FORUMS: list search recent posts

"Skewing" elements in high speed movement

COW Forums : Canon EOS DSLR

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Christian Reid
"Skewing" elements in high speed movement
on Jul 8, 2012 at 3:50:48 pm

Hi guys, I've captured some footage on a 5D MkII and they got distorted from high speed movement.

On one of the scenes, the camera was on a tripod, but the cars passing from side to side of the image got completely skewed, like bent back. They were going pretty fast, since it was a race.

Another example is when you try to follow the racing cars on a horizontal pan movement, the background gets distorted.

I've read something about the sensor that "scans" the image from top to bottom to create a single frame, and anything that moves fast enough to be in a different position from the start to the end of that scanning process, gets distorted. Makes sense to me!

Do you know of any ways to avoid that kind of distortion on the future AND to correct the distorted images in post-production?

If searched for a plugin for After Effects or FCP 7, but couldn't find anything.
Thanks


Return to posts index


Peter Burger
Re: "Skewing" elements in high speed movement
on Jul 9, 2012 at 9:35:46 am

[Christian Reid] " Do you know of any ways to avoid that kind of distortion on the future AND to correct the distorted images in post-production?"

There's no real way to avoid those distortions, other than avoing to record fast movement or moving the camera too fast...
Here's a nice article about "Rolling Shutter" and the skewing and wobbling with some insight: http://dvxuser.com/jason/CMOS-CCD/

The Foundry provides a Plugin that seems to at least reduce the effects in post: http://www.thefoundry.co.uk/products/rollingshutter/

------------------------------------------
"Tragedy is a close-up; comedy, a long shot." - Buster Keaton

Me on Twitter (english/german)
http://twitter.com/FastFoodVideo


Return to posts index

Christian Reid
Re: "Skewing" elements in high speed movement
on Jul 9, 2012 at 1:24:30 pm

Thanks a lot Peter! "Rolling shutter" is the name then, I didn't get that the first time I read about it.

Very interesting article and that plugin seems to be the nearest solution for my problem.
Since I really can't avoid high movement because my main jobs are related to sports, I'll just have to add the plugin to my future workflow.

Thanks again, Chris


Return to posts index



Bob Dix
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 3:38:30 am

Hi Christian,
2.5 years ago this happened at times ,but, with smooth panning and the right Canon IS lens and even the right Stabilizer in Premier Pro 5.5.2 you can eliminate your problem. Using an older Pro tape videocamcorder will also fix the issue and still retain HD quality.

Good luck

Freelance Imaging & Video
AUSTRALIA


Return to posts index

Peter Burger
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 7:18:40 am

[Bob Dix] "but, with smooth panning and the right Canon IS lens (...) you can eliminate your problem."

Hey Bob, could you explain that further? I agree with the "smooth panning", but how does stabilized lenses come to play with rolling shutter issues? They're caused by the sensor and the way it reads the picture information, aren't it?

[Bob Dix] "Using an older Pro tape videocamcorder will also fix the issue and still retain HD quality."

That's good advice! But you'll have to get shure to use a camcorder with CCD and not a CMOS sensors. Got the same rolling shutter issues with my Sony HVR-V1 (CMOS) and haven't them with the FX1 or Z1 (both CCD).

------------------------------------------
"Tragedy is a close-up; comedy, a long shot." - Buster Keaton

Me on Twitter (english/german)
http://twitter.com/FastFoodVideo


Return to posts index

Bob Dix
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 9:27:08 am

You are right Peter on 3CCD's, which we use in PANASONICS & CANON CMOS HDV/MPEG-2 tape NO ISSUES. With THE CANON 5D MARK II'S there was an issue as mentioned, but, if you have the dollars or euros, Canon has put out the # Canon IS 2.8f EF L series 70-200mm Lens with a special Image stabilization for fast horizontal panning some $2000+ Aud. Oddly enough over the past two years I only use IS lens as most work is done hand held, and better panning techniques @/ 1/50 second,25fps PAL I have never had the "rolling shutter problem" maybe just lucky.The stills out of this camera 5D mark II are magic and the video has nearly replaced all others.

Canon Service advised me of the release of this lens # but, I do not need the zoom.

Very cold in Australia...............

Ps. The older tape camcorders still do marvelous 1440 x 1080 HD video when needed.

Freelance Imaging & Video
AUSTRALIA


Return to posts index


Peter Burger
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 9:57:25 am

[Bob Dix] "Oddly enough over the past two years I only use IS lens and better panning techniques and I have never had the "rolling shutter problem" maybe just lucky."

Have to get better lenses to try! Thanks for the tipp! Yes, slow and smooth panning does a lot good!

I still like to work with my V1 even with it's CMOS. Great camera, glad I got it.

Weather in Bavaria is a pain at the moment... drops from 30°C to 15°C, then back up to 30°C... :(

------------------------------------------
"Tragedy is a close-up; comedy, a long shot." - Buster Keaton

Me on Twitter (english/german)
http://twitter.com/FastFoodVideo


Return to posts index

Bob Dix
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 12:35:39 pm

I know you use a Canon 5D Mark II, I use it mainly for stills and any thing that moves on 1920 x 1080 HD using mainly the Image Stabilized EF 3.5f 28-135mm lens. I agree the Sony V1 feels and performs like a real professional unit a bit like the old Canon EX1 Hi-8, dated now but, great video in it's time.

Technology is marching on and presenting new challenges, not all good.

Freelance Imaging & Video
AUSTRALIA


Return to posts index

Peter Burger
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 7:09:15 am

Glad, I helped, Christian!

I forgot another plugin called "Mercalli Pro" by Prodad. It's german though, not sure if they provide an english version. But it is a bit more affordable.

------------------------------------------
"Tragedy is a close-up; comedy, a long shot." - Buster Keaton

Me on Twitter (english/german)
http://twitter.com/FastFoodVideo


Return to posts index

Christian Reid
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 1:04:32 pm

Bob and Peter,

thanks for the replies! You helped a lot.

There was something Bob mentioned that reminded me of the answer I got from a friend who uses the 5D.
Bob, you said you use 1/50 when recording 25fps, and I was told to use 1/60 or 1/30 when recording my videos at 30fps.

It makes some sense to use the number of stops as a multiple of FPS, but I couldn't fully understand why he said that.

Why the heck the time it takes to record a frame can affect the way the sensor captures each frame?
And why does one need to be a multiple of the other?

From my point of view, the shortest period of time it takes to capture each frame, the less "rolling shutter" effect I would get.

Pretty complex! Can you give us a theory lesson here?


Return to posts index

Peter Burger
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 2:42:23 pm

[Christian Reid] why does one need to be a multiple of the other?"

Framerate and shutterspeed interact. Most of the time film-cameras shoot with 24 frames per second and a shutterspeed of 48. So each frame is exposed 1/48 of a second. The shutterspeed determines the amount of motion blur that's in the frame.

If you use higher shutterspeeds, you get some strobing motion because of the lack of motion blur. That can of course be a creative choice - well known examples: "Private Ryan", "Gladiator", etc...
Using slower shutterspeeds increases the motion blur. You get some "ghosting" effects. Often used in dream-like sequences.

Double the shutterspeed than the framerate gives you a balance. Doesn't strobe. Doesn't give you ghosting.

The sensor scans a picture from top to bottom each frame. So, when you record fast horizontal motion like a car that drives by and use a slow shutterspeed and/or slower framerates the car moves during the "scanning" of the sensor --> skewing

It's like moving a piece of paper while scanning it on your desktop scanner - if you understand what I try to say.

When you use higher framerates and/or shutterspeeds, the car does not have time to move as far as with faster shutterspeeds/framerates --> less skewing.

So, turning up shutterspeed should help a bit, but you'll get strobing motion, which you normally don't want. The only way to avoid Rolling Shutter skewing ist to record with higher framerates, which is on most consumer and prosumer cameras not possible.

You can shoot 50p or 60p with the 720p mode of the MkII, can't you? You'll notice lesser skewing than with FullHD.

Hope this helps a bit!

Ahhh, and excuse my english. I think I could have been more to the point, but I lack a lot of vocabulary and grammar :/

------------------------------------------
"Tragedy is a close-up; comedy, a long shot." - Buster Keaton

Me on Twitter (english/german)
http://twitter.com/FastFoodVideo


Return to posts index

Christian Reid
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 3:13:46 pm

Hey Peter, don't worry about the english, same problem here.

I know exactly what you're saying about moving a piece of paper on a desktop scanner and about the slower shutter speeds causing more motion blur.

But what I don't get is the reason why shooting in multiple numbers (1/60 at 30fps) gives me less rolling shutter than shooting 30fps at non-multiple shutter speeds, even when they are faster, like 1/160.


Return to posts index

Peter Burger
Re: "Skewing" elements in high speed movement
on Jul 10, 2012 at 3:28:05 pm

[Christian Reid] "But what I don't get is the reason why shooting in multiple numbers (1/60 at 30fps) gives me less rolling shutter than shooting 30fps at non-multiple shutter speeds, even when they are faster, like 1/160."

I wasn't aware of that. Doesn't make any sense to me either... Hmmm... Have to try that myself.

------------------------------------------
"Tragedy is a close-up; comedy, a long shot." - Buster Keaton

Me on Twitter (english/german)
http://twitter.com/FastFoodVideo


Return to posts index

Bob Dix
Re: "Skewing" elements in high speed movement
on Jul 11, 2012 at 6:30:05 am

Christian,
Some time ago Canon Service advised that to get the smoothest result out of the Canon 5 D Mark II set the shutter speed at 1/50 sec, PAL which is 25fps.However ,in bright sunshine the image could be overexposed, you may need to go to 1/125 sec or higher, check the LCD. Also, check this out > :http://www.videomaker.com/article/10418/2/

It appeared to improve the smoothness of the video.

For tape camcorders the default speed is normally, 1/50 or 1/60 sec

But, recently I needed to throw the background in video out of focus by using F/5.6 and speeds in some cases went as high as 1/2000 sec, Frankly I could not fault the smoothness of the video at any speed ? And that certainly gets rid of any dust spots on the sensor ?

This is also worth a look > http://www.canon5dtips.com/the-basics/what-is-the-best-shutter-speed-for-mo...

Freelance Imaging & Video
AUSTRALIA


Return to posts index

Christian Reid
Re: "Skewing" elements in high speed movement
on Jul 15, 2012 at 3:41:30 pm

Hey guys, thanks very much for the assistance.

I've made some testing yesterday and the rolling shutter effect has indeed been reduced with my settings to 1/60 at 30fps. And I tested on a FAST subject, an Audi R8 LMS! Really cool...hehe

I hope it fixes my problems from now on, but it is also true that narrowing your stops options to just 1/30 and 1/60 certainly is a pain when you get an overexposed scene. Had the chance to test that also. You were right Bob!

Thanks again, Chris


Return to posts index

Bob Dix
Re: "Skewing" elements in high speed movement
on Jul 16, 2012 at 12:21:20 am

That's good, not right all the time, have a win now and then

Freelance Imaging & Video
AUSTRALIA


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]