Hi,

with all the advances in the last ten years in technology, more specifically consumer products, it seems sensible to say we are now able to reproduce many effects found in Hollywood films.

The blue screen technique is now very much a feasible task, but, I was wondering :

How would one reproduce a moving camera with a blue screen, like George Lucas and his team first introduced with Star Wars : A New Hope?

The problem stems up from the fact that you need some kind of system to synchronise the cam's movements with the moving backgroud.

I KNOW it's feasible. I just have no clue HOW.

How could it work???

On the blue screen, you put refrence marks (normally a black cross) that you can motion track and apply the motion data to your background plate. You will have to manually remove the crosses when you pull the key, however.

I think volume 2 of the trish and chris myers books talk about how to do this in after effects.

Yeah what Joren said. Its difficult enough to do with a simple background but when you get into a 3-D background with position shifts (IE: City skyline where the perspective will shift the cameras perception of the buildings and cause some to cover others on the move) this gets tricky. With skill (or practice) and the right equipment this can be done though. Cjeck out the book mentioned.
R. Michael

"Luck, is when opportunity, meets preperation." "There are 3 sides to every story. Yours, mine, and the truth, and none of us are lying" -Robert Evans
Tizzy Entertainment "Redemption" Hi-Def trailer

yeah, if you have a background where perspective is important, if you're doing the BG in a 3d app, you can import the motion tracked 'camera data' from your compositor to your 3d app's camera, or if you're setting up the 3-d BG in the compositor (i.e. after effects), just setup a camera that has roughly the same focal length lens and motion blur characterisics (shutter angle in AE) as your live action camera and apply the motion tracking data to that camera. Personally, I think getting good, clean motion data is the most dificult part when doing this type of thing with DV25 footage (due to the image changing every frame because of compression issues). I still use commotion pro for most image tracking and then import into AE.

joren

Very cool!

Are there any good examples (of the technique, applied in the context of a short film) somewhere on the web? Maybe here?

There are a few things going on.

First, if the foreground and background are far enough from each other (say a distant landscape or stars in the backgroun) you can pretty much animate the background with key frames by eye-ing it and make it pretty convincing.

The trick is for objects that are very close to each other being done seperately.
One of the ground breaking things Lucas did in the original Star Wars movies was us motion controlled cameras for the space craft shots.
This way, they could shoot the exact same move over and over knowing the shutter would be tripped in exactly the same positions with zero error.

Today, most motion tracking is done with plugins for 3D CGI applications like Maya, XSI, and (more for the amateur and TV level) 3DMax. The motion tracking add ons can locate individual points (mostly corners of buildings or intentional markers on a bluescreen) and translate their motion in frame so the "camera" in the 3D application moves exactly the same way.

These add-on programs sell for thousands of dollars. There used to be a free program call Icarus, but it's been taken commercial and sells for a few thousand dollars. The old, free version worked great. You may still find it on the net somewhere.

Another free program is called Voodoo, developed at the University of Hannover. You can learn more about it at the Voodoo site.

As for an example, there's a amateur guy in Sweden (goes by the screen name "masterZap" on a few forums) that has been doing quite a lot of work with Icarus and 3DMax to motion track CGI effects onto moving people and environments. He did a little "experiment" flick to demo the effects called Intermezzo Dualis.

Hope this helps.
Have fun.

padawanNick,

thanks for all the tasty info!

I find it very encouraging that there is still a FREE plugin available on the net for this task.

I'm trying not to pirate anything, but it's pretty hard when you're a penniless, young filmmaker like me.

But that's for another topic...

Intermezzo Dualis is so funny, and nicely done too!

It never ceases to amaze me, what one can do with so little...

It's very encouraging. I recommend everybody to check it out.