PDA

View Full Version : Re: Camera synchronisation



tseeholzer21
07-15-2005, 01:13 AM
Dear Joanna

Consumer DV cameras (camcorders, usually connected by FireWire IEEE-1394) do
not have any documented input for synchronization (trigger). They simply
start running when they are switched on.
The best match of two or more cameras you can have is "closest frame", i.e.
the difference in time is half a field (10 ms for PAL, 8.5 ms for NTSC).

Some software packages use statistical methods to compute the time delay
between the cameras:
(1) They are watching the time information of all binary packets coming from
the cameras and determine the timing information during the video capturing
process.
or
(2) They pick a moving point (e.g. a bouncing ball), calculate the
coordinates of this point and try to find the time offset which produces the
smallest error when comparing the two trajectories. Some similar information
can also be found in:

Pourcelot et al. (2000).
A method to synchronise cameras using the direct linear transformation
technique.
Journal of Biomechanics 33, 1751-1754.

Both methods cut down the accuracy to about 1 to 3 ms.

If you want to be better than that you have to use another type of cameras.
Basler provides some models which are unexpensive and can be connected via
FireWire as well but which are not compatible to DV camcorders.
Unfortunately this is the reason why all popular video capture software
packages cannot deal with these cameras.
You will need a special software solution. We will be able to provide such a
software soon. It will be part of our new motion analysis system

www.contemplas.com?id=2

Since it is not available yet I cannot give a detailed price information but
I guess it will less than US$ 10000 for the capture software INCLUDING two
cameras. Please feel free to contact me if you have any questions.

You can also find some more information on the web:

www.highspeed-video.com

I hope this helps,

Regards,
Thomas.

Thomas Seeholzer
Contemplas GmbH
+49 (08133) 918295
seeholzer@contemplas.com
www.contemplas.com


> -----Original Message-----
> From: * Biomechanics and Movement Science listserver
> [mailto:BIOMCH-L@NIC.SURFNET.NL] On Behalf Of Joanna Kingman
> Sent: Friday, July 15, 2005 1:02 PM
> To: BIOMCH-L@NIC.SURFNET.NL
> Subject: [BIOMCH-L] Camera synchronisation
>
> We are looking to purchase some new digital cameras for the capturing
> of three-dimensional video data. We have a very limited budget.
> Please could anyone suggest the make and model of any, relatively
> cheap and commercially available, digital video cameras that
> allow the
> on-line synchronisation of frame rates using some form of physcial
> connection between the cameras. Thus allowing a number of cameras
> to be 'genlocked' together.
>
> Any help in this area would be much appreciated.
>
> Regards
> Dr Joanna Kingman
> Lecturer in Biomechanics
> Department of Sport and Exercise Science
> University of Portsmouth
> St. Michael's Building, White Swan Road,
> Portsmouth, PO1 2DT. UK.
>
> Tel: 02392 842651
> Fax: 02392 842641
> Email: Joanna.Kingman@port.ac.uk
>