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Re: spot vs line analyser for telecine



In a message dated 97-09-07 07:16:57 EDT, JP wrote:

<< Here is something I've been wondering about during the 
 CCD line vs Flying-spot discussions on the TIG.
 
 Would it be true to say that --in theory--,
 the 'dot' illumination of flying spot analysers --which only 
 puts light onto one pixel of the film at a time-- can produce 
 cleaner images than the 'line' illumination used for CCD 
 imagers in which all the clear/transparent areas of the full
 scanned line can be detrimental (through the unavoidable parasitic 
 reflexions in the optical path) to their opaque neighbours purity?
  >>

Hi JP,

If this were so, then one would expect there to be a limiting factor beyond
which no number of additional elements in a line array CCD would make a
difference.  The outputs from more, finer elements would just blur together,
yeilding the same (or worse) results as fewer, bigger elements.  While there
probably isn't much point in making CCDs with more elements than the optics
in front of them can keep separate, it does not appear that we have reached
that limit yet.  Film scanners such as Quantel's "Domino" or the Kodak
"Cineon" have CCDs with approximately four times as many elements as those in
the FDL-60 or 90 telecines, and produce correspondingly higher resolution
outputs.

It also has to be remembered that due to phosphor persistence, the "spot" in
a flying spot telecine is really more of a streak anyway.  Some compensation
is usually made for this downstream of the sensors in the machine's
electronics to prevent  blurring the image.  But at any instant, the sensors
(which typically have some latency as well) "see" an average of light values
for whatever part of the film is being scanned -- not discrete pixels.

I think it is the other way around -- the precise arrangement of pixels in
CCDs can produce images that are "cleaner" (in the sense you use the word)
than flying spot scanners will.  The way film captures an image, however, is
not "clean."  It is random.  So, unless a CCD scanner is specially designed,
this essence of film is lost and the image ends up looking more or less like
video.   

Christopher Bacon

+++
	Thanks to Kat Dalton for support of the TIG
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