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From: alanr@rd.bbc.co.uk (Alan Roberts)
Subject: Re: Film Media to Television Format Conversion
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Date: Fri, 12 May 1995 13:23:58 GMT
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Stephane Pigeon (pigeon@tele.ucl.ac.be) wrote:
: Hello!

: Does someone know what kind of format conversion is used when there is a need
: to display movies (24Hz-progressive) through the television (50Hz-interlaced).
: Easiest way reverts to speed up the movie to 25Hz-progressive, repeat each
: frame (->50Hz-progressive) and throw lines away (->50Hz-interlaced). Does it
: work fine? Are other techniques used in practice?

: Thank you beforehand,

: Stephane					E-mail : pigeon@tele.ucl.ac.be

That's about it.

The film travels at uniform speed through the telecine (tk) and is scanned.
Older tks use CRT scanners, the raster is half height on the CRT, the film
motion makes up the other half. Light is focussed through the film onto one
or three photomultipliers as sensors. This scan takes only 20ms. The second
field of the pair is taken in one of two ways: "twin-lens" tks focus the light
through a second lens further down the film, "jump-scan" tks move the raster
further down the CRT. Both generate the second field from the same frame, but
20ms later.

More modern tks use line-array ccds to generate the image of the entire frame
in 40ms, into a frame store. The interlaced signal is read from the frame
store by reading alternate lines. Nothing is thrown away. Filters might be
used to reduce the vertical resolution.

Scanning a film for 60Hz countries is much more interesting, I'll tell
you how if you're interested.

--
************* Alan Roberts **************
* BBC Research & Development Department *
* My views, not necessarily Auntie's    *
*    but they might be, you never know. *
*****************************************
