Re: Optical CRT eavesdropping from diffusely reflected light

From: Markus Kuhn (n05W28+mgk25_at_cl.cam.ac.uk)
Date: 07/12/05

  • Next message: Jan Panteltje: "Re: Optical CRT eavesdropping from diffusely reflected light" 
    Date: 12 Jul 2005 08:35:36 GMT

    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. 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);

      - 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.

    Markus 

    -- 
Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain
  • Next message: Jan Panteltje: "Re: Optical CRT eavesdropping from diffusely reflected light"

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