Lux, James P skrev:
On 5/10/09 4:26 PM, "Magnus Danielson" <mag...@rubidium.dyndns.org> wrote:
Lux, James P skrev:
On 5/10/09 12:15 PM, "Brooke Clarke" <bro...@pacific.net> wrote:
Hi James:
You might want to get a KIWI-OSD, Video overlay of GPS precision time
stamp. It adds HH:MM:SS EEEE OOOO FFFFFF at the bottom of the image and
so can be seen in every field. They have also developed a way to
calibrate the camera shutter in relation to the frame time by using a
number of LEDs. The main use if for star occulation timing.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
Have Fun,
Brooke Clarke
Yes, but that requires getting access to the video stream, which isn't easy
in a "camcorder" environment. Separate video recorders actually cost more
than camcorders.
What precision of anything do you need?
Expect 50-100 ppm oscillators in there.
Yes, but probably fairly good in the short run, and if you were recording
almost any sync signal (e.g. The 1kHz sine) you could calibrate that out.
Certainly, this is what I expect.
A very simple approach is to pull the audio-track down and post-process
it with say Matlab/Octave to pull out the frequency, if it is 1 ppm low
then the sampling rate was 1 ppm high. That's about all the things you
need to know from that I think.
Recorded material is compressed. Consider how that affects your readout.
Recorded material is said progressive/interlaced. This may not reflect
how the CCD is snapshot and readout. You may not have the expected 1125
or 750 lines per frame, and exactly what frame rate do you have?
I think that's something they'll need to experiment with...
Indeed. I think a pair of (fast) diodes blinking at some adjustable rate
and some motor rotating a pointer or something at a rate of 1 or a few
turns a second should be interesting objects to test on. They should
both be able to illustrate interlaced/progressive scanning and rate of
line-scanning/snapshot. The rotating object is easier to understand for
students while the blinking diodes can require a little more involved
discussions. Maybe three or four in a row would even more illustrative
since you can make the rate such that every other should be dark if you
adjust the frequency just right.
I think grey-scale contrast should be at about the maximum for best
result, since both vertical and horizontal sub-rate sampling can exist.
Keeping the picture free of other distractions can also allow the
bit-budget to be directed to the object of interest.
For your purpose I think progressive scan would be the best, if available.
Cheers,
Magnus
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