Slightly OT- reel-stream for HVX-200?

[Barry Green]

Well, what makes the JVC output so important is two things:
1) it avoids MPEG compression, which is a very good thing, and
2) it shows a signal that you can otherwise not get. No other camera in history, that I know of, had such a limitation — 60p display on the uncompressed, but only 30p on tape. That’s why it’s so interesting to people.

It’s also totally impractical, as recording it will involve $10,000 worth of gear, cables, and only get six seconds per gigabyte.

But I think the reason it’s talked about so much is because the camera cannot do 60p/”live video” in any other way… and avoiding MPEG-2 is a very good thing.

The other thing, which I think you brought up, is whether or not the video has been through the chroma decimation process. “Uncompressed”, as the term is being applied to these cameras, means that it’s avoiding the final digital DCT compression phase (whether DVCPRO-HD or DV or HDV). But that’s not the only compression the signal undergoes, of course. The very first thing that happens to a DV signal is that it undergoes chroma decimation down to 4:1:1. That’s basically a form of “analog compression”. Then it undergoes the 5:1 DV compression. But they’re separate processes.

The question I have is, what is coming out of the HDV camera ports? Is it pre- or post-chroma decimation? If it’s an analog equivalent of 4:2:0, it’s obviously a lot less interesting than if it’s an equivalent of 4:4:4 from the CCDs.

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Get the most from your DVX camera. The DVX Book and DVX DVD are now available at https://www.dvxuser.com/articles/dvxbook/ and at Amazon (https://tinyurl.com/54u4a)

[Toke]

[Barry Green] “Is it pre- or post-chroma decimation? If it’s an analog equivalent of 4:2:0, it’s obviously a lot less interesting than if it’s an equivalent of 4:4:4 from the CCDs.”

I’ll have to ask again: doesn’t all analog component have half of luma’s bandwidth in chroma channels?
If so, then analog output can’t be better than 4:2:2.

[Graeme Nattress]

Analogue is not 8bit, 10bit or 36bit, but noise limited, which can be equated to a bit level. Strictly speaking it’s not 4:2:2 or either, as that’s again a digital measure, but bandwidth can be equated to the equivalent digital x:y:z numbers. For what it’s worth, 36bit is nonesense – I doubt there’s any such thing and it’s totally impossible. I think what is meant is 3 channels of 12bit, which adds up to 36bits in total – like 24bit colour is 3 channels of 8 bits. To call some video 36bit sounds like creative marketing to me 🙂

For analogue outputs we need to know the frequency response within, say 3db levels, and noise levels in db, and then we can calculate what the digital equivalent would be. But converting to analogue and analogue transmission and subsequant conversion back to digital always incurs losses, so that’s why I made a point of saying earlier that I would never call a analogue output uncompressed – it may be devoid of digital compression with codecs etc., but it will have analogue losses of it’s own which make it a less than perfect representation.

Graeme

– http://www.nattress.com – Film Effects for FCP

[Graeme Nattress]

Say you’re shooting 60p, out of the component outputs to tape, or converted to SDI and captured direct to disk or something – what happens to the 30p you can record on the camera?? Does it drop every other frame or what? Surely the shutter speed would appear doubled on the 30p footage making it look very different to the visual appearance of the 60p?? Or are they going to do some magic smoothing jigger-pokery like they are giving the option for in the 24p mode?

Graeme

– http://www.nattress.com – Film Effects for FCP

[Toke]

I remember that these x:y:z notations come from analog equipment.
Number is just how many times of some base frequency you have bandwidth.

[Graeme Nattress]

I seem to remember the 4:2:2 notation first being used with digital video. Because with analogue video, the bandwidths of the chroma are never really integer fractions of the luma base bandwidth, I find it hard to see how such an integer based notation would have come about with analogue video. Anyone got any good historical reference on this? The only references I have are for digital video.

Graeme

– http://www.nattress.com – Film Effects for FCP

[Barry Green]

[Graeme Nattress] “Say you’re shooting 60p, out of the component outputs to tape, or converted to SDI and captured direct to disk or something – what happens to the 30p you can record on the camera?? Does it drop every other frame or what? Surely the shutter speed would appear doubled on the 30p footage making it look very different to the visual appearance of the 60p?? Or are they going to do some magic smoothing jigger-pokery like they are giving the option for in the 24p mode? “

You ask a good question. And until the camera ships, or Ken Freed weighs in, I don’t know that we have a definitive answer.

One thing I can say is that yes, it does have the “magic smoothing jigger-pokery” as applied for the 24p mode — meaning, they do have the ability to do 60p frame-blended down to 30p and recorded as 30p. What it looks like is still an unknown — at NAB they didn’t demonstrate the “Motion Smoothing” filter. Some have speculated that it’ll look like 30p shot with a 1/30 shutter.

—————–
Get the most from your DVX camera. The DVX Book and DVX DVD are now available at https://www.dvxuser.com/articles/dvxbook/ and at Amazon (https://tinyurl.com/54u4a)

[Jp Driscoll]

[Graeme Nattress] “To call some video 36bit sounds like creative marketing to me 🙂 “

Don’t get those marketing guys started!

Takes me back to the “old” SX and DX days of computers. I remember my dad explaining to me that a 386SX is really the same as a 286DX. Something about math co-processors in the DX but not SX.

Like my extended ASCII alpha-numeric user interface. (Or a keyboard to the rest of us.)

🙂

JP Driscoll