[opendtv] Re: France bids farewell to SECAM

  • From: Mark Schubin <tvmark@xxxxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sun, 04 Dec 2011 17:52:39 -0500

I guess I'm being too subtle.

Broadcasting is a chain, from lens and microphone to home TV set. Many standards are and have been used in that chain.

There are, for example, line and frame standards, like 405/24, 405/25, 525/30 (or 29.97), and 625/25. The last is often incorrectly called PAL (despite a 525/30) version of PAL broadcast in Brazil, and the one before that is often called NTSC. There WAS a 525/30 NTSC standard, the one that came out in 1941, but it was monochrome.

Then there are the ITU transmission standards: A, B, C, D, E, F, G, H, I, K, K1, L, M, and N. The UK version of PAL is PAL-I; the Argentina version is PAL-N. Both are 625/25, but the color-subcarrier frequencies are very different because the broadcast channel sizes are different.

Because there are different forms of PAL (as well as different forms of SECAM and NTSC), it might not be appropriate to refer to them as color-encoding standards but rather as color-encoding techniques. In NTSC, there is a single color subcarrier the amplitude of which affects color saturation and the phase of which affects hue. PAL is very similar, but there is an intentional phase alternation on each line, so that an accidental hue shift on one line would be cancelled by a hue shift in the opposite direction on the next line (ideally by using a delay line but otherwise visually). SECAM uses two subcarriers, both frequency modulated, with different color information transmitted on different lines, requiring a delay line.

That's the part from the color encoder to the TV set. But where is that color encoder in the chain?

In NTSC and PAL, it was common for color encoders to be part of the cameras. The NTSC or PAL signal could be fed to the production switcher (vision mixer). In SECAM, the color encoder is typically placed just before the transmitter, because SECAM signals cannot be mixed as NTSC and PAL signals can be.

That means that a "purely" SECAM production facility would have to mix component-color signals before color-encoding the final result. That's why I asked about whether anyone used a SECAM recorder (and should have said at a "broadcast facility"). It would have been exceptionally rare to have done so.

Until component-color became common in the 1980s, it was common for SECAM broadcast facilities to use PAL cameras, recorders, and switchers, transcoding from PAL to SECAM just before broadcast. After component-color, the nomenclature continued.

My point is that, although SECAM did reduce some color-TV reception problems, it was not an ideal system. Unlike NTSC or PAL, it couldn't practically be used for most of the production chain.

TTFN,
Mark


On 12/4/2011 10:51 AM, Olivier Houot wrote:
I thought the color processing you referred to was just transposition or
division by 4, in order to bring chroma back into the limited bandwith of
the system, but without essentially changing its nature as NTSC/SECAM/PAL.
I doubt there is complete color decoding that would convert it to something
independant of any video system.

But if you mean native recording of the signal without any reorganization,
ok, that is another thing.

I read somewhere that SECAM recording was used at the beginning, and a some 
point
they switched to PAL for archives. But i can't find any reference to that right 
now.

Several sites mention that SECAM can be recorded as is on a monochrome VTR 
provided
there is enough bandwidth.
Sounds logical as far as tape speed does not fluctuate too much.

This site mentions a 1 inch VTR that is said to perform equally well on
all 3 video systems :
http://videopreservation.conservation-us.org/vid_guide/5/5.html

One forum mentions early SECAM tests in US in 405 line format (!)
would need to be confirmed, i guess. But BBC did some early experiments with 
SECAM, at
a time when their 405 lines system was still in use, so that may explain the  
existence
of such a strange mix of scan format and color system.

http://missingepisodes.proboards.com/index.cgi?board=general&action=display&thread=683&page=2

One thing i can say for sure is that the quality of many french archives 
documents
that we get to see on TV is rather poor. Can't say if is only true for
one type  of archive unfortunately (PAL or SECAM).


Date: Sat, 03 Dec 2011 08:17:49 -0500
From: Mark Schubin<tvmark@xxxxxxxxxxxxx>
Subject: [opendtv] Re: France bids farewell to SECAM

A VHS recorder does not record NTSC, PAL, OR SECAM.  Color processing
is
used before the recording.  The same is true of V2000.

Perhaps I should have been clearer: Has anyone ever used a
DIRECT-recording SECAM recorder?  That's what broadcasters had to use
--
and COULD, in NTSC and PAL.

TTFN,


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