check it out

<Since the screen is in fact being scanned by the electron beam in the <monitor, the light that passes through the transparency and to the <photodetector depends on the darkness of a spot on said transparency <corresponding to where the electron beam is. As does the output of the <photodetector. Digitize that, synchronised to the scanning, and you have <a way to scan images. Flying spot scanner. Go back about 25-30 years and you could get one for test patterns for TV service, B&K was one vendor here in the us. The patterns were 35MM slides if memory serves. The box was a small CRT that was scanned at fixed bright intensity, a slide holder, lens and a phototube to translate the light to analog image stream. The same scheme would work to be viewed with a laser while viewing that with a photodiode with a lens focused to the resulting output could then be synched and broadcast or digitized. FYI this is the basic barcode scanner. The site is still a gag! Allison