Re: Optical CRT eavesdropping from diffusely reflected light
From: Jan Panteltje (pNaonStpealmtje_at_yahoo.com)
Date: 07/12/05
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Date: Tue, 12 Jul 2005 09:49:42 GMT
On a sunny day (12 Jul 2005 08:35:36 GMT) it happened
n05W28+mgk25@cl.cam.ac.uk (Markus Kuhn) wrote in
<davvco$ro1$2@gemini.csx.cam.ac.uk>:
>Jan Panteltje <pNaonStpealmtje@yahoo.com> writes:
>|> > http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf
>|> >
>|> Is that the best picture in that pdf that you got?
>|> There is still a significant error (smear) in the LF range.
>|> Line based clamp (DC component restor) + perhaps some LF compensation
>|> would further improve things?
>|> This sort of LF error can be compensated a lot by RC filters.
>
>I use already something far more sophisticated than analog
>RC filters, namely I properly deconvolve the signal (via FFT and a
>complex division in the fourier domain) with a close model of
>the exact impulse response. Any combination of analog filters can
>only ever be a crude approximation of that.
Well, analog, I dunno.
There is no theoretical reason that I know why analog could not do
what digital can.
> There are certainly
>ways to improve the quality even further by
>
> - even more acurate modeling of the phosphor impulse response
> (I simply stopped tweaking it when I was impressed enough
> with the readability of the result);
OK, and it is impressive indeed.
> - use of a filter wheel in front of the photomultiplier, and
> modeling the phosphor impulse response for narrower bandwidths;
> this will not only give you colour information, but it will
> also take into account that the impulse response can look rather
> different at each wavelength.
Very clever, how about 3 photo multipliers with each a R, G, and B filter?
Color wheel will cause artefacts on moving pictures, we want to be able to
grab the latest and greatest -Harry Potter?-, this actually made me think
about this system in theaters, as to grab the latest release, the new
theaters use a scanning system (no longer film).
So you need 3 UHF channels to send the 3 photomultiplier channels.....
Thing could be hidden before the show, somewhere where it picks up the screen
light, maybe disguised a some thing.
Hollywood will not like this idea... Sorry ;-)
No focus needed, no pointing needed.
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