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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Is the speed of the rolling shutter "fixed"?

michael zaletel

michael zaletel

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Just trying to understand the whole rolling shutter issue. I realize that when you are quickly panning a scene that contains nearby vertical elements, you will get tearing because of how the CMOS is exposed with the "rolling shutter" from top to bottom. I also understand the same thing can happen when there are high speed flashes going off in a scene (like at the Olympics).

What I don't understand is if that speed is fixed or if it increases as frame rate or shutter speed increases. In other words, if you know you are going to be quickly panning nearby vertical elements, can you just increase the shutter speed and open up the iris to minimize the effects? Or perhaps can you film at say 120 frames per second and then just extract every 4th frame in post to get 30fps. Will that minimize the rolling shutter artifacts?

Please advise,

-shooter
 
3 things I DO know (as opposed to all the things I don't ;)

1. panning, no matter how quickly will not result in a tear. It poor conditions you'll notice vertical lines appear to "lean", but they won't tear the frame.

2. There's nothing you can do to prevent this. You can be aware of it and try not to do things where you'll know it will turn up, but there nothing as an operator you can do to make it go away.

3. RED is continually working to make this issue less relevant. I have heard that when the cameras first came out the rolling shutter was much more apparent than it in now and Jim has mentioned that with future sensors they are developing you wont be able to notice it at all.

that EVERYTHING I know :)
 
As long as you keep a reasonable panning speed and exposure time, you won't see it, only with very short exposure times and fast movements (or flashes).
The Red is already handling this better than any HDTV camera with CMOS that I know of.
 
Changing your shutter speed does not speed up the rolling shutter. Photo-sites are activated at the same speed. Shutter speed determines how long that photo-site will remain active.

Red is working hard to speed it up more and more. In the mean time there are ways to deal with things like flash bulbs in post.
 
Nomad,
Just to clarify (and not to bash Red; I LOVE my Red One):
The Arri D-21, a CMOS-based camera, utilizes an array of processors to increase the scan time to a point where there is absolutely NO skew. You can use strobes, pan as fast as you like (being mindful of strobing as you would with any camera) and use as "skinny" as shutter as you like. Is it more expensive? Yes. Do you, as the owner, need to make excuses? No.
I've said this in other posts: before they set a price point on the Epic, they need to figure out how much money they need to throw at this (and other) problems to solve it. If they are going to truly make Epic a "pro" camera with no compromises, they need to learn from the Red One.
Cheers,
Harry
 
it IS a little tricky dealing with it when stabilizing motion, say from a hand held shot or shooting from the air..mostly if you know about it your fine...

Just know it exists and watch for things like super fast pans or big camera jarring impacts while shooting, like a big dolly bump, if your NOT stabilizing after the shoot in post you should be fine 99% of the time..
 
The clock speed of the CMOS sensor has got nothing to do with shutter speed. Increasing the SP doesnt make the skew go away. I'm expecting Mysterium X will solve this. As for now, there's no way to fix, just need to be carefull during shooting.
 
Harry, Arri uses a mirror shutter, and hence has the same skew characteristics are film....

Graeme
 
Thanks everyone. Didn't mean to start a war. :)

Just wanted to know if increase shutter speed or frame rate would minimize. Now I think I understand neither of those would make a difference.

I just noticed it in a slow pan of a scenic environment that happened to have a couple of power poles nearby. Granted, the lean or skew wasn't that bad but clearly the verticals were not remaining consistent from frame to frame and it causes a perception of tearing when watched at normal speed.

I should have chainsawed the power poles before shooting. Doh! :)

-shooter
 
Harry,

To my knowledge the only advantage of the Arri/Dalsa style system is that shutter artifacts are softened by the edge of the mechanical shutter which is a few millimeters out from the actual sensor surface and thus out of focus. My bet is that these cameras otherwise have similar readout times to Red, it's just that the readout happens while the sensor is physically in the dark, so the skew is determined by the mechanical shutter rotation speed instead

I think we are just seeing the tip of the iceberg in terms of what CMOS technology is capable of. My bet is that future fully digital CMOS sensor systems will outdo the mechanical hybrids, if they don't eliminate skew and rolling shutter artifacts entirely.

I personally like a little skew, but that's neither here nor there, I shoot dirty.

IBloom
 
...Just wanted to add that many of the same artifacts and effects for strobing lights are also an issue with film or mechanical shutter cameras too. When a strobe fires when a mirror shutter is half-way closed, you get a split-frame effect, just as you do with the rolling scan of a CMOS sensor. The only real difference is that mechanical shutters will typically wipe across the film plane at an angle and not create perfectly horizontal lines. And like Ian mentioned, they have a softer edge transition and not a hard-pixel edge.

This is indeed the tip of the iceberg for digital. Someday, I think we'll be able to dial in our scanning speed and even customize scan patterns to create desired effects that vary from no skew in the form of a "global shutter" to soft-edge angled scanning patterns that mimic various mechanical shutter systems.
 
Jeff and Ian are on the money.

The scan will only become more malleable as the great CMOS beast grows. There are some very diligent men and women working hard to make it so. The spinning shutter "help" works as they have described. I personally believe / hope that the X sensor will be a great leap forward in this regard.
 
my guess is the x sensor is a ground up design using global readout.
but this is a guess.... Why I even posted is a guess :)
 
Yeah, the argument was that a faster rolling shutter was better than a global readout because it emulated the look of a mechanical shutter more effectively.
 
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