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AF100 - dark fringes around edges on greenscreen

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Rick Bovill
AF100 - dark fringes around edges on greenscreen
on Apr 1, 2011 at 10:36:38 am

Hi guys,

We had an AF101 (AF100) to test for a few hours as we are looking at buying one for our university's visual effects course. The company sent someone over with the camera and a Lumix 14-140mm lens. We wanted to demo the nanoflash and other lenses too but they did not bring any.

Anyway, We asked the rep to zero-out the camera and take off any effects, changes or settings that may have been altering the image in anyway. We shot some test footage on our infinity cove and these are the results:

http://img696.imageshack.us/img696/1584/comparew.jpg

Straight away I noticed a very dark fringe around the right hand edges on the image. I'm almost certain I've read about this before when reading about dslr cinematography but I can't find any reference to it anymore. If we do go for the camera we will be getting a nanoflash to go with it so the recording quality won;t be an issue.

Is this dark fringe an artifact derived from the CMOS sensor, or something to to with either the built in 21Mbps recording; standard chroma sampling; lens at the time, or other factor? It might just be a deal breaker for us if it can't be fixed by either a missed setting in the camera or harnessing the nanoflash.


Thanks in advance,
Rick


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Guy McLoughlin
Re: AF100 - dark fringes around edges on greenscreen
on Apr 1, 2011 at 2:15:30 pm

It looks like your lighting needs work. The camera does not create dark edges, but merely records what you put in front of it. Below is a link to a DvxUser thread on using the AF-100 for green screen work, with some sample videos:

DvxUser Thread: "AF-100 for Green Screen Shooting"


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Jeremy Garchow
Re: AF100 - dark fringes around edges on greenscreen
on Apr 2, 2011 at 2:26:25 am

Reminded me of this thread from long ago:

http://forums.creativecow.net/thread/193/868436


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Noah Kadner
Re: AF100 - dark fringes around edges on greenscreen
on Apr 2, 2011 at 4:22:01 am

Also that lens is super slow and not that sharp. I'd highly recommend- a- working on the lighting a bit and b- getting some high quality primes. You can use the Lumix 45mm or 20mm or much better rent some Zeiss Primes and use an F-Mount adapter. The camera shoots incredibly sharp imagery- with the proper glass. The Lumix zooms are ok but not the best the camera can do.

Noah

Unlock the secrets of 24p, HD and Final Cut Studio with Call Box Training. Featuring the Panasonic GH2 and Canon 7D.


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Guy McLoughlin
Re: AF100 - dark fringes around edges on greenscreen
on Apr 2, 2011 at 12:16:34 pm

[Noah Kadner] "Also that lens is super slow and not that sharp. I'd highly recommend- a- working on the lighting a bit and b- getting some high quality primes."

The 14-140mm is actually a pretty sharp lens, but yes it's very slow. I don't think this lens was the limiting factor as far as shooting sharp looking green screen footage.

Prime lenses do make life a lot easier, and the least expensive entry point would be to use still photography lenses with a M4/3 adapter. I bought a Zeiss ZF 50mm f/1.4 to use with the Voightlander Nikon ---> M4/3 adapter, which produces a beautiful image. ( it's the same optics as the Zeiss compact primes without the beautiful/expensive cine housing )

Following the DvxUser AF-100 green-screen thread ( the link that I posted ) it becomes pretty obvious that controlled lighting is crucial to successful green-screen work. Some useful tips were posted like using the wave-form tool built in to the AF-100 to set up proper lighting on the background ( you should see a thin even line at 50 IRE if the background is lit correctly ), having your talent stand far away from the background, edge lighting your talent to ensure proper separation from the background ( you do not want any green background bleed ), and lighting your talent about 2 F-stops brighter than the background. And of course you want to try and match your talent lighting with the lighting of the final background image they are going to be composited into.

FYI: My first green-screen job ( about 10 years ago ) was a disaster mostly because I did not know enough about how to properly set up my lighting ( or how to process the green screen video for computer compositing ), but I swore it would never happen again, and since then I've had no problems.


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Rafael Amador
Re: AF100 - dark fringes around edges on greenscreen
on Apr 4, 2011 at 10:30:55 am

[Guy McLoughlin] "The camera does not create dark edges, but merely records what you put in front of it."
The lens doesn't creates black edges; the camera processor does.

In this case I don't see any Chroma Keying issue.
The fringe shows everywhere, not only against the green background.
For me the idea that this may be caused by any semi-pro lens, is simply a NO-NO.
IMHO is a camera setting or codec issue.
rafael

http://www.nagavideo.com


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Rick Bovill
Re: AF100 - dark fringes around edges on greenscreen
on Apr 5, 2011 at 9:20:07 pm

Hi Guys,

Thanks for the input so far.

We will be going for a whole host of lumix and other primes for this camera when we buy it; but the reps only brought one lens and the body (we did ask for more) so It's all we had to test with, and we did not have long at all.

The greenscreen was lit, albeit not to the level that we would usually light it (not all the lights were available at the time), but as Rafael pointed out: the fringes are not just against the backdrop - you can see them within the talent. We're quite used to shooting on this Cove now and you will notice that there is very little spill on the talent. We would usually spend a lot longer setting up though to be fair.

Thanks for the link to the dvx site; that's been helpful as it seems they are not having the same fringe issues as we had; suggesting it could be something which is not inerrant to the camera / sensor.

We've put the purchase on hold while we contact the rep's and ask them to come back with something that better resembles the kind of kit that we will be buying (nanoflash, primes and so on) It's nice to see that people are getting genuinely impressive results on keyed footage with this camera though!


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Guy McLoughlin
Re: AF100 - dark fringes around edges on greenscreen
on Apr 5, 2011 at 9:49:13 pm

[Rick Bovill] "Thanks for the link to the dvx site; that's been helpful as it seems they are not having the same fringe issues as we had; suggesting it could be something which is not inerrant to the camera / sensor."

I honestly think it all comes down to having very controlled lighting, as you will find that most of the DvxUser posts describe.


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Jeff Regan
Re: AF100 - dark fringes around edges on greenscreen
on Apr 8, 2011 at 2:43:19 pm

This looks like detail circuit overshoot to me, not an optical issue. If the rep. zeroed out the settings, it would explain the issue. Detail must be set below zero for green screen, or any natural looking image.

Try to find out where detail was set or redo with detail at -4 to -7 range. I have shot green screen with the AF100/Ki Pro combination with good results.

Jeff Regan
Shooting Star Video
http://www.ssv.com


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