Green screen exposure

Steven Prio · April 22, 2007

Hi all!

I just quickly want to ask a very simple technical question. What should be the exposure of a green screen in relation to your f-stop to help the post people do their job faster?

We are using greenscreens in computer monitors and mobile phone screens in order to replace the images afterwards.

Usually greenscreen reflected reading should be a stop under your aperture. Is this actually true? T

Thank you for your time!

Stephen Williams · April 22, 2007

Hi all!
I just quickly want to ask a very simple technical question. What should be the exposure of a green screen in relation to your f-stop to help the post people do their job faster?

We are using greenscreens in computer monitors and mobile phone screens in order to replace the images afterwards.

Usually greenscreen reflected reading should be a stop under your aperture. Is this actually true? T

Thank you for your time!

Hi,

1/2- 1 stop under is fine. For the mobile phone screens you may be making lots of extra work by using green screen. Even tracking marks can be a pain, the corners are easy to see in any case.

Stephen

Tony Brown · April 22, 2007

Hi all!
I just quickly want to ask a very simple technical question. What should be the exposure of a green screen in relation to your f-stop to help the post people do their job faster?

We are using greenscreens in computer monitors and mobile phone screens in order to replace the images afterwards.

Usually greenscreen reflected reading should be a stop under your aperture. Is this actually true? T

Thank you for your time!

Post houses vary. The latitude in the stock means you could be +2 or -2 it will make little difference. I generally go for the shooting stop so that tonally its a mid tone

Cant remember the last time I actually shot green / blue scree. The post houses generally prefer of rough match to whatever will be comped in these days.....

Stephen Williams · April 23, 2007

Hi,

My reason to slightly underexpose a green screen relative to key is to reduce green spill.

Stephen

Tony Brown · April 23, 2007

Hi,

My reason to slightly underexpose a green screen relative to key is to reduce green spill.

Stephen

Depends on your distance from subject to screen....... but yes if you are so close you are experiencing spill then it would be prudent to reduce the level

Steven Prio · April 23, 2007

I just want to thank you all for taking the time to answer my question

Thank you!

Steve

Stuart Brereton · April 23, 2007

I usually keep green screen about 1/2 a stop to 1 stop under. It helps with spill and increases saturation.

Mike Lary · May 4, 2007

For ease of keying, even lighting on the green screen is more important than its relation to the key. From a VisFX standpoint the screen could be lit a stop or two below or above the key, so you might as well go under to reduce spill.

Testing is imperative if you can afford it. If you hand the test footage over to the VisFX crew and have them key it, you'll know exactly what you need to do when principal photography begins.

Stuart Brereton · May 5, 2007

the screen could be lit a stop or two below or above the key

Lighting the screen a stop or two above key would reduce its saturation, whuch you definitely don't want.

Andrew Brinkhaus · May 6, 2007

So I'm not new to lighting, but I have in the past shot mostly video, and I am just now beginning to work with a meter. When you say "light the screen 1/2 - 1 stop under" Your referring to already having a predetermined stop, such as f/4, and then lighting the screen at a f/5.6 or something similar? Which means that the f/4 would be the foreground or talent's range? Just wanting to make sure i'm reading this right.

Andrew Brinkhaus · May 7, 2007

...Or does it mean, 1/2 - 1 stop under middle grey?

Frank Barrera · May 7, 2007

So I'm not new to lighting, but I have in the past shot mostly video, and I am just now beginning to work with a meter. When you say "light the screen 1/2 - 1 stop under" Your referring to already having a predetermined stop, such as f/4, and then lighting the screen at a f/5.6 or something similar? Which means that the f/4 would be the foreground or talent's range? Just wanting to make sure i'm reading this right.

if you want to expose your scene at an f/4 and you want to under expose your green screen by 1 stop then your reading off the screen should be an f/2.8. that would be 1 stop under.

Stuart Brereton · May 7, 2007

if you want to expose your scene at an f/4 and you want to under expose your green screen by 1 stop then your reading off the screen should be an f/2.8. that would be 1 stop under.

It's worth noting that we're talking about reflected readings from the greenscreen, not incident.

Frank Barrera · May 8, 2007

It's worth noting that we're talking about reflected readings from the greenscreen, not incident.

yes. on a film job i would use an incident meter for the subject to achieve the f/4 and then a spot meter to get the f/2.8. and for video with caucasian skin tone i would take some 70 IRE on the face and around 50 IRE on the green screen using a spot meter to check that the screen was lit evenly. of course the running joke is always that its doesn't matter how we light it because "with a mac nowadays you can key anything".