Overcome rolling shutter tearing with high shutter speed?

[michael zaletel]

Hi,

I've seen some footage in the past demonstrating the tearing that occurs due to rolling shutter in vertical elements near camera on fast pans. I'm wondering if it's possible to overcome this by using a super high shutter speed and then adding back in the appropriate motion blur for the frame rate in post?

Please advise,

-shooter

 

[Brandon Fraley]

AFAIK, a faster shutter only helps in that there's less amount of exposer time for it to occur. However, if a flash should happen during the exposure, it will still tear the same way. And because you're limiting the exposure time, you're also more likely to miss the flash entirely, which is usually not a good thing either.

So basically, there's no fix. if you have flashes, try to make sure they burn more than a frame.

 

[michael zaletel]

AFAIK, a faster shutter only helps in that there's less amount of exposer time for it to occur. However, if a flash should happen during the exposure, it will still tear the same way. And because you're limiting the exposure time, you're also more likely to miss the flash entirely, which is usually not a good thing either.

So basically, there's no fix. if you have flashes, try to make sure they burn more than a frame.

Hi Brandon:

Thanks for the reply. I'm mainly concerned with outdoor shots with plenty of light, landscape pans, arial footage, fast angled track moves (no flash). I'm thinking I could use less ND filter or even none and max out the shutter speed. Assuming software like Shake and After Effects could handle putting back in the appropriate motion blur for the frame rate, what would the drawbacks be?

-shooter

 

[Cail Young]

Drawbacks would be fake motion blur and render time required in VFX.

Don't forget that less motion blur will make the rolling shutter skew more obvious, not less obvious.

 

[Brandon Fraley]

if you're not worried about flashes or strobes, then don't worry about tearing. It doesn't happen. If you've seen tearing in pans or moves, there's something wrong with the camera.

 

[michael zaletel]

Hi Brandon:

I remember seeing the tearing in someone else's demo with poles right in front of the camera on a fast pan but I am probably more concerned about the leaning of vertical items like power poles, trees and etc. I found an old post where someone said the following and I've never really understood what they mean. Can someone explain further?

"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."

-shooter

 

[Brandon Fraley]

tearing means there's something wrong with your camera, but the skew is unavoidable. Just like the quote says, the activation of photo-sites is independent of shutter speed.

The skew has continued to get better with every build, but beyond waiting for future builds, no, there's nothing you can do about.

Do some tests though, the skew really isn't an issue. you only see it on fast pans, and that's only tech heads like us. If you're panning across a landscape, slow enough so that motion blur doesn't take over, you want see the skew at all.

 

[I Bloom]

In my experience skew will increase as you decrease exposure time. This is because the scan time is constant while the exposure time is decreasing. Thus in a longer exposure the majority of the exposure time happens while no scan is occuring, while in a short exposure almost the entire exposure can be happening during a scan, thus increasing the perception of skew.

Best thing is to try it and see.

IBloom

 

[Jannard]

Make sure you have Build 16 or greater. The read-reset times were cut down significantly after Build 15. Demo footage you saw may have been from early build? We have no one complaining of skew on the hundreds of jobs now being shot on RED.

Jim

 

[Deanan]

Hi Brandon:

I remember seeing the tearing in someone else's demo with poles right in front of the camera on a fast pan but I am probably more concerned about the leaning of vertical items like power poles, trees and etc. I found an old post where someone said the following and I've never really understood what they mean. Can someone explain further?

"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."

-shooter

Tearing is a playback thing on computers when one frame is drawn before the previous frame has finished drawing. It is not related to skew or camera.

The application needs to support swapping buffers on the graphics card properly. Not all do.

 

[Charles Angus]

As I understand the shutter speed/skew issue, there is a fixed rate at which the photosites activate. The first row begins collecting photons, then a very brief moment later, the next row down, and so on. This is fast - faster than the fastest shutter speed you can choose. This is the so-called "rolling shutter".

The shutter speed you choose in camera determines how long it is from first collection (when the rolling shutter opens) until the sensor stops collecting photons - but the rolling shutter has already "rolled" over the whole sensor at this point, even for very fast shutter speeds.

So the shutter speed has no impact on the rolling shutter effect.

(Disclaimer: I am not a sensor engineer; this is obviously a gross simplification based on knowledge gleaned from a variety of sources. Take it for what you will...)

 

[Brandon Fraley]

Tearing is a playback thing on computers when one frame is drawn before the previous frame has finished drawing. It is not related to skew or camera.

The application needs to support swapping buffers on the graphics card properly. Not all do.

AH, this is true, I've seen "tearing" in RED CINE playback, but yeah, it's not in the footage, and goes away in my NLE and quicktimes.