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XDCAM EX1 Hands-On - CMOS Rolling Shutter Strobe Artifacts
Published by Matthew Jeppsen December 29th, 2007 in Cameras, FreshDV, Hardware, News, Research, ReviewsThis article is part of a series of tests FreshDV conducted with the Sony XDCAM PMW-EX1. Thanks to Miami rental house and Sony dealer Midtown Video for providing a XDCAM EX camera. And thanks to DSC Labs for providing test chart patterns. You can read more about ours and others experiences with this camera here.
If you read FreshDV daily, you already know that we are testing a Sony XDCAM EX1 this weekend, courtesy of Midtown Video. It’s a beautiful camera that makes incredible images, I have been very impressed with it’s performance. For the most part, this one lives up to the hype.
That being said, we all know that every camera has an achilles heel. That’s just the way it works…engineering is all about tradeoffs. And the XDCAM EX1 is no exception. As the EX uses CMOS as it’s imaging tech, it is subject to rolling shutter artifacts. We recently talked about how rolling shutter artifacts are cropping up in Red Digital Cinema footage…and I noted the same issues are evident in EX1 footage shot this evening. Right-click the download link below for a half-resolution example of this strobe artifact. It was shot on the EX1 @ f/1.9, 1/48, 9dB gain at 1080/24p HQ (XDCAM35/VBR). Selecting higher shutter speeds doesn’t help, in fact the artifact becomes even more apparent. 1/32 shutter doesn’t fix it either. So it’s definitely an issue to be aware of in your production work…perhaps the EX is not the best solution for a fashion show or wedding reception…or police car strobes.
UPDATE: Quite a few people wrote in to tell me that the issue reportedly goes away when the electronic shutter is turned off. So I tested the camera with a flash in all the different formats, shutter ON vs shutter OFF. Here are two studio test framegrabs that show this issue less prominent but still present in 1080/24p footage with the shutter mode toggled off. The downloads are full-resolution frames exported from FCP timeline as jpeg-12. I haven’t spent much time digging into the footage, but the camera looks to be catching probably 40% or 50% of the flashes mid-roll. Small flashes that don’t light the whole frame slip through more easily it seems. So maybe 1 out of every 2 don’t appear to get caught.
EX1 Rolling Shutter Strobe Artifact [0:10m]: Download
HQ 1080/24p @ 1/48 electronic shutter: Download
HQ 1080/24p w/ electronic shutter off: Download(Focus on this shot is off a touch, and I’m shooting through tree branches. Not perfect. But it clearly shows the issue I’m talking about)
Thanks again to both DSC Labs and Midtown Video for making this EX1 test series possible. Stay tuned here or at our EX1 link page for more test results.
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And here I thought people were proclaiming my HVX’s reign was over. I think I’ll stick with CCD.
Matt,
Keep up the great work, this is camera torture FreshDV style…break it baby break it :) Our theory is by breaking a camera you know its strong points and you know its weaknesses. Weaknesses are inherent in every system but its important that you identify them so you know how to work around them and cater to the strengths. If you identify the weaknesses you will also be able to know if a system will work for your particular application.Good, bad or ugly you decide, what will work for you?
This problem is a good thing to keep in the back of your mind when choosing the right tool for the job although in most cases it would not be a deal breaker. Hell, an inventive DP/Director might even exploit this issue for creative gain….think music video with tons of stobes. It might be one of those FX that everyone asks “how did he do that crazy half frame light thing…in camera?”
The right tool for the right job… and you thought your HVX could do it all. Actually that light-hog HVX would not be able to pick up the dark detail that is the cop car, you’ d have a black image with blinking lights, although beautiful full frame blinking lights they’d be.
So much compromise so little time.
Excellent work. Maybe this is the reason REDs are being upgraded. I’ll call this the Strobe Test and, so far, no CMOS camcorder has mastered it.
Makes you wonder how digital still cameras using CMOS imagers do this without a problem.
It seems this effect disapear when you set the shutter OFF (meaning you are in natural shutter of 1/
It seems this effect disapear when you set the shutter OFF (meaning you are in natural shutter of 1/)
Shutter switch is located front of camera under lens. Shut it off for this shot.
It will then be whatever the frame rate is set at. For ex. 24P = 1/24, 60P = 1/60
I have heard shutter off solves this problem.
Thanks for that feedback, guys. I tested the camera in all modes with shutter OFF and also at common shutters…1/48, 1/60, 1/125, etc. Turning shutter OFF really does seem to help, but from my initial analysis does NOT completely solve the rolling/strobe behavior. I am staring right now at a framegrab of a digital camera flash shot straight into the EX1 lens @ 1080/24p with shutter OFF, and I see the top of the flash cut off in a smooth line. Similar to the clip shown above, only less obvious when played back at full speed. I am working my butt off to get this stuff shot, documented, and uploaded for you all to peruse. I will try to post full rez examples of this latest flash test sometime insanely late tonight. Thanks for all the assistance, feedback, and patience.
I want to make a quick note…even after seeing this strobe issue, and a few other concerns…I am likely to purchase one of these cameras for myself.
-Matt
Rolling shutter is not a CMOS issue per se, but an issue with a particular design of CMOS. And not all such are equal as many are faster (and less prone to issues) than others. CCDs are not perfect either and are known for such issues as flare. The shutter on film also acts like a fast rolling shutter, showing similar splitting artifacts on flashes and diagonals on pans.
Well stated, Graeme. I remember seeing a link on the Reduser forum the other day to a film-sourced shot of Pitch Black where they had apparently neglected to sync light sources with the film shutter…looked a lot like the image behavior we are seeing here.
-Matt
It’d be hard to sync the police car to the camcorder, and that level of technical image control is out of the hands of most indie shooters at the price level this camcorder is aimed at. Hollywood features can go to the trouble of replacing the car’s strobes with syncable film devices.
Also, unless I’m mistaken, aren’t film shutters round and have adjustable angles? As much as they may be “rolling” shutters and expose a frame of film in a rolling pattern, it would also seem that they would expose the film with an angle at the top and bottom because the blade of the shutter is not far enough away from the center of the spinning shutter disk to give a true horizontal line to the film frame.
http://en.wikipedia.org/wiki/Image:Moviecam_schematic_animation.gif
CMOS imagers, OTOH, offer the ability to sample the sensors differently than CCDs, which dump a whole image, at a specific frame rate. Sony has used this to offer “high speed” videography (a reduced image quality) on their consumer and prosumer camcorders. So why not make the CMOS imager dump the whole frame like a CCD?
I’m not saying one or the other is right… but as we move to more progressive display devices, progressive imaging (not a rolling shutter) really seems to be necessary to accurately represent what we “thought” we saw with our eyes.
Anthony
Anthony, you can do that, but there are trade-offs. It’s not simple and CCD is not the answer to all problems and creates some of it’s own.
Graeme,
I have often wondered, especially with my great interest in Red, what some of the limitations or problems with a global CMOS system might be. Can you elaborate for me please, this is something I have often wondered.
I’d love to, but I only know enough about sensors to be dangerous. I’m like one of those who say “I’m not a Doctor, I only play one on TV.”
But with any device that has numerous aspects of “quality”, you can often increase one aspect by reducing another. Similarly, size, heat, power, cost etc. All those parameters end up being interrelated, and you can’t just change one without an impact on the other.
Graeme
I really wish you would have done that flash test with your shirt off. :(
damn, i was all set in getting this camera in march or april.
I’m loving the thought of Matt hanging out in the weeds waiting for someone to get pulled over. You have a lot of experience shooting from the bushes?
ROFLING,
He’ll never tall :)
Guerrilla Filmmaking, baby! :-)
-MJ
You can see a few EX1 rolling shutter/strobe interactions in this clip from wedding filmmaker Daniel Boswell: http://homepage.mac.com/epiphany2002/25.mov
(spotted here: http://www.videouniversity.com/forums/gforum.cgi?post=406702#406702)
It’s a 60p overcranked shot that he slowed down further in post. The strobes hit the rolling shutter about 2 seconds into the clip.
-Matt Jeppsen
RE: You can see a few EX1 rolling shutter/strobe interactions in this clip from wedding filmmaker Daniel Boswell: http://homepage.mac.com/epiphany2002/25.mov
The strobing is not so bad when you play the clip in real time.
For a little perspective on this rolling shutter strobe failing of CMOS sensors, have a look at this footage from a RED camera.
http://ftp.datausa.com/imageshoppe/outgoing/SHUTTER_STUDIES/STROBE&ROLLING_SHUTTER.mov
Let me remind you of the price points we’re talking about here…
XDCAM EX1 = $6500-ish for a basic setup (SxS card, battery).
RED One = $25,000 - $30,000-ish for a basic setup (body, lenses, rods, CF storage, batteries, follow focus, etc).
Both cameras use CMOS imagers as the base (well that is singular for the Red), both exhibit similar rolling shutter artifacts. Neither camera can be discounted on this single issue alone though, they offer too many other options and capabilities, and many shooters won’t be affected by the strobe and skew issues. It all depends on where you are as a shooter, what your production needs are, and what you are willing to put up with at a given price point.
Just food for thought.
-Matt Jeppsen
Hmmm digesting brain food…still hungry…time to rummage for a midnight snack…I’m thinking codec compression and glass of milk, :)
I’ve seen the RED ONE camera’s rolling shutter artifacts. They match the EX1 very close.
Also, I heard the RED ONE upgrade impovement is only around 10%.
It’s still going to be there.
You still get awesome footage from the EX1 and RED ONE (RED ONE better of course).
As mentioned by many, all cameras are tools, some are better in some areas than others.
For instance, in the sub $10K the EX1 excels in rez and low noise and offers 10 bit 4:2:2
via SDI.
The HVX200 is still quite the capable camera and would come in great where shots that
are sensitive to rolling shutter.
It’s about what you’re willing to live with.
Myself, since rolling shutter artifacts crawl up far less than needing low noise and high rez,
I chose the EX1.
How would the EX1 handle say Blinders at a concert? How about others lights like Martins and the like. If I was shooting a concert professionaly what would be the maximum speed that the Lighting Directer can strobe?
It would need to be slower than 1/24th of a second.
I’ve been using my EX-1 for about 5 weeks now and absolutely love it. It’s the camera I’ve been waiting for (and the Red, of course).
I’m most impressed by the exposure latitude, which IMHO, is a more important factor for a filmic look than resolution (but of course with the EX-1, I get that too).
The rolling shutter issue is really the ONLY thing slightly negative thing I could say about the EX-1. That said, here’s what I’ve learned…
The problem rarely comes up. In the five weeks that I’ve been shooting with the EX-1, I’ve only had it crop up twice.
1. During a major ice storm that hit Missouri when I decided to brave the elements and get some shots of linemen repairing downed power lines. The strobes on their trucks exhibited rolling shutter very similar to the police car shot posted above.
2. While shooting 60fps slow motion 24P footage under fluorescent shop lights in a tire shop. I knew this wouldn’t work, but I shot it anyway.
A 35 mm film camera would also have issues in these scenarios that the DP would be expected to deal with. In actuality, the EX-1 makes them easier to deal with than a film cam.
I shot some additional flashing emergency lights with the shutter in SLS (accumulated shutter mode) with a 2 frame accumulation period and the rolling shutter disappeared. The extra light captured also made the nighttime exposure look perfectly lit using nothing more than available light.
Now if this were a fast moving shot or had people running through the shot, the 2 frame exposure would add too much motion blur (unless you’re going for a CSI crime scene flashback look), but for static establishing shots or shots with limited motion, it’s a great way to solve the rolling shutter issue and avoid breaking out the HMIs.
As for the tire shop scenario, I’m not sure if it would work. I don’t know if SLS is available when shooting in slow motion mode at 24P.
What we all do is part science, part art… I think by playing around with the camera and all of the many settings, a good DP can get remarkable results in most situations.
That said, I still probably wouldn’t use it to shoot a Radiohead concert. A camera that is suitable for 99.5% of shooting situations is still pretty damn good in my book though.
hi i have ex1 and this is just shutter seting in tlcs , speed 0+- and ON auto shutter 1/250
The more I read, the more I settle in this nice spot I have on the fence. I see shots where the rolling shutter is a big deal, and other shots where you don’t see problems at all. I see shots with skew on a pan, and others the shot looks fine. What do I do? I really want the EX1, but I’m worried that I will have a ton of problems unless I am shooting still shots of interviews. Is it going to cause me problems tracking points in post? My only other option is the HVX-200a. What say you?
DaveChap, the EX1 is a fine camera. Rolling shutter will exhibit itself on fast pans, speedy dolly moves, strobes, etc. But so long as you are aware of the limitations and work around them as much as possible, it creates a beautiful image and has very good dynamic range for an HD camcorder (it’s not that far from the Red, IMHO).
If you absolutely cannot deal with the possibility of skew, then go with a CCD option like the HVX. Or perhaps look into the new Ikonoskop camera. But the EX1 kicks the HVX’s butt in most areas, and I’d choose it first if you can deal with some CMOS issues.
-MJ
If you got the EX1 then you need the Hood-Pro accessory and you will never want for an EX3! See Phil Bloom’s and Adam Wilt’s reviews at http://www.hood-pro.com
I organised a shooting of a concert. Very low light and a photographer next to the cameras who was constantly shooting. Among other cameras we used two Ex 1s. Both of them have terrible artifacts on the footage. Other cameras XH A1 or Z1 dont. And apart from Ex1 being a great great camera this issue is unsolved and this concert will never be broadcasted by any tv station beacause of these artifacts.
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Great blog.Thanks a lot.