Keying

I have a rather large project coming up using primarily XDCAM EX codec. So, for rendering sake I think I?d like to keep it all all the time lines in that EX codec. However, we are doing some green screen interviews in Panasonic DVCPRO HD 720p.

When it comes to keying, does keying the DCVPRO clip in a 4:2:0 (XDCAM EX) timeline degrade the key? Or should it be in a 4:2:2 time line.

Thanks

Rob Jones

DVCPROHD degrades the key...yes. Much noisier format. More work to pull a clean key. Better have plenty of light for a smooth bkgd or it's hair pullin' time.

When life gives you dilemmas...make dilemmanade.

Wait. We need details here. What's your frame size in XDCAM? What are your deliverables? Are you able to do a live capture via HD-SDI to ProRes for the green screen shoot?



www.strypesinpost.com

Strypes,

If you put DVCPro clip in an XDCam timeline, it's still a DVCPro clip. The timeline is not gonna put color info back in the clip that wasn't shot in the first place.

When life gives you dilemmas...make dilemmanade.

>The timeline is not gonna put color info back in the clip that wasn't shot in the first place.

Point is, that he shouldn't render to XDCAM at all (except for offline preview, as he gets better RT performance editing native). He should be doing his final renders in ProRes, or Uncompressed HD if he has the storage capability.

If he drops a DvcproHD clip into an XDCAM timeline, it will be rendered to XDCAM EX, long GOP, 4:2:0, 35 Mb/s.

But I wanted to be safe, and make sure they didn't shoot at 1080 for the XDCAM EX footage, which will make the 720p DvcproHD footage look effectively like muck. Also, if he has not hit the studio for the green screen shoot, he could look into the possibility of capturing straight from the camera as ProRes, which is much better for keying than either codecs. But that being said, DvcproHD should be sufficient for keying if his final deliverable is SD.

As for the noise on DvcproHD, it depends on whether he's using a camera with 2/3" CCDs or 1/3" CCDs.



www.strypesinpost.com

Yeah, here's the deal with pulling a key.

Say you have a perfect on-set situation. The greenscreen is flatly lit, there's plenty of separation between talent and screen or cyc so you don't get shadows, the screen or cyc is totally out of focus so you don't pick up any texture variations ? say it's all just totally perfect.

And say, further, that you recorded it all on a really high-quality videotape format, like HDCAM SR for example.

You know what? You're still going to struggle a little with pulling your key.

The 4:2:2 chroma subsampling ? where you've got half the horizontal resolution in the color channels as you have in the black-and-white-only image ? just makes video inherently more difficult to key than a 4:4:4 format like scanned film. Yes, the tools have gotten a lot better, driven by demand in the visual effects industry to be able to shoot on something like SR but still pull decent keys quickly, but those tools are expensive and take great skill to use. It is possible to pull a perfect key off 4:2:2 material, but in order to do it quickly you need either some really high-end gear or a highly talented artist, or preferably both.

Once you start throwing compressed video into the mix, it just gets harder still.

What I would do in your case is this:

The footage you need to key has already been shot on DVCPRO HD at 720p resolution. (Actually, your post wasn't entirely clear to me as to whether it's already been shot in that format or whether it's going to be shot in that format, but either way, it's the same.) I'd take that footage, the stuff that needs to be keyed, into After Effects or Shake. Both have decent built-in keyers ? Shake's is much better but requires more practice to use well. I'd pull my keys there.

Then I'd scale down my keyed shots to the appropriate format. Your keys can be a little crunchier, because you're scaling them down to SD for compositing, so that gives you a little margin of error you wouldn't have otherwise had.

Then I'd render out fill and matte layers for each shot, bring them into my Final Cut timeline and do only the compositing there. If you're on a Final Cut 7 system, you can try using ProRes 4444 to contain both the fill and the matte for each shot, which would eliminate the step of using travel mattes in Final Cut to do your compositing, but I haven't actually tried that myself since I'm not on 7 yet, and I can't warn you of any potential pitfalls.

Yes, it's more steps. Yes, it's more complicated. But by doing the keying at full resolution in an uncompressed, 32-bit environment, you're going to get much better results. And once you've rendered out your keyed shots, you can composite them on your timeline to your heart's content without having to re-render the key each time you make a change.

That's what I'd do, but I'm just some weirdo on the Internet.

Thank you,

This has been very informative.

We haven't shot anything yet. The deal is we have 8 EX-3's for the event, and a panasonic hpx300 for interviews. I wanted to keep the rendering to a minimum and planned on staying with the XDCAM EX timetime. But when it came to the interviews on a green screen, wondered if laying those clips onto the XDCAM EX timeline would effect the key.

We send out daily podcasts of the event, and the end product is a DVD. But I'd also like to keep the footage for future reference so storage becomes an issue.

But that makes sense to to do the keying in after effects and send them out to the FCP Pro timeline. Keeping the footage as full as possible until it's keyed.

Am I understanding correctly.

To steal a concept from another thread:

If you're not sure, test it.


www.derekmok.com

Thanks.

I have some time so I'll work on it.

FW it's worth when shooting a Panasonic camera DVCPro HD 720p for green screen.
You will notice in the viewfinder of the camera with markers on
that a level is displayed in percentages in the lower left side.
This percentage is "luminance value"
While lighting your green matte zoom in to the screen and focus.
Pan the green matte left to right and adjust your bkg lighting so that the
percentage is constant and does not change
a 55% level is desired, but 55-60% is fine.
In FCP, first apply the color smoothing 4:2:2, then the FCP chroma keyer.
Viewing only the matte adjust the sliders using the Chroma Keyer tab vs, the Filters tab.
Apply the filter Matte Magic for big ears, wispy hair, green for white.
Lastly apply Color Correction to adjust skin tones but only after you pull the key.

A good rule of thumb is: matte 1/3 -2/3 stops under key.
Bump the chroma up in the camera +1 or +2
Cine D is less orange in the skin tones, but
Cine V is more saturated.
GREEN Saturation is the trick.
If your matte is brightly lit there will be less Sat and more Spill.
An 8' x 8' distance rule helps... Talent 8' from screen, camera 8' from talent.

Here goes: I'm using FCP 6 on a MacBook Pro with OXS 10.5.8. I have a Sony HDV 1080i camera model #HVR-A1U. I can also shoot in DVCAM or DV SD. I'm close to getting a job in which the client wants to put himself walking around on his web site. I'm thinking if I key out the background (perfectly) when I make the movie it will default to a black background. I need to know how to export a transparent background... hope someone can help. Margot