Don’t know if it’s possible but here’s my idea....
It stems from that moment we’ve all had when making the MTmini and using front illumination and we’ve thought “Why don’t we use front illumination! It works great and you don’t need infra red illuminators!” of course you quickly realise that you can’t as the projector will prevent any shadows being detected. But that got me thinking, projectors run at around 60hz which is the same as 60fps (I think) and the webcam runs at a similar rate. So here’s my idea, what if you could ‘lock’ the framerate of the webcam to the same as the projector, but then desynchronise the two, so that the webcam only captured images when the projector was between frames? That way the shadows from front illumination would still be visible, and the blob data could be passed to flash etc for the next frame of the projection. No need for leds, illuminators, lasers or anything. And a set up that would actually work better in daylight!
Of course I have no idea how you would do this, and the idea may well be impossible due to some reason of which I am completely ignorant. I just thought I’d sound the experts out in case someone did. Maybe someone on NUI Group would find it a useful idea.
Your thinking is very creative, but is the light actually off during that 1/60 of a second? Even if it was, there’s still the ambient light produced even when showing black.
Your thinking is very creative, but is the light actually off during that 1/60 of a second? Even if it was, there’s still the ambient light produced even when showing black.
A very valid point, and to be honest I don’t know enough about projectors to know whether they are ‘off’ between frames or not. I imagined they worked like a slide show, just a lot faster and therefore the bits between slides/frames would be when touchlib did it’s blob detection.
Im pretty sure the ambient light from projecting ‘black’ in between frames could be overcome though, or even factored out with good old fashioned background remove!
Interesting, but I’m not sure it’d work. The ramp time of off to on and on to off for projectors (if they even have that) may still cause the camera to see some light from the projector.
BTW, there is a Front Illumination setup that DOES work with projection. If you’re in a space or room that has enough infrared light already in it, and use infrared camera like other setups, then you have a front DI setup that allows for projection.
this got me thinking - If you take a picture of a TV with a still camera and the shutter speed at about 1/300 or faster, you will have a very difficult time catching more than the first few lines of the TV drawn. The way NTSC works on a CRT actually leaves the screen black for the majority of the time.
So an easy way to test it would be to take a pictures of a projected image at high shutter speeds and see how much light is leaked. I suppose it’s possible that with a high enough shutter speed you wouldn’t need to get the frame rates out of sync. Statistically you would get a few frames here and there that were full of light, but I bet those frames could be discarded without much trouble. But of course at higher frame rates you would need more light.
I think the image might work like a slide flashing from one to the next, But the projector lamp bulb I think is always on. I believe that if the bulb flickered like the image the life on the bulbs would be cut down. I really don’t know if the bulbs are always on but thats my guess. So there would be light from the projector at all times.
Single chip DLP projectors create images by having a “chip” filled with thousands of tiny mirrors (1 per pixel on the screen) that can tilt up and down. When they tilt, they send light to the screen, when they don’t tilt, the light stays in the projector.
To display images, LCD (liquid crystal display) projectors typically send light from a Metal halide lamp through a prism that separates light to three poly silicone panels one each for the red, green, and blue components of the video signal. As polarized light passes through the panels (combination of polarizer, LCD panel and analyzer), individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.
Theoreticaly it’s a great idea and should work , but the syncing would be almost impossible , the speed is also a big problem and touchlib would have to be modified.
Haha , well inovative thinking is what drives inovation , if you have any ideas however far-fetched they may sound , post them in this forums and we’ll analyze and try to make them happen , Cheers.
Very good idea actually, and having to 60hz rates switch between two feeds may not be that difficult. I remember a few years back, when I was into VR and stereoscopy, you could get some “Shutterglasses”, that was basically a 1-bit LCD-screen in front of each eye. Sitting in front of a 50/60 hz screen, it would switch images in rate with the shutters, making each eye see different images. I think it would be possible to take a pair of shutterglasses and use each panel as a filter for the projector and the webcam.
With the projector though, it would probably need to be applied BEFORE the optics, which would likely result in void warranty and such.
If the light is actually off for that 1/60 second, I think it would be.... light is quite fast, yknow Faster than our perception, anyway.
3d shutter glasses would work perfectly for this sort of application, Snap them in half ( if you can bear to do this ) with all the wires still attached, Ventilate the one in front of the projector or else the focused beam may well melt the lcd! and put the other one in front of the camera. Obviously the hard part will be to tune the cycles as the camera will be in the region of 30fps and the projector 50/60fps but if one had the kit one could tinker to the desired results,
Let me just say that this is theory. If you base it only on lightfrequencies ie. not have a programmable sync, I think you will realize pretty soon, that if something runs 60.02 hz it would make it all useless, without an option to finetune it all. That’s the good thing with shutterglasses.
I would prefer a 60 fps camera nevertheless.
I don’t think the projector would pose a problem, as it’s lightsource is even all the time, not blinking, it’s the update from the computer that does that.
Yes, I dont think shutterglasses would work after the optics, it would need to be applied before.
Hmmm, maybe you could actually just tamper with the power-cable to the projector lamp wiring it to the shutterglasses’ on/off keeping it in total sync. Should be doable, but nothing I would try out, though… seem’s like too much work, trial’n’error wise, compared to different approaches.
, Cheers.
Faster than our perception, anyway.
