Fast blinking LED's

[Thad House]

Originally Posted by techhelpbb

It seems highly unlikely that the LED was not fast enough.

In fact there's a trick I helped someone with where you walk into a pitch black room that stays that way but the camera sees you because it's switching on and off an LED IR light source in sync with the camera captures.

That same art display has the opposite trick. You walk into a blindingly lit room and the camera makes it look like it's night time. Not through a lense. By quickly turning off the LED lighting and snapping a frame in sync. Your eyes do not adjust quickly enough to match the very high quality camera used.

Couple of things:

1. Your camera probably has a white balance system built into it. Especially if it is a CMOS camera like a webcam.

2. How do you synchronize this because if the camera is digital there is almost always a delay that may vary for the capture and transmission of a single frame?

When you say track a change per frame can you use several LEDs?

Light them up in sequence fast enough and you should see a change every frame. Plus with several LEDs you can trick the white balance. I assume any preditable change is enough. So put several LED in a ring around the outside of the camera's field of view. Rotate around the circle lighting a single LED. You might miss a transistion or so but it will take time for the lit LED to rotate the full circle increasing the odds of you making this work. Or make a bar of LEDs and do the same. Scanning a single lit LED down the bar then starting over.

Ultimately this will likely trick a CMOS camera's white balance because with several LED you can effectively reach a nominal amount of light produced over the frame and achieved by different lit LEDs. The LEDs can change but the white balance will tend to stay more fixed which makes the camera's behavior more predicatable. In case you are, say, recognizing colors.

I can try using multiple LED's. Thats a good idea. And I was thinking as long as i made the switch happen more then the framerate, it would usually change by the time the next frame came around. One or 2 missed would not be a problem, but I think the multiple LED's would be better.