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Canon XL and GL Series DV Camcorders
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Old December 14th, 2006, 12:01 AM   #1
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Very quick n00b question about XL2 and greenscreen

I did a search but couldn't find the answer

I'm a total n00b and was wondering:

For indoor, tungsten lit greenscreen shooting, what frame rate (60i, 30p, 24p) and shutter speed (if that matters) will yeild best key out results?

thanks!
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Old December 14th, 2006, 02:05 AM   #2
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Hi Chris,

avoid interlaced video. It makes keying a nightmare. I don't think 24p or 30p would make much difference, but I lack the experience because over here in PAL land we just have 25p.
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Old December 15th, 2006, 04:47 PM   #3
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I've not had the pleasure of doing any myself for video (only still), but make sure that you have a fairly strong rim light/hair light to separate the foreground from the background and make sure that the green screen is lit as evenly as possible, to avoid different shades of green. This will make it easier in post to key out the green screen. Have fun and good luck. Be sure to let us know how it goes & maybe post a still when your done...

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Old December 16th, 2006, 10:14 AM   #4
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First off, for keying, if you want progressive, 60i/30p and 24p are completely different. If you want your video in the NLE to be a native progressive (non-interlaced) image, with the XL2, you only have one option- 24p. All 3 formats (60i, 30p, 24p) record the frames on the MiniDV tape as 60i, I would suppose to conform to minidv standards. The difference is in the way the sensor records the data, and the way it is tagged on the tape.

60i= sensor records 60i and records 60i to tape
30p=sensor records 30p, splices each frame into 60i, and records 60i to tape
24p=sensor records 24p, splices each frame into a set of repeating and non-repeating fields that add up to 60i, and records 60i to tape.(depends on frame pulldown method used, 2:3 vs 2:3:3:2)

Anyways, If you want "true progressive" video, you have to use 24pa, and then when you capture the footage on your NLE, apply a frame pulldown removal, which will back-convert the 60i interlaced image to look exactly the same as the original 24p image that the sensor recorded.

For a clear explanation on how 24p and pulldown works, check out this page: http://www.adamwilt.com/24p/

Once you have your 24p footage captured, you can edit it as normal, just make sure you use a editing timebase of 24 fps, non-interlaced. If outputting to DVD, encode the MPEG2 at 24 fps, and author the dvd as normal. If outputti back to MiniDV, VHS, or some other analog source, you must re-apply the frame pulldown, using your NLE.

Regarding the greenscreening, there are just a few key points to remember:

1- Make sure the screen is evenly lit.........very important!!!
2- Keep subject as far away from screen as possible to avoid color "spilling"
3- use a shallow DoF (large aperture) to blur out irregularities in the screen
4- Use an overhead kicker light to light the subject from behind, and give them a light "aurora" around their body. This will help avoid green spillage as well as separate them more definitively from the background.

Hope these tips help. Good Luck!
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