Shooting green screen background plates

Ryan K · March 2, 2005

As far as I know, shooting background plates for film is done on 70mm for a higher resolution. Does anyone know if it is advisable to shoot background plates on HD for HD? Does the resolution hold up?

Landon D. Parks · March 2, 2005

I dont think I know what your talking about, but I'll give it a try.

As far as I know, shooting background plates for film is done on 70mm for a higher resolution.

Yeach, if your shooting an IMAX film! Most people probably still use 35mm.

Does anyone know if it is advisable to shoot background plates on HD for HD? Does the resolution hold up?

Depends on what your shooting and what format your exibiting it in.

P.s) You didnt supply enough info for people to help you. Just asking if HD is quality enough for a background plate is kind of basic.

PSS) I gues it makes enough since for me to say that if you shoot the greenscreen subjects in HD, then the background plate should be HD. If you shoot the Greenscreen subjects in 35mm, you should shoot the background plate in 35mm, and if, unlike 99.999% of the people you shoot your greenscreen on 65mm (It's not really 70mm!), then you should shoot the background on 65mm.

Shooting a 65mm backgrounjf plate and shooting the bluescreen on HD would look pretty horrible, same thing if you reverse it.

Edited March 2, 2005 by Landon D. Parks

Ryan K · March 2, 2005

Well, it was my understanding that 70mm (or 65) was used to shoot green screen backgrounds for projects which are principally shot on 35mm. The reason being that the increased detail in the larger format would result in a greater quality in the background plate. N'est pas? No problems with grain or resolution if all the green screen backgrounds are shot on 35?

Perhaps I'm wrong. It was this belief which informed the question of whether I would get good results with shooting background plates on HD for a project on which principal photography was also shot on HD. Obviously mixing formats would look peculiar but I thought it best to see if there are any particular reasons why a HD background plate might throw up problems.

To explain further, this relates to shooting outside the window of a stationary train with a greenscreen on the other side of the carriage upon which the moving background plate would be pasted in post. It's a short film and it will most likely be digitally projected as there are no plans for a blow up.

Patrick Neary · March 2, 2005

I dont think I know what your talking about, but I'll give it a try.
Yeach, if your shooting an IMAX film! Most people probably still use 35mm.

Depends on what your shooting and what format your exibiting it in.

P.s) You didnt supply enough info for people to help you. Just asking if HD is quality enough for a background plate is kind of basic.

PSS) I gues it makes enough since for me to say that if you shoot the greenscreen subjects in HD, then the background plate should be HD. If you shoot the Greenscreen subjects in 35mm, you should shoot the background plate in 35mm, and if, unlike 99.999% of the people you shoot your greenscreen on 65mm (It's not really 70mm!), then you should shoot the background on 65mm.

Shooting a 65mm backgrounjf plate and shooting the bluescreen on HD would look pretty horrible, same thing if you reverse it.

<{POST_SNAPBACK}>

Why am I reminded of that classic Onion headline:

FACTUAL ERROR FOUND ON INTERNET!

Anyway, back to Ryan's question, American Cinematographer had a cool little article a while back about Fox's "24" shooting their background plates (for either front or rear projection) using PD-150s and dvcam. It seems that you'd be very safe using HD!

The list of 35mm films that used 65mm for effects work is a long one, the issue being one of image degradation in the days when effects were an optical/photochemical affair rather than a digital one.

David Cox · March 2, 2005

Yes, Patrick is right.

When opticals were achieved optically (der!), this entailed a number of passes through an optical printer and this would mean a build up of grain. For example, a background plate would be shot on film, then re-printed to another piece of film through a matte roll. The result would be grain from the original background film, plus grain on the new "master" film. Larger format film was then used (such as VistaVision) to minimise this build up of grain so that the effects shots did not look notably different to the unaffected shots.

In a digital environment, there is no such grain build up. So generally, you should aim to shoot your foreground / background shots with the same format and camera in order to help the composite look as seamless as possible. If they are shot differently, there could be an issue with different grain / noise structures, lens aberrations etc that will make the foreground look "stuck on".

The only potential issue with HD green / blue screens is that of color resolution. HDcam at 3:1:1 or highly compressed HDV have very compressed color channels and so have reduced color separation than uncompressed HD pictures. This *could* result in poorer key edges and so less convincing composites. In an ideal world, you should shoot your green / blue screen foreground shots with a camera capable of 4:4:4 and record as such uncompressed to hard drive. Failing this, record 4:4:4 to compressed HDcam SR. Failing that to 4:2:2 tape such as HDcam SR or HD D5. Failing that, HDcam or HDV and don't tell your compositor :-) The background plates have no such restrictions, because you're not actually doing anything with them.

David Cox

Managing Director

Baraka Post Production Ltd

London

baraka.co.uk

John Sprung · March 2, 2005

As far as I know, shooting background plates for film is done on 70mm for a higher resolution. Does anyone know if it is advisable to shoot background plates on HD for HD? Does the resolution hold up?

<{POST_SNAPBACK}>

Actually, a lot of effects work is shot on the side-pull 8 perf VistaVision format. As far as the labs are concerned, it's just plain old 35mm, and goes thru the same soup. Bringing up a 65mm developer for a few plates would be horrendously expensive, and no real advantage over Vista. It's unfortunate that Jim Martin's 12 perf side pull system never got off the ground.

As for HD composites, the best way to go would be 4:4:4 for your green screens. If you have to go 4:2:2, a luminance key works better.

-- J.S.

Kevin Zanit · March 3, 2005

Yes, 65mm was common, and Vista Vision is still very common.

You can get away with lower quality B.G. plates if you are shooting something with minimal depth of field because you are just going to throw the rear projection (if you were doing something like 24 does and not just green screen) out of focus, thus its more forgiving.

An advantage to using a larger format for B.G. plates is also the ability to resize it for tweaking a composite without as much of a loss in quality (assuming you scanned it at a resolution high enough to preserve that ability).

And if you want to increase vertical resolution on your foreground plates you could turn the camera on its side (assuming you can fit what you need in frame - i.e. miniatures).

Kevin Zanit

David Mullen ASC · March 3, 2005

Besides less grain / more detail with larger negatives, the other reason why 8-perf 35mm (VistaVision) or 5-perf 65mm is still used sometimes for efx plates is that if the main production is being shot in 35mm anamorphic for a 2.35 image, then sometimes they don't want to shoot efx with anamorphic lenses too, particularly miniatures because of focus and depth of field issues -- but also it can be hard to composite over anamorphic footage with its unique distortions, especially wide-angle anamorphic photography. So working with spherical lensed footage is easier, and since Super-35 framed for 2.35 would be a smaller negative than anamorphic, the only solution that doesn't compromise the size of the negative is to use VistaVision or 65mm for efx photography for a 35mm anamorphic production.

However, there are examples of anamorphic shoots using Super-35 for efx work, like "Lost in Space" did.

Elhanan Matos · March 3, 2005

All this talk about effects reminded me about a picture I took of a camera that I thought looked really cool. I would love to see if anyone on this forum can recognize it. ;)

David Mullen ASC · March 3, 2005

Looks sort of like the "Empireflex" VistaVision camera built for Empire Strikes Back, or some sort of VistaVision camera, although IMAX cameras can also use the "butterfly" design as well since that is also a sideways format.

Elhanan Matos · March 3, 2005

Wow... You're good. That's exactly what that is. I saw it over at ILM and thought it was the coolest camera I have ever seen, the body is made of carbon fiber. They also had an Arri camera with a Mitchel movement, that was neat.

March 6, 2005

As far as I know, shooting background plates for film is done on 70mm for a higher resolution. Does anyone know if it is advisable to shoot background plates on HD for HD? Does the resolution hold up?

<{POST_SNAPBACK}>

I'd say that uncompressed HD is a very nice solution. My biggest problem when keying are limited color resolution and especially grain. The pixel res is enough for most cases.

The lack of grain and the stability of the image are really welcome for comp work.

So uncompressed footage from cameras like Viper/D-20/genesis should in many cases be even slightly easier to work with than standard 35mm footage. That was at least my impression when working with Viper footage.

If you can, stay away though from normal HDCAM. It looks nice but I had serious problems keying this. Although as always with time and efforts you can get some ok result, I would not recommend this. Haven't worked with SR material though...

-k