On Mon, May 15, 2006 at 06:33:05PM +1000, Michael Todd wrote:
> I'm hoping that someone ot there might have already tried this sort of thing
The CCD sensor in webcams, digital cameras and video camera are (usually)
sensitive beyond the human visual range into the near-infrared. This is
an inconvenience because it can produce undesired effects in sunlit
pictures. So manufacturers usually include a filter to prevent infrared
light reaching the sensor. When Nightshot mode is selected on a Sony
video cameras this filter is mechanically moved so infrared light can
reach the sensor. Sony video cameras also include a infrared light which
is turned on in Nightshot mode
Here is an image from a webcam with the infrared filter removed and
the scene illuminated with infrared-led array:
http://www.cse.unsw.edu.au/~andrewt/kangaroo_infrared.jpg
The scene would be pitch black to a human. The kangaroo probably
can't detect the infrared illumination either. Many birds have more
elaborate color perception than us giving them a visual range extending
significantly further into the ultra-violet than ours. But what little
I've seen suggests birds can't see the infrared illumination either.
The web cam is connected to computer with software which triggers
capture of a high resolution colour image with a flash:
http://www.cse.unsw.edu.au/~andrewt/kangaroo_flash.jpg
The system is powered with solar panels (+batteries). The interesting
thing on the software side is to trigger image capture for animals and
not for moving vegetation, lighting changes, insects etc. The goal is
a system that can be left for (say) a year to capture an image of every
mammal/bird/etc that visits a location, like an arid zone waterhole
Andrew
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