Green Screen

NorthernRebel · Mar 19, 2009

I'm helping friend who has asked me to do production stills for a short movie he is making. Aside from the standard set shots and press kit stuff, we are shooting in front of a green screen this weekend. Since I've never shot in front of a green screen, I have no idea what I'm getting myself into.

The screen is at a studio, and while I'm assuming there will be some type of lighting available at the studio, I'm going to bring along my CLS equipped Nikon with a couple of remote flashes and diffusion umbrellas........just to make sure we have enough light.

Have any of you done any green screen stills?? If so, is there anything in particular I need to watch out for?

Thanks!

Big Mike · Mar 19, 2009

Are you planning to remove the background for the still images? If so, then try to watch out for any green back spill on the subject. Keep them farther away from the backdrop.

NorthernRebel · Mar 19, 2009

As I understand it, that is the intent (put a different background behind the subject).

Does depth of field matter? Should I attempt to shoot at a smaller aperture to keep the green screen more in focus, or does that not matter?

Big Mike · Mar 19, 2009

Yes, the green screen is for extracting the subject and replacing the background...I'm just wondering if they want that for the still photos as well.

I don't think it matters if the backdrop is in your DOF or not...as long as it's not blending into your subject, you should be OK.

NorthernRebel · Mar 19, 2009

Yes, the green-screen session is for the stills. As far as I can tell by looking at the schedule, late afternoon on Sunday we will do a still shoot at a local park, then green screen stills Sunday early evening at some studio I haven't been to yet.

No production videography is scheduled as far as I can tell.

Thanks for the tip on the green bouncing back onto the subject. I'll keep them as far off the wall as I can.

table1349 · Mar 19, 2009

One other quick piece of advise that goes along with what Big Mike is talking about. The green screen needs even lighting to make it's removal simple, quick and seamless in post production.

NucleaRR · Mar 20, 2009

gryphonslair99 said:
One other quick piece of advise that goes along with what Big Mike is talking about. The green screen needs even lighting to make it's removal simple, quick and seamless in post production.

In another life I worked at a stage lighting company. We installed many green and blue screens. Usually they have a row of border lights (long strip of lights) pointed down and a row on the floor pointed up to evenly light the screen. You may want to make sure they have this and if not rent your own from a stage lighting supply.

Double H · Mar 20, 2009

As others have states, even lighting is key, no pun intended. Jewelry tends to pick up the green, and blonde hair is much better shot in front of a blue screen. Try and get some matte spray to get rid of shine and sheen. Have fun.

NorthernRebel · Mar 20, 2009

Thanks for the tips everyone!

Moglex · Mar 21, 2009

It's better if the green screen is out of focus so that it is a even as possible.

Alpha · Mar 24, 2009

While not an unreasonable assumption, most still photographers, having seen green-screens on video or movie sets, assume that if they want to replace a background they need to shoot against one.

Of course, that's totally wrong. Sure, it's possible, but in a lot of cases you're making your life harder. If you want to replace a background, shoot against white, not green or blue. You're likely to get a higher contrast ratio between subject and background, which will make it easier to mask off your subject in Photoshop.

Moglex · Mar 25, 2009

Alpha said:
While not an unreasonable assumption, most still photographers, having seen green-screens on video or movie sets, assume that if they want to replace a background they need to shoot against one.

Of course, that's totally wrong. Sure, it's possible, but in a lot of cases you're making your life harder. If you want to replace a background, shoot against white, not green or blue. You're likely to get a higher contrast ratio between subject and background, which will make it easier to mask off your subject in Photoshop.

From the POV of green (of blue) screen processing software I'd have to disagree with the above.

The idea with green screen is that the background is pure, saturated, green (and should have a CT matched to the sensor that you are working with [even if you use film as an intermediate medium]). The software can then look for all pixels that are very close to having the green channel saturated and the red and blue channels null. This will work well provided that you have nothing that is pure green within the required foreground.

If you use white it means that whatever software you use will be confused by any white highlight. You would effectively need to ensure that subject did not have maximum dynamic range.

You can easily see how well blue/green screen works by observing how well weather forcasts appear on screen (although there is a very amusing clip on Tie Color Fail « FAIL Blog: Pictures and Videos of Owned, Pwnd and Fail Moments where the forecaster has an incompatible tie which displays the current background

). Remember that this is done entirely without human interention and in real time.

JerryPH · Mar 25, 2009

If using Photoshop CS3 and up, using green screens is almost unnecessary now a days. One could pull almost anything from anywhere and place it on top of another layer in a couple of minutes.

Using a green screen is for the benefit of the software to make it easier to distinguish where your "subject" starts and stops as Moglex said, but not mandatory.

The thing with green blue or white backgrounds is that you must take into consideration colour casts. If your white subject is on a green screen, if you do not do it right, you will get green fringing on your subject and then you are in trouble. Using the same colour background as what your final shot will use is the easier and more complete solution.

For example... had I used a subject jumping from a green screen, the result would not have been as good so we used a white background in this case.

Alpha · Mar 25, 2009

Moglex said:
From the POV of green (of blue) screen processing software I'd have to disagree with the above.

The idea with green screen is that the background is pure, saturated, green (and should have a CT matched to the sensor that you are working with [even if you use film as an intermediate medium]). The software can then look for all pixels that are very close to having the green channel saturated and the red and blue channels null. This will work well provided that you have nothing that is pure green within the required foreground.

If you use white it means that whatever software you use will be confused by any white highlight. You would effectively need to ensure that subject did not have maximum dynamic range.

You can easily see how well blue/green screen works by observing how well weather forcasts appear on screen (although there is a very amusing clip on Tie Color Fail « FAIL Blog: Pictures and Videos of Owned, Pwnd and Fail Moments where the forecaster has an incompatible tie which displays the current background ). Remember that this is done entirely without human interention and in real time.

I've masked out subjects from white backgrounds probably thousands of times. I can't say PS has ever been confused. Green and blue make sense for video/film. White works as well, if not better, for stills.

nikonguy · Mar 25, 2009

i use a photoshop plugin for removing the green screen.. its called "Digital Anarchy" its expensive though.. i think they were asking like 300 bucks for it or something...

it works really well though.. it removes the green screen and the spill in a matter of seconds.. even if your lighting isn't even, you select the area that is green, and it removes it all..

as an example... (BTW, i know this photo is terrible.. it wasn't suppose to be good.. i had just bought the green sheet, slapped it up on the wall, and told my wife to stand there for a minute)

before:

after:

this only took about 3 minutes... if i had of taken a bit more time to refine the greens, you wouldnt have the slight cast on her shirt..