[jitter] Re: Re: 2d Position Tracking in Low Light

On Sun, Apr 27, 2008 at 9:24 PM, kevin <deerwolf at gmail.com> wrote:

>
> Thanks again yair for your detailed and helpful response. I've so far
> built a small array of LEDs and attached them to the performer and done some
> tests with jitter.
>
> cv.jit.track does a pretty good job tracking the LED, but still I wonder
> if it would work better in a situation where the stage was bathed in IR
> light from a large IR source and the performer was wearing reflective tape.
> I wonder this becuase thie cv.jit.track optical flow algorithm seems to
> track SHAPES, and a single point in the dark from a few leds forms more of a
> POINT than a recognizable shape.


i use jit.cv.label > cv.jit.sort

>
> I recall your warning about CCTV type IR LED arrays often used for
> security and how they can have a too narrow angle. But then I saw this:
>
> http://www.columbussupply.com/products/?productid=669&price=1278
>
> Not cheap but claims a 360 degree IR light visible from long distance
> ($120).


if you shine a led (even a fairly cheap one, *straight into* the sensor you
will see it from a long distance, this is not true for reflective
illumination (flooding) , there are wide(er) beam ir leds

>
> My main problem though has been getting the LEDs bright enough to really
> be visible from a distance when mounted on the performer. I've tried a ping
> pong ball, but it was too opaque for my weak IR LEDs to illuminate.
>
> I am using these IR LEDs
>
>
> http://www.mouser.com/Search/ProductDetail.aspx?qs=vs%252bWWTB4QKYLfZ6uf%2fu%252b0Q%3d%3d
>
> They have a beam angle of 50 degrees (not bad) and a wavelength of 940nm.
> If anyone can recommend a brighter LED, or any techniques to improve their
> output it would be appreciated. Right now I am using 4 of them with a nine
> volt battery stepped down with a 150 ohm resistor. Not very bright at all.
>

the led you use peak at 940nm which is too high, check the sensitivity of
your camera sensor. most are more comfortable with 750-880nm wavelength.
940-950 is for remote control.
what camera\ir filter are you using?
also it claims to have a blue lens filter, am not an optical genius but
looks to me you want a clear white lens on your led.
and one good led is enough for a each pingpong ball.

http://search.ebay.com/infrared-led-pcs
http://search.ebay.com/infrared-led


> Again thanks for any help.
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