Shooting through a window into Greenscreen

[Brad Webb]

I'm in pre-production on my first big feature, so this will probably be the first of many annoying questions I post over the next month or so.

Here's the scene (I'm going to try to give as much detail as I can)
The are several scenes where the main character is looking out his apartment window and into an apartment across the street. One shot I want to do is have the camera behind the character (back to camera), looking out the window and seeing the other apartment with the character's face reflected in the window.

Something like this, only with a reflection of the face and at night.

The apartment is probably going to be all shot on stage. So there will be no apartment across the street. The shot will be out of the window into greenscreen.

My questions are:

1. How do you set up the lighting to get the reflection of the character in the glass of the window and not get the spill from the green screen out of the window?

2. Is the reflection going to work if it's not dark outside the window?

3. Should I try and shoot this on location instead, or just cheat this one shot?

Thank you for your help.

 

[Pietro Impagliazzo]

If you set up a second camera in the opposite side you can have a 'reflection plate'.

If the greenscreen is fairly lit, I'm not sure how the reflection in the actual glass would pop up, I guess the greenscreen would have to be dimmered and it wouldn't depend if it would key well on your post workflow.

If the actor is still I'd measure the distance until the window and position the camera at the other side to shoot the 'reflection plate' that could be inserted as you like in post.

And in the end it all comes down to testing... Get a piece of green tissue and try in your home's window? :biggrin5:

 

[Cail Young]

2. Is the reflection going to work if it's not dark outside the window?

Most window glass isn't particularly reflective, so to see a reflection, even with black behind the glass you will need a ton of light on the subject. This means you'll probably be overexposing the foreground.

If you put a half-silver mirror in the window frame and put black behind the subject (i.e. off to camera right in the example photo) then you won't need as much light to achieve a reflection.

You may be better off trying projection behind the window rather than attempting a post key as keeping a reflection over a keyed area is very hard. Not impossible, but very hard.

 

[Vinit Borrison]

Cali has a point, you'll have to light the subject pretty heavily from the outside, though I think you can find a happy medium where the reflection is actually visible and the subject is not overlit. Setting up a green screen far enough away from the window and lit just enough for exposure without overpowering the lighting inside will help with not getting spill inside.

 

[Elsie N]

As a back-up, shoot the actor through the window from the outside looking in. Then if the shot as originally planned fails, maybe post can mirror the shot and insert it opaquely into the window as a layer.

 

[Shane Kelly]

My questions are:

1. How do you set up the lighting to get the reflection of the character in the glass of the window and not get the spill from the green screen out of the window?

2. Is the reflection going to work if it's not dark outside the window?

3. Should I try and shoot this on location instead, or just cheat this one shot?

Thank you for your help.

If the greenscreen is far enough away from the window you are not going to have many green reflection problems. I would use an 8x8 or 12x12 frame.
You are not going to get much of a subject reflection with the green screen out there, you might have better luck with blue. However ,it's still not going to be as strong as it would be if there was black beyond the window.
What if you used green or blue for the majority of the window and placed a piece of duvatene over the areas where you wanted to see the reflection? If you then also shot a clean plate of this setup ( without the subject), a combination of chroma and difference key could maybe solve the problem.
I'm a cinematographer, not a post guy so maybe some aftereffects wizard could tell us if this could work.
The second camera is an interesting idea but that introduces it's own reflection problems, that of the greenscreen reflected in the window. A polarizer could take care of this. Cool idea, though, I'll have to test it.
Shooting it practically introduces its own set of problems in that you have to base your exposure of the cityscape and light from outside the window but frees you up for camera movement. I like this option the best if the reflection is the important part of the shot.

 

[Jake Bastian]

If you're going to be using a half silvered mirror to get the reflection, why not go one step further and put the green screen inside the room instead of out of the window so what you're keying isn't the actual screen, but it's reflection. That way you can light the interior as bright as you need to to get a reflection and get a good key without the two objectives interfering with each other. At this point you could throw up the duvatene outside the window to make the reflection pop even more.

 

[Joe G.]

One tutorial suggested that leaving it black is better than green when you want to use the reflections. If you can get the outside completely black, you can pull a luminance key, and also use the reflections in the glass.

I've never done it, though. The example was a cell phone screen, and not a window. Basically, if you want the reflections, black is a good choice, with no green spill.

 

[Leo Ticheli]

This is easy. Shoot your FG subject in green screen with two synced cameras, one for the main shot, the other for the "reflection." Then key both shots as needed.

Good shooting and best regards,

Leo

 

[Kwan Khan]

In Real world, Out side the window basically parallax is zero Change. So you just need to change Pan, Tilt and Camera Wobble.
You can do it by tracking a single point (two If there is any rotation).
Solution:
1- Placer your Green Screen Outside the window as far back as possible and make it huge
2- Two tracking marker on green-screen out side the window
3- Use 2D Tracker

 

[Matt W.]

The only way to get a good reflection in normal glass is to overexpose the face (and have a fairly dark area behind glass so the reflection shows up). I've done this once or twice (on the hvx) and the reflection is always a couple stops under and the face itself is usually overexposed, but hot backlights look nice so it works; it's just a balancing act getting the exposure right and finding a place to put the light so it doesn't reflect in the glass and isn't at an awkward angle.

But the way of doing what you want is so elegant I can't believe no one has suggested it:

You put a standard mirror in the window frame and have your talent stand in front of it as he normally would. Then you put a large green screen IN THE ROOM maybe fifteen feet BEHIND the talent (and behind the camera, which is at an angle so it won't reflect in the mirror) and light the green screen to a standard one or two stops under key. You need to adjust camera position/green screen position/etc. to get it right but the reflection in the window will be of the talent's face, approximately as bright as his actual face is (and this can be taken down to more realistic levels in post because of course no reflection is fully opaque, but of course your compositing artist will be using the screen/add transfer mode anyway)--and with a perfectly lit greenscreen behind it from which to pull an easy key. Plus, you don't need extra space outside the window to hide the green screen. So you can rent a smaller stage.

If you're using motion tracking just pick some points in the room and then get your compositing artist to extrapolate motion from that for what would be outside. Alternately, you could use a tracking point on the greenscreen and this would work, too. Easy!

Edit: I do compositing as a hobby and this is not a hard shot to composite realistically--if lit correctly.

 

[Noah Kadner]

I'd just do it with the glass and light it properly. If you don't it will look weird unless you have ILM doing your VFX.

Noah

 

[Pietro Impagliazzo]

I'd just do it with the glass and light it properly. If you don't it will look weird unless you have ILM doing your VFX.

Noah

They'd prolly say: Beep that, shoot handheld in your home and we make the 3D model of the actor and animate the reflection, no biggie.

:emote_hanged:

 

[Matt W.]

If you're going with glass I'd use duvetyn rather than a green screen, then, since you're layering two additive elements and you'll pull a better reflection form a black background. Pull a garbage matte, crush the blacks and use the "add" transfer mode.

 

[Noah Kadner]

I'd be careful- luminance keys are really tricky when there are dark values on the foreground- like hair, eyes, costume, etc. Shoot some tests first. Nothing wrong with a green screen and a piece of glass. I shot miles of people in cars with all sorts of glass windows for a movie and we had no major issues. Reflections looked natural and keyed nicely to the green screen.

This site has some nice test examples you can try:

http://www.hollywoodcamerawork.us/greenscreenplates.html

Noah

 

[Matt W.]

I guess I'm full of bad ideas today...

I wasn't suggesting a luminance key, though; simply rotoing the window (or using a luma key on just the window), crushing the blacks a bit, and superimposing the background with an "add" transfer mode. A compositor would use "add" anyway, when superimposing a reflection, so this would be the most realistic approach and much cheaper since no need to back up a big green screen. A green screen would be more flexible, though, so if it's a complex shot with camera motion or whatnot, sure go with that.

 

[Shane Kelly]

there's a free greenscreen/window shot here if you want to play around with it:
http://www.hollywoodcamerawork.us/greenscreenplates.html
it's halfway down the page.

 

[Matt W.]

Just to reiterate: reflections are composited additively (linear dodge and screen can also work). You can't realistically composite a reflection as you would a normal object with standard green screening. In real life, a reflection against pure bright white approaches invisibility; a reflection on a highly reflective black opaque surface (such as a mirror) approaches being opaque; everything else is in between--and you need a different transfer mode to emulate that.

The two methods I offered above are ideal for additive compositing because they near-perfectly isolate the reflected image (black reads as 100% transparent with add/linear dodge/screen transfer) and don't require a large green screen outside the window; they do require additional rotoscoping and tweaking, but it's of a window so you could do that in motor in like five minutes, unless the talent crosses the window in which case it would take a little longer or you could combine the key and roto work if the talent has frizzy hair.

Since this is a night scene and the background outside the window will presumably be dark, "add" and "normal" transfer modes will both look relatively similar and standard keying may return an okay result assuming the reflection isn't composited over bright areas or lights. Otherwise, it will start to look funny... But what do I know? I'm only a compositing artist and DP (of the unpaid amateur variety, admittedly).

 

[Brad Webb]

Thank you everyone for your input. Now that I think about it, the greenscreen may not even be necessary for this shot. I'll have to test that tho. I've got a window and a 7D line skipper (as Jim calls it) at home.

I want to do as much of it as possible in camera. I'm not going to fake the reflection, that is just going to look bad.

I'll post the results as soon as I have some time to do the test.

Again, thank you everyone.

 

[Noah Kadner]

Yeah I mean you could always just rent a translight (such as http://www.westcoastbackings.com/) or even do it with a self-painted background and little LED lights for stars, cards and buildings- assuming we're at night. You can get away with murder on a long lens with the 7D if shot carefully.

Edits and sound effects go a long way toward selling the effect. And I'm a huge fan on in-camera. Better for the actors, better for the DP and you are not spending your whole life in post just getting a shot that looks unnoticeable.

Noah