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Chris Cooke

Greenscreen

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I'm a Director and an LD at the Miracle Channel. I'm also an aspiring cinematographer. We have a greenscreen at our station that's been painted by Rosco chroma key paint. The way that we've lit it works great when keying it out on our Quantel but when we try anything on our Velocity Q's, it just has trouble getting rid of that notorious green halo. Right now I'm using Videscence to light the green screen and Fresnels to light the talent. Also, the amount of light hitting both the talent and the greenscreen is fairly similar at about 60 fc. Does anybody have some suggestions in a better way to light it so that our Velocity's can handle it. The camera's that we're using are Ikegami HL-45 W's and a Panasonic D-910.

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Have you tried underexposing the screen by a stop or two? Your compositing software may prefer a less bright screen. A dimmer screen would also reduce spill problems.

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I always light the screen 1 stop under key (unless the effects house has a preference; for example ILM wanted the screen 1 over for some reason).

 

This, as David said, helps reduce the spill problems. You could also try using a polarizer to see if you can "dial" out some of the reflectivity of the hair.

 

The best approach is just to have enough distance from your talent to screen.

 

 

Kevin Zanit

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but when we try anything on our Velocity Q's, it just has trouble getting rid of that notorious green halo.

 

The chroma keyer in the Velocity Q is quite poor. I know, I have one.

 

I always use the new Master Keyer in Smoke to pull chroma keys. With a good green

screen it is usually one click and I am done. :)

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Without seeing it's hard to know, but here are some thoughts:

 

Make sure you have detailing on your cameras turned off because that can create edging which when keyed can look like a halo at times.

 

Sometimes people think it's good to send some backlight on the actors to separate them from the screen... don't do this - it makes a natural looking composite impossible and has a "haloish" effect - unless the scene itself is set that way

 

But from the follow-up comments - it really sounds like it is your software. All compositing software is different - kelight, primatte, and ultimatte all work pretty well, but I prefer keylight as ultimatte is pretty uncontrollable and it's spill killing creates awful artifacts.

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We ran into something similar in Phoenix, and fixed it by lowering the light level on the green by adding full green to the flouros lighting the greenscreen, and adding quarter minus green (later cosmetic rouge (spelling???) worked as well) to the back lights. I believe this increased the differentiation of the chromanance between the light on the actors and the green enough to make the mat palatable to the computer. Like someone said, the backlights "outlined" the talent, however, for the subject matter that we were doing it worked just fine. Interestingly enough, adding CTO to the backlights did not have the same effect.

 

Hope this helps,

 

Mike Hall

Glendale, AZ

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HI, my formula for green or bluescreen lightning is working green as my middle gray ( if it is rosco or matthews green screen butterfly cloth / rag ) but green paint may change in tonality being it a little bit darker or lighter depending on manufacturer. So I read w spotmeter and dial that into the lens, It gives green the proper saturation and video level, So I start working out from that reading for the rest. I have a Sony DXC-D50 and for keying purposes I do 2 things that help me pretty much. Detail level 3/4 or 1/2 from full detail level, Saturation to a 1/2 of it's full, and Hue 1/8 from being full ( they are all in scales of -99 to +100 ) and so thet would be detail ( master control ) to a 50 -chck on the H/V detail level for jaggy on edges and frequency level Detail level before. Sat set to 25, Hue to 15, Master Black set to 0. Velocity keyer is not the finest, try keying in After FX with Primatte Keyer or either you can use Combustion Keyer ( discreet logic ). And for backlights they are suposed to get rid of that green invasion on hair and skin. I always use two sort of kickers with 216 and 1/4 minusgreen, they do help, watch for intensity, they might give you that "unnatural halo" but either way, you can soft the edges a little bit. That's my formula and always worked perfect, on primatte key, even with STrata Sphere keyer and with FCP keyer.

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maybe it depends on situation and what de you consider is the perspective of the shot. Let's say if it is a person talking to cam in a very 'normal" situation, Ill try to get the person at least 15 ft away. And if it is not a wide shot, let's say a medium shot, If the floor is green, I'll put some black cloth on the floor for talent to stand over it. Ive shot people lying horizontally on a 20x20 greenscreen, used 20x20 as cyc with person standing over it, what are you planning to do, then we can all give you a more accurate opinion or method, therefore you choose what's best for you

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