Published online by Cambridge University Press: 12 April 2016
The Automated Photographic Measuring (APM) system at Cambridge was started many years ago to analyse Schmidt plates, and its progress has been reported at a number of these conferences. Only brief details of its design will be given in this paper.
The system consists of a very accurate laser-beam scanning microdensitometer connected to a series of on-line computers. The microdensitometer (Figure 1) uses a 5500 kg x-y table to position the plate. The plate transmission is digitised to 12-bit accuracy at a rate of one sample every 4 microseconds, although the image processing hardware limits this speed in practice. Special-purpose hardware exists to convert the transmission measurements into density or intensity estimates, to smooth the spot-size digitally, to measure the background and to compute image parameters.