to as an internegative (IN). In internegative is most always used to make the release prints. Shown in theatres, prints can have excellent quality, being bright and sharp with clear and vivid colors. However, when transferred and viewed on a video monitor, a print often appear bloated and grainy with poor colour fidelity. The reason is that prints have a contrast range of more than 100:1, while the contrast range of video is only 20:1, because the light output of the phosphors used in picture tubes is limited coupled with other inherent electronic design deficiencies. It is possible to electrically adjust the detail and contrast range, but it often increases the noise in the picture, making prints unsuitable for ideal transfers. |
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Film chains and Flying-Spot Scanners |
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In the early days of broadcasting, most TV-stations transmitted films using
a somewhat crude devise known as a film chain. A film chain is actually
nothing more but a video camera locked together with a film projector. As
the colour camera is equipped with three pick-up tubes, one each in red,
green and blue, it is combined with an optical system using filters or
prisms to separate each colour from the displayed film colour image. There
have always been a variety of problems with film chains considerable
degrading the overall picture quality. Without going into details, the
problems were as follows: Lack of sharpness and colour straying because of
poor combined registration of the tubes always being in need of adjustment.
Shading errors and image smearing in dark scenes thanks to the aging
characteristics of light bulbs and camera tubes. These things basically
meant poor quality, but still the average cost for a film chain was well
over $100.000 for a basic 16mm/35mm set-up. When home video made its debut in the late 1970s, films were usually being transferred on broadcast-grade films chains from mediocre 16mm or 35mm prints. Many collectors than naively expected that the quality on pre-recorded cassettes would be better than a battered print shown on late night television. It was not until 1980 that the TV/video industry widely began using a revolutionary new device for improved film transfers; the Flying-Spot scanner, also known generically as a telecine. The telecine had actually been around since the late 1930s in various incarnations, but had not worked properly until Rank-Cintel, a division of the British Arthur J. Rank organization, developed and perfected the technology for industrial and commercial applications. Instead of a light bulb with somewhat uneven distribution, the telecine uses a high-resolution picture tube as the light source for the film, with each particle of phosphor illuminating a single area of the film through a cathode light beam that scans rapidly back and forth through the film in an interlaced manner. Dichric mirrors than splits the picture into RGB components fed into pick-ups called photo multipliers. The signals are then amplified and processed separately, then finally translated into a conventional PAL or NTSC composite video picture. This process allows the telecine operator to analyze and break down the individual scenes for adjustment in colour, contrast and brightness. Even individual color spectrums can be enhanced without affecting the rest of the picture. In fact, flying spot scanners do not have any of the problems described earlier as the film chains. Film transport on telecines is equally sophisticated, using smooth rubber capstan rollers, gently pulling the film through the gate when it is scanned. This reduces the risk of film damage compared to film chains with ordinary projector mechanisms. The best transports deliver rock-steady pictures, thanks to "Real-Time-Pin-Registered" precision gates, designed to almost eliminate all horizontal and vertical weave in the film element. The gradual success of the Rank-Cintel flying spot telecine has caused a revolution in the broadcast/video industry, providing superior pictures in all aspects. Over the years, image quality have steadily been improved, almost to the point of perfection, thanks to the introduction of digital signal processing. This includes special noise reducers, which can digitally remove film grain inherent in dark or poorly-exposed scenes or eliminate film dirt and other flaws in the celluloid. Such full-blown telecine systems with top colour-correction computer and additional gadgets is as of early 1995 prized at around $1.000.000 and requires constant maintenance by highly specialized personnel. The only consumer medium where this transfer quality really can be appreciated is LaserDisc, where the quality is almost as good as the professional digital master tape from which it is sourced. The film studios today acknowledges this fact and many transfers are done especially for LaserDisc (ie. letterbox transfers) to ensure the highest possible standard. This has also benefited the quality of films being broadcasted on many TV-stations plus VHS cassette releases, as the same transfers in Pan/Scan versions are distributed worldwide on various videotape formats. |
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Film Elements and Video Transfers |
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No matter what kind of device is used for transfers, the single most
important aspect of the final transfers quality is the film element itself.
Since normal prints are regarded as unsuitable, as discussed earlier, a
laboratory pre-print or specially processed film element is used instead.
The great thing about flying spot telecines is their ability to revert the
image polarity of film, which means that transfers directly from negatives
are possible. Ideally, one would therefore think that either the original
camera negative (OCN) or a duplicate internegative (IN) was best suited for
video transfer. However, transfer from negatives are often problematic because
of physical editing splices (OCNs) or small holes that are cut into the
edges of the negative (INs) in order to trigger the colour settings when
making a colour timed print from the negatives at the laboratory. These can cause frequent bumps and other instabilities when running the negative through the gate of the telecine. Another problem is noise in the highlight of the the picture, as these represents the darkest parts of the negative when inverted by the video processing circuits in the Rank. With careful attention and thorough scene-to-scene colour correction by an experienced telecine operator, these problems can be overcome and the transfer quality from a negative can be quite stunning with a "sheen" look unmatched by any other element. However, almost all feature film transfers today are made from interpositives (IP). As IPs are based on a yellow-masked negative stock, they can at times be difficult to transfer since they have virtually no contrast and poses an inherent yellow coloration. With careful adjustment of the contras to a normal level and enough blue colour added to compensate for the yellow characteristic, most video engineers, studios and transfer supervisors agree that IPs make the best overall film-to-video transfers. Some studios prefer to use a special low-contrast print film (lo-con), made directly from the camera negative. Some say that lo-cons more closely resemble the look of a print seen in a theatre, but generally IPs are considered to have more transfer detail. Although well-timed prints are easier and faster to transfer, the extra step of making a print is apx. $5000. This effectively adds to the cost of a usual transfer, normally about $10.000 for a two hour "A" title feature, which takes about 25 hours to do. Additional letterbox transfers cost $3000 and only 8 hours to do, since no time consuming panning-and- scanning are required, plus the fact that all previous scene- to-scene colour correction settings etc. have already been stored in the computer system. |
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