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-   -   Rolling Shutter (https://www.dvinfo.net/forum/sony-nxcam-avchd-camcorders/487778-rolling-shutter.html)

John Strickland November 20th, 2010 12:50 PM

Rolling Shutter
 
I'm sure this has been documented before, but I have a question about the rolling shutter on this camera.

I've read online that the slower your frame rate the more the "Rolling shutter" shows up.
It seems that even when I shoot at 60 frames per second I still have major problems with the middle of the screen getting very jittery.

And I'm not talking about on wild and crazy pans either, I'm talking smooth slow pans on a tripod.

Any advice?

Thanks.

Felix van Oost November 21st, 2010 03:37 AM

What shutter speed are you using?

I've had few problems with mine, and I shoot fast-paced action sports.

Arkady Bolotin November 21st, 2010 04:09 AM

John:

As you probably know, rolling shutter (or line scan) is a method in which an image is recorded not as the whole but rather by scanning across vertically or horizontally. As a result, this method can produce such distortions of fast-moving objects as skew (the image bends diagonally) or wobble (the image shakes or vibrates, so-called the jello effect).

What you describe in your post allegedly coincides with the jello effect (“the middle of the screen getting very jittery”).

However, the wobbling effect is more common in hand-held telephoto shots, or when a camera is attached to a vibrating moving vehicle, and neither of those conditions is applicable to your recording situation (“smooth slow pans on a tripod”).

Therefore, I can assume that something else – not rolling shutter – causes jittering of your recording.

Have you tried to switch off any of stabilization functions (steadyshot)?

Greg Fiske November 22nd, 2010 06:55 PM

Check out deshaker, mercalli 2 and
ROLLINGSHUTTER | CMOS Motion Artefact Correction | The Foundry

John Strickland November 22nd, 2010 08:12 PM

that's the strange part to me.
All the examples of rolling shutter that I've seen online seem to be the wobbly effect throughout the entire frame.
Mine only seems to be through the absolute center of the fram horizontally and only a couple pixels tall.

I may have spoken a bit too soon when i said at 60 frames per second it's still there.
The tests I did today seem to show that at 60i it's buttery smooth.

But at 24 and 30 the very center of the frame has this odd jitter to it.

Aaron Holmes November 22nd, 2010 09:24 PM

What are you watching your footage on? Camera attached directly to an HD monitor/TV? Or are you playing the footage back on a PC/Mac in some media player app? This definitely doesn't sound like a rolling shutter thing.

Best,
Aaron

John Strickland November 23rd, 2010 07:13 AM

I'm playing it back in the media import application that came with the camera.
Also playing it back in Premiere Pro Cs5.

It only shows up when the camera is moving so it must be attributed to the shutter in some way right?

I just realized I had the steady shot turned on while it was on the tripod.
Could that be what I was seeing? Some type of stabilization trying to work when it wasn't needed?

Arkady Bolotin November 23rd, 2010 08:13 AM

John:

That was exactly that came to me while I was reading your first post: the camera-shake reduction function might cause the jitter.

This is the well-known and well-reported phenomenon: when on a tripod, the camera’s slow panning movements can mislead the shake reduction function resulting in the image shifting up and down a pixel or two.

John Strickland November 25th, 2010 09:17 PM

I plan on trying this this weekend.
Happy thanksgiving guys.

John Strickland November 27th, 2010 06:11 PM

1 Attachment(s)
Ok guys this is blowing my mind a bit.
When I watch this video inside Premiere Pro cs5 as well as in Sonys import program there is a line of pixels that go completely across the screen horizontally that appear to be shifted or distorted.

When I watch this video that was exported from Premiere Pro Cs5 there is no line of pixels, it appears the video is flawless.

Previous videos have been progressive scan so I'm pretty sure I'm not seeing interlacing noise, especially since it only appears in certain areas of the screen.

This video is interlaced.

It is also not on a tripod, it is handheld from my lap.
Steadyshot is turned on.

Really if the end result video is fine there isn't a reason to worry, I just would like to know what it is that I am seeing.

Thanks guys.

Aaron Holmes November 27th, 2010 06:22 PM

What you're probably seeing is something called "tearing," which is when the refresh rate of your monitor and the video playback in Premiere (or whatever playback app you're using) are not in sync. Consequently, when the monitor decides it's time to present a frame, the app may be only partially done drawing the current frame and so you see part of the current frame and part of the previous frame.

Nothing to worry about, IMO. Just Premiere showing one of its many sharp edges.

EDIT: I'm still on Premiere CS4, by the way, and it has many, many terrible problems playing back AVCHD. More than just lines, high-contrast or high-motion areas of the video frame get slowly out-of-sync and then snap back into place every half second or so. So, when it comes to the quality of Premiere's previews, I've learned not to care. It's what you see when you scrub that you should be most concerned with (again, at least in CS4), as this is a more accurate representation of what the final render will look like.

EDIT#2: Your vid looks wonderful to me. Silky smooth, and the kids look like they're enjoying the Kinect. ;-)

Best,
Aaron


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