Beware Digital Green Screen material

Shooter

Shooter

Veteran
FWIW:

Recent experiences (costly lessons actually) and tests have proven to me that the Green Screen material known as Digital Green is far more difficult to deal with than Chroma Green or Chroma Blue.

It is difficult to control in a studio situation because it is literally so bright and then difficult to work with in post subsequently.

Its quality/ feature is that it is bright and requires less light.

That is true and fact is it is actually 3 stops brighter than Chroma Blue and two stops brighter than Chroma Green (reflectance measured on a spotmeter). Its hard to believe your own eyes and thats part of the problem.

I feel it overpowers the camera (HVX202) , the monitor and it also over powers the eye. It is difficult to establish a "correct" level with the f.g / subject even with careful use of scopes.

One of our tests was to run Zebras on a white bg at 100% to let the three chroma chips in frame establish their own levels. There was a grey scale in the frame also. Green in this instance is eye wateringly "bright".

It is difficult to know exactly how to get the exposure on it down enough or conversely the exposure on the subject up enough to compensate. Sort of defeats the purpose of the material IMHO (ie. lose light one side, add light the other = the same lighting cost and time)

Tested by them selves ...the Digital Green seemed to "overdrive" the gamma ie. shift the gamma.

I have just purchased new 20'x 20' Chroma Green & Blue screens. Wont touch Digital Green in the studio ever again! (Save it for exterior film shoots)

Any one else got thoughts - similar /otherwise?
 
Hmm. I have used "digital green" but never did any keying with it.

I would think as long as you keep it a stop to two stops under the key and keep spill off the subject, you should be fine.

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You have to treat your greenscreen as if it's a wholly separate plane than the plane your subject is on. That means you need enough distance between the subject and the greenscreen to light each independently of the other.

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I am very aware of that and have lit literally hundreds of chroma screens over many years.

It has been my practice to keep the illumination on the screen under the level of the subject. (Usually 1 stop under) . This creates chroma saturation and minimises bounce.

When using digital green which is three stops brighter than chroma blue and two stops brighter than chroma green this creates the difficulty and impracticality. (and I do not mean impossibilty because it is do able).

To make up the difference in levels the subject needs additional lighting to bring down the screen level. Three stops is a huge amount of light, heat and increases unit sizes. In fact it is eight times the wattage or eight times as many lighting units.

It is my belief that the digital green screen is well suited to exterior shooting where it would serve best unlit (in shadow) while subject is lit naturally and with supplementary lghting.
 
So you're saying the Digital Green material produces its own light?

You should be able to make the greenscreen show as nearly black if you have enough distance and light control.

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Chris Santucci said:
So you're saying the Digital Green material produces its own light?

You should be able to make the greenscreen show as nearly black if you have enough distance and light control.

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Not at all. It simply has a very very high reflectance value that is easily demonstrable by a spot meter or a reflected light meter (ie not incident). As mentioned it is three stops brighter than Chroma blue and two stops brighter than chroma green. Given fact is one stop of light is twice as bright, two stops is four times as bright and three is eight times as bright . Thats a hell of a lot of light (and heat) that needs to be applied to the subject to drop the screen to a working level. (Do your own test)

The only way it would ever be black is almost total absence of light or a very high f stop (and absolutely nothing to do with distance.)
 
Sure sounds like a pain in the keyster, including green bounce. Probably best where the screen is way back behind the subject, avoiding any spill from key/fill lights.

Thanks for the heads up,

Michael
 
moonlitnite said:
Sure sounds like a pain in the keyster, including green bounce. Probably best where the screen is way back behind the subject, avoiding any spill from key/fill lights.

Thanks for the heads up,

Michael
Click to expand...

It's not a pain at all, it's much easier than taking all the time to light your background. It doesn't matter if there's spill from the keylights or anything, it will still work great. Your talent only has to be 3 feet away from the screen itself, and as long as your camera is 10' off the talent, you're golden. It keys fantastically, and saves a ton of time in setup lighting. I'm not sure why the guy above doesn't like it, we've had nothing but great results using it at our studio, and so do other users, which is why I'm such a cheerleader for it. Still, to each their own
 
@RandomHero.

Your 10' / 3 ft technique would not work for me at all.

I use an appropriate lens and then position the camera to the talent so I can composite it properly with the bg. eg If I have a wide angle bg I need to use a lens that matches the feel and position the subject so it fits the bg. (Fundamental compositing rules that include DOF.)

Your 10 ft camera distance would be "shapeless" and inflexible in compositing.

Your 3ft from the bg goes against all common wisdom of chroma key lighting because of bounce issues.

As for why I dont like it and prefer Chroma blue or chroma green... I think I have explained it as well as I can. It reflects too much light and requires so much additional fg lighting to bring it down to a level practical for keying.

Note. The screen I am working with in the studio is 30 ft wide and twenty feet high. It requires some lighting to keep it even. As minimal as that maybe , there is a limit too how minimal you can apply because of the lighting units. eg 1k broad cyc lights.
 
Shooter said:
@RandomHero.

Your 10' / 3 ft technique would not work for me at all.

I use an appropriate lens and then position the camera to the talent so I can composite it properly with the bg. eg If I have a wide angle bg I need to use a lens that matches the feel and position the subject so it fits the bg. (Fundamental compositing rules that include DOF.)

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Click to expand...

I'm trying to do some chroma keying, can you explain why DOF is an issue with it? As with the 10' rule I'd think it'd be irrelevant unless you had some REAL props on the set, otherwise any defocusing of the keyed in background would be done in post right? It seems you're saying there's benefit in creating a defocused greenscreen?
 
Shooter said:
@RandomHero.

Your 10' / 3 ft technique would not work for me at all.

I use an appropriate lens and then position the camera to the talent so I can composite it properly with the bg. eg If I have a wide angle bg I need to use a lens that matches the feel and position the subject so it fits the bg. (Fundamental compositing rules that include DOF.)

Your 10 ft camera distance would be "shapeless" and inflexible in compositing.

Your 3ft from the bg goes against all common wisdom of chroma key lighting because of bounce issues.

As for why I dont like it and prefer Chroma blue or chroma green... I think I have explained it as well as I can. It reflects too much light and requires so much additional fg lighting to bring it down to a level practical for keying.

Note. The screen I am working with in the studio is 30 ft wide and twenty feet high. It requires some lighting to keep it even. As minimal as that maybe , there is a limit too how minimal you can apply because of the lighting units. eg 1k broad cyc lights.
Click to expand...

I understand that it doesn't work for everyone. As for the 3' rule going against common green screen wisdom, this is because reflecmedia is not typical green screen material. Since you don't have to light your backdrop, spill over from behind is no longer an issue when using the Chromatte background. You can light your talent however you wish, and it won't affect the backdrop key or risk any spill over.
For the 10' rule, this isn't saying you can't zoom back in, just that since the LED ring attaches to your lens, it has to be that far away from the subject so you don't get light from the LED on them, thus making keying very difficult.

As far as big projects or extreme close up projects, it might not work sometimes. But i was suggesting it because it's been great for our uses so far, and people like to know their options in certain fields.

If you'd like to see exactly what it can do, watch this video. It shows the matte, the keying, versatility using talent including candles and other strange things for compositing, and potential with something like this may be more useful to some people in here than others.

I'm not knocking any other forms of key, and I use other means myself from time to time. But if my project will allow me, I'd pick this stuff any day.
 
Sorry Random hero - I thought you were discussing Digital Green.

My comments about compositing with lenses at correct distance to subject so that bgs match/fit still stands though.

@brianluce.
DOF is part of the compositing process to make fg and bg work together believably if thats what one wants. It pays to shoot keys and props sharp and use post to assist the DOF illusion. Obviously if the subject is shot with a wide angle lens the keyed in bg will be sharper than if the subject was shot with a longer lens.
 
Shooter said:
Not at all. It simply has a very very high reflectance value that is easily demonstrable by a spot meter or a reflected light meter (ie not incident).


The only way it would ever be black is almost total absence of light or a very high f stop (and absolutely nothing to do with distance.)
Click to expand...


The screen may reflect more light (than white, I doubt it) but it can only reflect what it's getting. What I'm saying is, if you have proper control, yes which includes distance apparently since you seem to have a lot of spill from your keys (maybe), you should be able to have the screen show as black/nearly black, or pure white. You should have that much control.

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No the digital green does not reflect more light than white. (I never said that)

I have no problem with spill or bounce from the screen (but I do have to work harder at controlling it than if I use Chroma Blue or Green). There is more potential for bounce with Digital Green than the chroma screens. In fact 2-3 stops more potential.

Distancing a screen so far back so that one could make it expose as black would probably involve it being so small it would not cover the subject. Distance practically in a studio space does not change the reflectance value of anything.

To expose the screen as white is easy. Too easy and thats the point.

(A thought - I could expose the screen as black but that would involve shooting it with the lens cap on.)

Chris - just for my information... when you shoot a key. Where do you "sit" the screen on your waveform relative to a skin tone / grey scale. ( ie at what percentages ).

My guess is your digital screen is at 75- 85% and your skins at 60-70%.

I prefer the screen below the skin.

Last week I shot all chroma green and my results are far superior. The keys are better and it was quicker and easier to light. Bonus ...the talent was not subjected to the extreme heat from additional lights. All good.

Now - back to the Edit suite to finish compositing.
 
Shooter said:
Chris - just for my information... when you shoot a key. Where do you "sit" the screen on your waveform relative to a skin tone / grey scale. ( ie at what percentages ).

My guess is your digital screen is at 75- 85% and your skins at 60-70%.
Click to expand...


I use a light meter and place the screen's exposure at 1 to 2 stops less than the level for the subject. And I generally try to get the screen 15 to 20 feet behind the subject.

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An incident meter? (Which does not measure the reflectance from the subject)

No waveform Monitor? A true indication of reflectance and clearly shows BG to subject. (like a Spot Meter)

Zebra Level?

I also place my screens 12ft+ behind generally. Less for objects like packs/products.
 
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