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Compression artifacts


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#1 Paul Bruening

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Posted 09 March 2009 - 11:25 PM

I just saw a little movie called Clancy. It looked like it was shot in HD of some kind. It was projected via industrial grade DLP from a BluRay disk.

My question concerns the stuttering motion that occurred when the camera panned and/or tilted. Slow pans revealed a slight stuttering as if someone was ever-so-slightly tapping on the side of the camera. It didn't look like a bad head. I suspect that it was a compression-motion artifact. Is that a thing that happens under these circumstances? I found the stuttering to be more than a little irksome.
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#2 Andronico Gonzalez

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Posted 10 March 2009 - 01:12 AM

This is called "Rolling Shutter", and is a problem in the cameras with a CMOS sensor without a global shutter. Almost all new digital cinema cameras, Red, SI-2K, Nikon D90, Canon 5D, etc, have it.

Barry Green published in DVXUser a very good article with a lot of examples that helps to understand this problem.
http://dvxuser.com/jason/CMOS-CCD/

Rolling Shutter is inevitable in this cameras, but there are many ways to minimize it:
Use more wide-angles
Align the sensor cmos in the axis of the tripod, so the angular momentum reduces when you rotate.
When doing paning and tilt instead of doing a hard stop you can decelerate the movement.

If still this isn't enough you can always use more expensive cameras or workflows, like a Phantom, a Genesis or using 35mm or 16mm.
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