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mwilliams49
11-17-2000, 08:43 AM
Dear all,

I have attached a summary of the mail I received regarding the questions I
posted on the list about 'high speed cameras'. May I thank those who
replied, they were all a great help. For those of you who showed interest
and are in the same position as us, we, at present are still considering the
JVC 9800. However, we intend testing them ourselves with the aid of our tech
support.

Here is the summary:

Although I have no answers for you (sorry !) I would appreciate a summary of
your response, we are looking into do the same here at UL. From my
understanding Ariel offer a conversion tool to transfer the JVC output
(which is specific to that camera, I think) to a readable avi file by their
system. The rumours are Peak are working on something very similar, but
knowing Peak it will cost a couple of thousand!!

Ross

_______________________________
ROSS ANDERSON
Dept of Sport and Exercise Sciences and
Centre for Biomedical Electronics
University of Limerick
IRELAND
Tel - +353 (0) 86 6090866 or +353 (0) 61 202810
Fax - +353 (0) 61 330431
e-Mail - ross.anderson@ul.ie
WWW - www.ul.ie/~pess/staff/ross/

MORGAN WILLIAMS wrote:

>a) Is the picture quality at 200Hz suitable for accurate identification of
>reference markers, or will they appear blurred?

Depends on the shutter speed, among other things. The shutter speed could
be
anywhere from 1/200th of a second down to whatever the system will do (my
60Hz
camera will do a *shutter speed* of 1/10,000th, for example). As for
blurring,
note that faster shutter speeds require more light (or the image gets
darker),
and using high shutter speeds at ambient light levels can ultimately drive
the
depth of field down, so that if your motion of interest isn't planar,
parallel
to the image plane of the camera, you can get blurring simply because it is
not
in focus. Lastly, reference marker size matters, as does contrast: light
markers on a black background can create spread edges, decreasing precision,
while black markers on white can do the opposite.

Good luck,
Chuck Pell

>a) Is the picture quality at 200Hz suitable for accurate identification of
>reference markers, or will they appear blurred?

They will appear blurred if there is not enough ambient light. At that
frequency the spatial resolution is about 256 x256 pixels.

>b) Is the image of a stationary object stable? That is, will it have a
fixed
>pixel position throughout successive frames.

In case, the problem could be to forget disabling the image stabilizer
facility inside the camera. This could obviously cause inaccuracy in
kinematic and kinetic assessment.

>c) If two or more cameras are used can they be fired by remote and scan at
>the same time (or genlocked)

I am not aware of any syncronization device apart frorm the remote
controller. The two of those could certainly modified, or a universal
remote controlled could be modified to be simultaneously operated from the
second one.

>d) Can one video be captured by a peak motus system, and can the higher
>speed (100 or 200 Hz)images be captured in digital format?

I am designing my own motion capture software by using LabView because,
when the camera is used at 200 Hz, each frame comes out as composed by 4
smaller frames, sequentially assembled. I am not sure, but I do not think
that Peak System can work with such a composite images.
>
>e) I assume that the mini DV tape duration is sixty minutes, if recording
at
>50 Hz?

The duration of the tape is independent from the acquisition frequency. It
could seem strange, but it is explained by the fact that when you double
the frequency (100 Hz) each output frame is composed by 2 frames, and, as I
said, when you double it again (200 Hz), 4 of those compose a single output
frame.

I hope this will help.

Yours

Alberto Minetti
__________________________________________________ ____________________
| Alberto E. Minetti MD | email: a.e.minetti@mmu.ac.uk |
| | a.minetti@newscientist.net|
| Professor of Biomechanics | |
| Dept Exercise & Sport Science | teleconferencing: 149.170.138.179|
| Manchester Metropolitan University| |
| | voice: +44-161-247 5585 |
| Hassall Road, Alsager | fax: +44-161-247 6375 |
| ST7 2HL - UK | mobile: +44-788-757 3934 |
| | +39-347-365 7357 |
| |
| www.mmu.ac.uk/c-a/exspsci/research/biomex/Minetti.htm |
|_________www.mmu.ac.uk/c-a/exspsci/research/biomex/Biomech.htm________|


Dear Morgan:
You will be happy to find the resources at:

http://24.16.71.95/topics/Tutorials/capturing_with_dv/index.htm

We are using the Gait system for months with the JVC 98000 and you could not
ask for better clarity.
Gideon Ariel, Ph.D.
www.arielnet.com

I was disapponted with these cameras as the maximum shutter speed is only
1/250s which is not fast enough for most hi speed action.
Also the cameras do not perform that well in low lighting compared with
other cameras we use.
The 100 and 200Hz images are 1/2 aand 1/4 of normal size and therefore you
will also need special software to reformat these images. Ariel does have
this software.

From:Margy Galloway of reference markers, or will they appear blurred?

quality is the same as in "normal" mode, but remember that maximum shutter
speed is 1/250 !

>b) Is the image of a stationary object stable? That is, will it have a
>fixed pixel position throughout successive frames.

yes.

>c) If two or more cameras are used can they be fired by remote and scan at
>the same time (or genlocked)

no.

>d) Can one video be captured by a peak motus system, and can the higher
>speed (100 or 200 Hz)images be captured in digital format?

"normal" or "highspeed" - mode are exclusive. That means one camera is not
producing both at the same time!

>e) I assume that the mini DV tape duration is sixty minutes, if recording
>at 50 Hz?

recording time is the same in all modes since video output is always 25
frames per second (NTSC: 30)

Best regards,

Thomas Seeholzer
SIMI Reality Motion Systems GmbH
Tel: +49 89 321459-0
Fax: +49 89 321459-16
Mail: seeholzer@simi.com
Web: http://www.simi.com


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