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Telecine - no drift !



In response to a couple of statements raised by Mr. Swinson, I would
like to post the following

>BTW this type of correction is identical to CCD telecinies which use a
system know as FPN ( Fixed Pattern Noise ) correction, and I can assure
you light bulbs age a lot faster and over a much greater brightness
range than CRTs.

This tends to indicate that FPN correction is to compensate for
differences in light level from the light source - almost correct - it is
actually for correcting the minute differences in light level output of the
CCD photosites, if these are not corrected then a vertical striping effect
is seen on the picture output. Although the light level of the illumination is
considered in the automatic correction the circuits used for FPN are
deriving small delta corrections for each pixel relative to the incoming
level of light independent of what that level is. 

Concerning the speed light sources age, well we are experiencing
feedback from customers who are getting between 3000 and 6000
hours of life from a single lamp on the Spirit. The Xenon lamp selected
for use in the Spirit has absolutely zero spectral drift from the day it is
switched on till the day it expires and the light level is regulated to 0.1%.

>Bear in mind that CCDs are analog detectors that do drift quite
considerably, so while the latest CCD telecinies have feedback to help
avoid the relatively large variations in their light sources, what is done
second to second or even hour to hour to remove CCD drift ? maybe
something or maybe not.

In the Spirit we actually use a optical feedback circuit which is looking at
the light level in the diffusion chamber directly beneath the film plane. We
can regulate the light level to an accuracy of 0.1%, second to second,
hour to hour, month to month, year to year or whatever - even across
lamp changes. Considering we can push approximately 300W of light
through the film, this percentage relative to this light level is invisible on
the output of the machine. When illuminated, you cannot look at the lamp
on the Spirit it hurts your eyes there is so much light, yet one can easily
look at a CRT running 300uA so I would assume the automatic light level
compensation circuits used in those scanners are far more accurate. I
do not have a figure for this.

I have a problem responding to postings such as this, which an obvious
snipe at our ( Philips ) technology. Cintel are a very well informed and
professional company and if this is really the technical level of 
knowledge they have about competitive products then I am very
surprised. We as a company will not be drawn into a public war on the
TIG over relative technologies used in this market. We both do things
differently and the products stand on their own in the market place.
Regardless of the technology, and the bits and bytes used to make the
technology work, what is of major importance is the image quality,
feature sets and benefits of our products to the end users - our
customers and their clients. We ( manufacturers ) use this forum to get
feedback from users which helps us better our products - we do not
really care about the competitors product or how they do things - our
focus is on making what we have right, so while we could post lots of
dirt on competitive technology, or pose seemingly innocent questions
appearing ignorant, we will not - it serves no purpose to the group.

Steve Russell
Marketing Manager - Film Imaging Products
Philips BTS 

++
thanks to Dave Corbitt for support of the TIG in 1997
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