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Sony HVR-Z1 / HDR-FX1
Pro and consumer versions of this Sony 3-CCD HDV camcorder.


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Old December 9th, 2004, 05:35 PM   #1
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Fx1 and moving objects

First of all, Im stunned by the beautiful images I have seen so far. But it seems as if every moving object I see blurs. You guys think the Z1 will have the same problems?

Thanks for your time!
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Old December 9th, 2004, 08:43 PM   #2
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Yes it will, as that's the nature of MPEG compression, especially a long-GOP form like HDV employs.

It's not very bad, but it is there. It definitely prefers still shots over moving pan shots.

The other odd artifact you'll see is that when you stop moving, the camera will kind of gradually sharpen back into focus, as the GOP catches up with the new still shot. On an I-frame-only compression scheme like DV or MJPG, it'd snap into sharp focus immediately, but on MPEG-2 it may have to take several frames to resolve the detail (at least until the next I-frame hits). It can take 1/4 to 1/2 second to "sharpen up" -- almost like it's using autofocus but it isn't, it's the compression system at work. Think of older internet web video, where you'll initially see a blocky image that gradually sharpens up into nice footage -- MPEG 2 works like that, but obviously much much better of course.

The MPEG-2 algorithm works fantastically well on still shots however. It works best when there's not much changing between frames. On a moving shot, every pixel changes, so the compression is least efficient. On an interview shot, it'd do superbly well, because all the background would stay stationary, with comparatively small changes per frame.
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Old December 9th, 2004, 08:55 PM   #3
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How about them companies come up with a new ProHDV spec which calls for a 40Mbps data rate, using AVC H.264 compression with 5 GOP for both 50i and 60i?

And hows about them companies also coming up with a HDD recordin' system that dont use tape which is source of dropout headaches.

ProHDV, I hope it coming soon.
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Old December 10th, 2004, 03:43 AM   #4
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Hi Barry

I've been playing around testing the FX1, but so far most of my footage has been fairly stationary objects and headshots..

I've been shooting in HDV and using the in camera downconvertion.... (No real point in trying to edit or use HDV yet)

Are you suggesting that for faster moving subjects I'd be better off just shooting in regular DV... ????

I did notice some of the shots of my son did show some artefacts and blurriness, despite the overall sharpness and crispness to the footage.

Guess I'll have to do some side by side tests...

Regards

Gareth
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Old December 10th, 2004, 10:57 AM   #5
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<<<-- Originally posted by Barry Green : On a moving shot, every pixel changes, so the compression is least efficient. On an interview shot, it'd do superbly well, because all the background would stay stationary, with comparatively small changes per frame. -->>>

You think this problem will be resolved in the near future? I mean after all - panning is a pretty important feature - at least IMO..
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Old December 10th, 2004, 11:26 AM   #6
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<<<-- Originally posted by Jonas Hansen :
You think this problem will be resolved in the near future? I mean after all - panning is a pretty important feature - at least IMO.. -->>>


Well, at last we are arriving at the limitations and less pretty things every compromised system must have. After all we can't pretend to have a completely free lunch, can we?

Panning and movement is really very important: perhaps that and the dropout problem are the more serious limitations the HDV system has that won't be able to be cured too soon.

A new recording media, such as flash cards or hard disks will solve the dropouts.

To cure the MPEG related problem a new algorithm has to be developed. If I am not wrong, MPEG-2 (or every MPEG?) can be upgraded automatically when new improvements come along in the future. So that might be the only way around that problem. Sony or other parties are probably working on it as we speak.

For now it's good that we accept there's a problem there and start to see what we can do about it.

As I see it, perhaps certain stories might be not be right for HDV if they require fast action or fast camera movements when blocking a scene. But medium to slow movements, made with a pan, a dolly or steadicam may do fine. As long as the start and end of the movement is slow and gradative, MPEG might be able to accomodate and be more transparent.

These are just first thoughts though. We may and should find more ways to hide the problem.


Carlos
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Old December 10th, 2004, 02:20 PM   #7
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<<<-- Originally posted by Gareth Watkins :
Are you suggesting that for faster moving subjects I'd be better off just shooting in regular DV... ???? -->>>

In general, no -- if you want HDV shots, just stick with HDV source. But if what you're saying is that you're making a DV production (shooting HDV and downconverting to DV in the camera) and you're bothered by the lower-resolution on motion shots, then for that case you can certainly try DV. DV also gets a little lower in res during motion, but DV has a much more consistent bitrate per frame so its degradation is a) less, and b) isn't variable.

But that's only if you're doing a DV-only production. If you're planning on eventually making an HDV version, definitely stick with the HDV mode, and try to see if you can structure your shots so that the lower resolution is less noticeable (through shot composition, panning speeds, whatever...)
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Old December 10th, 2004, 02:27 PM   #8
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<<<-- Originally posted by Jonas Hansen :
You think this problem will be resolved in the near future? I mean after all - panning is a pretty important feature - at least IMO.. -->>>

I don't see how it can be resolved, unless someone produces a more-efficient hardware MPEG-2 encoder that can somehow know how to optimize shots for motion -- but even then, it won't be applicable to the FX1 or Z1 because that hardware's already set.

Yes panning is an important feature. The thing is, cinematographers have always had to adapt their techniques to the medium being used. Panning in film/24P video is way different than it is in 60i video, and you have to adapt your technique or risk making unwatchable pans.

With DV we have to adapt again, trying to avoid high-contrast scenes, avoiding wide shots, concentrating on close-ups...

With HDV, we may need to adapt again. You may want to shift to doing more whip-pans as a way to reposition the camera, rather than gradual reveal-pan type of stuff... it's a new format, and may need new techniques to get the best from it.
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Old December 10th, 2004, 02:32 PM   #9
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Carlos, I didn't see your post before I wrote my long-winded response, or I would have just said "ditto to everything Carlos just wrote!"

As for dropouts, yes a hard disk recorder or flash media recorder would solve that problem completely. I hope the FS-4 supports HDV -- that'd be a great solution!
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