Flickering Brightness caused by HDV-Compression? at DVinfo.net

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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old August 10th, 2008, 05:23 PM   #1
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Flickering Brightness caused by HDV-Compression?

Hi to all,
just watched footage which was slightly underexposed (All controls manual, 25f mode with 25 shutter, gain up to +6db) I can see a slight flicker or rythmic pulse in brightness, especially in the middle and darker areas. It resembles a bit to a bad filmprint.
But the pulse is rythmic and seems to follow the GOP.
Is this caused by hdv compression? Or should compression work that way, that I should
only see artifacts caused by moving objects?
Another example:
Because I do not have a card reader, I make photographs simply by recording to tape.When I filmed a non moving object from a tripod against a white wall, (the wall had fine structures) I also had this pulse, but now in sharpness.

All the best,Salar
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Old August 10th, 2008, 06:38 PM   #2
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No, that's not an HDV problem. My guess is that you were shooting with the auto shutter on. You may have set it at 1/25 but it might still be on auto in the menu. The panning situation could be caused by using the camera on a tripod while the optical stabilizer is on. Or you could be in the noise reduction no. 1 mode; I understand that can do something similar to what you're describing. Also, if you're shooting 25f, the standard shutter speed is 1/50; shooting at 1/25 can cause some blurring on a move.
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Old August 10th, 2008, 09:17 PM   #3
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Salar... If Bill says it's not an HDV compression issue, I'd tend to believe him.

That said, I've experienced the same problem and I know that I was shooting full manual. The flickering is visible at +6db gain and gets just insane at +12db. If it's not related to HDV, I have no idea what causes it.
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Old August 10th, 2008, 10:51 PM   #4
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My guess is it's the same luminance pulsing when zooming out while certain modes such as TV, AV and without EXP Lock on. I've posted several times on this issue long ago and no one made comments noticing it. A co-worker's A1 has the same issue, so I know it's not just my unit. It doesn't bother me though since I always shoot with Exp Lock on.

*edit* then again, it's not a flicker, which to me would suggest it being rapid. This is relative to the zoom out speed. On average it's maybe every second or so.
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Old August 12th, 2008, 08:27 PM   #5
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Bill... OK. But I get the same thing on full manual when not zooming. What you describe might exacerbate the situation but I think we're still looking for an explanation.
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Old August 12th, 2008, 11:50 PM   #6
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I noticed a flicker/pulse while watching A1 footage played on my philips HDTV from camera to composite cable connection. When I replayed the footage with a component connection the flicker was gone.
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Old August 13th, 2008, 12:41 AM   #7
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I've had this issue in SD shooting interviews in a warehouse with fluorescent lighting. Ballast must have been a tick off the 60hz cycle. Didn't see any problems in my b/w viewfinder...but it showed color shift and brightness 'breathing'. Bummer.
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Old August 13th, 2008, 01:27 AM   #8
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If this problems occurs in Final Cut Pro, it's the preview that sucks. When you export, the flickering is over.
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Old August 13th, 2008, 03:42 PM   #9
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If your auto shutter is on, you can get that sort of thing when shooting under fluorescents.
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Old August 15th, 2008, 11:47 AM   #10
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I've definitely noticed this problem too in Final Cut. I haven't gotten a chance to figure out whether it's a playback thing or if it's actually really in the footage.

I notice it most when I'm looking at a static shot. I shoot with everything on manual...

It's exactly what you're describing, though. A rhythmic pulsing brightness - about once a second or so. I hope it's not an HDV compression issue.

--Colin
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Old August 15th, 2008, 01:02 PM   #11
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Actually, I had an issue like that with FCP one time. The footage was good in playing back in camera, but when captured there was a pulsing. The only thing that had changed from the previous capture session was that I had installed the Flip4Mac software because I needed to make some WMV compressions. I went in and trashed the preferences, and all was well. Often I see pulsing in the capture window, but the capture itself is fine. If you don't know how to trash the preferences, go to the LAFCPUG and search for it.

There's an easy way to check to see if this is an issue--open up your free iMovie and capture a clip in iMovie. If it's OK, then that indicates a preferences problem.
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Old August 15th, 2008, 07:44 PM   #12
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As this problem occurs in Windows with Premier Pro in my case, I expect that Flip4Mac is not the root cause. Although it might exacerbate the issue.

The more I read about this the more I start to suspect either HDV compression or something in the low light (manual) handling in the A1 is at fault. If the flashing occurs once a second (exactly), that would encompass two complete frame groups. This would point to HDV compression.

On the other hand, it could be the way that the A1 encodes HDV. The code in the A1 might go all pear shaped when it tries to encode video shot in low light and lose it's grip on the luminance.

This, of course is only my theory and I have nothing to back it up aside from my experiences. I am periodically wrong. In fact I am becoming wrong so often that I have little time for anything else.
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Old August 22nd, 2008, 12:20 PM   #13
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Thanks for the tips!
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