Hi, guys,
i’m setting up my DI box, i use 4X48 850nm illuminators at the 4 corners, not directly to my screen, my screen is 10mm acrylic 640mmX480mm, and with tracing paper on it, in my setup with touchlib(beta V2.0), i could get a clearly blobs, but there is a question about blob, when my palm is near to the screen but not touching the screen, except the finger tip blob, there is another blob of the palm of the hand, please refer to the photos with different contrast and brightness, i used 2 layers of exposed film as IR filter, then i added it to 3 layers, it’s nothing help, how do you guys handle this? this problem troubled me a few days, very appreciate with your suggestions!  thanks!
and i replaced tracing paper with Rosco grey, Rosco grey didn’t get the good results as tracing paper does, but i saw someone in this forum got a very good results with Rosco grey, i’m not sure what happened, i will try different materials to see the results.
Ps, i take the picture for blob, my camera is not on the right middle of the screen, i’m testing it, so please ignore it.

Yes, I have had this hovering problem also, and it’s quite common in DI-setups, I think. Actually I still have it, but I’m going to try to solve in various ways, which you may follow in my AMIGO-thread in the future.

Looking at your pictures, I would say you have a few things you could try out already.

First, I’m pretty convinced you’ve missed the point with using photographic negatives as an IR-filter. It should be OVEREXPOSED, meaning you should’nt be able to look through it with your naked eye. It’s pretty obvious on your images, that they are not fulfilling the demands here… Basically take an image directly into a lightbulb, per instance, so the whole image get’s white, and use that negative instead. I had to use two layers. You could go for professional bandpass-filters, but I had better results with negatives. I heard some also used floppy-discs and even black plasticbags, but I doubt the results.

Second, I’m not sure your light gets diffused enough. When the IR-rays hits the diffuser, their direction should become non-linear, and less reflection would come from things above the surface, than things touching the surface. I would definitely go with the Rosco grey you have, and not count it out because of some worse results. My guess is, if it becomes worse using Rosco, the problem is elsewhere (look above!).

Third, you should rethink your config.xml. Somewhere in this forum, very hidden, I found a magic key, and I think it was Cerupcat who supplied it. Brightness/contrast is NOT suitable for DI-setups. When I heard that, I went through these forums berserka-style, and found all filters available in the config-app, what they do, when to use them etc. You should probably do the same… on a sidenote, I’m actually still using Brightness/contrast on my DI-setup, but it’s very late in the filtergraph… As I remember it, my filtergraph is like this:

CMUCapture
Smooth
Backgroundremove
Simplehighpass
Scaler
Brightness/contrast
Rectify
Smooth

Quite dirty, but it works, and I get some fine blobs, after hours of finetuning the filters - especially the Simplehighpass (better than regular Highpass, simple is often better, hehe) was a hassle to adjust. So don’t expect anything to work right away, and don’t get frustrated, get stubborn finding out why, and these forums hold all the answers, I assure you. My problem is, that the blobs looks nice in Config-app, and my hovering is down to 2 cm. above the surface, before it even considers making a visible, trackable blob. All applications disregard this though…

Fourth, and this may be a longthrow, but I had luck with finetuning the power for the IR-lights. It could be, that your IR-illuminators are too powerful, why the diffusing get’s so bad.

All in all, please use these forums more. You could have found all the answers in here already, if you bothered… if you don’t your results would probably reflect this accordingly, that’s my best advice.

thanks for your advise and sharing your experience!
i got the film from Kodak shop, i just bought a new roll film and the sales person help to pull it out from the case, let it exposed in the room under the room light, then developed for me, is this the right procedure for this? my film could look through it by my naked eyes. i will get an overexposed film and try again.
I bought some reflection materials from Camera shop, they use this to do reflection when people take the photos, like a umbrella, i cut and tape it inside my box, i don’t kown what material is. but seems like a Al foil coating on the plastic.
I will try the filter as your suggestion, hope it works for me.
thanks again, i will check your Amigo setup thread closely, hope i have some points could share with each other.

I agree with Entity. The light is definitely not getting diffused enough. Try both the Rosco Grey and the tracing paper to see the difference in diffusion. I am using frosted glass for my DI setup and with the right amount of filtering, and diffusion, you should be able to avoid most of the ‘hover’ effect.

Also xiehuangdouhua, your config.xml is set up for FTIR. You need to change to the rear illumination config.xml

My config.xml filtergraph looks like this:

Hope this helps.

xie, try 2 layers of tracing paper.

Fairlane, I tried your settings, and they are the best!

firec - 11 April 2008 04:33 AM

xie, try 2 layers of tracing paper.

Fairlane, I tried your settings, and they are the best!

Glad they worked out for you Firec. Just play around with the settings depending on the lighting environment and away you go.

Thanks, Fairlane,
I went to the Kodak Shop and asked them to give me a section of overexposed film, but i didn’t try it now, i use a floppy disc cut out put in my camera, and your filtergraph works perfect! i could use it under the light doesn’t like my FTIR prototype can not work under the light, and hovering problem seems gone! but i can’t move it under Sun light to try it now, maybe later.
but i still have a little issue with the Projector hotspot, i use a front surface mirror but it’s there when i touch my screen harder, i will try to get a IR filter for my projector.
Thanks Again!

I’m glad the FilterGraph worked for you. Play around with the settings as they are optimized for my setup and may need minor adjustments for your setup.
As for the hotspot issue, there are many threads on this forum relating to hotspots from projectors, see:

http://nuigroup.com/forums/viewthread/975/P0/

In most DI cases, if the diffuser is placed on the underside of the projected surface, then the hotspot should be eliminated. In my case, I am using frosted glass, which means the frost layer is closest to the projector and does not reflect the light coming from the projector back to the camera - problem solved.

where is your diffuser placed?

yes, i finetuned a little base on yours, but it’s really cool!
currently i’m using acrylic with tracing paper on top, my hand touched the tracing paper, i will do some test with tracing paper on the bottom, also i got a piece of frosted glass, it worked too, but the touch doesn’t feel good in my opinion, it’s a little hard compare to tracing paper or Rosco grey, it’s just my point, maybe i should test it more. did you just using frosted glass without any layer on top? i did a FTIR prototype before, and Rosco Grey + silicon rubber layer feels much better than the hard acrylic or glass.

Yeah I’m just using frosted glass with a tiny bit of glass cleaner to smooth the surface slightly. If the tracing paper is on top of your setup, then the acrylic will reflect the projector’s concentrated light, so placing the diffuser on the bottom will solve that.

Sure, i put the tracing paper under the acrylic, the projector hotspot gone, also frosted glass doesn’t reflect the projector’s light, thanks!
i compared the frosted glass to tracing paper + acrylic, my frosted glass didn’t get the very clear image as tracing paper does, the frosted surface made the image looks grainy, and tracing paper looks very natural, i’m thinking a sandwich structure, glass + tracing paper + glass or Acrylic + tracing paper + acrylic, maybe better, will update the finding soon, but i need to find some materials put on glass or acrylic could feel very comfortable when your finger on it.
what’s your suggestion? BTW, glass cleaner should be liquid, right? after volatilization just add in a little bit?

Yeah, just a little bit of ordinary glass cleaner in a can is what I’m using. I’ve heard people using oil, wax, basically anything with a tiny bit of residue or smoothing property, as long as it doesn’t leave your fingers all greasy.
I just spray a little of the cleaner on to get rid of any dust and it’s really smooth!

I got a piece of LCD protection sheet could use for touch screen, i put it on the acrylic and it does work, and the spec said it’s tough for nail scratch, the touch feeling is better than bare acrylic or frosted glass, but the only thing is how i can fix this sheet tightly with acrylic and no bubbles or wrinkle left, it’s a problem, i will try to find some way and will update.

hi xiehuangdouhua,

just wondering which country are you from?

xiehuangdouhua - 17 May 2008 12:33 AM

...how i can fix this sheet tightly with acrylic and no bubbles or wrinkle left, it’s a problem, i will try to find some way and will update.

xiehuangdouhua, use a PVA and water solution. Apply the solution to the acrylic and the back of your protection surface. Lay the protection material on to the acrylic and use a credit card or similar wrapped in a thin cloth to smooth any bubbles out, working from the middle of the screen towards the edges. If your protection material is self adhesive then obviously you won’t need the PVA but you can use the same technique with a touch of washing up liquid to get a bubble free application.

Some info here;

http://www.purlfrost.com/instructions.php

Hope this helps.

@Progen, I’m from China,
@technodai, thanks! actually i have done this step by step as your suggested, i saw someone using purlforst film and i got 1 piece from Hardware store, i will try PVA soon, the frosted film works really well, but i still wish i could use the projection film, after all it’s professional film using for projection display. thanks!