Automatic video comparator photogrammetry - works over very wide brightness range and produces alarm signal if image changes

摘要

The system has a first scanner (101) which scans a given area of a first image cyclically so that a scan having a given video pattern is obtained. Photocells convert each video pattern into electrical signals which are fed to a frequency-selective fitter/amplifier (103) which accentuates the components lying in an intermediate frequency band. A quantiser converts the signals from the filter/amplifier into binary reference signals representing a reference image. Output signals are then generated which represent differences between the two sets of binary signals.