DIY LiteRing Chroma Key POC

Hey all,
the other day I got intrigued by the idea of crafting my own version of the light ring based chroma key systems.. I did some digging..

If you dont know what Im talking about, check out the high end reflectmedia

http://www.reflecmedia.com/education/media/video-gallery/litering-camera-action.htm

$2500 for a setup..

A better priced knock of can be had at

http://www.bhphotovideo.com/c/produ...0_KIT_CKL_200_Dual_Color_Chromakey_Light.html

The trick here was figuring out what the backdrop was made out of... retroreflective material.. once I got that far, I found a 3M supplier that sent me a 12" x 9' sample.. pretty cool, until today I wasnt sure I had the right stuff.... so I spent a few minutes, with what ever leds I had lying about, I set this up in about 15 mins..


(sorry about the strangeness in the first few seconds.. )

https://www.youtube.com/watch?v=86XH2cypiNA

Here is a quick keying attempt.. Iv never done keying before..

https://www.youtube.com/watch?v=UxlB_E-m6o0

Now, that fabric is very expensive, about $35 a yard, so its still too rich for my blood. But you can save a LOT of money doing it your self if you want to try this. I am looking for a knock of supplier out of china....


EDIT: So the shadow was made WORSE by being balanced for sunlight, and not florescent... in further tests, the shadows are just another shade of green (not brown like this example) and caused only small issues in keying.
 
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I was able to tape together the remaining sample fabric and make a backdrop 3'X5' (no cost for the sample by the way)

I also tried it with the blue LED's (I have red green and blue in that same form factor, 2 each) and that works fine.

Ill have to make a ring that does both blue and green.

Here is my second try at keying..

https://www.youtube.com/watch?v=cApuiU8UuUM

color tweaked going for that old 1950's cinema look, ala the Music Man..

I used only native CS3 tools for the keying. The subject was lit with 1 500W photoflood key, a bounce card fill and a CFL for the hair light. The subject was about a foot out from the retro-reflective backdrop and nothing was done to light the backdrop. The 500w photoflood was pointed RIGHT at the backdrop...

easy as pie!
 
Those chroma-rings have always confuzzled me.

I understand basic light-rings (for in-your-face closeups/docs, etc), but not how the chroma ones work. Does it rely on preventing light from bouncing back from the background? Why does the object (in this case, the card) not pick up a green tint since it has green light radiated at it?

Why do you have 3 cameras?

You have a gray background with green light... instead of a green background with white-ish light...

I 'spose my overall question is this: If the camera has a ring of green lights (that gives a green hue to anything in the direction it faces), how do you chroma out just the "behind" of the subject... who should also be tinted green from the incoming light from the camera ring?
 
I'll try to explain it for you, Zensteve. I've never used one, but I think I get the basic concept. The background is a retroreflective material made of little beads that reflect whatever light hits it directly back in the direction in came from. Looking at it from a regular angle it will make it look a greyish color. But if you looked at it from the same angle as a colored LED shining on it, it would look the same color as the LED. So you put a ring of LEDs around the camera lense, and the camera just sees a colored backdrop. The LEDs technically would give a slightly green hue to the subject, but they are so low powered that they get drowned out by whatever lighting you use to light the subject. This doesn't affect the backdrop because it only reflects back in the same direction, so the camera only sees the green from the LED and not the other lights, because they get reflected back in whatever direction they hit the backdrop.
 
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chilipie

Pro Member
indiePRO
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Zensteve - I don't understand it completely, but I can probably answer a few of your questions…

The backing is made of retroreflective material, more commonly found on road signs, car and bike rear reflectors, safety jackets and cat's eyes on roads. "Retroreflection" means that the light is reflected directly back at the source, unlike a mirror (for example) which has a flat surface, so the angles of incident and reflection apply to it. Retroreflection is particularly useful on the roads for two reasons - a relatively small amount of light makes the surface highly visible, and because it reflects straight back to the source of the light, the chances of dazzling or distracting another driver are much reduced.

Unlike typical green screen setups, where there may be thousands of watts of cycs and spacelights illuminating the screen and bouncing green light everywhere, all of the green light is reflected - because of the ring light - straight back into the camera lens. As I'm sure you know, ring lights are effectively shadowless from the camera's POV, which makes them brilliant for a setup like this. Wheat's example shows that you can get away with lights covering only the sides of the camera lens, but you may need more as you move the camera around.

So, the subject does not pick up a green tint for two reasons: 1) there is really no spill, because all of the green light bounces back straight to the camera lens, and 2) the green LEDs are actually very weak and easily overpowered by the subject lighting, but the brightness is effectively magnified by the retroreflective surface.

Edit: …aaaaaand beaten to it!
 
I've spoken to a guy in the light business (selling setups like this and other kit to production houses) who said that in the first couple of seasons, "House" used this precise system for all of the rooftop shots.

I love that this gets perfectly even lighting on the background! Screening would be so simple with this.
 
Zensteve,
You've been well educated by the other post, if not a bit technical... just think of cats eyes in the head lights.. if you weren't in the car you wouldn't see the glowing eyes.. same thing... now pluck the eyes from 1 million kittens and glue them to a bed sheet.. there ya go..

Knightly,
That looks interesting. 3M also makes a "dye" that you can use, but the reflectivity is about 1/20th of the manufactured fabric..

Mr. Funk, Yes, the subject does oft refer to him self in the 3rd person, if its bothering you, Ill have a talk with him ;)
 
also, something that baffles me still is why no cool glowing ring of green lights reflects in my eye.. I guess its just cant compete with the 500w flood..

edit; On close inspection on the 2nd try keytest video, I see in the subjects left eye (right screen) that the main sparkle might be keyed out with the white clouds in the bg. or something funny going on between 0:04 - 0:07
 
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this is more appropriate than my kitty analogy.. lol..

retrodiagram.gif
 
Knightly,
Yeah, I knew from reading that blond hair is a pretty tough key, so I figured it would be a good test.. Also, that BLUE is better than GREEN for this purpose. .. I now have BLUE and GREEN LED Bars on my cardboard ring. :)

I did NOTHING to the background.. just gaff taped it over the stand and set up the lights for the subject... (part of the test)

I used AE and keylight.
Keylight is a pretty dang good tool.. this was my first time using it. and, well, its just works.
 
Knightly,
Im not sure how the chroma key works on a math level.

Whats crazy about the test footage. If I mouse over ANY of the background, regardless if its lighter or darker, the Blue value in the RGB readout for all the background pixels is EXACTLY the same as any other.. Maybe that's why the retroreflective systems key so easily. The other white light that might cause a lighter area is still reflecting that pure led light.. shrug..
 
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