Forums > MaxMSP

OT CMUcam as sensor

May 31, 2007 | 9:02 am

Has anyone gathered any experience using a CMUcam? Specifically: if used as a sensor for the production of MIDI-data, is there any hidden latency which is not documented in the pertinent documents?

For the uninitiated: the CMUcam2 claims to do frame differencing at 26fps and color tracking at up to 50fps. Both of these framerates are fine for using the CMUcam as a sensor (although the 50fps is a very promising value, even at a low resolution as a zone sensor). I am worried that there is additional latency somewhere in the design which would exceed values sufficiently low to be used for music.

Anyone know anything about this?


June 5, 2007 | 4:16 pm

Here’s a partial answer to my own question:

The CMUcam2 can track colors at 50fps (a very respectable rate, more than low enough for musical timing) if the resolution is set low enough; meaning a vertical resolution of 65 (I assume this means horizontally 85). If the thing being tracked is, say, the musician himself, then the left, top and bottom-most extensions of the person in the field of view create a rectangular area, which is what is being sent as data and discrete zones are possible only in a limited manner. Although this is not a very good resolution for MIDI, it can be interpolated with [slide] to emulate a better resolution.

Frame differencing is possible at 26fps at a resolution of 8×8.

I could not find any information leading me to believe that there is any extra latency in the system; the baud rates available are more than enough to use for a good MIDI translation.

I’ve gotten used to precise definition of discrete zones and responses using 320×240 resolution with Jitter and various motion-tracking schemes, so it seems a shame to limit the possibilities, but it would be nice to have a stand-alone vision-sensor which can send out MIDI and leave the computers to do other tasks.


June 5, 2007 | 4:28 pm

One more thing:
I now see that it IS possible to do line-mode analysis, so discrete zones CAN be set up. Interesting; this could be quite a useful device…


June 6, 2007 | 8:25 pm

dont you love when you write the whole thread yourself.

Sounds like a cool device, im gonna check it out.


June 7, 2007 | 8:25 am

Dayton schrieb:
> The CMUcam2 can track colors at 50fps (a very respectable rate, more
> than low enough for musical timing)

This is 20ms jitter, unacceptable for rhythms, but fine for controller
data…
20ms latency could be handled by a musician, but not 20ms of jitter…

Stefan


Stefan Tiedje————x——-
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