Hi,
Thanks for the discussion so far about the problems I was having
digitising off of a videotape. We were pretty careful about the
setup of the system: a Panasonic industrial VHS VCR with a 2-metre
cable connecting it to a b/w monitor and then from there to the
computer via another 2-metre cable. The monitor had inputs and output
connectors for this. But anyway, we got the same effect if the monitor
was out of the loop. I tried different cables and a different VCR too.
So the only commonality was the videotape itself and the BT878.
The effect that I was seeing was that over a substantial part of the
image plane the luminance was at its maximum value (ie being digitized
as white). Looking at the histogram of luminance values there were no
low values of luminance either. This wasn't readily apparent on the
monitor because you could change its brightness/contrast knobs to get
what looked like a decent picture.
To get decent luminance ranges I had to drop the brightness register
value on the BT878 to -64 and reduce the contrast register to 200. But
even with these changes, the local contrast is not particularly good.
Another "feature" is that the BT878 is overscanning horizontally: there
are columns of black pixels on either side of the image. Another thing
that is possibly relevant is that when recorded, the VCR wrote a visible
timestamp (in white) onto the video.
What I am asking is "Do other people have problems like the above
digitising off videotape?", or is the consensus that something is
problem wrong with the tape in this case.
Thanks
Alan
