Last Modified: December 3, 2014
There are a few basic guidelines to follow when creating background plates for use in Previzion.
Use a similar perspective
A big thing to keep in mind when using Previzion to play background videos is that Previzion is creating an illusion of depth using a flat image. This means if the camera goes to far to any side of the video plane the background will start to look 2 dimensional. For that reason it is important to create plates that are from a similar perspective in terms of camera height, and perspective to what you plan to use on shoot days.
The biggest thing to keep in mind where and when your scene is supposed to take place. What I mean by that is that if your scene is supposed to take place on the 20th story of a building don’t shoot background video at a location that looks like it is only on the second story with the tops of trees in it. A very easy mistake to make is to have the background look too close to the set. This is a common problem, and one that is harder for the background shooter to detect when they are shooting. For example if we wanted to have a cafe with a street outside of it about 2.5 meters away one might think all they need to do is take a camera out to any sidewalk along a street and just shoot cars passing by. However the problem with that is if the camera shoots the plate from the sidewalk it wont be able to see the sidewalk it is sitting on and will look too close to the cars. So when you take that clip into the cafe scene it will make it look like there is no sidewalk and that cars are driving just outside the cafe door less than 1/2 a meter away.
Be cautious of lens flares, because they most likely will not look right in the back ground plate, since they will not move, and will be behind the physical set, which is not how real lens flares work.
Keep the camera level. Even if the more interesting stuff is lower or higher in frame it is important to keep the camera level or very close to level. If plates are shot with a camera that was tilted off level the background will not look correct in the final composite and will require the Previzion operator to raise or lower it in frame leading to seeing off the edge of the background.
Shooting Multi camera video plates.
In order to get the best results with multi camera video plates it is best to do some prep work with your cameras before going out to shoot the plates.
The most important thing is to keep everything the same between all of your cameras. That means try to use the same model camera with the same model lens, at the same focal length and same aperture on both cameras. Beyond that however it is important to make sure that all of the cameras have the same settings on them including ISO/gain, white balance, knee and detail or sharpening. It is also better to keep Automatic features turned off so all cameras are doing the same thing regardless of what they are looking at and aren’t thinking for you.
In the field the cameras should all be placed at the same height and as close as possible to one another with a 20% overlap in the video. Make sure that both cameras are tilted to the same angle and are level, so that their horizon lines match when they are put into Previzion. It is a good idea to look for things that the video seem can be hid in like trees or light poles.
If your setup has fast moving objects or people who will be moving from video plane to video plane it is a good idea to genlock the cameras so the action can sync up perfectly in Previzion.
Timecode is great for keeping cameras in sync, but as a backup I like to have something visual in the shot of all of the cameras which I can use to sync them later. Something like a camera flash, or a movie slate or just a person clapping once makes for a quick and easy reference as to weather the clips are in sync in post when they are assembling the footage. If you are using more than 2 cameras you may have to temporarily pan the cameras over to see the action.
These images are mockups for demonstration purposes created in Photoshop using creative commons images from Flickr, not from Previzion using a green.