Re: software for measurements from video images?

[brian whatcott <inet@intellisys.net>]

I think Bob slipped a factor of two...

In motion picture projection, the 'frame-rate' was initially a hand-wound
16 frames per sec. Motion was jerky.
The frame rate increased to 24 frames per sec and motion was relatively
smooth, but flicker was apparent on highlighted scenes.
 The rotary shutter which occulted the film during its indexed motion
was next provided with an extra occulting sector, so that the same frame
flashed twice. Now flicker was reduced acceptably and frames were presented
at 48Hz.

 In setting TV standards it was initially thought that field
synchronization with power line frequency would minimize objectionable bars
drifting down frame.
 30 and 60 Hz appeared to be sensible rates, by comparison with motion
pictures.
A field is displayed in 1/60 sec, a frame in 1/30 sec.

Accordingly having settled on 525 lines per frame ( in the US system)
 half of them are used in each of two fields which interlace.
 Of these, 30 or 40 lines do not contribute to the visible image.
 The time allowance is 60 x 525/2 lines per second.
This contributes a characteristic line whistle at 15.75 kHz

However, because we display at these rates does not necessitate we capture
the image at the same rate: ( 1 frame = 1/30 sec, 1 field = 1/60 sec.)

 We COULD capture a frame of information in 1/1000 sec and play it onto tape
at the slower rate. That's what the manufacturer leads us to expect when he
claims this shutter speed. My references do not clearly substantiate this
view however.

Brian
(ref: Electronic Communication. Shrader, McGraw-Hill)

At 14:07 10/24/97 -0500, you wrote:
> Ludwig wrote:
> > . . .  The shutter speed was 1/1000.
> > Ludwik
>
> Each TV line takes roughly 50 microseconds,  each field about 8 ms and 
> each frame about 16 ms.  Furthermore the two fields which make up a frame 
> may be interlaced.  Given this, how does one interpret data taken 
> with a shutter speed of 1/1000 sec (1 ms)?
>
> Bob Sciamanda           sciamanda@edinboro.edu
> Dept of Physics         sciamanda@worldnet.att.net
> Edinboro Univ of PA     http://www.edinboro.edu/~sciamanda/home.html
brian whatcott <inet@intellisys.net>
Altus OK