Green Screen shooting

Jon Rosenbloom · December 15, 2004

Hi all,

Two questions: First, how does the search engine on this forum work? I enter key words like "green screen," and get no response.

Second: My next assignment involves a green screen. I've been present on plenty of green screen days as a technician, but this will be my first as the shooter. Here's what I'm planning: Light the screen (12'x20') evenly w/ kinos, and hang black teasers and curtains right up to the frameline. (I'll keep the "set" in front of the teasers. My actor lights are tungsten, so I'm going to have the green screen lights be tungsten too, or, will it help to put some daylight bulbs in the kinos?

Even though I'm shooting on the DVX-100a, I might bring my incident meter. How should the green screen exposure compare to the actors' exposure? Same stop, less, more??

We'll be shooting in 24p or 24pa. Will the plates have to be shot in the same format? In fact, if I shoot in 24pa, will the principal photography and the plates will have mismatched judder frames which will ruin the whole thing?

What else am I missing? I'm good at getting everything together, and lighting and shooting, but I tend to blank out when considering digital shooting, and post options. (Keep in mind my thread in the SDX-900 forum.)

Thanks for the info.

Joe Black · December 16, 2004

Hi all,
Two questions: First, how does the search engine on this forum work? I enter key words like "green screen," and get no response.

Second: My next assignment involves a green screen. I've been present on plenty of green screen days as a technician, but this will be my first as the shooter. Here's what I'm planning: Light the screen (12'x20') evenly w/ kinos, and hang black teasers and curtains right up to the frameline. (I'll keep the "set" in front of the teasers. My actor lights are tungsten, so I'm going to have the green screen lights be tungsten too, or, will it help to put some daylight bulbs in the kinos?

Even though I'm shooting on the DVX-100a, I might bring my incident meter. How should the green screen exposure compare to the actors' exposure? Same stop, less, more??

We'll be shooting in 24p or 24pa. Will the plates have to be shot in the same format? In fact, if I shoot in 24pa, will the principal photography and the plates will have mismatched judder frames which will ruin the whole thing?

What else am I missing? I'm good at getting everything together, and lighting and shooting, but I tend to blank out when considering digital shooting, and post options. (Keep in mind my thread in the SDX-900 forum.)

Thanks for the info.

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I think this guy pretty much did it as good as it gets as far as home affordable greenscreen techniques...

http://www.dvxuser.com/cgi-bin/DVX2/YaBB.p...;num=1096268069

You should ask this guy.

He did a pretty damn good job with this shot.

Edited December 16, 2004 by Joe Black

Phil Rhodes · December 16, 2004

Hi,

That's actually not a bad result - especially considering that really is an atrociously badly lit greenscreen.

Phil

Vivian Zetetick · January 5, 2005

The brighter the green the better! Also, don't forget: during the green screen shoot, make sure you turn off the "cine-gamma" settings. Go back to the original "standard" factory settings on the camera so the image has the most "punch". this will help separate the green from the non-green.

I recently worked on a short movie using the DVX100a, and we did some green screen work which came out pretty well, but we regretted not having brighter lights on the green screen itself.

Since we were using moving still photos for background plates, I cannot comment on what the image might look like if the plates were shot live in a different format. Also, our image was so highly processed in post (like the "sky captain" example above) that many artifacts disappeared in the mix. Here's a sample:

http://pentaworks.org/blackballoon/blackballoon72dpi.jpg

That image was actually shot on a perfectly clear day -- not a cloud in the sky. We used the blue of the sky as a poor man's blue screen. The clouds were added in post, as was the "film damage" effect and the circular blur which gave the image a narrower depth of field & disguised some obvious DV stair-stepping on the narrow bamboo rods holding up the balloon. I think a heavily processed look helps hide things a bit. To see it all in motion looks even better.

Riku Naskali · January 7, 2005

The brighter the green the better!

Wouldn't this depend on the compositioning program? I think Ultimatte works best when the screen is something like one stop under? I've had the assumption that every compositioning program is a little bit different? I'm sure I've read about this many times before on some archives, maybe on cinematography.net

Phil Rhodes · January 7, 2005

Hi,

The problem with making the screen bright is that you inevitably increase all three colour channels. If you can decrease them all to the point where the two you don't want are zero, you have achieved 100% saturation irrespective of how dim it is and you're giving yourself the best possible chance for the key. If you make it so bright that the green channel is full (if you're keying on green) but the red and blue are at 25%, then that's less saturated than just having 75% green and no red and blue at all.

Phil

Vivian Zetetick · January 8, 2005

Good points, I think. Our challenge in post was that the green screen wasn't lit evenly, so that some areas were a slightly darker green than others, and therefore resisted keying. It's a challenging process, especially when, like us, you are flying on a wing and a prayer.

Mark Allen · January 8, 2005

The brighter the green the better!
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I don't know about that. I think a big screen too bright can lead to a lot of wrap around which is not good for compositing.

good things -

1) mask off whatever is not behind the actor or their shadows (if you're using shadows). Minimize the amount of green showing as much as possible - if the floor is green and your shots are waist up - lay down the duvateen. Spill is the killer.

2) just not that most light khaki is not a green friendly color - it likes to absorb it and then key out.

3) get your actors as far away from the screen as possible (if they are far enough away even defects in the screen will blur out.

4) personally i don't worry about cables or lights or anything that isn't in the way of something i want in the movie 'cause it all gets garbage matted out anyway.

Edited January 8, 2005 by Mark Douglas

Jon Rosenbloom · January 8, 2005

Forgot that I started this topic. Well, the shoot happenned before the holidays, and the results were pretty laughable, but fairly instructive. Here are the details: The director bought a Canon xl-2, so that's what we used (Mini DV 4:1:1 color). We set it at 30p. We lit the greenscreen w/ four kino's, and we tried to get it 2 stops under the actors' key, but we were down to one bulb at low on each kino, so the difference was more like 1.5 stops. The greenscreen looked great. We bought a little hand steamer, and steamed out the wrinkles. When the gaffer first metered it he said everything was w/in a third to a half stop. We tweaked the lights, and got it to w/in a tenth. The backround plates in the finished piece are seamless. HOWEVER, we shot the plates after shooting the foreground. In shooting the FG, we didn't have much time to keep the talent, and we didn't have any big lights - just a bunch of inkies, really, so I lit it hard, like a warm, sunny afternoon. The BG, of course, was shot on a completely gray, dark, overcast day, so the combination of FG and BG is quite preposterous. (I did suggest waiting for a sunny day.) Last, the director put the elements together using Final Cut's compositor.

All in all, I think the results confirm everything that one is likely to read in these various forums: Mini-DV is not suited for chroma-keying, and Final-Cut's compositor is pretty weak as well. Last, the director was the one doing the compositing, and this was his first experience w/ this sort of project.

More later, if anyone's interested. (I can describe "preposterous.")

Mark Allen · January 9, 2005

Last, the director was the one doing the compositing, and this was his first experience w/ this sort of project.

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People always forget that compositing is really an art and craft as much as doing anything else... like photography. Main mistake most first time compositors make is the work on the entire frame and not pieces of it.

Also DV really isn't great for compositing screen work - those darn big blocks of compression are just hard to get around - but i do see samples of people keying with it now and then - usually pretty stylized though.

Stuart Brereton · January 9, 2005

Hi,

I 've done some bluescreen work with the XL2 fairly recently. Obviously DV compression is an issue, but the editor had no problems with keying it.

The screen was lit with tungsten lamps with Full CTB to about 1 1/2 stops under key. Key light was high, soft and frontal. The was also a soft backlight, although this was a part of the look we wanted, rather than an attempt to remove spill.

It is possible to get a good green or blue key on Mini DV, it's just that DV's compression makes having a correctly and evenly exposed screen essential.

Stuart

devon read · January 19, 2005

Also DV really isn't great for compositing screen work - those darn big blocks of compression are just hard to get around - but i do see samples of people keying with it now and then - usually pretty stylized though.

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To all dv users frustrated with keying a 4:1:1 compressed image, dig:

Check out dvmattepro from DVGarage - the key to what they are doing is using the luminance channel for the details/outline of the subject and the chroma channel for the main chunk of the matte of the subject - i had my doubts hearing about it, but seeing the results i am truly impressed - this certainly does not remove any of the need for a good well lit and even shot, but, shot correctly, the keys that are produced by this pluggin are pretty phenomenol

i'd like to know, however, how well this process would work with Sony's new HDV cam, the FX1? Considering it is being processed through an MPEG2 compressor as it is recorded to tape, I worry that it will be even more difficult to key - anyone have any inside word on this/ seen any tests?

thanks

Phil Rhodes · January 19, 2005

Hi,

The MPEG-2 codec in the FX1 records a 4:2:2 image, so the subsampling is considerably less than you get on NTSC DV - even if it wasn't higher res, which it is. On the other hand, it's really really heavily compressed, which may counteract the advantage. Test time!

Phil