Safety in places such as football grounds and nightclubs could be improved by a people-counting thermal camera developed by a UK company called Irisys.
The high-performance sensing technology is aimed at bridging the gap between expensive, accurate and high-definition imagers used in sophisticated military applications and the simple, low-cost infrared-beam sensors used in homes and offices to trigger automatic doors and turn on lights.
The essential technical difference between these two application extremes is resolution. A military imaging system supports a resolution of more than 100 000 pixels, while the simple intruder detectors and automatic door systems are based on single-element sensors that can only register a change in radiant energy in their field of view.
The infrared integrated systems (Irisys) detector counts the number of people in the field of view irrespective of the lighting conditions. It can even find out the speed and direction in which people are moving, their sizes and how long they have been in the field of view.
The equipment has a detector array comprising 256 elements formed by a pattern of electrodes on the surface of an electronic chip. It is connected to a silicon chip that controls the output of the detector elements and allows the data to be processed.
A viewing window attached to the detector has a filter that selects the radiation wavelength that falls on the element. Because a human body radiates most intensely around 10 µ, a filter is chosen to let in this radiation to detect people.
Most importantly, the detector is accurate and only responds to changes in temperature. It can detect a temperature change of up to 0,5°C, thereby avoiding individual static objects in view known as 'scene clutter' and saving a lot of computing power compared with video-based systems.
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