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Old August 4th, 2007, 10:48 AM   #1
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lighting for full length chromakey

I've done a few chromakey shots recently and have read through the bounty of info there is on t'interweb about how to light greenscreen backgrounds.
Lots of tutorials talk about how to light a background, with the person standing a few metres in front, lit seperately. Normally these setups are for a 3/4 length shot, or a headshot.

I'm trying to shoot a full length person, using a 9' background paper roll.

I can light the background fine - i'm just not sure what to do with the floor and area around the subjects feet etc.

Also on a similar issue - i'm doing some product filming on green screen.
A product sits on the green screen, then a hand lifts it out of shot.
My problem is again, with lighting the area that the product sits on - i tried it using a couple of red heads, but the product was white, so to avoid that bleaching, i had to lower the exposure, which then meant my green was quite dark and i'm struggling to get a decent key from it.

Any advice or tips from people who have done this kinda thing before?

Cheers,

Rob.
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Old August 4th, 2007, 03:53 PM   #2
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Sounds like some separation issues where moving the product further away from the screen would help. Lighting the screen and the foreground subject are two different layers and you shouldn't try to economize by using the same lighting for both. That way exposure issues of screen and subject can be controlled separately. Also, some backlighting of the product or subject may be necessary to get a clean key (majenta gelled backlight for green screen / amber gelled for bluescreen). This is a lot less necessary today though with the spill control algorithms in most keying software. Many times a spacelight lantern setup is used in a green screen stage for evenly lighting the green screen especially when the floor is involved too. Because of the 360 degree lighting coming from this setup, sometimes the person is well covered too by the lighting but may still need some special subject lighting.

The poor man's spacelight is a chinese lantern and that might be a good solution for your screen lighting. Soft diffused lighting on the foreground subject and even on the background so you can control the exposure issues separately. Just try to make sure its even lighting on that screen with no hot spots.
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Old August 5th, 2007, 01:49 AM   #3
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Full-length keying is done fairly often.

It was done with Carl Sagan in a PBS special. He was inserted into re-created environments through a combination of 3D animation and matching bluescreen sets. It enabled the production to put him into locations that no longer exist such as the library of Alexandria.

Some of the scenes in Titanic, including the one where DiCaprio and the other actor playing an Italian immigrant go running to the bow of the ship, were full-length green screen shots. The railings, deck and other ship structures were replicated and painted green, and later matched up with 3D renderings to create the entire ship, ocean, sky, etc.

I did a little of this as well with one full-length shot done with green screen.

I'm using After Effects with Primatte to do the keying. Primatte is a lot more flexible than Keylight or any of the built-in keying filters in FCP. In addition to doing the basic keys, it can control spill, blend in background elements in the edges, maintain details, differentiate among various shades of green, blue or red (whatever it is you're using as the keyed color) and you can also tell it what to keep. Quite powerful and worth the price.
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Old August 6th, 2007, 10:40 AM   #4
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Hi guys,
Thanks for the responses.

I'm kinda on a budget here, but i've hopefully got quite a bit of this work on the way, so i want to get a good setup sorted...which i guess means spending a few dollars...
I can see how seperation would help, but how should i do it for something like the following image?

http://www.visual-ice.net/temp/image...screen_mug.jpg

The mug is actually resting on the greenscreen background. And as you can see, my screen is quite dark, so that the mug doesn't bleach.

I guess chinese lanterns would help here - do these need more powerful lamps than standard 100W domestic types?

Any tips or pointers?

thanks
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Old August 6th, 2007, 11:41 AM   #5
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I can see why a clean key on that shot would be difficult. Subjects are casting several levels of shadow on the screen, and the screen is unevenly lit.

Were it me, I'd get about 18" of 1/2" wood dowel, put a base and a little platform on it, paint it to match, and put the cup on it to get the cup and arm away from direct contact with the screen, trying to reduce/eliminate the shadows as well. It would be nice if you had 4 or 5' of separation between the subjects and screen, it would really make the lighting easier.

Then, you may still have to do some by-hand masking/rotoscoping on the dowel, but, at least most of the cup and all of the arm will be clean.

A good trick for lighting the screen is to turn on camera zebras, and see if you can light the screen such that you get even zebras across it. Usually, you'd then lower the camera exposure by a stop, and put in the foreground pieces (cup, arm), and light them till you have good exposure.

2 chinese lanterns could be a great way to get even screen exposure. I'd first try to mask their light from falling on the subjects and light the foreground separately, but, sometimes you can combine foreground and background lighting.

One thing that is *super* helpful as you're getting first experiences with green screen is to have a laptop or desktop at the shoot with the compositing software you use. If you can cut a clean key and like the look of the foreground lighting, you're done.
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Old August 6th, 2007, 03:46 PM   #6
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First off, the white balance seems too red. That can be a major problem from the start.

And, as Seth mentioned, the lighting is very uneven. While you can have directionality and shadows, you really need to make sure the screen itself gets even illumination. Otherwise you'll find yourself in a rotoscoping nightmare.

The text on the mug has a green similar to your green screen. Another rotoscoping task.

The green of the screen seems warm. Could be related to the white balance of the shot. A purer green would help greatly in keying.

You seem to be shooting interlaced. Shoot progressive for better edges. Also, turn all edge enhancement and sharpening in the camera off. You don't want edges, just transitions. It makes keying easier and more realistic. What can also help is shooting in a format that has good color encoding, something with 4:2:2: sampling. The difference between 4:2:2 and 4:1:1 is dramatic, especially when it comes to those critical edges.

It's possible to eliminate those edges with Primatte's Lightwrap feature but you can also lose the shadows. I kept the shadows in this example.

Attached is what I did with After Effects and Primatte. It's just a rough job but you get the idea.
Attached Thumbnails
lighting for full length chromakey-greenscreen_mug.jpg  
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Old August 6th, 2007, 05:19 PM   #7
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Quote:
Originally Posted by Rob Hughes View Post
Hi guys,
I guess chinese lanterns would help here - do these need more powerful lamps than standard 100W domestic types?

Any tips or pointers?

thanks
Something like this is what I recommend:

http://www.teksupply.com/webapp/wcs/...7C35054&isDoc=

The 200w 8U bulb or a tree of smaller spiral bulbs made with Y socket adapters is also a common solution to this problem. If you use the fluorescent's you may not need a chinese lantern unless you need to tone them down a bit and diffuse even more.

Otherwise, a Photoflood bulb would be the common incandescent placed in a Chinese lantern.
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Old August 6th, 2007, 06:16 PM   #8
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Quote:
Originally Posted by Dean Sensui View Post
...Also, turn all edge enhancement and sharpening in the camera off. You don't want edges, just transitions. It makes keying easier and more realistic....
It's possible to eliminate those edges with Primatte's Lightwrap feature but you can also lose the shadows. I kept the shadows in this example.

Attached is what I did with After Effects and Primatte. It's just a rough job but you get the idea.
ahaha, very nice Dean. I especially like the sand stuck to the arm! At least that's what it looks like. My keyer doesn't have that setting :-)

If you look at Dean's example closely, you will see a black outline around the arm and especially the cup. This is an artificial effect of the in-camera edge enhancement/sharpening that he mentions.
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Old August 6th, 2007, 06:31 PM   #9
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Originally Posted by Seth Bloombaum View Post
I especially like the sand stuck to the arm! At least that's what it looks like. My keyer doesn't have that setting :-)
Some filters create film grain. These filters create sand grain... :-)

Also we should do more to support our country's economy and stop buying Chinese lanterns. Let's encourage everyone to buy American lanterns!!
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Old August 7th, 2007, 05:32 PM   #10
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Cheers for the comments.

I shot this on a sony Z1. I'll have a look and turn off the sharpening etc - i assume this is possible?!??
Quote:
Originally Posted by Dean Sensui View Post
You seem to be shooting interlaced. Shoot progressive for better edges.
since i'm shooting 4:2:1, interlaced, does it help at all to resample the footage to a progressive format before keying?

Photoflood bulb in a Chinese lantern looks good to me. I'll give it a test try before the next job comes along!

Quote:
Originally Posted by Dean Sensui View Post
Attached is what I did with After Effects and Primatte. It's just a rough job but you get the idea.
Dean - thats a pretty good key. I used keylight in AE CS3, but I still had to roto quite a lot - luckily the shots weren't too long!
Did you get that key by having a quick play with the primatte plugin? ie, you didn't have to mess around with any masking etc?
If so, then primatte might be worth the 450....

Cheers,

Rob
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Old August 8th, 2007, 08:31 AM   #11
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oh, and is this the 'primatte' keyer that you refer to?
http://www.redgiantsoftware.com/primattekeyer.html

thanks.
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Old August 9th, 2007, 06:44 AM   #12
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Hi Rob...

"I shot this on a sony Z1. I'll have a look and turn off the sharpening etc - i assume this is possible?!??"

Should be. Just have to rummage through the menus. For example, I thought it wasn't possible with a Sony PD170 but it is.

"since i'm shooting 4:2:1, interlaced, does it help at all to resample the footage to a progressive format before keying?"

It's possible to convert to 4:2:2 with something like the Nattress filters. Primatte also has a feature which helps with reducing artifacts from DV, HDV, etc.

"Did you get that key by having a quick play with the primatte plugin? ie, you didn't have to mess around with any masking etc?"

No roto work at all. Strictly Primatte. That plug-in not only has the user define what's green, but it also has the user define what's not green. A major plus.

Also, there's features such as Lightwrap which helps with making edges look a lot more realistic without having to sacrifice much detail, or having to choke the matte too much.

"oh, and is this the 'primatte' keyer that you refer to?
http://www.redgiantsoftware.com/primattekeyer.html"

Yep, that's the one. I already had Commotion and got the crossgrade. Having used both Keylight and Primatte, I pretty much work entirely with Primatte. Keylight will give you a key that's 95% good with a single click, but getting it to 100% takes a lot of fine tuning.

Primatte will give you an excellent key but it defnitely takes several steps to get there.

When I do green screen work I'm very picky about my screen lighting. 10 minutes spent on set can save several hours in post. Taking the time to make sure it's done absolutely right will help ensure the best results on the screen. And the opposite -- cutting corners -- can almost guarantee a cheesy looking shot.

I light the green screen at 60 IRE. I'll set my camera zebras to 60 and set the lighting and exposure to the point where the zebras are just starting to appear. This is the most efficient way of nailing exposure at the zebras will instantly show where the dark and hot spots are. I'll try to get the exposure as even as possible, a quarter-stop. Or at least a half-stop.

The green is a fabric from EEFX.com. Great stuff. Even if you store it folded it'll flatten out in a reasonable time. And it lights evenly. The green seems purer, too. I recently got some paint chips from Home Depot and hope to find a close match that will work under both daylight and tungsten.

Once the background is set, you can light your talent.

In the case of full-length, however, your screen light IS your talent light. So you'll have to work to make sure quality, quantity and the direction of light matches your background plate if you're trying for realism. That's where the EEFX fabric helps -- it seems to allow you to light it off-axis, yet it will still look decent enough for a good key. You might still end up having to create false shadows.

Commotion had a plug-in that could create realistic shadows. Dang. I really miss that application!

An excellent, inspiring example of full-length green screen work can be found here:

http://www.studiodaily.com/main/searchlist/6503.html

Take note that the talent and props are generally on artificial surfaces and not green or blue screen. Those surfaces are then blended into the "virtual backlot". Ingenious!
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Old August 9th, 2007, 10:49 AM   #13
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Dean, thanks for such a comprehensive reply.

I think i'll be taking a serious look at Primatte.....although i may see how Keylight in AE CS3 performs with a better lit screen first and see how it copes!

I've had a look at the EEFX site and their product looks awesome - its just the shipping to the UK is $70 which is quite a bit!

Thanks also for the tip on camera setup.

As you've probably guessed, i'm just getting into this, but my production company has just got a contract for quite a bit of green screen work. Talking heads, product stuff etc - mainly for flash web delivery.

I'm looking at investing in a lighting and background setup that will sort us out for anything that the clients can throw at us.

My ideas are to get a full length setup - as wide as possible in the studio. Probably a paper roll or fabric drape.
Then go for a slightly smaller setup - ie a portable chroma background (one of those fold up jobs) with blue and green sides.

Then lighting for all of this.

SO.....what lighting would you guys reccommend for someone in my position?
I'm thinking a couple of Arri 1K fresnels, a 150w junior head (for backlights), then some 650w fresnels for general lighting?
Then go for a few Chinese Lanterns for all purpose soft lighting.

Any thoughts or suggestions would again be appreciated!

Cheers,

Rob.
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Old August 9th, 2007, 01:13 PM   #14
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I'd start off with several chinese lanterns or 200w 8U fluorescent CFL daylight bulbs above in a regular pattern which then evenly and flatly light the screen area then just see what happens when someone is in the middle of all the green; then figure out what else may be needed for the effect on the subject being motivated by the composite plate lighting and what you would expect to see on them. If they're walking around in the shot quite a bit, your rim light will be more complex and much harder to achieve and will require more instruments than just one as opposed to if they're just still in the shot.
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Old August 9th, 2007, 01:38 PM   #15
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If your company has a contract to do a lot of this work, I'd highly recommend getting the tools that will do the job as good as possible. If it doesn't meet client expectations, it might mean losing repeat business. And that's a lot more costly than buying or renting the right gear.

Be sure to do a lot of experiments prior to the actual job. That way you'll have a formula or two which you know will work.

I use a pair of Lowel Totalights to illuminate the screen. They have broad coverage, can take lamps of fairly high wattage, and are compact enough to stay out of the way.

Whatever you use to light up the screen, be sure to white balance for that particular light source. That's to ensure the green is the right color.

For the talent, you will have to light accordingly. Soft light, hard light, etc. And since you're white balancing for the green screen light you'll have to select the lights based on those instruments. It sounds a little backward, but keep in mind that the software will key only on what it thinks is to be dropped from the image. It doesn't care what the foreground elements are.

Congratulations on the contract, and good luck!
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