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Old May 22nd, 2006, 07:44 PM   #1
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Faking a lead-up to a "T-Bone" collision

I posted this on a different forum, but I though I would ask here to get some more opinions...

I'm prepping a low-budget short that starts in a few weeks, shooting on an HVX200 in 720/24pn.
We have a scene in which a husband, wife, and son are in a car backing out of their driveway when a truck suddenly slams into the passenger side, killing the wife and son.

Since budget doesn't allow for us to actually crash the cars, the director still wants to see the truck come into view and then cut to black right before impact (then fade in to the aftermath). The camera will be on a hostess tray mounted on the driver side looking through to the passenger side. (a la the Volkswagen commercials or Adaptation)

My first idea was to play everything in reverse and then flip it around in post, so the truck would start against the car and reverse fast as the car creeps slowly foreward. Then I realised that the acceleration of the truck will look like deceleration when reversed. We want it to look like the truck does not hit breaks at all for a more sudden effect.

Maybe shoot at 12 fps and have the truck move slowly foreward, and then speed it up more in post? Green screen had also occured to me, but I'd like to do this practically if possible.
Matt Irwin
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Old May 22nd, 2006, 07:59 PM   #2
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I did something like this recently...I ran into the problem of showing the tires of both vehicles in the shot, so it kind of broke the illusion, but long focal lengths contract space. I actually set the cars up across the street from one another. With the camera half a block away, I zoomed all the way in. It brought the cars quite close together. If you get a static shot through the window from a ways away, even starting out 5 feet away and reversing should get them to seem very close together, if going forward and catching it at a slight angle, you should be able to have the truck drive just behind the car (couple of feet clearance)...camera taken from where it was planted straight t-bone and rotate around the accident site 20-30 degrees toward the hood, with the long focal length, it will pull the truck in slightly optically. Since you'll be cutting away at the moment of impact, it should work.

Another common practice is to have the cut go to the interior of the car where you can show the impact by having crew rock the car and having the actors react inside...some blood FX and makeup and you've got a real live accident (what's your target rating/audience?).

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Old May 22nd, 2006, 10:17 PM   #3
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I think the simplest way is to drive the truck towards the car and stop it as close as possible to the car, cut to black and add the sound effects of screeching/crashing etc. But please do it safely - you can always speed it up in post to keep the actual speeds down.

Another thing you could try (much safer) is keeping the camera in a fixed position and and doing 2 takes - one with just the car in its position and another with the truck driving down that section of the street (without the car there).
In post, split the frame just in front of the car and fill the rest of the frame with the footage of the truck driving. This will allow you to get the truck really close (in the video) without worrying about hitting anything at all, but depending on surroundings, may be difficult to pull off.
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Old May 22nd, 2006, 10:49 PM   #4
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Thanks for the replies guys!

I think we're going to do a green screen test, an "act in reverse" test, a 12+ fps test, and some other stuff. I have a feeling green screen will be the way to go...
Matt Irwin
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Old May 23rd, 2006, 09:52 AM   #5
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Green Screen! Or at least this is what I would try.

Get the angle of the sun relative to the camera and the street and have the truck do a close by on the camera (danger close!) as viewed from the passenger window. Now, green screen behind the passenger window and maybe a little of the front and rear side and get a light sources to match the angle and reasonable radiosity (do the truck first and you can use it for continuity). Act up to the impact and put it together in post.

Also, remember that you do not need to show the impact. Not until the last twenty years have pictures gone to that level. It leaves more to the imagination to not show the impact, but do show the aftermath. If you did it this way, you could even cut straight to a funeral.
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Old May 23rd, 2006, 10:23 AM   #6
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Sounds like a great shot.

If it were me....
1) Shoot the car stationary, camera locked on a tripod, outside, greenscreen setup outside the car "covering" the visible area out the windows (don't put GS on the windows ... leave I nice gap to help avoid green spill).
Performers act out the scene as though the car backs out and gets hit.
This is the foreground element.

2) Mount the camera on the PASSENGER SIDE pointing in the direction of the oncoming truck. Shoot video of the car backing out ... NO TRUCK IS COMING YET ... also don't stop the car where you expect impact ... just back right out like nothing is going to happen .... just like the story's driver expects.
BTW: Shoot at a fast shutter speed to get crips still images. This won't be used as "video" per se ... but as a series of still photos.

3) Shoot the oncoming truck with the camera locked off on a tripod. Do this in forward time so the truck can slam on the breaks for more realism.
For safety, put the camera on the sidewalk, 90 degrees to the street, shooting in to a mirror out in the street. This way, if the truck passes it's mark, all you get is 7 years bad luck ... which is much easier to live with than loosing an HVX and it's operator.

4) Post production ....
a - Use the frames from step 2 to stitch together a wide still image of the view out the car window.
b - add the truck video over the wide image. Very easy for a locked camera shot over a still image of the same scene.
c - Do a 2D track of video from step 2 and apply this motion to the image created in 4b .... you now have a background of the view out the passenger window of the car backing up to discover a truck slamming it's breaks as the car enters the street .... too late.

d - comp the greenscreen foreground plate from step 1 over the animated background.

It's a really cool sounding shot.
If you like ... I'd be interested in taking a crack at doing the effects work if you'd like to try the approach outlined here.
Nick Jushchyshyn Matchmoving, Compositing, TD
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Old May 23rd, 2006, 02:10 PM   #7
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I would shoot POV from the drivers window as the car backs out you see the truck bearing down. The family is unaware.

Then mount the camera on the front of the truck using a long lens, as was done in the chase scene in the French Connection. Under crank the camera or speed up the video in post to get the proper look of speed or to make it look faster than it actually is. If you speed up the video or under crank, the film/video from the truck make sure the car is already stationary so it does not move unnaturally or have the car moving slower that it would normally be so it looks natural.
Watch the monitor and run that shot right into the horrified faces of the family as they turn to see the inevitable event that awaits them.
With a long lens you still should have enough time to stop the truck before you endanger the occupants of the car.
Fade to black, with load screeching tires and metal crunching, screaming etc..
Scene fades in to the carnage left from the accident.

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