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Old December 7th, 2008, 09:58 PM   #1
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Green Screen Tips EX3

Hello All -

I'm brand spanking new with my new EX3. I demo'd the camera from Rule before I bought it and as part of the demo I did a simple green screen test and was very impressed. (Brought it into FCP 6.0.4 and even before much tweaking with the green key filter the stuff looked great with my test subject). Well I have a client interview(s) portable green screen shoot this week and was wondering if anyone had tips on green-screening with an EX3 - with the idea that the final product will be an SD DVD and also web enabled content. I have done some minimal green screen with SD cameras in the past but never shot green screen in HD.

I hope to be able to contribute as well as ask questions going forward so thanks in advance for the welcome.

Jay
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Old December 8th, 2008, 03:57 AM   #2
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The key to good Chroma Keying is to make sure you have good lighting on the green/blue screen. Move your subject as far away from the backgound as possible to avoid colour reflection back onto your subject.

I get much cleaner keys with HD than SD, once keyed out I then convert back down to SD
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Old December 8th, 2008, 07:10 AM   #3
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You mention portable green screen, and by this you mean a Reflecmedia set up or
a traditional green screen set up? The two set ups have different challenges and recommendations.

I use both set ups. It depends on what´s best for the shot. Reflecmedia is great for interviews, but not so great scenes with shiny objects (ie glasses). By the way, with a Reflecmedia set up there is no need for you to move your subject far away from the screen. With a traditional green screen set up it´s vital.

The EX-3 is a suberb camera and very suitable for chromakeying work, even if the EX-3´s color space isn´t 4:2:2. Full raster 1920x1080 is clearly an important factor in getting a useable key. I get better keys with the EX-3, than I do with my Panasonic HVX-200, which is able to utilize the prefered 4:2:2 color space.

If you have the right equipment you can record directly from the EX-3´s HD-SDI output instead of recording to the SxS-cards. You´ll get 10-bit out, and the possibility to choose a more suitable codec for chroma keying. If you´re on a Mac, the ProRes HQ is good. You need to find the balance between result and the codec your system can handle. But don´t be afraid to use EX-3 files via XDCAM Transfer.

Even so, I would spend some time to get the lighting right (if you already know what background to use). As Mr. Oliver suggest, an evenly and well lit green screen is needed to the proper results. Avoid spill light and mixed color temperatures. The light ratio between the screen and the subject is also something to concider.
I always test shoot BEFORE I do the actual job (when I have new equipment or need to explore unfamiliar techniques). Be prepared.

FYM: The software I use when I key is After Effects and/or Shake. I´ve never used FCP to key. A good keyer is vital to use. An interview (head shot) is of course more forgiving when it comes to choosing a keyer. I mainly use The Foundry´s Keylight and Red Giant´s Key Correct Pro (check out the keying tutorial for this software).

I´ve had good results shooting with the EX-3 "on the side", to make the most of the available pixels. This gives me also more leeway when it comes to composing the subject in the frame (zoom in and out).

And remember to keep the Details settings in the camera down or off. You can search the web for more info about this. The best of luck with your upcoming session.

-terje
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Old December 8th, 2008, 06:16 PM   #4
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If you really have to stick with the 8 bit 4:2:0 MPEG2 footages, you might want to shoot progressive rather than interlaced. 4:2:0 mpeg2 interlaces the chroma in a pretty destructive way, sampling the color information in between actual lines, leading to artifacts that really lower the quality of your keys.

I totaly agree with the superiority of the full raster source. For some picture comparisons you could have a peak to this page XDCAM EX1 comparé au DVCPROHD HVX200 (it is in french, but you can try automatic translation if you want to read the Translated version of http://www.barrhauss.com/projets/repaire/ex-vs-200/). It features side by side analysis of the luma and chroma of the hvx200 (4:2:2 but from a SD pixel shifted sensor) and the ex1 (4:2:0 from a full raster sensor).

However, if you can solidly record the full raster 10 bit 4:2:2 signal from the HD-SDI output you will really get better results
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Old December 8th, 2008, 06:44 PM   #5
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Quote:
Originally Posted by Jay Childs View Post
if anyone had tips on green-screening with an EX3 - with the idea that the final product will be an SD DVD and also web enabled content.
If you use FCP, get thee a copy of DVmatte Pro from DV Garage.

It's GPU enabled, quick and very high quality. The built in chromakeyer is a toy by comparison.

It helps XDCAM-EX footage by rebuilding the detail lost in some 4:2:0 chromakeys from the luminance channels.
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Old December 8th, 2008, 06:53 PM   #6
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Thanks for the article, Forest. It was an interesting read. It just comfirms that we never should take "old truths" for granted (that 4:2:2 color space is a must for doing chroma keying) and that technical specs are only the half story. Even so I´ll be one of the first to purchase the new Panasonic HPG-20 when it arrives. Utilizing the HD-SDI on the EX-3 is very temping for anyone doing chroma keying regularly :-)
(Owning a lot of P2 cards already makes the HPG-20 the most interesting solution for me, even if there are other excellent alternatives out there.)

-terje
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Old December 8th, 2008, 07:55 PM   #7
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Well HPG-20 is a total other story here. Full raster HD 10 bit 4:2:2 AVC-I matched with a proper Full raster Sensor camera on those well known P2 absolutly seems to me the way to go.
The AVC-intra stuff is however not easy to edit for the time being, as it is pretty heavy on the processing and appears to be not very strong in recompression cycles so this should at least require some testing in order to make sure one can cope with the format, but it sure is a very decent solution, probably one on the best ones at that price level.
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Old December 10th, 2008, 02:48 PM   #8
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Boris chromo key plug-in for FCP works very well for me.
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