[Tig] film scanning

Robert Houllahan rob at cinelab.com
Fri May 17 17:45:19 BST 2013

> some things to consider:
>          nyquist
>          the tradeoff between pixel size and light gathering, and...
>          the mechanical precision this requires to do proper hires scans, which...
>          will probably lead to the downfall of any physically "upgradeable" scanner.

There is no pixel alignment issue with a full frame area sensor and an intermittent movement, which can be physically pin registered or registered on the perforations with overscan and machine vision. The film is stationary and color is made by taking three (or four with IR) shots with the sensor but with multiple colors firing for each color. Think about the Arriscan or Lasergraphics Director both use this system instead of line array scanning.

So for example I am using a 4K 1-tap monochrome full frame sensor with 10micron pixels right now and for a color picture the machine runs at about 1 FPS. A 2K scan of S16mm is using a area of about 3100x1900 so nyquist is good. There is a new 29Mp Kodak (trusense) sensor which is available in 2-tap or 4-tap versions with a resolution of 6600x4400 which in a monochrome version will run at about 2-5 FPS depending on the window of pixels on the sensor. If we wanted to get really picky we could get a temperature stabilized CCD for astronomy with even bigger pixels and dynamic range, although I don't know about the business model of putting a $100K sensor on a MP scanner.

I personally think the only 'real' way to scan film for DI is with a full raster scan of each color, and the obvious advantage of an area sensor in an intermittent movement is that you can make as many 'strikes' of each color for HDR. The Arriscan can do 2-flash HDR and the Director does 3-Flash HDR so even the most contrasty positives and densest negatives can be scanned at full dynamic range.

There are now scanning systems being built around a telecine style transport (kinetta, flash scan, etc.) which use COTS servo components and Bayer camera systems with LED illumination and trigger for camera and illumination by perf detection. These scanners are vastly less complex than a Spirit and in the case of the Kinetta the imager is entirely interchangeable. These machines offer good quality and speed at low cost. 

I think what I have just described above is the effect of the ever progressing march of computer technology, what was once highly technical and difficult to implement is now available in a simple low cost box for a low price. Take a look at Galil servo systems, you can get a servo controller which is more sophisticated then a metaspeed in a 8" x 6" x 2" box for less than $900 now. The engineering is really in building a quality film transport, which is mechanical engineering, and then the Imager and illuminator can be modular.

Robert Houllahan
rob at cinelab.com
VP - Colorist

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