Shooting with a chroma key backdrop

I have a gig shooting kids in theatre costume in front of a chroma key backdrop. The theatre is providing the backdrop, I'm providing the lights.

We will provide digital images for the theatre's marketing department for their use in advertising and promotion. Their people will do the background removal and other artwork.

I have never used a chroma key backdrop before. In terms of being able to digitally remove the background, does it help to throw some extra light on it? I'll be using studio strobes to light the subjects but it wouldn't be too hard to set up a flash unit on each side to get some extra light on the backdrop, if that would help.

Thanks.

Curtis N wrote in post #8587815
I have a gig shooting kids in theatre costume in front of a chroma key backdrop. The theatre is providing the backdrop, I'm providing the lights.

We will provide digital images for the theatre's marketing department for their use in advertising and promotion. Their people will do the background removal and other artwork.

I have never used a chroma key backdrop before. In terms of being able to digitally remove the background, does it help to throw some extra light on it? I'll be using studio strobes to light the subjects but it wouldn't be too hard to set up a flash unit on each side to get some extra light on the backdrop, if that would help.

Thanks.

Hi Curtis,

The few times I shot with a Chroma Key backdrop I lit the background about 1 stop brighter than the subject but what I find to be the most important aspect of subject extraction from a background it that the background should be lit very evenly. I try t analyze the subject (the outline of the subject) carefully to determine my background exposure. If I see colors or contrast that is too close to the background I adjust for it.

I've gotten very good results extracting from pure white backgrounds that were lit evenly so I believe it's all about the evenness of the lighting and the contrast between subject and background.

If there actually are 'rules' for how to properly expose the chroma key, I don't know what they are and from what I've seen it doesn't make a difference.

TMR Design wrote in post #8587968
The few times I shot with a Chroma Key backdrop I lit the background about 1 stop brighter than the subject but what I find to be the most important aspect of subject extraction from a background it that the background should be lit very evenly.

+1

Also, make sure your subject is at least 8 feet away from the backdrop. You don't want blue/green (depending on the color of the the chromakey) spilling back onto your subject.

Separation is the key for us. We light the background as well and as evenly as possible. Keep the kids as far away from the background as you can. Say 8 to 10 feet if possible. Make sure the kids are lit as well as possible too...

We go a bit overkill on lighting the background. We use two 1,000 watt constant lighting sources in soft boxes to keep the background nice and bright. Our background is fabric so we also pay extra attention to any wrinkles. The fewer wrinkles or shadows on the background the better and easier the replacement process will be. The people doing that work will appreciate it.

As mentioned above, watch out out for color spill on the subjects. You can gobo them if necessary but it will be more work for the retouchers later if it can be seen in the shot.

Jon.

Curtis, I know you won't do the replacement work but check out Photokey. I use it at the school for ease of use and how quick it works. I do over a hundred kids at a time so fast, easy and good quality is critical.

Photokey Website

I have the color code for over the counter paint if you want to try it out but I'll have to find it. Buying the "green screen" paint from places like TubeTape.com would work but it's more expensive.

Edit: Here's a quick link I found on chroma green paint. http://www.detonationf​ilms.com …et_chroma_green​_paint.htm

Jon.

As mentioned controlling spill is the key. Might want to add a hair/rim light on the subject to washout any color spill from the background.

Thanks, everyone.

8 feet away? spilling is a pain to deal with. But for a full body portraits w/ a 10x20 green screen, the subject will have to be 2-4 feet away unless i miss something here.

Galaxy99 wrote in post #8589023
8 feet away? spilling is a pain to deal with. But for a full body portraits w/ a 10x20 green screen, the subject will have to be 2-4 feet away unless i miss something here.

You can't shoot Chroma Key at 2-4 feet from the background. You absolutely must have subject isolation and no color cast from the background back to the subject area.

TMR Design wrote in post #8589066
You can't shoot Chroma Key at 2-4 feet from the background. You absolutely must have subject isolation and no color cast from the background back to the subject area.

Yes you can if everything is lit right. Also there are suppressor tools to manage spill if it comes to that. I like to use After Effects for video and still keying and the Foundry's Keylight plugin is frigging amazing.

Terjay wrote in post #8590197
Yes you can if everything is lit right. Also there are suppressor tools to manage spill if it comes to that. I like to use After Effects for video and still keying and the Foundry's Keylight plugin is frigging amazing.

I should have been more specific. Most people, given generic lighting and a no special tools or modifiers can't work that close to the background or they will experience a lot of the common pitfalls and it will bite them in the arse when they try to do the extraction.

I do this all the time. I shoot annual school portraits and do 300+ heads at a time using a Chromakey background and get perfect results even on blonde wispy hair. I do NOT light the BG separately. But I do have a set of tried and true measurments that I use that work everytime.

First off I suggest using Savage tech 43 green paper. And two lights with umbrella modifiers at 45 degree angles to the opposite corners of the backdrop. Meter the subject at f/11 and the backdrop will be f/8 consistently across the entire width.

The suggestion of lighting the bg a stop brighter than the bg will cause spill from the green reflection coming back at the subject, having it one stop under eliminates this problem. I don't know why people keeping suggesting this method, It is backwards.

Another thing is that you must use custom white balance or the flash pre-set. Never use AUTO.

I have used many different extraction methods with this setup and never had issues with spill, I send the files to a lab and they do the knock out and send the proofs back with options to have 10 different backgrounds for the students to choose from. This is a simple, tried and true method that works very well. Trust me, I have done literally thousands of these images with this set-up.

Camera does not need to be 6 feet as I suggest below...it depends on your lens etc.

HOSTED PHOTO
please log in to view hosted photos in full size.

BCRose wrote in post #8590448
The suggestion of lighting the bg a stop brighter than the bg will cause spill from the green reflection coming back at the subject, having it one stop under eliminates this problem. I don't know why people keeping suggesting this method, It is backwards.

It may not work for you with your particular setup but it does work fine. To call it backwards doesn't make sense. It works. I wouldn't do it if it didn't work and it helps create separation between subject and background.

But it all depends on how you're lighting the shot. You're lighting the entire scene quite differently from the way I've lit my shots and I do light my background independently so that I can creatively light my subject, as opposed to cross lighting equally from both sides.

I'm not debating that your method doesn't work. I'm sure it works fine for you. It's just not how I have done it or do it.

I did a +1 on the lighting the background separately in a post above, but misread the background being 1-stop brighter. I have shot some green screen and use Primatte to do the extraction. I light my background with two umbrellas on each side of the paper. I used the advice from Primatte. Lighting a Chromakey Screen

Gatorboy wrote in post #8590555
I did a +1 on the lighting the background separately in a post above, but misread the background being 1-stop brighter. I have shot some green screen and use Primatte to do the extraction. I light my background with two umbrellas on each side of the paper. I used the advice from Primatte. Lighting a Chromakey Screen

Other than the fact that I light my background 1 stop brighter I essentially use that setup shown in that link. The subject is lit as I would light a standard portrait and then I use 2 lights on the background to create the even light at the desired exposure, independent of subject exposure.

If there is enough distance then that ratio works. I think that if you have limited space and the subject has to be closer to the background then I'd be inclined to drop the background exposure so as not to conflict or have light from the background returning to the subject area.