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HVX and Green Screen

Published : 16th January 2007

I'm shooting a music video that we've decided to shoot green screen instead of rear projection.

It will be 2 actors in front of a 12x screen. What ratio screen:subject should there be? green at key? green 1 stop over/under?

Thanks,
Donavon Burke
L.A., CA


A lot of it depends on what software you're using to key with.

It's most important to make sure that the screen is greener than anything else in the shot by at least 40 units, so if you're not shooting full body (including feet standing on the screen) use green gels to pop it up a bit. A hint of plus green works marvellously, or I've used Geoff Boyle's suggested gel, Fern Green, with great success. Any time you light a surface colour with light of that same colour you improve the colour saturation immensely. It doesn't take much.

Also, make the screen brightness as even as possible.

The best way to set levels in video is by using a waveform monitor.

I've shot successful green screens at all sorts of levels but usually around 60 units works fine. If you don't have a waveform you can try setting your zebras to your desired level (50, 60 or even 70 units) and rough it in by eye.

Green spills like crazy so you probably don't want to light it any brighter than you have to. You can go underexpose a little if you add green gels to the lights illuminating the screen since most keying software cares more about saturation, and how different the screen colour is from other colours in the shot, than brightness as long as the screen is lit evenly.

If you're doing full body green screen try to light bright enough to use a polarizer. That helps take the shine out of the floor that results from using backlights or spacelights.

I'd suggest shooting a test first. I haven't done a lot of work with the HVX but from what I've seen it's fairly noisy, plus I'd worry a little about the kind of edge definition you're going to get out of a 1/3" chip and inexpensive optics. I assume you're shooting DVCProHD for best results, but don't shoot anything worse than DVCPro50. It'd be best to shoot DVCProHD for the key and then down res the results to NTSC, if that's your delivery format.

That's my $.02.

Art Adams
Director of Photography
Film | HiDef | Video
www.artadams.net


class="style15">>>Green spills like crazy so you probably don't want to light it any >>brighter than you have to.

Also, you only need green backing or green floor where an edge of the character will cross into the green. So spread black or grey drops/carpet/grip blankets on the floor in front and to the sides of the subject and hang in front of the green background grey or black drapes or curtains or fabric in all the areas that the subject won't pass in front of. This will cut spill enormously.

Of course, if you have to do a live key with no ability to cut in garbage mattes to take out the backdrops, this won't work.

Steven Bradford
Collins College
Tempe Arizona

Blue Screen lighting tips page:
http://www.seanet.com/~bradford/bluscrn.html


With regards to the spill etc., I agree with Steven on this.

However if you are able to key with any colour on whatever box of tricks you are using, then a colour as close to the background to be keyed in will help enormously, if possible. Say orange/red for bricks, green for, er, greenery and blue for sky.

Regards

Chris Maris
Director of Photography
0044 7956 251061/0046 7340 76003
www.chrismaris.com
Frostbiten; GRANDE PRÉMIO/Best Film Award winner, Porto 2006
www.frostbiten.se

'Life is a tragedy when seen in close-up, but a comedy in a long-shot'
.. Charles Chaplin


I'm currently shooting a large amount of green screen, we move on Monday to the 360' * 45' screen

I'm lighting the bigger screens with Kino green tubes, 525nm, and the smaller screens with tungsten and fern green as Art describes.

Exposure is 50% green and as little as I can of anything else.

It seems to be working well.

Cheers

Geoff Boyle FBKS
Director of Photography
EU Based
www.cinematography.net


class="style15">>>I'm lighting the bigger screens with Kino green tubes, 525nm, and the >>smaller screens with tungsten and fern green as Art describes.

Those green tubes are killer. It's amazing how few of them you need.

Art Adams
Director of Photography
Film | HiDef | Video
www.artadams.net


I'm new here and I'm not a filmmaker on film stock, I use video and I'm also a 3d animator. I've found unto now that blue screen gives me a better editing cut off point (Less smoothing needed, more accurate than the green cut off point). I use Premiere Pro but I have used Final Cut Pro when I did my media course at college. Why do you guys favour green screen? Do you find it easier to light?

Oh by the way strange question I know but why do the majority of camera personnel and film crews appear to be male? I'm female.

Sandy
Ramsgate UK


Sandy Lacey wrote :

class="style15">>>Why do you guys favour green screen?

If you separate the colour-channels, green has the cleanest signal (least
amount of noise).

class="style15">>>Oh by the way strange question I know but why do the majority of >>camera personnel and film crews appear to be male? I'm female.

That's how it has grown, but the times are changing. Sometimes when still living and shooting in Sydney/Australia, half of my crew was female.

Cheers

Martin Heffels
/filmmaker/DP/editor/
Maastricht, the Netherlands


class="style15">>> Oh by the way strange question I know but why do the majority of >>camera personnel and film crews appear to be male? I'm female.

Historical precedent, gradually changing with the times as most industries are.

More and more women every year in the technical crafts, and it is a most welcome change.

Many "above-the-line" people are female (writers, directors, producers, performers).

The technicians are catching up, slowly.

Doug Hart
1AC, NYC


As previously stated, green is the cleanest channel (and the channel luminance is derived from). Blue is a bit noisy, surpassed only by red, which is an extremely noisy channel. Don't live next to red, you'll never get any sleep.

Also, people are less likely to wear green than blue, so it's a bit easier for the wardrobe department.

And... the green commonly used is a bit brighter than blue and takes less light to illuminate, so it's an economic issue on larger sets.

Also, when the director tells the DP that the next shot is two 360 camera moves, one horizontal and one vertical, the DP can stand in front of the green screen and his or her flesh tone will appear normal.

As for why there are more men on film crews than woman, it's because women are, for the most part, more intelligent than men.

Art Adams
Director of Photography
Film | HiDef | Video
www.artadams.net


Sadly this is true and yes, it does seem to be changing ever so slightly though I know very few female DOP's, and those I do know oft suggest they must work twice as hard to succeed in an old boys club.

I have had a lot more female AC's though, over the years, maybe because male AC’s find it easier to move up the ladder, I don't know. It can't be the age old stay at home with the family nonsense as there are equal, if not more girls in production etc.

An old Russian lighting teacher called Knajinsky, who I had the fortune to be schooled by, suggested to a girl, who was a part of the course, that she was too weak to be a DP because she could not lift a camera.

Red rag to a bull.

Oh and Doug, are you a technician? Horrible title methinks.

Sounds like you solder bits of wire together all day for someone else

Regards

Chris Maris
Director of Photography


class="style15">>>As previously stated, green is the cleanest channel (and the channel >>luminance is derived from). Blue is a bit noisy, surpassed only by red

I have a question regarding this blue or green screen discussion. I was told that black could also be used. What baffles me is, how do you light a black screen to use in place of either a blue or green screen ???

I was also told that the Dubarry Black Velvet would make the best black for using for this purpose. That it was used in the old days for trick photography and motion pictures.

Does anybody have any thoughts on this ??? I'd like to hear.

Daiquiri St John
P.O. Box 180402
Los Angeles, CA 90018


Chris Maris writes :

class="style15">>>Oh and Doug, are you a technician? Horrible title methinks. Sounds >>like you solder bits of wire together all day for someone else

I don't mind the title "technician."
An AC's job is very technical.
"Craftsman" sounds like we watch Martha Stewart to see how to make Christmas decorations out of household trash.
"Artist" sounds like we make collages out of torn magazine pages.

How would you describe what we do, if not "technician?"

Doug Hart
1AC, NYC


Doug Hart wrote :

class="style15">>>"Craftsman" sounds like we watch Martha Stewart to see how to make >>Christmas decorations out of household trash.
>> "Artist" sounds like we make collages out of torn magazine pages.

Heh heh. Good point. Are not DP´s in the USA these days known as Authors of Light?

class="style15">>> How would you describe what we do, if not "technician?"

As Wikipedia puts it : A technician is generally someone in a technological field who has a relatively practical understanding of the general theoretical principles of that field, e.g., as compared to an engineer in that field. They are generally much more versed in technique compared to the average layperson, or even the professional in that field. A mid-level of understanding of theory, and a high-level of technique, is generally mastered by the technician in order to become expert in a specific tool domain.

I have none of those qualities but I can make pretty pictures.

Chris Maris
Director of Photography


class="style15">>>I have a question regarding this blue or green screen discussion. I >>was told that black could also be used. What baffles me is, how do >>you light a black screen....

You don't light a black screen. You keep light off it.

Black screens are commonly used to shoot elements such as smoke, snow, and rain. Essentially, elements that have no colour, only differing shades of grey. A soft luminance key can separate these elements and provide a cleaner matte than you would get using a colour difference process, without any colour contamination.

Mike Most
Chief Technologist
Cineworks Digital Studios
Miami, Fl.


class="style15">>> I was told that black could also be used.

Black can be used for lumakeying, which is often preferred for Mini-DV and DVCam because their luminance resolution is so much better than their colour resolution.

I've used it very successfully with Final Cut Pro, when compositing talking heads. The subjects have to be wearing clothing that's at least a couple of shades lighter than the black background, and they should be lit as evenly as possible, avoiding deep shadows. Even so, you often need to add an 8-point Garbage-Matte to prevent particularly dark areas from breaking up the key. Ergo this approach doesn't work well for moving subjects -- but for static shots and simple subjects it can be quite effective.

Dan Drasin
Producer/DP
Marin County, CA



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