FreeTrack Forum

Hi,

I have completed a week ago my first three points cap for FreeTrack using the recommended SFH485P IR LEDs in series with a current of 20mA.

I also modded my first webcam, Envision V-CAM II, because its IR filter was too strong. For the visible light filter I use a floppy disk.  It works great and displays a solid 30fps with jitter of 7-9, 8 en average.

During testing, I noticed that if one LED is occluded then all of them would disappear in the camera Preview in some case - with all AE, WB auto modes switched off of course.  It is not happening all the time either but when it does it is a sticky behavior which does not go away.  Why is this happening in FreeTrack preview?

I will leave an update if I can reproduce this more consistently.

I noticed that the manual exposure setting is a little confusing and seems to not clearly register.  What is happening is that all three LEDs disappear if I am moving a few inches too far away from the camera (about 2-3 feet). I change the exposure and it does not make a difference, even stopping and starting the tracking/video stream between change of values.  On the other hand, putting the auto exposure back on clearly display my LED bright and clear even when much farther.
Any suggestion on how to handle the exposure issue?  (Note I also played with the FT sensitivity/threshold slider and the Force Exposure and not to avail, I loose my LED in manual exposure).
Should my LED be driven with more than 20mA?  Is the visible light filter also affecting the IR beam from these IR LEDs?

I also have a second webcam, EZonics CAM IV, which works great with its IR filter still on using the same floppy disk as visible light filter.  It displays a solid 28 to 29fps but the jitter is very high, 28!
What do I need to do to bring the jitter back to the recommended level of 10 or less?
What such high jitter is due to?

I would appreciate if anyone has suggestions regarding these three issues I encountered so far.

Many thanks in advance,
Donat

DPLUIGI @ 05/02/2008 - 04h09 a dit:

During testing, I noticed that if one LED is occluded then all of them would disappear in the camera Preview in some case - with all AE, WB auto modes switched off of course.  It is not happening all the time either but when it does it is a sticky behavior which does not go away.  Why is this happening in FreeTrack preview?

See if you can get this to happen in another webcam app besides FreeTrack.

I noticed that the manual exposure setting is a little confusing and seems to not clearly register.  What is happening is that all three LEDs disappear if I am moving a few inches too far away from the camera (about 2-3 feet). I change the exposure and it does not make a difference, even stopping and starting the tracking/video stream between change of values.  On the other hand, putting the auto exposure back on clearly display my LED bright and clear even when much farther.
Any suggestion on how to handle the exposure issue?  (Note I also played with the FT sensitivity/threshold slider and the Force Exposure and not to avail, I loose my LED in manual exposure).
Should my LED be driven with more than 20mA?  Is the visible light filter also affecting the IR beam from these IR LEDs?

Driving the leds at more than 20mA will make them brighter and the visible light filter is reducing their brightness a little but it sounds like this is of little concern because your main problem is that you don't have complete control of manual exposure. If you've exhausted the options available in your webcam software (make sure you've got the correct drivers for your webcam and the latest version) and you can't get Force Exposure to work then there isn't really much else you can do.

I also have a second webcam, EZonics CAM IV, which works great with its IR filter still on using the same floppy disk as visible light filter.  It displays a solid 28 to 29fps but the jitter is very high, 28!
What do I need to do to bring the jitter back to the recommended level of 10 or less?
What such high jitter is due to?

Don't worry too much about the jitter measurement, it may look red and alarming but it only indicates a potential reduction in tracking quality.
It seems high jitter and good tracking is quite common.

Kestrel,

I took the time to do more testing today.   It became apparent that these issues are related.  It is correct, for the Envision v-cam II I have no control of the manual exposure.  The application used to drive this webcam is AMCAP v8.12.  It has been updated to the newest drivers from envisiondisplays.com and this is not resolved.

In manual exposure the values always seems very high irregardless of the selected value so that just the three LED shines against a perfect black/Red background (in either RGB24 or I420 mode).
AS it wass described in my previous post, the problem is that no matter manual exposure value I select, they only are visible within 1 to 1 1/2 feet away form the webcam, any further they disappear.  Interestingly, under such manual exposure, if one of the three is occluded the other two disappear too - the screen goes blank/black as if no light is detected.
None of these two behavior happen in auto exposure mode, the LED can be seen from quite fare, the FT threshold slidder takes care of most of the background light to isolate the three IR LED spots and occlusion of one or more LEDs does not make the other disappear.

This weird side-effects are displayed in either FreeTrack Cam preview or AMCAP or Windows XP Explorer preview (i.e. by double-clicking on the webcam icon in My Computer folder).  So it is a problem with Freetrack but the Webcam or video capture application.


The value for the exposure runs from 0 to 255.  If I am not mistaken, 0 corresponds to the short exposure et 255 max exposure, isn't it?
Even at high value,  I do not observe more detail showing up around the LED, such as my cap and face as is displayed under auto-exposure.

Note that with auto exposure FreeTrack is reporting a frame per second of 8 no matter what video resolution I use, even with the lower ones.  It only displays 30fps for 640x480 or lower (as advertised) in manual mode.

Regarding the FreeTrack forced exposure (values between -20 to +20), -20 is the smallest values (i.e. sensor displays only the brightest details), and I would need to go towards positive values, isn't it?

"On the bright side," I used the EZ Cam IV for 2 hours solid flowlessly. even with high jitter values, just like you explained.  It also seemed to have a greater viewing angle that the Envision and it did not require the IR filter to be removed.  It tracks at 28fps which seems fine.   Also it does not display any of the problems I reported above in manual exposure settings.

I was wondering if there is a debug mode for FreeTrack to look into these issues, which would give a log of effective exposure, fps, jitter, ...., used by the active webcam during the tracking session.
It would be particularly useful since it is not clear in my case what the Envision V-CAM II is using as manual exposure value.  Also, it would be interesting to see how FT is behaving once minimized (and FPS/Jitter are not displayed) and during tracking in-situ, with an application using the tracking data derived from the webcam capture.

In conclusion the envision might be useless if I cannot resolve this manual exposure setting.

Thank you in advance for your suggestions.
Donat