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Old April 11th, 2009, 04:52 AM   #1
Ben Jones
 
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Chroma Key on an EX - any good?

I know people DO use SD DV for chroma key and often get away with it, confounding the theory behind its 4:1:0 (PAL) colour sampling not being good enough for the purpose.

However I have a CK job next week and need to do it at NTSC framerates and in HD. I though the EX3 would be a good hire. How does it's 4:2:0 sampling stack up for CK though - anyone tried it?

My brain doesnt get the 'silly' zero in the sampling ratio equation as I know it DOES sample the red component, at least more than ZERO times asecond!!!! Boffins ehh!!!

Any feedback will be very useful - thanks.

BD
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Old April 11th, 2009, 06:43 AM   #2
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Shoot progressive and it'll key very well.
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Old April 11th, 2009, 07:02 AM   #3
Ben Jones
 
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Thx Craig - have been trawling herefor the past 2 hours (and its sunny outside :-( ) and this together with putting detail menu at 0 seems to be key (if you forgive the pun;-).

What happens when I want to output to an interlaced DVD though? Guess I trawl some more ;-)

BD
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Old April 11th, 2009, 07:19 AM   #4
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Shoot 720p50 and output 25i (which is 50 fields of course).
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Old April 11th, 2009, 07:33 AM   #5
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I have used 60i SD background with a 720 30p keyed talent, and pulled a perfect key in AE.

Final output was 60i SD DVD, it worked beautifully.
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Old April 11th, 2009, 09:52 AM   #6
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Works Great!

We shoot in 1080p, key in FCP.
see example http://www.keystv.com/dynamic/?news=83
we use fabric from CHROMA KEY Blue Green Screen Fabric & Greenscreen Backdrops Effects
we keep the green screen around 50 zebra
Soft boxes on talent
Best, Craig
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Old April 11th, 2009, 02:07 PM   #7
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Hello Ben,

The EX-cameras (EX1 and EX3) is quite suitable for chroma keying. It depends on what type of chroma keying job you´re talking about? (Full body shot incl floor, which is a real challenge. And what type of background/scenario you need to composite into?) If this is your first chroma key challenge, you really need to spend some time planning the job. Maybe even do a test session a few days before the job. Test your keyer and your light rig. Proper lighting is essential to pull any key. Avoid mixed color temperatures during the session (tungsten vs daylight) During the shot, please don´t use sharpening (detail) in the EX-3. Shoot progressive (as other users already have mentioned). If you expect a lot of movement during the shot you should really plan ahead.

Shooing interviews (in a close space) I prefer to use a Reflecmedia rig. (But be careful with shiny objects and/or glasses.) If you have the space and enough light a chroma key fabric is just as fine.

I´ve done quite a few chroma key jobs using the EX3. Due to copyright I´m not allowed to upload footage on the web. But I include a link of a project done by a friend. He uses both EX-1 and EX-3 to do chroma keying: Lene V - chain of fashion stores on Vimeo


Best of luck to you, Ben.

Terje Rian
Producer

Med På Notene
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Old April 11th, 2009, 02:19 PM   #8
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I recently did a chroma key test shoot shooting 1080 30p HQ. When the model was framed down to her waist only, the key looked great. But the client wanted to see the model walking from a distance toward the camera. Because the model was a short distance away, she was about 1/4 the size of the video frame. When I tried to get a good key on her at this distance, the edges didn't look that great (stair-stepped, pixelated). Having your model be as large as possible in the frame really helps you get a good quality key.

Anyone have any experience using the EX1/EX3 chroma key for a "virtual set" where the model is at a greater distance to the camera?
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Old April 11th, 2009, 04:25 PM   #9
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Hello Mitchell,

I recently did a full body chroma key session with the EX-3. I ended up shooting with the camera "on the side" to maintain resolution (1080). The keying was done in AFX using Keylight and Key Correct Pro. The end result worked really well against the white background. As long as the actors where standing still I had no problem pulling the keys I needed. For every actor I ended up using three to five keys. I also had to do some rotoscoping during their movements. Floors are usually a great challenge to master during a chroma key shoot, regardless of what camera you´re using. With the EX-3 you really need to plan shots like this very carefully, but they´re definitely possible to pull it off.

Terje Rian
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Old April 12th, 2009, 07:34 AM   #10
Ben Jones
 
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Thanks for the input guys.

Terje, which Reflecmedia product did you use for that? Does it really work just by reflecting 'horizontal' green light from the LED lights around the lens - wow!

Tussen takk!

BD
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Old April 12th, 2009, 08:09 AM   #11
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Hello Ben,

I use the portable Chromaflex (with both a blue and a green ring, which I can choose from) and a BaseMatte, which makes me able to do full body shots. The rig is excellent for most interviews, BUT you need to experiment a bit with lighting and the background vs foreground luminance balance. Even so, I find it easy to get useable results in small spaces.
Try not to spill light onto the background fabric. You don´t want light hot spots. Even if the rig is very forgiving, it´s always better to maintain foreground vs background light isolation.

For your information a use mainly two KinoFlos Diva Lite 400 (daylight tubes) and a Zylight Z90 as a "top light" in a interview situation (with the Reflecmedia rig).

Værsågod! (You´re welcome!) Your Norwegian is quite good... :-)

Best,
-terje
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Old April 12th, 2009, 04:50 PM   #12
Ben Jones
 
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Thanks for the advice Terje - interesting solution (ohh and the kind comments on my Norwegian - did a few jobs for TV Norge once upon a time & picked up a bit). Hat de bra!

BD
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Old April 12th, 2009, 11:52 PM   #13
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"Chroma Key on an EX - any good?"

As Sarah Palin might say, "you betcha!"

I shot 1080p30 with an Eefx.com green screen. Simple lighting setup with two Tota lights illuminating the background and a single light for the talent.

I posted a reference elsewhere: http://www.hawaiigoesfishing.com/vid...t_2009_psa.mov

Here's another: http://www.hawaiigoesfishing.com/vid...erey_intro.mov

The background is illuminated at 50 IRE and is consistent to within a quarter stop or so. No backlight. No edge lighting.

Compositing is done with After Effects with Primatte. The software can key smoke, hair, transparent items, veils, etc. Primatte is not cheap but it sure has some great tools to fine-tune a key.
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