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Old Jan 16, 2008, 8:18 AM   #1
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Okay, so we've finally given a name to the wavy, skewing effect we have all talked about.. We now know it is officially called "rolling shutter." Now, there has been some debate as to whether this issue is caused by serial vs. parallel imagers, frame-buffering, or is it simply a fact-of-life dealing with CMOS imagers. Well, I think I have an answer now. I found this article:

http://www.machinevisiononline.org/p...ls.cfm?id=2157

Essentially, the article says that CMOS sensors can use rolling or global shutters. However, using a rolling shutter gives it the ability to capture at a faster frame-rate. This explains a phenomenon I've wondered about for a while. That is, Aiptek products do include a flash, right? I've often wondered how it scans in an entire 3.0 MP image at once when the flash is used, if it couldn't use a global-shutter. Well, appearently it can switch between them. Too bad the firmware doesn't offer the ability to switch between that mode for video, even if it meant a lower frame-rate.
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Old Jan 16, 2008, 8:33 AM   #2
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Oh.. This article is even better, with graphical illustrations of different shutters..

http://dvxuser.com/jason/CMOS-CCD/

It also mentions that while CMOS sensors can use global shutter, no current production models do.
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Old Jan 16, 2008, 1:18 PM   #3
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your last Article found, is the reason I preferre cmos over ccd. no smear but the GO-Hd will show smear so how much depends on the position andcamcorders still.
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Old Jan 16, 2008, 8:36 PM   #4
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Actually, the entry-level CMOS sensor didn't implement global-shutter. They implement global reset. So it usually work with lens mechanical shutter. But most entry-level DVs didn't have mechanical shutter. It cost more money.

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Old Jan 17, 2008, 12:21 AM   #5
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Thanks adric22 for the research. That explains a lot of things.

According to the Hybrid List, Aiptek has offered only one ccd hybrid while Mustek has offered two ccd hybrids. The rest are all cmos. Whereas Digilife seems to be splitting 50/50 between ccd and cmos.

All the hybrids from first-tier manufacturers have been ccd, with the exception of the dreadful Sony NSC-GC1.

While I really dislike the smearing and blur effects of ccd sensors, most of my footage is handheld, "action" type shots, mostly with the camera and me in motion. Looking at older footage I took with cmos hybrids (Aiptek DDV4500, Digilife DDV-720, Digilife DDV-S670), I can see they're full of slanted content and gross amounts of wobble. All my current cams (Digilife DDV-920, 5120A, 730, and Samsung i6) are ccd, so I haven't been noticing this problem.

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Old Jan 17, 2008, 1:11 AM   #6
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If you study high-end DVCs and DSCs, almost all use CMOS sensor. CCD sensor has more theoretical limitation. It can't reach high video framerate or high resolution. But it is definitely good in sensitvity if you are talking entry-level products.

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Old Jan 17, 2008, 8:30 AM   #7
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Well, this information has definatly made an impact on my future purchasing decisions. Used to, I had no particular prejudice against CMOS imagers. However, now that I realize 99% of the time they are going to be using a rolling shutter, I will think twice before buying any product that uses one. That is, until they start using the global shutter option on them. Now, keep in mind, I'm talking high-end stuff. Obviously, if I'm buying something as a cheap toy for $50 or something, I'm not going to care.

Now I have some security cameras on my house that are CMOS, and some are CCD. I've done testing and can't see any of the rolling-shutter issues on these. So they must be using the global shutter on these things.
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