Time Lapse behind normal paced guy

Phil Beastall · January 30, 2008

I'm looking to do a shot of a guy walking over the bridge of a motorway at normal speed. However, in the background I'd like to see the motorway sped up so that the sun goes down behind him, by the time he has reached the other side of the motorway. So a time lapse shot with a guy at regular speed on the bridge.

What would you say is the best way to film this? Obviously considering the lighting on the character would change during the shot. Would it be best to stick to green screen?

Thanks in advance

Phil

Dory Breaux DP · January 31, 2008

I'm looking to do a shot of a guy walking over the bridge of a motorway at normal speed. However, in the background I'd like to see the motorway sped up so that the sun goes down behind him, by the time he has reached the other side of the motorway. So a time lapse shot with a guy at regular speed on the bridge.

What would you say is the best way to film this? Obviously considering the lighting on the character would change during the shot. Would it be best to stick to green screen?

Thanks in advance

Phil

Greenscreen? Or maybe something like twixtor pro and motion vectors? Never tryed either myself... just a thought.

Scott Fritzshall · January 31, 2008

If you do greenscreen, you'll need a way to change the light pretty significantly over the course of the shot, but that's probably the best way I can think of to do it. You could also just get it all in-camera by having your actor walk really slowly, but that's probably going to be really difficult for him, and will produce some kind of weird movement.

Phil Beastall · February 3, 2008

Cheers for responding, below is an example of what we're after...Any ideas how they did this?

http://www.youtube.com/watch?v=ZrreuOybZs4

Scott Fritzshall · February 4, 2008

That video is clearly very effects-heavy, most of that was probably done with a motion-control rig and either a greenscreen behind the guy or a bunch of roto. Motion-control is really expensive, but that's really the only way to do a shot like this with camera movement. What you want to do adds an extra layer of complexity since it involves changing lighting conditions, so I think it might be best to shoot the actor seperately on a stage and try to simulate the real-world lighting as closely as possible.

Phil Beastall · February 7, 2008

We've decided to limit the amount of light change within the shot because we simply don't have the facilities to produce it. So one of the of the shots if of a guy walking over a bridge and we wanted the cars in the background to be speeding past, while he walks at a normal pace. I know in Final Cut you can use garbage mattes and make sure the guy is in a segment you can crop off, however, I want the guy to walk in front of the cars that are speeding past. So unless I was somehow able to draw around the guy in each frame to then make him a separate layer, is there a way to do this?

Surely it's possible, because in films, if someone is being held up by wires and they need to be removed in post, do they not film the background on its own first, and then shoot the actors on the same background so they can then overlay the two shots and erase anything from the foreground that they need to, leaving them the same background behind in its place. Or, do they do this a different way - either way it will be great to learn what's going on?! The shots I'm suggesting we do this in will all be static so no need to motion track or anything...

Michael Sousa · February 9, 2008

Eliminating wires vs eliminating a highway of cars passing by are 2 completely different things. Like stated above, you could roto it. If you have a high enough resolution and good colour sampling, and a lot of time on your hands, it might work out nicely. Then again, if you had high resolution and colour sampling, green screening would be possible.

Keep in mind, you really can't roto it in final cut because for some stupid reason you're only given 8 verticies to work with. I suggest After Effects, or another compositing program to cut a nice mask.

Hope all goes well, Goodluck!

Scott Fritzshall · February 9, 2008

Ah, today is the day you are introduced to the wonderful world of compositing :) The word you're looking for is Rotoscoping. In effect, you are drawing a matte around your character for every single frame, which allows you to isolate him from the background, and then put just him in front of something else. Take a look at programs like Shake, After Effects, Combustion, Nuke, or Fusion. Rotoscoping a whole character can be really hard though, especially if he's got hair that's blowing around. If it's possible, you might consider putting a greenscreen behind him, so that you can just key him, but depending on your location, that might be difficult or give you way too much green spill on him. If you've got any storyboards or especially photos of the location, that would be helpful.

Phil Beastall · February 13, 2008

I've added rotoscoping to my brain dictionary. Thanks.

Out of interest, how do they remove wires in films? It's something I've always wanted to know!

Hugh Macdonald · March 18, 2008

Painfully!

There are some tools that will get you quite a bit of the way for a first pass - Furnace WireRemoval being the one that I use most often.

If you're lucky, you'll get a clean plate for the shot. You can maybe track this into the background, create a roto around the wires, and a holdout roto around the person who's being held up by the wires.

Most of the time, though, you'll have to paint up a clean plate from various other frames in the shot.

Things that make it harder:

1) Lots of movement and motion blur

2) Smoke

3) Wires going over clothes. Especially when the person wearing the clothes is moving. As they would be if they're hanging off wires.

4) Many other things that will never cross your mind until you see them.

In the end, there's usually a lot of painting frame by frame involved (although this is very much a last resort, as painting can cause all sorts of nasty flickering)

Edited March 18, 2008 by Hugh Macdonald

Markus Manninen · April 4, 2008

Can you explain more the shot composition you are thinking of?

I can see a couple of options.

The most affordable one I can think of right now - similar to the video, where the guy was in a studio, and everything outside was a green screen stage, so that they could control the lighting, you can do something similar.

The affordable way is basically to avoid foot contact visibility (environment contact) and camera rotations. Shoot the A camera on location using a straight track that you can "speed up" to make the actual background element you want. Time the changing light scenario out based on that.

If you have the camera track with him walking (B camera) you can put him on a treadmill in a green screen stage. You can do a bunch of lighting rigs that allow you to make it look like time is passing by matching the timing of the A camera. You can probably do multiple takes and preview easily with a rough composite. If traffic lights need to hit the actor you are in for some timing experimentation. If some of the light rigs become visible, you will need to roto them out.

If the A camera move has some natural wobble to it, you may want to stabilize the move and after compositing add some natural post wobble motion back, or the same wobble if you liked the original "speed up feel".

Just a thought.