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reflections and glass


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#1 Andre LeBlanc

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Posted 26 May 2010 - 02:41 AM

Hi all,

I'm doing some visual effects tests in the next couple of weeks for a sci-fi project, and was looking for some thoughts/ideas on techniques. The scene I'm testing takes place in a room with a large digital screen (the screen is maybe 5ft wide by 3ft high). It's essentially supposed to be an oversized security monitor giving visuals into different rooms in a building. An actor would stand in front of the screen, controlling what he/she sees on the screen with a controller.

The contents on the screen would be entirely done as a post production comp. But some of the things that concern me are 1) reflections and spec hits, as the screen is supposed to be glass and 2) light being emitted from the screen.

I've had numerous suggestions involving Plexiglas with a green sheet behind it, or even the use of a mirror or mylar as the screen where we'd only see the actor in the reflection. I have an extensive compositing background, so how to put all this together is less of a concern then making sure I get all the right elements. Trying to fake reflectivity and spec highlights in post always falls apart... especially if the camera's moving. And of course, there's the issue of the light that would come from the screen!

Anyone have any ideas or previous experiences they'd like to share? Thanks for you input!
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#2 Robert Costello

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Posted 26 May 2010 - 10:12 AM

The few things that come to mind are :
Why does it have to be glass? Does it shatter or does someone’s use the word 'glass' to describe it?
Is there something that happens in the reflection? (not looking for spoilers)
It seems like a lot of work to mimic specular highlights and reflection for what might be a minor detail.

The use of a reflective material is not a bad idea at all, with the image they are viewing composited it might
balance the reflection so as not to seem so much like a mirror...and maybe have a separate diffused layer or Gaussian blurred layer to create the glow of the screen..

Maybe not moving the camera in a way that would make the effect extraordinarily difficult.

Or a possibility is to have what they are watching created 1st and then have that actually going on the screen rather than having to match it up later.


I think people will accept an idea or concept even if it is not 100% accurate as long as it is visually
correct enough, not distracting and forwards the scene...

And considering it is science fiction, you are pretty free...
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#3 David Mullen ASC

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Posted 26 May 2010 - 10:42 AM

If the actor is standing in front of the 5'x3' screen, then you are talking greenscreen unless you want to roto him, so the question is really if you want a sheet of glass in front of the greenscreen to simultaneously capture his reflection and movements. You'd have to give him a strong key so that his reflection is bright enough to read. If you really need a reflection -- you could say that the screen is non-reflective and bright, unless you are talking about a dark background on the screen image.

If you want to get fancy, and your actor's moves are non-repeatable (so you can't do separate passes), you could try poking a hole in the center of the greenscreen (no glass in front) and putting a another camera on the other side looking back at the actor with a wide-angle lens in order to capture the reverse angle simultaneously and build a reflection in post. Could even be a DSLR shooting video, or DV, it doesn't have to be a great image if it's just a ghostly reflection. You'd have to fake the dimensional move in the reflection (some sort of post 3D distrotion) created by the moving camera facing the greenscreen.

If the actor can adequately repeat their motions, then just shoot a reverse angle from the screen's perspective of the action, with a revered dolly move mirroring the dolly move behind the actor, sort of a poor man's motion control.
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#4 Andre LeBlanc

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Posted 26 May 2010 - 01:11 PM

Thanks for the input! I think the idea of putting a camera behind the screen to catch reverse action is interesting. On key shots where we'd really expect the reflection, it could be matchmoved to the original plate. I also like the idea of using reflective material when the actor is not right in front of the screen. This might make for an interesting shot where we only see the actor's reflection, and not the actor in the foreground (a clean shot of the screen). It seems like there's about 10 different solutions... each one getting you about 50% there.

To answer Robert's question, yes, it's actually a window that doubles as a video screen (it's supposed to be modern OLED technology). And yes... it will eventually shatter. Is the story that obvious? :)

I'm not 100% sure what I can get away with, but maybe I should be selective. Only worry about the actor's reflections when we're close to the screen, and it's prominent in the shot. In those instances I could consider all the options discussed above (green screen, reverse camera, reflective mtl). Otherwise, maybe highlights and spec hits will do.

Any thoughts on mimicking the light that would be emitted from the screen? The only time I see this being critically noticeable is if we're on a CU of the actor's face watching the screen as it changes. In that case, I'd expect almost a dithered effect to the light hitting their face. Might be as simple as waving a cookie cutter pattern in front of the light.
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#5 Lester Dunton

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Posted 26 May 2010 - 02:05 PM

I have used video projectors off screen playing back plate material to produce specular highlights within the set and on artists.(eg Knight bus sequence in Potter 3) I have found synchronization not too much of an issue if carefully planned. It is also important to diffuse the light from the projector eg hampshire and 251, and desaturate the plate material, and if possible use projectors with a xenon light source.
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#6 Andre LeBlanc

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Posted 26 May 2010 - 03:25 PM

Very good idea with the projectors! Seems like an obvious solution for the lighting fx when you mention it, but i hadn't even thought of it.
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#7 Sean Lambrecht

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Posted 26 May 2010 - 03:53 PM

What if the green screen is behind the actor, and the "OLED" screen is a half-silvered mirror? Keeping in mind my green screen experience is next to non-existant... Just a thought.
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#8 Andre LeBlanc

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Posted 26 May 2010 - 05:39 PM

What if the green screen is behind the actor, and the "OLED" screen is a half-silvered mirror? Keeping in mind my green screen experience is next to non-existant... Just a thought.


Interesting idea... although I think it would get a little bit nutty on this project!

After giving this more thought, it seems like the 75% case will be the Plexiglas with the greenscreen backdrop. Ensuring a strong enough key on the actors to get a reflection on the Plexiglas. And when it's not the 75% base case, it sounds like there's a multitude of more unique solutions (reflective materials, etc...) when we need to get really specific.
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