Obviously Im new to this forum and learning quite a bit every day, but I need some clarification from the geniuses around here. Most of the cameras people on these forums are choosing to use on their DIY kits are fairly basic low-res webcams. Usually in the 640x480 area, typically the xbox live cam or the Fire-I cam. MY question is why are these the cams being used when logic would say they can’t provide the accuracy necessary for a usable MT display? Logic would say the camera would have to have a resolution comparable to that of the LCD panel or projector being used (baseline 800x600, 1024x768, and up.....) increasingly providing more accuracy as the cams res matched that of the display or projector. Ive seen many viedos of these DIY kits that show the inaccuracy.

Any clarification on this would be much appreciated and any information on cams or other users that have pulled this off would be much appreciated.

Hi and welcome.

I think you may be mistaking inaccuracy in videos for ‘latency’ not inaccuracy. 640 x 480 and even 320 x 240 is actually fairly accurate. More important than resolution is fps. The fps of the camera will determine much of the latency (lag that you see). Most people are using cameras with 30fps, which will lead to lag. 60fps and higher is really something that is needed for low latency. There aren’t many cameras in the 800 x 600 and 1024 x 768 range that have high frame. Ones that do have both high resolution and high framerate also carry a very high price ($500-$2000+). Matching the camera resolution to the screen resolution isn’t entirley necessary and calibration takes care of accuracy issues).

OK, I think i understand latency a little better now, as I have seen this lag in the videos, but maybe you can explain the rest as well. Doesn’t (somewhat) matching resolution between camera and display result in the camera more accuratley realizing what position were touching on the surface is referencing a particular spot on the computers UI. Ive seen this lag you mentioned, but Ive also seen people fiddling with there kits where the movements in the UI are actually several inches away from where theyre actually touching even AFTER calibration and checking for clear blobs. How is this explained?

Yes, the higher the resolution of the camera the better. 640 x 480 is really the standard of most webcams/cameras though. Going higher resolution means lots of money or very low framerate (15fps or less). I haven’t seen a real issue with accuracy. Some of the videos out there haven’t done calibration beforehand and so yes, the accuracy is going to be off. Also, if there’s lag, by the time a button or other object is shown to be pressed, the finger may no longer be on that object and therefore look like it’s inaccurate. It really comes down to calibration and with good calibration you’ll really get pretty good accuracy. As said before, accuracy isn’t as much an issue as FPS is which is why some people go as low as 320 x 240 resolution so they can get higher framerate which results in better overall performance.

Makes sense. Thanks so much, at least I wont be freaking out about this now when making all my buying decisions about cams and materials........
thanks…

As long as your blobs are bigger than only one pixel, the resolution does not matter nearly as much as one would think. Or, to make it more obvious: In a usual setup, your finger is be far bigger than one projected pixel. Now, if your images are 640x480 and your projector resolution is somewhere around the standard 1024x768, then this means that your camera is roughly as accurate as two projected pixels. That’s quite accurate even for bigger touch screens.

Wow, your right, that actually makes a ton of sense! Somehow that makes it a lot easier to understand. I guess it only makes so much of a difference.

Most standard non hd tv’s are only 720 x 576! Depending on your country of origin (Pal , NTSC, secam) they all hover around the 640 x 480 mark.  Even HD 1080p isnt really that much of a leap comparing it to your computer monitors 1280 x 1024 res! Alot of smaller projectors ie 1000 lumens have a native res of 1024 x 768 but will upscale to the standard 1280 x 1024.