Green screen question

I've only ever used standard backgrounds for model shoots but tomorrow I will be using somebody elses studio for a work manual where I need to take hundreds of photographs of an individual performing certain actions. I'm talking still photography only, no video.

I am being forced by work to use the work studio that only has a green screen which sounds great but i have no idea what i'm doing. In the past when using a white backdrop everything went fine except that there were undesirable shadows which couldn't be avoided due to the studio being quite small.

Here are my two questions though:

1. Is it a simple process to remove the green background and replace it with a white background in post processing? I am nervous that it's not as easy as 'magic background' removal and that I'll have to manually remove all of the backgrounds - which could years.

2. How do i white balance for the green screen? Do i just use the standard white A4 page or grey card to set a custom white balance as if i'm using any other type of background or is there something specific that I need to do?

Any assistance would be greatly appreciated with this.

Cyrus

Cyrus wrote in post #15183776
1. Is it a simple process to remove the green background and replace it with a white background in post processing? I am nervous that it's not as easy as 'magic background' removal and that I'll have to manually remove all of the backgrounds - which could years.

I suppose you can do it using just Photoshop, but you really ought to use what's called a "chroma keyer", which is often set to automatically detect green/blue screen and will do most of the work for you. I'm sure there are Photoshop plugins that do this.
The most important part of the screen itself is that it be lit completely evenly, and is well saturated, however you must absolutely avoid the light from the screen bleeding onto the subject; bleed is a PITA to get rid of. If there are hot spots on the screen or not enough light, it'll drive you crazy.

Just set the WB ahead of time. If you're going to be using studio flash, just set the WB on your camera to "flash" or manually set the temperature to 5200/5400k.

I think Kolor covered it all nicely.

Any light reflected from the screen onto your subject will be a huge pain and is nearly impossible to fix in post.

Metering and White Balance is still set the same way as any other background.

Any variation in the background light will impact how easily you can key it out.


And finally, there is a big difference between keying out a green screen in video and keying it out in stills.

Video has a LOT less resolution to work with and the software is able to use before and after frames to reference what needs to be removed and what stays. Small errors don't get noticed and process is much easier to automate.

On a still you have a LOT more information to work with, make sure you subject has tightly controlled hair, preferably tied back if it is long. Any fly aways require extra time and tools to fix, or have to be manually removed.

If you can light the background evenly, look at DSLR Remote pro which has a photobooth mode that includes a pretty good chromakey feature.
I've played with it and it does an ok job under very controlled set ups.

Moppie wrote in post #15185498
Video has a LOT less resolution to work with and the software is able to use before and after frames to reference what needs to be removed and what stays. Small errors don't get noticed and process is much easier to automate.

Well, the question of resolution in video is a tad complicated, on one hand having to manage only 1920x1080 pixels is easier overall, but you get superior and quicker results by keying the data from a high-resolution source (like RED cameras) and down-sampling to HD later.

So it depends on delivery, if these photos will end up being 1024x768 web jpegs or 4" thumbnails in some printed source, very little correction will be needed as 90% of potential artifacts will be lost in the end result.
If it's going to be a double-page spread for a top magazine, OP wouldn't be asking this question to begin with...