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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

composiitng/greenscreen shooting

J

Joe Riggs

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Hello,

My greenscreen/compositing experience is limited to pretty much talking head interviews and I was kind of thrown into this after the fact.

So there's a couple of scenes in this short, that are rather advanced for me.

1. We want this monster to climb a wall and end up on a vaulted ceiling like this
blog2.jpg
.

The shot is static so we shot a plate of the empty ceiling and took some measurements, but what do I do on the greenscreen set? How do I have actor move, and camera positioned/angled to make this come together in the composite.


2. There's a part where a person with a flashlight comes across the monster and the monster moves toward them. So the light from the flashlight illuminates the monster.

We shot a few plates, as we were not sure which would be best, we shot one with flashlights on the background and one without.

So we have a few options on the greenscreen and I'm not sure what will be best for the composite. Just to be clear we don't see the actual flashlights in the composite, just the light from them.

1. shoot the actor with flashlights, and composite him into the plate without flashlights.
2. shoot the actor without flashlights, and composite him into the plate with flashlights.
3. shoot the actor and flashlights separately.
4. cgi the flashlights?

Any help is greatly appreciated.
 
How do I have actor move, and camera positioned/angled to make this come together in the composite.
Click to expand...

Position the camera on the green screen exactly the same as the still was shot with the same focal length, height from the ground and orientation. Figure out where the actor would be standing in relation to the still photo and not be inside of a coffee table or couch.

So we have a few options on the greenscreen and I'm not sure what will be best for the composite. Just to be clear we don't see the actual flashlights in the composite, just the light from them.
Click to expand...

None of the above? Why not shoot the actor with a flashlight... and composite him into the plate with the flashlight. More importantly, if you have the location and not just a still of it, why not just shoot the actor on location and skip the greenscreen?
 
Who is your compositor? If you do not have a vfx supervisor you should ask the person who is putting this together for you--they may have a preference and a method in mind already. If you are doing it (I'll put on my vfx supervisor hat for you now) your best bet is probably to skip a greenscreen and shoot the actor and flashlight* on set, shoot it all on set, then just add the monster and additional lighting fx in post. You could even do a person in costume for lighting reference in a separate take so you have both versions... one with visual reference and one without. You could even do a human monster-only take for reference. ps. Always good to have a clean plate of the scene.

*Dimmed, so there is a bulb lit, but not creating shadows or lighting things on set. Brighten/add flares, etc in post.

Fun stuff, good luck and let us know how it goes!
 
Gavin, Sarah, thanks for your input, no vfx sup yet.

Sarah, the monster is live action not cg, so at least for #1, I would need a greenscreen.

Gavin, with the following advice:

Position the camera on the green screen exactly the same as the still was shot with the same focal length, height from the ground and orientation. Figure out where the actor would be standing in relation to the still photo and not be inside of a coffee table or couch.
Click to expand...

I don't understand how I would film from that angle and wind up with a composite where the actor is on the ceiling. Wouldn't I have to film the actor on the greenscreen from above (taking all that info recorded on set camera height, distance, etc...and invert it so we are shooting from above) and then flip it in post for the composite?
 
@Joe

Oh I see! In that case, just do a traditional overlay on set and direct your actor through it. Overlay being software or switcher hardware to allow the greenscreen camera orientation overlay with the livingroom cleanplate or with actor on livingroom plate. Then you'll see the temp composite in real time and be able to direct the action and camera angle to fit. Your DIT should be able to set this up for you.
 
As it is supposed to be (mostly) practical, get as much as possible in one take in the camera. Static means lock off shot for you, right? Then:

No CG means you need to get as much practical light as possible from the shot. Flashlights produce bounce light and specular high lights on the monster as well as on the walls. So you should try to get both, actor and monster, at the same time in the shot. Light is delicate and a big give aways for bad VFX if done not well.

Create a climbing structure for the monster, paint it in the colors of the set, from the camera perspective! In that way it is already nearly invisible. And contact areas will not show up with a different color. I wouldn't paint it green, as it produce spill. Have the actor and the monster interact during the shot. You get the best performance from both if they share the same space and time.

Without moving the camera, get the climbing structure out of the set and take a clean plate, just with the same light as the shot was taken. And one with the flash light moving around to get both light situation.

The only thing that your compositor needs to do, is to replace the climbing structure with the clean plate. Simple Rotowork (more or less, the devil is always in the detail). No CG needed, and the flash light works nicely and is timed correctly.

My best wishes for the shot.
 
Oh gotcha. I assumed it was a CG creature too. Yeah. Shoot your actor on set locked off (or maybe turn the camera sideways to give you vertical tilt). Then you have to figure out where the camera would be if the ceiling was the floor. This is where your highschool geometry will come in handy. You'll need to measure the height to the start of the ceiling slope, the peak of the ceiling and the width from the bottom of the ceiling slope to the center line. Then you can use trig to figure out what the slope of the ceiling is. That's when things start getting tricky. You now have to take the distance from the spot on the ceiling the camera is and rotate that so that it's in "Ceiling space". Then shoot your 'monster' on the floor and presto! Monster on the ceiling. Easy right? Alternately you can just guesstimate about where the camera would be relative to the ceiling and hope for the best.

As to the lighting question then. I would shoot both the character in the living room and the monster with practical flashlights. You won't be able to convincingly fake the flashlight in post. However, you will want to light the green screen and then use something extra bright like a 2k spot so that you still have some contrast. Think "day for night". And budget time for a lot of roto since pointing a spotlight at a green screen generally isn't going to make your composite very easy.
 
fxphd.com did a recent class on something like this, two ASC's explained it in a very interesting way ... basically they use the static shot (making sure they get the exact lens and camera settings), then put that same camera setup in a large room with the exact same settings. Then they did a overlay from the live camera feed with the actual picture, and moved stuff around in the large room till some props lined up between the live picture and the original picture. Then they simply shot the practicals. They did this with zero math, and it also allows you to put the picture on the side, so you could have the monster crawl on the floor, which is really the wall (i.e. when you line up the prop's have the original picture flipped 90 degree's).

( i think this is exactly what Sarah C said).
 
Thanks so much for your help.

To be clear there is no other actors in the shot interacting with the monster. It's just the ceiling and the monster hanging on or attached to it.
I'm willing to give up the crawling, just as long as I can make it look like monster is on or attached to the ceiling.

In hopes of obtaining more sage advice, here's the plate.





I don't have the actor but here is what I'm thinking, like a bat, the actor would look like they are hanging or attached to the ceiling. (they don't have to be upside down necessarily).
 
flip your image over and pretend like the ceiling is the floor. do the math, guesstimate, or use an overlay. it's probably going to look funny. only other option is to construct something for climbing or find the nearest jungle gym and roto away.
 
Dare I offer another $0.02? Pennies are adding up!

With this last bit of information, your plate is very simple geometry. You could really old school this one: simply get the plate image on your camera LCD/monitor and trace the basic lines with a grease pencil(or other media that will clean up well)--directly on the LCD or monitor glass. Go shoot your actor on GS using these marks as guidelines. --Like I said, REAL OLD SCHOOL. But it would work. Those little 7in monitors atop the camera flip easy don't they?
 
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