Film scanner

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A film scanner ( FAT for short ; also called film transmitter or telecine ) is a device in television technology that reads cinema films and other film material and uses them to generate an - analog or digital - video signal.

Other uses are


At the radio exhibition in Berlin in 1938, the television company showed a mechanical universal scanner for 441 lines in the interlaced process . He worked with a Nipkow disk that ran in a vacuum and rotated at 10500 rpm.

The next step in development were the camera scanners or storage tube scanners , in which the film images were projected directly into a television camera via a projector. This procedure is no longer used in the professional sector.

The next generation, the flying spot scanner , a development by the BBC , had a picture tube on which a point of light moved in the television grid. This point of light shone through the film image and was directed onto one or, in the case of color scanning, onto three photocells . There, line by line, an image of the brightness and color information of the film image was created. In the further electronic processing, the desired video signal was created at the output. The advantage of this method is that a still image can also be scanned.

When CCD sensors became available at the end of the 1970s , the FDL 60 from Fernseh GmbH (Fese) was the first CCD film scanner . The principle differs fundamentally from the light point or flying spot method mentioned above. CCD scanners use a halogen lamp (3200 K) as the light source. The light shines on the film image through a slit optic. One or more CCD lines with a resolution of up to 4000 pixels serve as the receiver. The electronic image of the line is digitally processed and is available at the telecine output as an analog video or digital data signal. This process can be compared with a flatbed scanner, in which, however, it is not the scanning head that moves, but the original.

In addition to the line scanner , which scans the film line by line, there are also cheaper area scanners that record all of the film images at once.

PAL speedup and 3: 2 pulldown

If the sampled signal is to be output on a conventional interlaced television, different processes are used depending on the television standard .

For PAL , which works with 50 fields per second, the scanned signal is initially accelerated from 24 to 25 frames per second. The picture appears as calm as in the screen version. For the interlace method, all lines of an image must be divided into even and odd lines, each of which results in a field. The correspondingly accelerated audio signal sounds about a semitone higher. However, the playing time of the material is reduced to 96 percent.

With NTSC you would have to play the film 25 percent faster (approx. 30 frames per second), which would be very noticeable. Instead, 4 images are converted into 5 images using a telecine process called 3: 2 pull-down . Telecine entails various technical difficulties if it has to be reversed using inverse telecine for recording or playback on a non-standard tube television set (LCD, plasma, 100 Hz tube, etc.).


A relevant parameter for the quality during scanning / exposure (FAZ - film recording ) is the resolution . The necessary resolution is determined by:

  • Spatial resolution with the help of a model : The MTF is the measure of how many sine functions can be recorded per mm
  • photochemical principles : A film grain has a diameter of approx. 16 µm for some types of film. If the pixel size is set to half the size, a resolution of 2750 × 2000 pixels is calculated for a 35 mm film (22 × 16 mm). However, some types of film have a much finer grain. B. Black and white films with a film grain diameter of only 0.2 µm - 2 µm.
  • Re-exposure test : very good film material is scanned in different resolutions, exposed again and compared with the original material.

These tests are mostly carried out in the Academy format , i. H. 1.37: 1 aspect ratio (approximately 4: 3 TV format) on 35mm film material. In general, a resolution of 2k (2048 × 1556 pixels) is used, which usually achieves a sufficient result.

The improvements that can be achieved with 4k and 6k (5485 × 3996) can only be seen as differences to 2k for more experienced eyes, but open up better reserves for post-processing. In the private entertainment sector, 1920 × 1080 pixels are typically used.

As the resolution of the image increases, the time required for the scanning process increases.

Therefore, most of the scans are done in 2K or HD resolution. 4K resolutions are often used in complex visual effects shots, such as B. Green or blue screen recordings are used to edit even finer images in compositing .

A secondary parameter is color resolution . In order to avoid artifacts in color gradients, typically 10, sometimes 12-16 bits per color channel are scanned.

Use in post-processing

After scanning, the image information is available as a digital data record on a storage medium. The data volume is up to 50 megabytes per image. This digital material is used in post production. The material is then converted into a digital master in accordance with DCI or re- exposed on 35 mm film for mechanical theatrical performance . The use of telecine scanners is common today with any material shot on film. The process is also used for film restoration .

However, the material is only exposed again if it is to be shown in the cinema, i.e. mainly feature films. In the past, advertising was always exposed again after editing, but the big cinema chains nowadays already use digital projectors for advertising or the main film. This approach enables better quality, as the digitally listed works no longer wear out, and the production companies save time and money, since no more film material has to be paid for for printing and the finished film is available more quickly.

More pictures

See also

Web links

Individual evidence

  1. Kurt Thön: Mechanical universal scanner for people, film and slide transfers . In: In- house communications from research and operations at the television company . Issue 2/1938 ( digitized version )