How to build a Multi-Touch surface

Step 4 Modify the camera

 In order to pick up infrared light the PS3 Eye camera will need to be opened up and modified.  A PS3 Eye camera is used since it is a) cheap and b) supports  a high resolution (640x480) at 60 fps.  This speed and resolution are perfect for a multi-touch surface since they provide the detail needed to pick up small blobs and the speed to make gestures appear smooth.

In order for the PS3 Eye camera to work, the IR filter needs to be removed and an IR bandpass filter needs to be put in its place.  The IR bandpass filter ensures that only the IR light with the utilized wavelength makes it into the system.  Therefore it is important that the IR bandpass filter's centering wavelength matches that of the IR LEDs present in the IR strip used for illuminating the surface.  A video guide created by Peau Productions for modifying the PS3 Eye camera can be found below.

Comments

[aismail6]

some one please respond? how manny layers of arcylic do i have to use ?

[fredbana]

three see step 5

[DHaworth]

So, I got the PS3 Eye camera and the IR filter from Peau Productions. Peau productions says the filter will rest on the camera sensor, so don't screw the screws tight, just snug.
My question is, won't this shift cause the camera to be out of focus?

[jck112]

The IR filter will refract light coming in, so in the end the image will be in focus.

[tonwac01]

can u just use any camera; like a webcam?

[jck112]

 Ya you can.  But you want to make sure you can get at least 640x320 at 30fps, otherwise the accuracy/smoothness of the touches will be less than desirable.

[technoguy94]

Couldn't you just use a Wiimote, since it already tracks up to 4 IR points?

[jck112]

(removed by author or community request)

[hovis]

Having worked with Wiimotes as IR cameras for a while, I'm pretty certain that you haven't.  I don't want to be rude, I just also don't want you to confuse people - so please allow me to clarify the points you've made and add some more useful information.

The wiimote is an active IR receiver and only works when IR light is shined directly into it.
Wrong.  The IR camera on a Wiimote will pick up any IR light source available.  Warm light-bulb reflections in glass are enough to register.

Also the wiimote's bluetooth interface will not be fast enough to get very smooth movement.
Wrong.  Having used the bluetooth connection for whiteboard and head-tracking, it is more than fast enough for real-time tracking of blobs.  (Think about it, it's more than fast enough to track the games, isn't it?)

For a table like this the contrast is not nearly enough to use a cheap receiver like a wiimote.
I think it could work, considering some of the very faint IR sources I've used in the past.  If someone in the Willamette Valley (OR) has an FTIR, I would be happy to test this with you. ([e-mail])

The real limitation for using a Wiimote as your IR camera is that the Wiimote pre-processes the blobs, and is limited to tracking 4 blobs at a time.  (The Wiimote simply passes 1-4 X,Y coordinate pairs, measuring blob strength from 1-6.  This means:
1> You'll never get more than 4 touch points.
2> You lose all ability to calibrate the camera/blobbing algorithm.
I do not recommend trying to build a table using a Wiimote camera, but if you have one lying around already, and you don't mind taking the time to hook it up (GlovePIE?), maybe you can make it work.

[jck112]

 Sorry, my previous answer failed to correctly identify the pitfalls of using a wiimote.  It has been a while since I have worked with wiimotes (since they peaked in popularity about a year or two ago).

You are right that a wiimote will work with any IR source since you can calibrate the sensor.  Also you are right that the bluetooth interface is fast enough, since the wiimote technically only has a resolution of 164x124 or 352x288.

The problem lays in this resolution.  A resolution like this is fine when you are playing a video game in 480p, but when you are trying to run a computer with 1080p resolution this is a problem.  Additionally you are touching directly on the screen, whereas in normal operation of a wiimote you are at least 8 feet away from the screen.

The PS3Eye camera, which is the same price as a wiimote, gives you 640x480 resolution at 60fps.  This speed and clarity allows for very accurate and fluid movements on your multi-touch surface.  However this resolution is still not enough for most professional systems, and many are holding our for the new point grey usb 3.0 camera which will offer 1080p at 30fps.

Again to reiterate, a wiimote could and probably would work with some tedious calibrations, but if you are already spending upwards of $2000 to build a professional quality surface (like the one detailed in this guide) then why would you skimp on the $35 camera purchase.

[isracg]

 Why do i have to modify the camera? i can see it IR light just fine.

[jck112]

 It is to block our the non IR light, that way less processing needs to be done on the image and so you get better results.  The IR bandpass filter allows only IR light through and blocks out all visible light.

[hovis]

jck112 is correct.

The goal of the bandpass filter is to only allow the correct "color" (frequency) of IR radiation (light) through to the camera's sensor.  This is especially important because we're projecting a lot of visible light at the rear projection screen, and that will totally drown out any IR touch-blobs from the FTIR (IR touch screen).

[isracg]

 Yeah, but cant i just use the negatives(iR filter) on top of the lens?? that way i get the same effect.

[jck112]

 You can use overdeveloped film negative (I believe that is what you are talking about), but they will not work nearly as well as an optical grade bandpass filter.