Re: Help lighting a chroma backdrop

Ian,

While I can't speak for EVERYONE who has responded to this post... I can speak on behalf of Bill Davis. I've known him for over 10 years! He is an amazing editor and has a VAST amount of experience! In fact, I believe Bill was the guy in the chair on several of my "first attempts" at pulling off a key... I've learned alot since those days, believe me! Although an accomplished shooter, I believe Bill's perspective is coming from the edit chair. He's spent COUNTLESS hours editing anything you can think of... He KNOWS what he's talking about in the post production world.

Even though some of your decisions may seem sound and logical, those with experience may have a different approach. That doesn't mean that one approach is better or worse, it just means that someone has PROVEN results with a certain method.

I agree, I WOULD NOT use green gel on the background lights! That is overkill to the point of possibly being a detriment... It could result in MORE kick back or spill from the background... if anything, I typically go a completely DIFFERENT route and light my background in the OPPOSITE color spectrum from my talent (tungsten/daylight, separate, but equal!) I learned that from someone I know who works at ILM... if it works for them, why not! They are the KINGS of special effects shots. You know what? IT DOES WORK!

I'll also tell you that I have several sound technicians in my metro area that work for me AND my competitors... they've watched my methodology and then told my competition, only to have dismal results! I'm actually cool with that! There are certain tools that actually make the difference between a successful key and a lousy key.

Bill is correct... I've never put it in the terms of "geometry" but none the less, I agree. Separation is EVERYTHING when it comes to "spill" on your backgrounds. Now... keep in mind, if you are just going to have head and shoulders shots, you CAN have the background "seem" too small in your shot, as long as the subject NEVER leaves the green area. You CAN use, as Bill indicated, a "garbage" matte to "fill in" the areas you don't have enough green, provided that your subject has no "entrance" into that non-existent green area (i.e. hands waving around outside of the green background). Also, if for what ever reason I do shoot all tungsten lights for example for my keying efforts, I will use GEL on the back-light of the subject, only! I will use a 1/4 - 1/2 magenta gel to COMBAT the green spill in smaller set ups. That's an OPPOSITE color than green and helps reduce the spill. Nothing aids the loss of spill more than "space" ("Z" space if you will) between the subject and the background. I typically WILL NOT SHOOT A KEY in an environment where I CAN NOT get at LEAST 10 feet of separation! It will not work, without a LOT of post work... sometimes including roto-scoping!

We are often hired to come in behind others as a "last ditch effort" to get a good clean key... I've written SEVERAL posts on my methods, and I'm sure you can find them if you take the time... I will reiterate one thing: get a waveform monitor to measure your lighting on the background! My same buddy at ILM shared this fact with me about 8-9 years ago... I can't thank him enough for that one! That is the true "secret" to pulling off a clean, successful chroma key, especially in HD! Because Zebra stripes occur when a certain, designated IRE level is present... there is no way to know what that level is without a WFM! You may have the stripes set at 75, but the light level is really 82... the stripes will still be there! So even if your ENTIRE viewfinder has stripes... it may not be evenly lit! If you measured your light levels with a WFM, you'll KNOW if it's even! If you don't own one, RENT one! It WILL be worth it!

Pulling off a good key is all about lighting... it's not so much WHAT KIND of lights you're using, but how they are used. I will agree, these lights look a lot like Westcott TD5 Spider Lites. I use those nearly every single day as my "key light / fill light" for interviews... HOWEVER, I don't think they are appropriate for lighting a chroma background. I'd suggest a florescent along the lines of a Kino Flo or equivalent, or a "fresnel" that you can spot and flood. Again, if you don't have them, and they are accessible, consider renting them! They aren't that expensive to rent.

Many try to cut corners when shooting on a tight budget... unfortunately this can present NIGHTMARES in post when trying to key... I know... I tried everything for years... it never worked well... now, when I use a WFM, light evenly, and have enough separation, I can typically key something in 5 clicks of a mouse or less in "Keylight" inside of After Effects, with phenomenal results!

Bottom line is this: TEST, TEST, TEST! Set up your gear and shoot something... go back and try to key it in post! It may or may not work. YOU WILL LEARN something if you do that! I promise. Hopefully, the next time, if you had less than expected results, you won't make the same mistakes... After enough shoots, you won't make any! Don't make them in front of your client! That's the worst!

One last thing... I'd recommend that you do some research on your NLE or post application to find out what LEVEL of IRE to light your background for keying... for example... I had a client recently who wanted me to key the background at 40 IRE! That's nearly 1/2 of what I normally would do! He was CERTAIN this was correct... He told me he used "Ultimatte" do pull the keys. I emailed the company, they sent me specs. They prefer a 1:1 ratio of lighting for the subject and background. "If anything light the background BRIGHTER than the subject... The closer you can get the background to 80-82 IRE, the better!" (keep in mind, this is for THEIR program!) I shot the footage the way the client wanted... it was HORRIBLE! It didn't work... At the end of the shoot... I took 5 minutes to rearrange the lighting, put a subject in front of the camera, and shot about 10 seconds with an IRE level set to 81. I took a picture with my cell phone of the WFM, showing the "recommended settings"... The client later told me "the last little interview worked... the rest didn't!" Since, I've contacted EVERY manufacturer of a "keying" product, to find out the specified requirements for the best key... they vary, but if I ask a client what they're using, it always works out.

Good luck. Let us know how it comes out!

Curt

Curt Pair
Picture This Productions
Sony ICE Team
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Phoenix, AZ