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Old May 11th, 2008, 04:06 AM   #16
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Originally Posted by Richard Andrewski View Post
Not necessary to gel these to match your subject lighting. Green is green for the most part and daylight color temp is IMHO better for getting a truer green. You'll white balance to the subject / foreground lighting hopefully with the green screen lighting turned off. Then after white balance, turn the screen lighting back on and you're ready to go.
Cheers Richard. I guess then it's a case of not mismatching colour temps on the green screen itself but as your lighting the screen and subject separately this will not matter.
The fluorescent tripod worklight I purchased might be handy as a fill but on quick tests last night not so good as a 'directional' key. Still toying with trying one of the cheaper halogens for this purpose, keeping the (when I pick them up) flori twin tubes for the screen itself. I probably sound panicky and anxious here but such is the fast turnaround (and never having done this before) that I can't help it...forgive me!

Thanks alot all.
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Old May 11th, 2008, 04:24 AM   #17
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Actually, you need to light and white balance for the green screen. That green has to be green. Not tinged with yellow, magenta or blue. The foreground can be lit with anything, as long as it's not spilling on the green screen.

If you're doing full-body work, then you'll have to light for the green environment and do any color grading in post. Some Hollywood productions use partial sets, with realistic floors or ground surfaces surrounded by green screen environments. http://www.studiodaily.com/main/casestudies/6503.html

Chroma key is, by definition, keying with color. So having a unique background that's different from anything else in the frame is the "key" -- pun somewhat unintended.

Primatte can pull some amazing keys in trying conditions -- I did it with a guy who happened to wear a green shirt -- but give yourself the best chance of doing it well and get that green screen as close to perfect as practically possible.
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Old May 11th, 2008, 04:25 AM   #18
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Surprised that having a back light or not having one has split opinions, hopefully when I play with Primatte I'll get away with not having one.
Cheers.
A hairlight will seperate your subject from the background and that is what you often want, however when you are compositing your main goal is to match the lighting in the background.

As you intend to use a white background, using a hairlight will, imho, be nessesary to prevent the finished product from looking 'flat'.

George/

P.S. Haven't you shot anything yet?
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Old May 11th, 2008, 04:35 AM   #19
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Just a thought: If this is a shot that's absolutely going to end up with a white background, then why not just shoot with a white background?

Light the white backdrop to get around 90 to 95 IRE, then light the talent seperately. Similar principals to lighting for green screen, but the goal is to get a nice bright white behind the talent.

All lights will have to match in terms of color temperature and spectral distribution.

And, yes, a hair light will give that needed sparkle to keep it from appearing drab.

Shooting against green to get a white background is a complicated approach to a simple problem. I should have read the original post more carefully.
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Old May 11th, 2008, 04:38 AM   #20
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Originally Posted by Dean Sensui View Post
Actually, you need to light and white balance for the green screen. That green has to be green. Not tinged with yellow, magenta or blue. The foreground can be lit with anything, as long as it's not spilling on the green screen.
Hi Dean,

This looks confusing. You must correctly light 1) the bg and 2) the talent.

Sure you must get an even bg without hotspots (near the subject), but whitebalancing for the bg lighting is not correct, especially if you're using different, uncoordinated lightsources for lighting the talent.

You should whitebalance to the talent. It is much easier in post and the bg color is far less important, especially with a good keyer.

Spill is more of a problem when the bg color spills onto the talent, which can be tricky to get rid of although 'modern' keyers have good spill supression. If foregroung lighting spills onto the background, you get hotspots; always good to avoid those as well.

George/
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Old May 11th, 2008, 05:17 AM   #21
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You should whitebalance to the talent. It is much easier in post and the bg color is far less important, especially with a good keyer.
Over the past few years I learned (the hard way) that the background is critically important in getting the best possible key. That's where I see a lot of guys end up struggling in post. While you sometimes can get by with a badly lit background, there's always a lot less pain and suffering if it's correctly and evenly lit.

A badly exposed background can force a compositor to resort to masking several layers with different keys to deal with problem areas, or even having to rotoscope fingers.

I've done my share of rescuing bad green screen and invariably it's because the shot wasn't planned or executed properly. In one case it was a guy who wanted a certain pastel look, and programmed that in-camera. Tough key because there was seldom enough good chroma data for the keyer to lock-in upon.

Another time a director asked to warm up the shot in-camera to compensate for pale skin tone. I told him we'd do that in post -- the scene had to be kept "straight" to ensure a good key off the background. Warming it up would skew the green and possibly make it tough for any keyer to do the best possible job.

You're right about lighting the foreground properly. In fact, ideally everything should be carefully lit using matched sources. Mixing fluorescents with halogens and HMI's will create a nasty mess of odd highlights and contaminated shadows.

Still, if someone wanted to put the talent under some dramatic gelled lights, that's not a problem. At least as long as they're not actually seen standing on the green field itself.

I'm in the process of doing a small job where some footage shot with a Red One was delivered here, and neither Primatte nor Keylight could do a good job of it. The shot was extracted from the raw source undersaturated. The green in some parts were almost grey. Blue objects couldn't be separated from the green screen, and that's unusual for a keyer like Primatte.

I re-acquired the footage from the Red Raw source, and gave it a normal amount of saturation. It made a world of difference. Having a good green channel gives the keyer the best chance of extracting a clean key. And if the director wants to desaturate the scene or heavily grade it, he can do it after the key is extracted.

But first, it is vitally important to get a good chroma value in-camera. Trying to achieve a given chroma value after the fact in post is never as effective. An extreme example would be shooting green screen with black-and-white film. No post-production process will ever get that green value into the image.

It's a similar principal when trying to fix a skewed green in post. While the green might end up in the right place with enough tweaking, the relative values of the rest of the scene could get pulled right along with it. And soon fine details like hair disappear, translucent objects become transparent, and smooth edges turn rough.

Sometimes 15 minutes spent doing it exactly right in the studio will save 15 hours of trying to get it right in After Effects. This is a lesson I learned the hard way.
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Old May 11th, 2008, 05:25 AM   #22
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A hairlight will seperate your subject from the background and that is what you often want, however when you are compositing your main goal is to match the lighting in the background.

As you intend to use a white background, using a hairlight will, imho, be nessesary to prevent the finished product from looking 'flat'.

George/

P.S. Haven't you shot anything yet?
I haven't as yet...but I will be later on today. My main concern was getting a light set up on an extremely restricted budget, and not getting the incorrect mix of lights. As it turned out the lights Richard and others have mentioned (flori twin 4 footers) have been out of stock virtually everywhere in my local region. I have just found another store which states they are in stock so I'm nipping there shortly.

The light I did pick up (flori on a tripod) seems good for a fill, but less so for a key and I'm worried that it will spill onto the screen (unless I can 'park' it to the left/right of the subject and miss out the screen.
The other option was to use either a 150w or 500w halogen worklight for the fill/key - but confused over whether mixing lights temp is ok (bearing in mind you treat the bg and fg separately).

Those flori's always look a little cold to me...perfect for 'post modern russian sci fi' flicks...or is it just me?

Cheers.
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Old May 11th, 2008, 05:38 AM   #23
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You're right about lighting the foreground properly. In fact, ideally everything should be carefully lit using matched sources. Mixing fluorescents with halogens and HMI's will create a nasty mess of odd highlights and contaminated shadows.
I guess that answers my question about mixing lights!

Just worried I wont get a decent key with the flori's...in the ideal world have a direction arri key would be fantastic but that's not currently possible. I suppose I could create a barn for the tripod flori (or purchase one of Richard's). Good thing about these I suppose is the lack of heat.

How does this set up sound?:

left and right for green screen - 2 x twin 4' flori tubes with diffusers.

flori on tripod (possibly with mocked up barn door).

flori on clamp/tripod for back light?

Go with white balancing the subject rather than the screen?

Cheers...it's been a wonderful crash course over the past couple of days...hopefully I can apply the knowledge fairly successfully in the physical realm today.
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Old May 11th, 2008, 01:08 PM   #24
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OK folks...

couple of pics from the set up, whilst my camera warms up.

For the most part the screen is flat and evenly lit (had to 'rope' the sides to pull the cotton tight) only a slight issue over the top fifth starts to darken a little, but as the 'subject' in the test will be sat down this more than likely won't be seen by the cam (it looks a lot worse on the digi camera shots by the way). This is due to the Flori 4' lights not being high enough up but until I can find (or build) a tripod I'll have to use people sat down or small people (such as my daughters :) ).
I could've perhaps done with grabbing higher rated tubes - they came with 36w inside but can take up to 58w.
The subject will be around 5' from the screen and lit by the flori tripod (from their left and virtually no spill onto the green screen.

So here's my first attempt a setting up...hardly kinoflo in hollywood (see third attachment) but hopefully I can get something out of it...

http://farm3.static.flickr.com/2283/...acfd57.jpg?v=0

http://farm3.static.flickr.com/2248/...19785d.jpg?v=0

http://www.kinoflo.com/Image%20Gif/P...0Screen/1a.gif

Comments, as always, most welcome....now to start a test shot...
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Old May 11th, 2008, 03:39 PM   #25
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David, you may or may not need to "barn door" your screen lights off the subject. See what it looks like.

If you do need to, you can probably mask all you want with some duct/gaffers tape, cardboard, and aluminum foil.

Do test your key through a trial composite before shooting something that matters.
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Old May 12th, 2008, 10:16 AM   #26
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David, you may or may not need to "barn door" your screen lights off the subject. See what it looks like.

If you do need to, you can probably mask all you want with some duct/gaffers tape, cardboard, and aluminum foil.

Do test your key through a trial composite before shooting something that matters.
It was fairly hard for my [untrained] eye to gather whether light from this tripod flori was spilling directly onto the screen or whether this was a small amount of light bounced back from walls/ceiling. It was very limited, but I made up a cardboard 'barn door' anyway.

See here (suppress the giggles at the back!):

http://farm3.static.flickr.com/2218/...4dfb24.jpg?v=0

I think for further tests I'll add 4 x 58w (instead of 36w) for the screen.
I don't suppose you can purchase tungsten and/or daylight balanced tubes for the shop lights (as with kinoflo)? I guess that's asking too much of them isn't it?
I may also add a further tripod flori (energy saving type) as a backlight.
Met with the client today but that was to discuss another job...I'll be attempting the keying later today.
Cheers.
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Old May 12th, 2008, 10:45 AM   #27
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It was fairly hard for my [untrained] eye to gather whether light from this tripod flori was spilling directly onto the screen ...
I think for further tests I'll add 4 x 58w (instead of 36w) for the screen.
I don't suppose you can purchase tungsten and/or daylight balanced tubes for the shop lights (as with kinoflo)? I guess that's asking too much of them isn't it? ....
Sorry, on the run this morning but will look at pix later. A little spill is OK. I was concerned about screen lights spilling on subject. But that may be ok too, depending on color temp.

Here in the colonies, "warm white" is usually approximately tungsten. "Cool white" is usually aproximately daylight. If you go to the bulb manufacturer's web site you can find actual color temps and cri.
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Old May 12th, 2008, 10:53 AM   #28
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^^ I don't think the screen lights were spilling to be fair. The 'subject' was about 5 foot away and the bulbs at 36w (x4) aren't that bright. When I pick up some higher watted types I may think of building some kind of shade for tube lights (like you see with the kinoflo's).

Thanks Seth.
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Old May 12th, 2008, 02:15 PM   #29
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David,

What Fluoro light are you using for your key?

mike
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Old May 12th, 2008, 02:56 PM   #30
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David,

What Fluoro light are you using for your key?

mike
This 'beautiful' beast...it's the only one I could find to match the fluori tube/shop lights without resorting to halogen. Adhering to my blinkin tight budget I've used this as both fill and key:

http://www.screwfix.co.uk/prods/4993...gle-Tripod-42W
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