Green screen / key test results opposite of expectations

[Scott H. Jones]

So we're doing a green screen test. Lit with daylight we get noise in the shadows on the keyed subject (AE / Keylight). Lit with tungsten we get a clean key -- no noise at all on the keyed subject. WTF? This is the opposite of our expectations since the sensor records at 5000º. Using build 17. Any input would be appreciated.

 

[Shawn Booth]

examples?

What are you doing to the footage from media to AE? As in, what format is the footage going into AE to get pulled? What is your workflow?

 

[Graeme Nattress]

Daylight can be noisier than tungsten if the tungsten is a lot brighter.

Graeme

 

[Scott H. Jones]

We're taking the RED footage straight into AE4 and pulling a key using Keylight.

Here's the latest: When we lit the subject with tungsten and the green screen with daylight, we got a noise-free key (we stayed color balanced for daylight and thus had to color correct the keyed subject, but I don't think this is of any real significance to the issue). When we lit both with daylight, we got noise in the shadows on the keyed subject.

Here's our working theory: When you pull a green screen key, you inevitably pull green out of the foreground subject, too, just enough to cause noise in the keyed subject. But if you light the subject with tungsten, you're adding red to the foreground object, thereby reducing the amount of green in the subject, enough so that when the key is pulled, less color is pulled from the keyed subject, resulting in less noise. I should mention when we tried lighting both the green screen and foreground subject with tungsten we got the same amount of noise as lighting with all daylight. I need to test lighting the green screen with tungsten and the foreground subject with daylight.

This may be an AE / Keylight problem. If anyone is interested in testing another keyer, we'd be happy to upload a couple of test clips.

 

[Jannard]

Since you are testing... why not consider Build 20 and make sure to do a black shading calibration? Just a thought since Build 20 will soon be a release build and the color science is so much better.

Jim

 

[Raul Gonzo]

Scott- have you tried using the sun as the light source? This can limit how you light your talent, but you should then get a very even green screen and more than enough light.

 

[BigLu]

Keylight gives noise in its keys.
Send me your AE project file. And it give me a good description of what you are doing when you pull your keys.
Basally your step by step process.
That way i will know exactly what you are doing and what im looking at.
I dont need the raw files the project file is fine.

But also take SCREEN shots of your video directly sitting in AE so i can see to what noise you are referring to.

Ive been fighting keylight for 2 features and a full music video now.
It can give very nice results but it must be done with multiple mattes and used sparingly in conjunction with Color Key / Hue Saturation and noise reduction.
Not all keys are treated the same.

My email is
googulplx@aol.com.

I might be able to help with some of my findings.

 

[Kenn Michael]

Since you are testing... why not consider Build 20 and make sure to do a black shading calibration? Just a thought since Build 20 will soon be a release build and the color science is so much better.

Jim

So much better indeed!!!!

Can't wait for the CS4 and FCS plugins to be updated so we can use that new color goodness inside the Apple and Adobe apps.

 

[Ian Laurie]

having just done a keys for a feature using CFC keylight in shake, where both foreround andbackground were lit 5000, I can say it sounds like an AE problem, as the keys i ended up with were very clean. I figured that was the joy of high res images.

 

[Robert Niessner]

1. Keying works basically by comparing the green channel to the red channel (or blue channel to the red channel). The larger the difference, the better the key. That might be the reason why in your particular setting tungsten light works better than daylight.
Check the RGB values of your footage and compare the different light situations.

2. Try to put green gels onto the lights for the greenscreen. That can help by purifying the green in the background, giving a better key from the start.
3. Make sure to key at least in 16bit mode.

4. Create garbage masks inside the keyed subject. It doesn't have to be roto quality but can help tremendously in keeping subject opaqueness intact.

5. Play with the settings in Keylight. Especially wrong screen matte settings can influence the shadows to look very noisy. That is because the pulled matte is not clean enough.
Try to set "Clip White" to about 80-85 to clean up the non-transparent matte.
Try to set "Replace Method" to "Hard Color" instead of "Soft Color". That is very often the solution to the problem.

I did some experiments and you can see the problem of the noise clearly when setting Keylight view to "Status" - it's in the white areas where G=255 and RG are a little bit lower sometimes. That creates a kind of pattern in the shadows.
I found this to be related directly to the greenscreen RGB, meaning a more saturated greenscreen helps a lot to prevent the problems.

 

[Dominic Jones]

It is, as others have said, almost certainly an issue with Keylight, and not the footage per se. Keylight in AE is great, but can produce some very noisy keys if not handled right...

Try to set "Replace Method" to "Hard Color" instead of "Soft Color".

That's solved 99% of the problems I've ever had with noisy keys from Keylight in AE.

HTH,
Dom.

 

[Bruce Ingram]

Thanks for the advice guys. I'm the guy actually working on the key and while I've found a workable solution to it, I'll be testing some other keying options to see if I can ease the workflow. And thanks for the heads up an Shake, Ian, I'm going to test that out as well. We will also be testing Build 20, but my expectations are low since I am pretty sure it is more a Keylight issue, as noted by others, rather than a footage issue.

 

[Michael Epple]

I don't know too much about keying, but I have shot plenty of green screen with tungsten lights and had great results. I have to admit that the people doing the keying were really good. I think people overthink the necessity to shoot at exactly 5000k. Sure, technically it should give the best results, but a well lit green screen under tungsten works beautifully, pulling out stray hairs and the like.