Motion Control Sync with Blue/Green Screen

[Landon D. Parks]

I was not real sure where to post this, so I posted it here.....

 

When you are shooting a Bluescreen/Greenscreen Movie, and you plan to sync the HD shot footage up to the exact moves when you shoot minatures and for the CG guys to sync up the camera moves to the Animation, Does this require shooting with Motion Control cranes / Dollies ect?

 

I noticed on some behind the scenes stuff they always use these huge motion control rigs, but people like robert redreguez seem to have no problem in syncing up the Bluescreen footage with minatures / CG ect without Motion control rigs....

 

How exactly is this done by the average production?

 

Thanks for all your help (In Advance) guys! B)

Edited January 12, 2005 by Landon D. Parks

[Mark Allen]

I'm asking a similar question about using motion capture (which I've never had the luxury to use) in another thread which is up right now - but without that you are using set markers (tape, ping pong balls, whatever... sometimes just the shape of a building and it's corners) and a 3D tracking application like bijou or match mover or icarus - check out the websites for those and they'll probably have examples.

 

If you see the white markers on the green/blue screens in behind the scene footages - that's what those are there for. If it's pretty simple camera move you can almost get away with a 2D track though it's not technically as accurate.

 

Several times I've had to supervise parallax tracking to crane shots with no reference points at all. That's... really fun. :) One shot in particular the production said "we blew out the BG for you, so it would be easier to key" - which 1) it's not at all easier to key - so DPs... please don't do that. because... 2) the buildings and such that were blown out were exactly what we would use to help us track the shot.

Edited January 12, 2005 by Mark Douglas

[Landon D. Parks]

I'm asking a similar question about using motion capture (which I've never had the luxury to use) in another thread which is up right now - but without that you are using set markers (tape, ping pong balls, whatever... sometimes just the shape of a building and it's corners) and a 3D tracking application like bijou or match mover or icarus - check out the websites for those and they'll probably have examples.

So, if you use the track markers and software instead of motion control rig... I have 2 questions...

 

#1: Does it matter where the markers are set at? Or do you just put them at variouse locations around the set? I seem to recall watching one of the making-of's to king kong (2005) and I seen them using "Markers"... However, they where alos using a survey thing to surbey the markers..... what was with that?

 

#2: Will the results be just as good as if you used a motion control rig?

 

Thanks!

Edited January 12, 2005 by Landon D. Parks

[Phil Rhodes]

Hi,

 

Some software requires you to give it numbers on the location of the tracking markers, some software just requires them to be in a square or otherwise known rectilinear formation, some software (which usually requires a larger number of markers, 3D Studio has plugins which will do this) will track random markers and just work it out. Various approaches give you varying results; almost all software tracking has to be manually tweaked for perfection, but then again so does most moco stuff.

 

Phil

[Guest Kai.w]

So, if you use the track markers and software instead of motion control rig... I have 2 questions...

 

#1: Does it matter where the markers are set at? Or do you just put them at variouse locations around the set? I seem to recall watching one of the making-of's to king kong (2005) and I seen them using "Markers"... However, they where alos using a survey thing to surbey the markers..... what was with that?

 

#2: Will the results be just as good as if you used a motion control rig?

Thanks!

<{POST_SNAPBACK}>

 

3D tracking will only be applicable when inserting CGI into the footage because you create a virtual camera in sync with your original. Of course this does'nt help with miniature shots.

In general try to get a good distribution of markers over space: they should not all be on just XY or XY space (floor or walls) (although at least three on one 2D space helps)

Having some measurements (measurements of distances of markers to camera/ground/to each other) helps but is not always necessary.

If possible use a fixed focal length.

 

Here are a few tracking tips

 

http://www.fxguide.com/fxtips-273.html

 

-k

Edited January 12, 2005 by Kai.w

[Bob Hayes]

If you are filming a green/blue screen and your moves are limited to panning and tilting or simple camera dollies you really don?t need Moco these days. You must use tracking marks on the green screen to give the program something to lock on to. Even if the camera is hand held the shot can work because the programs are very good at tracking can work. If your move would really change the perspective on the background then you need moco.

[Chris Keth]

I'm asking a similar question about using motion capture (which I've never had the luxury to use)  in another thread which is up right now - but without that you are using set markers (tape, ping pong balls, whatever... sometimes just the shape of a building and it's corners) and a 3D tracking application like bijou or match mover or icarus - check out the websites for those and they'll probably have examples.

 

If you see the white markers on the green/blue screens in behind the scene footages - that's what those are there for.  If it's pretty simple camera move you can almost get away with a 2D track though it's not technically as accurate.

 

Several times I've had to supervise parallax tracking to crane shots with no reference points at all.  That's... really fun.  :)  One shot in particular the production said "we blew out the BG for you, so it would be easier to key" - which 1) it's not at all easier to key - so DPs... please don't do that.  because... 2) the buildings and such that were blown out were exactly what we would use to help us track the shot.

<{POST_SNAPBACK}>

 

 

Who let them light the set like that? That's just dumb and irresponsible (and possibly expensive..?). To key well, don't you usually light the background a stop and a half or two stops UNDER the subject?

[Mark Allen]

http://www.fxguide.com/fxtips-273.html

<{POST_SNAPBACK}>

 

Very good link! I'm sending this onto a lot of people.

 

Even if the camera is hand held the shot can work because the programs are very good at tracking can work.

<{POST_SNAPBACK}>

 

Actually, when the camera is moving the tracking is sometimes easier because you have a lot more visual leeway - the hardest would be something like hand held trying to stay on a subject. Then, it isn't really stablization and it isn't a move... it's that very subtle hard to track stuff.

 

Who let them light the set like that?

<{POST_SNAPBACK}>

 

Well, I stopped asking these questions a long time ago just makes you frustrated and makes other people feel bad. Sets - even nice, enjoyable ones - are a controlled chaos. There are a thousand things to worry about - When I was visfx supervising I figured my job was to fix everything - not just the effects, but the mistakes, the misjudgements - it was all part of the job description. There was always a reason something was done - even if it wasn't logical - usually it was done with good intentions or done because there was simply no other logistical way to do something.

 

However, maybe someday someone should write a little website or flash movie called "FX for DPs" - just to nail some of the big ones.

Edited January 12, 2005 by Mark Douglas

[Keith Mottram]

You actually need very little reference points these days, if you have decent tracking software such as boujou. If I remember correctly on the first LOTR extended edition peter jackson talked about how they were initially quite conservative when filming scenes for gollum to be comped in, later when they got back to WETA the fx guys pointed out that there is very little that software and a good operator cant track. If there are no stationary objects and you are shooting blue screen then the more track points you have the easier it is to track, the downside is those track points have to be erased which means more rotoscoping and a reduction in the quality of the matt. Motion controll gives you the option of doing away with track points, thus giving you a far simpler job at the compositing stage. If your moves are not too complicated then a 'junior' motion control system such as Arrimotion could serve your purpose. Finally if you are using software to track you must avoid motion blur as this will screw up the computers ability to track.

 

 

Keith

[Phil Rhodes]

Hi,

 

I've been doing (2D, but it's the same deal) motion tracking on 2K film material for most of the last couple of days, and it works fine. I've been using one particular test shot of a guy in a car from a camera mounted on the front - there's a lot of vibration, resulting in a lot of blur but no actual movement. If the software had a problem with it you'd expect a lot of unwarranted movement in the track, but it's rock-solid. This is in Baselight 2.1, which in my opinion has a fantastically good tracker. Most importantly it has the option to update the template every frame, so you can track gradually-changing targets, such as motion-blurred features, much more easily.

 

Phil

[Landon D. Parks]

I looked at match mover software on there website... It looks pretty complete and has a lot of features.

 

It claims you dont need to place tracking markers.... or anything for that matter. Just shoot the greenscreen and then In post the softeware creates E-Marker's....

 

Will this work just as well without placing tracking markers?

[Bob Hayes]

Realize there is a big difference when you shoot green screen to be composited later with a digital model or set. As long as you have tracking points a digital folks can fit your stuff into their digital world. The tough part is when you want to shoot a green screen and then marry it to a real miniature shot or a practical location. For example if you did a plate shot of stairs in a mansion and then later did a green screen of a ?ghost? walking down the stairs. You need the stairs to be an exact replica of the set. The camera needs to have the same lens and same height as the original. If both cameras are locked of it is pretty easy. If you are panning and tilting you may be able to motion track it in post. But once that camera starts moving around you are going to find speed and angle charges are insurmountable with out Moco.

[Landon D. Parks]

I sort of figured that..... After watching Spy Kids 2 making of, I noticed that on that when he shoot the minatures and the greenscreen, he had the camera locked off. I am guessing this was because he did'nt use a Moco rig on these shots.

 

I understand it would be pretty easy if you locked the camera off and shoot both the minature and the Greenscreen. You would just have to be sure you use the same lense size's and other technical jazz.

 

Let's say one was to use a moco rig.... One good enough to get the job done. What would you be expected to pay for this? As fare as like daily rental fee's, Operater Fee's, ect? I know you can usually get deals and stuff, but just giv me a quote on what it would generally cost to operate a moco rig for say, 3 weeks (5/days week, 10 hours/day)

Edited January 13, 2005 by Landon D. Parks

[Phil Rhodes]

Hi,

 

Further to Mr. Hayes' points, the other problem with using motion control to marry computer-generated and moco work is that the capabilities of the moco device are limited by conventional physics, whereas those of the computer aren't. I believe it's customary to design moves in a computer, output them to the moco rig to do the shot and then make adjustments to the data such that the moco is actually capable of performing the move. Then you can re-export the move from the moco software to the computer and have something that matches up.

 

I've read about people creating all kinds of lightning-fast moves in 3D Studio or whatever, then finding out later - at great expense - that the motion control device simply wasn't capable of performing it.

 

Phil

[Guest Sean McVeigh]

I was compositing some effects onto 15 year old VHS footage for kicks last year and can also vouch for the fact that software is pretty good these days. I was using Maya at the time and I just picked out some rocks in the grass to use as tracking points, told the tracker that they were constrained to a plane, and off it went recreating the handheld camera shake for me. I can only imagine how well it would work on a high quality scan with some nice fluid movements.

 

-Sean

[Michael Most]

I've read about people creating all kinds of lightning-fast moves in 3D Studio or whatever, then finding out later - at great expense - that the motion control device simply wasn't capable of performing it.

 

People who obviously didn't feel the need to actually hire a visual effects supervisor.

[Landon D. Parks]

Yes, but in the making of to Spy Kids 3 it shows how robert rodregues combined the main actors into a single image combing blue screen and Live Back ground plat without a Moco Rig. The scene at the very end before they throw the little reobt up into the air and the end titles.

 

If you look at the "Effects of the film" featurette, it shows a greenscreen plate of each actor being electronicly plced into a circle on the Background plat of Austin, tx.

 

How did they do that?

 

From What I can see it looks like the software they where using XSI. It has a built in compisition tool of some kind.

 

I dont know how they did it, but I thought I seen a lot of shots in SK 3 that combined Greenscreen with Models and Live backgroumd plate, and yet I could swear I heard robert say he did'nt use a Moco rig at any time.

 

Is this another one of roberts make-shift ways of saving money? If so he did a good job, because the final result looked real to me.

Edited January 24, 2005 by Landon D. Parks

[Phil Rhodes]

Hi,

 

> People who obviously didn't feel the need to actually hire a visual effects supervisor.

 

They wouldn't have needed to actually hire a visual effects supervisor - just someone with half an acorn's worth of intelligence!

 

Phil

[Michael Most]

Hi,

 

> People who obviously didn't feel the need to actually hire a visual effects supervisor.

 

They wouldn't have needed to actually hire a visual effects supervisor - just someone with half an acorn's worth of intelligence!

 

<{POST_SNAPBACK}>

 

Not necessarily.

 

One of the problems with the use of computer graphics techniques is that there is now an entire generation of "effects artists" who have little to no knowledge of or feel for the physical world. It is often difficult to explain the limitations of real world production to those who never have to deal with it. Because they don't have to deal with it, they often ignore the real world numbers that the software can produce in favor of simply changing things until the shot works. By the time they're finished, they have a great looking shot, but they have a camera moving 400 feet on two axes in 2 seconds - hardly something that can actually be accomplished physically. Part of the job of being a visual effects supervisor is to bring a knowledge of physical production to the proceedings and come up with shots that can actually be executed. I don't necessarily expect someone who never works in physical production to understand the limitations of it, but I do expect a supervisor to be keenly aware ot it.

[Landon D. Parks]

Also I think XSI has a built in compositing tool, as most CG programs should. If I was to do a CG movie, and I was to set-up a small CG office and hire people ro do the CG work, most likly I would use XSI software.

 

Of course how good the built in compositor is, I don't know.

[Phil Rhodes]

Hi

 

I would have thought the way to do it would be to perhaps pre-vis the move digitally, but make very sure you program it and create the final on the moco, then take that recorded data and give it to the computer. That way you aren't relying on a physicaly device to do something, and the computer can by definition perform any move you like.

 

Phil

[Ratheesh Ravindran]

Hi,

 

Some software requires you to give it numbers on the location of the tracking markers, some software just requires them to be in a square or otherwise known rectilinear formation, some software (which usually requires a larger number of markers, 3D Studio has plugins which will do this) will track random markers and just work it out. Various approaches give you varying results; almost all software tracking has to be manually tweaked for perfection, but then again so does most moco stuff.

 

Phil

 

I have a totally different question.I want to know whether there are any basic rules that you have to follow while doing a greenscreen shoot.Like exposure for example,is there anything like you have to maintain the same exposure values for the screen and tha actor.some advice on this please....

Ratheesh.