A Thousand Words...HV20/Brevis short.

[Dennis Wood]

Ted Chung and Thomas Colett came up with this amazing short done on the HV20/Brevis combination using our CINEFUSE 1 imaging element. We developed our Pentax K mount for these guys specifically, and boy, was it ever worth it.

Discussion on the piece.

[John Papadopoulos]

Dennis,

we are developing a 1/2" model of our camera, what are the imaging requirements for using it with Brevis? The optimal focus screen size and focus distance?

Thanks

[John Papadopoulos]

The rolling shutter if very obvious in some shots.

The story is not exactly original. You might have seen this Patryk Rebisz film shot with a still camera:

http://patrykrebisz.com/stills/FINAL_movie.html

It is not exactly an unknown film. It was on abc news, filmmaker magazine, it received some awards and was screened at many festivals.

http://www.patrykrebisz.com/films_between.html

[Peter Moretti]

Are you referring to the banding when she leaves the train carrying the box (37s to 39s) and when he picks up the camera (50s to 53s)? Is that really rolling shutter from the HV-20 or something else freaking out?

If it's rolling shutter, then the HV-20 is a fundamentally flawed tool for serious work involving any kind of panning. And I can only hope other CMOS cameras do a better job.

Is there a way to fix this in post?

[John Papadopoulos]

Global shutter cmos is as good as CCD so that's the CMOS feature you need for total camera motion freedom. Rolling shutter can be ok if you don't do much vertical camera motion. But you can't run with the HV20 or do fast vertical camera motion or hardmount on a vehicle on a rough road, it will not look shaky like film or ccd, it will look very distorted and unnatural. Shaky footage can be fixed in post but rolling shutter is almost impossible. Deshaker, a virtualdub plugin, has an option for rolling shutter but even with the intended camera model it does not work very well.

I don't think all viewers will notice it, but there are some rolling shutter issues at:

00:12, 00:42, 00:52 (a little)
02:14-02:25 (a lot)

There is nothing obvious at 0:37-0:39, perhaps your player does not double buffer? Step through frame by frame using the quicktime player. It shouldn't have any banding.

[Daniel Lipats]

Originally Posted by Peter Moretti

Are you referring to the banding when she leaves the train carrying the box (37s to 39s) and when he picks up the camera (50s to 53s)? Is that really rolling shutter from the HV-20 or something else freaking out?

If it's rolling shutter, then the HV-20 is a fundamentally flawed tool for serious work involving any kind of panning. And I can only hope other CMOS cameras do a better job.

Is there a way to fix this in post?

CMOS cameras are used in professional environments and are gaining popularity. CMOS and CCD sensors both have limitations and its important to be aware of them and know how to work with them. Just because a camera has a CMOS sensor does not make it a poor tool.

Generally unless filming in uncontrolled circumstances shaky footage, or footage containing distortions should be avoided and reshot. Relying on post work to correct errors is always a bad idea. However, I have read about compensating for shutter distortion in post by using a second, smaller camera.

Deshaker will cause a loss in resolution, and at times extreme. This is especially a problem when shooting 720p since it can easily lower resolution down to SD quality. I have also found that shaky footage is also prone to other problems for example lack of focus due to the shutter. In my opinion it should be only used as a final and last desperate resort.

[Ben Winter]

Originally Posted by John Papadopoulos

02:14-02:25 (a lot)

Ahh you know what that is? I don't think that's rolling shutter actually. That's motion blur from the aftereffects of a shake-correction plugin. I've gotten that kind of artifacting a lot when smoothing out shaky dolly shots with after effects' tracking. What's happening is, after a shot is tracked to cancel out the motion of a shaky shot, the motion blur is still in the shot so even though an object stays in the same location in the frame, the motion blur from the object is still there and is unnatural.

If you ask the creator of this short I can almost guarantee he'll confirm this for you. The artifacting is very characteristic.

You'd have to do some digging to get to the points I'm referring to but on my website, "Broken Minds" has a scene towards the end when a character steps out of a car and the camera does a rotation around him. I added a de-shaker filter to this shot and the artifacts are readily present. Also, in "The Lifeguard" the first "fantasy" sequence (in sepia-tone) contains a lot of this artifacting as it was all done handheld and I decided it was too nauseating to watch without some kind of post-pro stabilizing present.

I tried very hard but could not find the issues you were talking about at 12, 42, or 52.

Also I do remember seeing a while back that stop-motion-esque film you referred to; this is indeed quite curiously similar.

[Peter Moretti]

John,

Thanks so much for your reply! It was a problem with QT. When I went through frame by frame (didn't know that left & right arrow could do that) what I saw went away.

I don't know if it's my computer: it's a 3.0 gig P4 with 2 gig of RAM and an Nvidia Quadro FX1100 AGP 8X video card. Problem solved: I moved the file from a 7,200 RPM IDE drive to a 10,000 RPM SATA drive and the banding went away. I belive the first drive just couldn't keep up.

Would it be possible for you to post a "classic example" of rolling shutter from some of your footage? I know it's caused by the image moving too much before the CMOS sensor has had a chance to completely write. I just want to know what I should be looking for, what it acutally looks like.

Thanks.

[John Papadopoulos]

Peter,

This is cmos rolling shutter. Andrey shot it with the Elphel in a very difficult situation.

http://www.archive.org/download/Roll...rCMOS/cmos.wmv

You can also see the black borders on top and bottom go in and out of the frame sometimes, wrong setting:)

It looks life a fast shutter speed and deshaked quite well. On horizontal panning you get verticals lines to change angle back and forth depending on the direction of shake/camera motion. On vertical camera motion you get compression and decompression of actual object size. This is as extreme as it will get I believe.

You will sometimes see banding if the motion is combined with a refresh of the screen. This is not on the video of course. Stepping through shows it's not there and other player will play it fine. It has to do with drawing on screen while a refresh is being made. Normally you prepare the frame and draw in a single transfer so no refresh happens in the middle of the frame.

[John Papadopoulos]

Ben,

I'm pretty sure it is rolling shutter. Deshaking will create blur that goes on and off, not distortion. That shot has a little flunctuatiing blur but is also visibly distorted on the vertical axis. Deshaking makes rolling shutter easier to see because it removes any camera motion that is masking it.

[John Papadopoulos]

Daniel,

How is the second camera used to remove the shutter distortion? I haven't seen that.

Deshaker has parameters that allow to control the ammount of correction. It's not much if you loose 5 or 7% to get extra stability. With a fast shutter it can be artifact free in other aspects. With CCD and global shutter cmos you have an option at least.

[John Papadopoulos]

If you step frame by frame from 2:20 to 2:22, it is pretty obvious that the house on the far left appears to be made of rubber and the frame is distorted bue to the (probably) diagonal movement.

[Dennis Wood]

Ben, in the original thread over at Cinevate, Ted confirms exactly what you had suspected but it was Final Cut's Smoothcam program. You have a sharp eye!

John, our upcoming relay lens will address your camera's needs if you're planning to use the B4 standard.

[John Papadopoulos]

You can also see rolling shutter problems in this Silicon Imaging clip on the horse riding scene at 2:28-2:35: (2:31- on youtube).

http://www.archive.org/download/SirL...irLateALot.wmv
http://youtube.com/watch?v=H5yD2IutHFU

Better than a Sony HC1 or a Canon HV20 perhaps, but still quite severe vertical distortion.

[John Papadopoulos]

Originally Posted by Dennis Wood

Ben, in the original thread over at Cinevate, Ted confirms exactly what you had suspected but it was Final Cut's Smoothcam program. You have a sharp eye!

John, our upcoming relay lens will address your camera's needs if you're planning to use the B4 standard.

A C mount lens should be ideal for a relay lens I believe. But what are the actual requirements so we can chose one?