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Re: Coments re: Film Reg. (combined responses)



> > Brad Hunt wrote:
> > First off, Sony's engineers should be commended on the brilliant
> > approach they came up with for correcting image steadiness. They
> > use several small capacitance sensors in the perforation area to
> > measure the vertical and horizontal position of the perforation.
> > Since film base acts like a dielectric, the capacitance value
> > varies across the sensors as the perforations go by the sensors.
> 

To which Michael C. Kaye replied:
< snip >
> First of all, in order to provide corrections as the film is
> being scanned in continuous motion, the relative position of
> the film (or perfs) must be measured at a rate very close to
> that of the horizontal scanned image.  It must also be measured
> as continuous as possible in the longitudinal direction for
> vertical correction.  The more H & V samples, the better.
>  < snip >

	As has been stated in this thread while Michael was out of town, the
Sony telecine 
uses an intermittent-motion film transport.  The greatly simplifies the
scanning
process to determine the misregistration of the film.  The capacitive
sensors don't 
have any real 'density' in the way that a CCD array has 'density'.  The
film is 
allegedly scanned in 8 places per film frame, which would probably mean
a total 
of 16 sensors (one each for X & Y position detection for each film
performation).  
The varying proportion of air -vs- film stock within the gap of each
sensor
changes the dielectric constant of the capacitor formed by the gap,
which is easily
converted into a error signal.
	The moving glass used to reposition the image doesn't need to move very
quickly 
in this application.  During the time period in which the film is not
being scanned, the 
telecine must move the next frame into position, wait for it to settle,
detect the registration
error, and move the translation plates the proper amount to correct this
registration
error.  A 48th of a second or so should be ample time in which to
accomplish this, 
especially given the voice-coil technology currently being applied to
millions of computer
disk drives.


Hans Lehmann             | hlehmann at encorevideo.com
Encore, Hollywood        | hlehmann at pacbell.net

"Missed me by that much" - Maxwell Smart.

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