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Old June 17th, 2009, 09:26 AM   #1
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Shutter speed for green screen shoot

Hi guys
I have been doing a number of green screen tests (JVCgyHD110) for a video I'm shooting this weekend. I have noticed that shooting at 1/50th faster movment of hands causes motion blur and keying starts to struggle.

SO...should I simply shoot at an increased shutter speed to sharpen this up !???

Many thanks
Mat
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Old June 17th, 2009, 10:16 AM   #2
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Not unless you want your comps to scream fake.

The art to compositing is making something seem realistic. The key is to make people not even think something was created this way. If you get rid of all the motion blur your comps will end up looking very computer generated.

You need to get better keying tools that can deal with motion blur.
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Old June 17th, 2009, 11:35 AM   #3
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I'm using keylight 1.2 in after effects CS3 - The green screens will have a lot more light on the actual shoot so this should help to get better keying.

This is the clip and the problem is in the hands.
Green_screen_close_test_01 on Vimeo
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Old June 17th, 2009, 08:54 PM   #4
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Shoot with your normal production shutter speed and use better software...

:)
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Old June 18th, 2009, 03:00 AM   #5
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Care to give me a heads up on what 'better software' to look at !?
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Old July 5th, 2009, 02:46 PM   #6
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Primatte works well.
Red Giant Software: Pro Keying Suite 2008
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Old July 8th, 2009, 01:30 PM   #7
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As does my app, dvmatte. :)
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Old July 10th, 2009, 07:27 PM   #8
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I'll put a vote in for Primatte.

You can key translucent plastic, smoke, veils and motion blur. It's worth every penny.
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Old July 11th, 2009, 06:51 AM   #9
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Primatte is great, keylight and ultimatte are also good. if the key is not perfect usually you'll need different keying layers for different parts of the picture. Shake is the best keying software for apple (it has primatte and keylight inside it). It has also some great rotoscoping tools that might help.
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Old July 14th, 2009, 04:05 PM   #10
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I think it's harder to key the higher the shutter speed. It's easier for me to key 30 than 60 (I'm NTSC). It may be be because 60 is interlaced with my set up, and 30 is progressive. But if the higher shutter speed introduces grain for example it will be very difficult.
DV matte is a great tool, but it no longer exists for after effects. I use my older computer to key, just so I can use DV Matte w/ AE.
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Old July 26th, 2009, 12:51 AM   #11
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Hey,
I just finished a shoot with my jvc hd100 using green screen.
My project is 30fps. I got the best looking footage using 30 and 60 shutter.
I still have shmutz on fast moving objects. I used Primatte.
Going frame by frame it doesn't look good but at full speed it isn't too bad.
What I did was used at least two layers, the bottom layer I keyed for the edge, So the bottom layer had a lot of holes, or transparent parts, but the edges and motion blur looked ok. Not great, but ok. Then I made a copy of the layer and adjusted it so there were no transparent areas. The edges were real bad so I used the simple choker and pulled the matte in 2-3 pixels then used the blur edges set at 2-3. On some areas I had to use a 3rd layer to address problems with shmutz and other edge problems. By the time I added a small light wrap, and did the color correction, the footage looked good enough for what I wanted.
The HD 100 isn't a good camera for keying, but I was happy I was able to get my footage looking as good as it does. I think you need to use this method no matter what keying software you use. Also I used animated garbage mattes and kept them pretty tight on all the footage. Hope this helps a little.
Jon
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Old October 4th, 2009, 11:26 PM   #12
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it's very rare to get a good pull using just one keyer. there are a couple methods similar to this that really help yield a good result. my favorite method is to take your original image and distort it with various color tools/brightness/contrast etc... you're effectively trying to cheat the image to make the keyer work better, once you pull the key, the then apply the alpha that your keyer creates to the original footage (via an image mask). doing it this way allows you a few more options in modifying the edge detail, a nice trick is applying blur to selective color channels (ie. the blue channel on film is usually really grainy and putting just a blur on the blue allows the detail in the red and green channel to come through without getting a lot of salt and pepper noise from the grain) you can also use erode and blur tools to modify the edges, directional blur applied to the alpha can help to smooth out hard edges where there should be motion blur.

i'm also a huge fan of using multiple keyers to attack specific areas of the frame, i like using a detail keyer (as weak a key as possible to cut the BG out but maintain translucency for hair/windows/etc. usually this leaves semi transparent areas where you don't want them so you combine the alpha with a more aggressive keyer that is more solid but usually has a really sharp nasty edge. i then shrink/erode the key and/or blur it.

i'm currently working on a big budget movie where there are many long sequences of BS/GS where the actors are sitting in a truck or plane with and without windows and most of the windows have a ton of dirt and crap that has to be retained not to mention reflections. the above plus a couple other little tricks make it a lot easier and require as little roto as possible. when you have 100's of GS shots, roto is the devil.
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