[Tig] hdcam aliasing and illegal luminance

Steve Roberts steve.roberts at bbc.co.uk
Mon Mar 21 09:14:05 GMT 2011

I would imagine that the artefacts are produced because of the sample
conversion between 1920 pixels incoming to 1440 on tape and then back
out to 1920 again on replay - maybe a sharpening algorithm? Not seen
this myself, but then again we tend to be pretty much SR only these days

Steve Roberts
Senior Post Production Engineer
>BBC Studios and Post Production 
>020 857 64556
>Room B093 Television Centre, Wood Lane, London, W12 7RJ

BBC Studios and Post Production Ltd, Registered Office Television
Centre, Wood Lane, London W12 7RJ, Registered Number 3593793 England

-----Original Message-----
From: tig-bounces at colorist.org [mailto:tig-bounces at colorist.org] On
Behalf Of R. Adam Berk
Sent: 21 March 2011 08:16
To: Telecine Internet Group
Subject: [Tig] hdcam aliasing and illegal luminance

Sohonet http://www.sohonet.co.uk sponsors the TIG.
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So I've just been through a weekend from troubleshooting hell.  A few
good things did come of it, one of which is that we've without a doubt
confirmed for ourselves that any mac application that uses quicktime for
video i/o is completely unreliable and is under no circumstances to be
used or trusted for mastering, but I digress.  I'll spare us all the
immense list of details but what it all boils down to is some issues we
had with recording an hdcam master.

Viewing a scope being fed 75% smoke bars coming from tape, it was clear
that there was a bit aliasing.  To be expected of course.  The confusing
part is that some of the aliased peaks fell above 100IRE, and some below
0IRE.  The signal coming from the smoke did not exhibit these anomalies.
The tape was first recorded on an F500, then repeated on an SRW-5500 in
HDCAM recording mode.  Recording the same signal to HDSR on the 5500 did
not exhibit these anomalies.  What's worse is that the actual program
material also threw up illegal luminance errors here and there in the
log.  Some of these errors went as far as -9 IRE and 109 IRE.  Again,
the same program recorded to SR throws no errors into the scope's log,
and running a full qc report on the actual signal coming from the smoke,
pre-vtr, reports no errors also.

Has anyone dealt with this one before?  We usually master to SR and
rarely go to HDCAM so if this is old news, please excuse my dumb

thanks so much to the collective experience in advance

R. Adam Berk
Creative Director
office +1.415.513.5918
mobil +1.330.310.3950
ichat   adam at ct-sf.com
San Francisco


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