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Chroma key question

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Roli Rivelino
Chroma key question
on Jan 18, 2012 at 1:30:27 pm

I'm having a go at my first green screen edit and I'm using the chroma keyer in FCP (first mistake maybe?).

First of all, I'm fairly sure the shoot could have been lit better and the subjects at the back of the studio were too close to the green wall, so not sure if I'm fighting a losing battle here.

On most of the shots I've managed to key out the green, but the problems I'm having is, when one of the subjects, a blonde girl, is on screen her hair looks terrible, it goes all blocky and weird.

I've tried using the spill suppressor and messing about with the parameters in the keyer to no avail.

Is this a common problem, or should I simply be using Shake or Motion instead?

http://www.rolirivelino.com/

System
Mac Pro 2.8Gb quad core
8Gb RAM
1x 320Gb 7200 hardrive
1x 1Tb 7200 hardrive
Nvidia Geforce 8800 512mb Graphics card
1x 1Tb external WD 'My Book' eSata

Equipment
Panasonic AG-HVX 200
Firestore FS-100


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Jeremy Garchow
Re: Chroma key question
on Jan 18, 2012 at 1:54:26 pm

I would not use the built in FCP keyer for this.

There are a multitude of third party keyers for FCP/Motion, most have free trials. If you have shake, I'd try that too.

Of the subject is too close to the wall, you might have a tough time, but try some more capable plugins first.


Keylight
Ultimatte
Phyx
Boris
Red giant

All make chroma keyers for FCS. That should get you started!

Jeremy


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Chris Tompkins
Re: Chroma key question
on Jan 18, 2012 at 2:42:25 pm

Yes, Keylight in AE will work far better.

But up front, with chroma key, Lighting, Lighting, Lighting.

Chris Tompkins
Video Atlanta LLC


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Roli Rivelino
Re: Chroma key question
on Jan 18, 2012 at 3:11:21 pm

Excellent, thanks guys I just had a quick mess around with motion and already got better results.

http://www.rolirivelino.com/

System
Mac Pro 2.8Gb quad core
8Gb RAM
1x 320Gb 7200 hardrive
1x 1Tb 7200 hardrive
Nvidia Geforce 8800 512mb Graphics card
1x 1Tb external WD 'My Book' eSata

Equipment
Panasonic AG-HVX 200
Firestore FS-100


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Joe Barta IV
Re: Chroma key question
on Jan 18, 2012 at 3:14:40 pm

Keylight is excellent and works as a plugin in FCP. Plus, there are many free online tutorials to help you get the most out of it.


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Mark Suszko
Re: Chroma key question
on Jan 18, 2012 at 3:52:43 pm

Nobody said what codec the original project was in. If it's a DV code, it's going to look worse than pro-res or uncompressed or whatever.

I have several keyers available to me but I never get the hate for the stock FCp chromakeyer - it almost always works just fine for me, once I tweak the settings. OTOH, I always try to shoot the source footage very carefully, so as not to make my job toughter.


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Dave LaRonde
Re: Chroma key question
on Jan 18, 2012 at 4:02:02 pm

[Roli Rivelino] "...I'm fairly sure the shoot could have been lit better and the subjects at the back of the studio were too close to the green wall, so not sure if I'm fighting a losing battle here."

Oh, I feel for you. Good lighting is probably the biggest part of pulling a good chroma key.

Next is a camera that can actually record the range of colors that the camera sensor picks up. If you see a camera than can record 4-2-2 color, that's a good chroma keying camera.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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jerry wise
Re: Chroma key question
on Jan 18, 2012 at 4:08:12 pm

dvGarage/dvmatte pro works well also.


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Roli Rivelino
Re: Chroma key question
on Jan 18, 2012 at 7:10:38 pm

Many, many thanks for this wealth of info, I'm going to go with Motion for now because it seems to work at a level my poor lil' brain can handle :-).

It's good to know I'm not alone with these problems.

Oh btw it was shot on a DSLR not sure which one, but if there are any other potential pitfalls/benefits with shooting green screen with or without a DSLR I'm all ears.


Cheers all!

http://www.rolirivelino.com/

System
Mac Pro 2.8Gb quad core
8Gb RAM
1x 320Gb 7200 hardrive
1x 1Tb 7200 hardrive
Nvidia Geforce 8800 512mb Graphics card
1x 1Tb external WD 'My Book' eSata

Equipment
Panasonic AG-HVX 200
Firestore FS-100


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Dave LaRonde
Re: Chroma key question
on Jan 18, 2012 at 7:24:39 pm

[Roli Rivelino] "...it was shot on a DSLR not sure which one, but if there are any other potential pitfalls/benefits with shooting green screen with or without a DSLR I'm all ears."

There's a pitfall: lousy color resolution, aka color sampling.

The video in the following link is sort of old, but it illustrates the difficulties brought on by poor color resolution:







It's probably the best non-technical explanation of the issue I've seen. It's worth 15 minutes of your time. You should know that the color resolution of a DSLR is the same as that of DV, which makes it's "worst case" appearance near the end. But the entire thing is worth watching.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Andrew Somers
Re: Chroma key question
on Jan 18, 2012 at 11:13:15 pm

You should know that the color resolution of a DSLR is the same as that of DV,



Actually, NTSC DV is 4:1:1 and most dSLRs are 4:2:0. The difference is significant for color keying.

As a guide:

4:1:1, the color has full vertical resolution, but only 1/4 of the horizontal resolution.

4:2:0, the color has 1/2 vertical res, and 1/2 the horizontal res.

4:2:2, the color has full vertical resolution, and 1/2 of the horizontal resolution.

4:4:4, the color is "full res" both horizontally and vertically.


It is better for keying operations to have 1/2 res in both axis, than 1/4 res in the horizontal axis. Note that in 4:2:2, there is only 1/2 res in the horizontal axis, and that makes 4:2:2 less than desirable for keying as well. Nevertheless, people do get useable keys from 4:2:2 and 4:2:0 material, though 4:1:1 is horrid to try and pull a key from.


Your best keys will be from 4:4:4 material - 4:2:2 and 4:2:0 with the color being 1/2 res in one or both dimensions will not give the cleanest key. 4:1:1 material with color being 1/4 in the horizontal dimension will give the *worst* key. 3:1:1 (Sony F900) is also terrible for keying.


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Andrew Somers
Re: Chroma key question
on Jan 19, 2012 at 12:15:23 am

I'm having a go at my first green screen edit and I'm using the chroma keyer in FCP



The built in keyer in Final Cut is pretty much worthless.

A plug-in that *is* pretty useful for FCP is:

http://www.dvgarage.com/dvmatte-pro

And it does a surprisingly good job with material that has limited color resolution (4:2:2 and below).


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Roli Rivelino
Re: Chroma key question
on Jan 19, 2012 at 8:25:55 am

Wow, I've never started such an informative thread before, my cup runneth over with info :-).

I'm soaking it up, watching the video and checking out the plugins. Many, many thanks.

http://www.rolirivelino.com/

System
Mac Pro 2.8Gb quad core
8Gb RAM
1x 320Gb 7200 hardrive
1x 1Tb 7200 hardrive
Nvidia Geforce 8800 512mb Graphics card
1x 1Tb external WD 'My Book' eSata

Equipment
Panasonic AG-HVX 200
Firestore FS-100


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