Part 2 of 3:
The first thing to take into account is that photoshop uses tools that select based on similarity, you must have an evenly lit background if you want to be able to select it and remove it in photoshop effectively. Since the extraction is based on selecting the green screen, you want to keep that green as close to the same tone as possible.
The first thing to take into account is that photoshop uses tools that select based on similarity, you must have an evenly lit background if you want to be able to select it and remove it in photoshop effectively. Since the extraction is based on selecting the green screen, you want to keep that green as close to the same tone as possible.
I want the chroma to be the same f-stop as my main light. This keeps everything nice and bright and means that my camera settings are really easy. I’m using a 9 foot background and one light on either side to light it. The lights are about 4 to 6 feet from the background. To make the light super even you’ll need to have the lights crossing each other (your right light is lighting the left side of you background and vice versa) this gives the light a little time to spread out keeping hot spots from appearing on the background. Our background lighting set up looked like this from camera position:
You want to loosely set-up your lights and then start metering. Thats right, dust off your meter and start checking the background. I use f/8 so that I have enough DOF for my subject (like I said earlier, my background and my main light will be the same intensity) so if I want to shoot at f/8 then I will be tweaking my lights until the center, left, and right of the chroma read f/8. If one side is brighter you willl need to do one of the following;
-change the angle of your lights
-move your lights father away
-adjust the power of the lights
It will require a combo of all three on both lights to get an evenly exposed chroma. Do tests! Do them before you go on location. Its much easier to set-up under pressure if you know the approximate set-up ahead of time. This will cut your set-up time in half and your cuss words will be reduced by about 72% (yes I stole that cuss word bit from Zack Arias ...... get over it). Speaking of the One Light Master there are some space requirements that we need to cover. I do the basics, if you want to see where I took my info from the link is Zack Arias’ multi-part studio set-up blog post. A 20x20 foot space is what you need, due to our initial tests and the space constraints of our client we asked for 10x15, this made relative sense to us as our background is 9 feet wide and lights are pretty small on each side. Now..... most of you are like cool, that works, right? NOPE! As we realized the average light stand has a footprint of about 3.5-4 feet (call it 4 for mathematical simplicity). About 2 feet of that is going to overlap your background stands, BUT 2 feet won’t. So you realistically looking at about 9 + 4 feet (2 on each side) that 13’s. Not 9 like we budgeted for, luckily there was a bit of extra room for us to work with, 15-20 feet would have kept the profanity in check better.
As far as length goes there is no question, you need 20 feet. When lighting the background, that light (which is green because its bouncing off a green source) is bouncing back and hitting the subject. This will give the subject (especially their hair) a green cast on there edges, causing you a lot of grief in the extraction. Keep this a minimum too, move your subject at least 10 feet from the background. Do a meter reading of the back of the subjects' head without your main and fill light on The light bouncing off the background and hitting your subject should be at least 2-3 stops under your main light. If your main is f/8, the bounce back should be under f/4, preferably f/2.8.
The other benefit of moving your subject off of the background is that the lights on the subject no longer affect the background. This keeps those lights from creating hot spots or shadows that will interfere with your extraction. The lighting is up to you I like small softboxs in this situation. This project was clean soft light, fill light above camera position high, and main light camera left, high and on a 45 degree angle to the subject. The fill lights power was set a half stop under the main. The main was f/8 (the same as the background so that everything’s copacetic) this makes the fill about 5 and a half (photo translation about f/6.3). The benefit of this set-up is if some of that green light from the background gets on to your subject (which it should not) the soft even light from the softboxs will wash the green out. As well soft boxs are very directional and keep the main and fill lights off the background. This is hard to do with umbrellas because they throw light everywhere. Our fill was about 5-7 feet off the subjects position in a direct line away from the background, the main was the same distance on a 45 degree angle (don’t get out your protractor, eye ball it, this is not critical) from the subject. Nice clean, corporate and easy to extract. Go as crazy as you want there is no perfect light set-up for this, the important part is that you background is even and that your subject is not getting green spill bouncing back onto them.
Next week I’ll hit on:
Shooting Tethered: its not magic, just orginization
Photoshop: Templates, templates, templates....
I had no idea you were doing green screen photography, is this something you and I could play with? Or does the space needed make this impractical outside of a proper shoot on location like you mentioned above?
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