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Greenscreen For Low Light

Published : 7th January 2007

Hi there

I shot some greenscreen yesterday for Varicam. Has anyone had any experience for Varicam with greenscreen? We were testing it on set capturing via a Panasonic 1200a deck with a firewire into final cut pro HD on a G4 laptop. At the beginning we had major compression artefacts and the after effects guy's opinion was that Varicam is compressed so much that was the reason why. Somebody's opinion was that apple's final cut pro codec is a bit dodgy for this sort of work. So the after effects guy downloaded a new codec and already that improved the quality 10 fold and almost eliminated the compression artefacts.


Any thoughts?

Also - this is more related to lighting. We had a scene where a guitarist is supposed to walk out across a stage and join some other musicians who are already playing on the stage. The lighting on stage was spot front lit, looked like by a leico or some other follow spot. The guitarist would in fact be walking out in shadow, and then into the spot light.

My question here and I discussed it with the after effects guy on set, we had this discussion late as it was a last minute add in shot, was to light for the green and have him lit right with spot and he would make the first part of the guy's walk to be in shadow, rather than have me light for the shadow and then have the green under exposed in parts. The only problem this caused was to match the style of lighting in the background footage, ended up causing a hard shadow on the green screen.

How would one normally compensate for matching a style of lighting in background footage that doesn't treat green screen lighting well, like for perhaps this scenario?

Cheers as always

Matthew Woolf
NYC DP


class="style15">>> I shot some greenscreen yesterday for Varicam. Has anyone had any >> experience for Varicam with green screen?

You are trying to send a boy to do a man's job. the Varicam, has 40% less Megabytes per second, so the data you are capturing in not conducive to clean mattes, a lot like 16mm. the F900 with 144MBPS is gathering more than 40% data vs, Panasonic.

Also to consider, Varicam only offers 1M pixels, the f900 2m . . .both are progressive

The f900 is the same system used when Lucas did star wars.

Compare the F900 in a similar set up and you'll find that even if you are not clear on how to set up the camera you are going to get clean mattes.

Good luck.

Rick Thompson
Richmarc HD


Interesting... I have noticed artifacts on every TVC I have shot with the Varicam. Always in the tone around a stop darker than 18% grey.


A frustrating phenomenon. All these jobs were edited on Final Cut Pro in FCP's DVC PRO HD codec, and graded in SHAKE. Do you remember the codec plug in name, or where I can find it?

I would Very much appreciate the downloadable source...

Cheers,

Dan Freene
Director of Photography
Advertising Advantage, Sydney. Australia


My experience shooting green/blue screen with the Varicam is that capturing all footage in 10-bit 4:2:2 uncompressed and do the keying in that codec gives superior results to capturing through FireWire/1200 deck/DVCPRO HD codec. Only let the camera do one generation of DVCPRO HD compression. Then stay away from that codec in post.

The material I have shot with the Varicam for SD delivery/post have achieved the best results by doing a hardware downconversion and then key on the 10-bit uncompressed SD files after that. Capturing through FireWire with the 1200 deck and doing a software downconversion with f.ex. Apple's Compressor 2 does not look as good.

When I shoot in FilmRec mode (which I do about 95% of the time) the camera seems to be sacrificing some bits in the shadows for bits in the highlights, so sometimes the shadows look kind of blocky. In the new Varicam H-version there is an option for "Dark" compression, supposedly allocating more bits to the dark parts, although I have not tested that yet.

Just my 2 cents...

Cheers,

Aasulv Wolf Austad, fnf
Director of Photography


Matthew et al

Yes. I have shot an entire feature in front of a greenscreen for Scott Billups regarding those artifacts :

I'll bet they were not caused by compression. More likely the firewire choked on the bit rate. Scott and I captured via HD-SDI. I also wonder about the processing speed of your laptop. We usually lug around a G5 with dual processor. You are asking a lot of a little engine by relying solely on a laptop.

I will try to answer your lighting questions, but I am thumb typing on set right now....

Later

Joe di Gennaro
DP
North Hollywood CA


Joe

Thanks for the post - would love to tap your brain re : the feature sometime

Cheers

Matthew Woolf
NYC DP


Guys, this really isn't a camera issue, it's the post system that's the problem.

If you use a true uncompressed post system, so the only compression is that done in-camera, the results will be a lot better.

In actuality, the true difference between Varicam & HDcam (f900), both recording to in-camera tape not external capture, is very little due to the heavier compression, pre-filtering, pixel reduction & 8 bit recording of HDcam.

What you need are men's post toys, not boy's!

Steve

Steve Shaw
Digital Praxis Ltd
www.digitalpraxis.net


I shoot green screen with my Varicam regularly, and have none of the problems referenced above, nor artifacts in low light. I am posting with an AVID HD Adrenaline, and suspect that some of your problems come from your keying software or technique. Obviously, the green needs to be clean and evenly lit, but with this accomplished you shouldn't have any camera realted problems in easily coming up with a clean key.

Rod Paul


class="style15">>> What you need are men's post toys, not boy's!

Whilst Steve and I may differ at times I can only say that he is spot on here.

Geoff

Listmum



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