FORUMS: list search recent posts

Green screen --> set the Kelvin (WB) , so the green matches the color-bar (vector-scope) green. Good or Bad??

COW Forums : Cinematography

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Lennart Holterman
Green screen --> set the Kelvin (WB) , so the green matches the color-bar (vector-scope) green. Good or Bad??
on Sep 5, 2017 at 8:19:57 am

Hello there,

I am looking for a second opinion:

A local guy, who has his own professional green screen studio, advised me to adjust my Kelvin (WB) in the camera, so that the green from my green screen matches the color bar green. In other words it matches the green in the green spot on the vector scope. He said that it makes the keying much more reliable. After the keying the character has to be color corrected back to its original state.

The following pictures show:
-1x - the kelvin (WB) matched in the camera, so that the green hits the vector scope green
-1x - the Kelvin (WB) set in the camera with the use of a white balance card (so a proper WB setting)






My question is:
-is this a good idea or not? cause at the moment i can;t see the advantage of it, cause i tried keying both and i can't find an advantage keying the footage with the Kelvin (WB) set, so that the green hits the green spot in the vector scope.

I hope somebody can explain me why to do it? Or why not to do it?

Thanx in front
Greetz Lenny


Return to posts index

Todd Terry
Re: Green screen --> set the Kelvin (WB) , so the green matches the color-bar (vector-scope) green. Good or Bad??
on Sep 5, 2017 at 2:41:37 pm

I would never do that, and have never heard of anyone doing that.

I would always... ALWAYS color balance my camera for the temperature of the light I was using on my talent.

Maybe your friend just doesn't have a very good keyer, or is not super proficient at compositing, and has found that particular shade of green works best for him. I have no other explanation for it.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



Return to posts index

Chris Wright
Re: Green screen --> set the Kelvin (WB) , so the green matches the color-bar (vector-scope) green. Good or Bad??
on Sep 6, 2017 at 2:19:57 am

it's actually a 2 part question because you want to light your setup so that color bar green is [G] in vectorscope.
on waveform luma, green should be 45% ire luminance, YC 55% chrominance. the talent should be lighted separately at camera's native iso and transformed 18% grey, 20 ire/yc to whatever luma curve its using. i.e. rec. 709 41%, slog2 32% grey.

your screenshots look way off because color bar green should point directly at [G] as a single line for a good key. any variation means that you have many shades of green and won't key well. should be within 0.5 f-stops deviation.

the vectorscope should be hardware connected in-line with your camera so it matches precisely what your camera sees and is going to record. you will white balance to your greenscreen because of different temp of lights. The only thing that matters is if you can record native color bar green into your camera's codec.

If you light your talent separately, you should have moderate control over how they look, but that is a secondary concern, once you get your clean alpha matte. the closer they match in white balance, the less you'll have to pull 8 bit codecs around.

here's a quick video illustration how to setup chroma and luma in vectorscope for greenscreening.






it's all pretty straightforward. The reason people get confused is from a barrage of bad information making everyone think they need blindingly bright green to get a good key. Actually, the opposite is true.


Return to posts index


Chris Wright
Re: Green screen --> set the Kelvin (WB) , so the green matches the color-bar (vector-scope) green. Good or Bad??
on Sep 6, 2017 at 3:01:27 am

oh, btw, the studio guy has white balance and hue angle confused. If he was trying to do what I think, the correct way to fix this problem(if he bought the wrong key color and gels) would be to rotate the master hue in the camera so that they aligned to color bar green. this is not recommended unless you have a 10 bit or raw camera or you could get posterization when color grading the talent in post.


Return to posts index

Lennart Holterman
Re: Green screen --> set the Kelvin (WB) , so the green matches the color-bar (vector-scope) green. Good or Bad??
on Sep 6, 2017 at 6:19:34 am

He Chris,
Thanx for the post! Very interesting video from Kinetek. I understand how to do step 1-4, but i don't understand how i could do step 5 in post. I willl have to dive into Davinci resolve and see how to do this ☺
Greetz lenny


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]