Corporate Training Video Production - e-Learning Design - Interactive Multimedia - IT Software Training
GREEN SCREEN VIDEO PRODUCTION
Green screen or Chromakey is a handy and economical way of pretending the camera and presenter or actors are somewhere where they are not. This involves filming the action in front of a bright green or blue screen; the blue or green is then replaced with a background of your choice. This background can be video, a still image or a graphic.
For a recent project we needed to film some army officers (actually actors) supposedly in a war zone in northern Scandinavia. The purpose was to illustrate an IT software training multimedia e-learning / CBT for the military, creating a scenario that would engage the learners and provide a series of lifelike practical exercises for them to carry out, using the actual computer software.
Tips for successful green screen effects
Have a large enough green or blue background for your chromakey. In a studio this is usually not a problem, so long as you have booked one big enough. It is possible to use a portable, pop-up backdrop if you need to shoot green screen on location, but really only for static shots of one or two people.
Light the backdrop evenly to get the best chance of a “clean” key. Make sure there are no creases in it.
Place your actors far enough forward so they do not cast shadows on your blue or green screen backdrop
Match the lighting of your actors or presenter to that of the background image that you will be using, so the effect looks natural. You don’t want strong sunlight from the left in your background scene if the lighting on the actors is from the front or the right. The colour of the lighting also needs to match the background.
If using still photos for your chromakey background, make sure there is nothing in the photo that should be moving - people, vehicles, water, etc.
Avoid any bright green (or blue if using a blue screen background) in the actor’s or presenter’s clothing or props. We chose very drab camouflage fatigues for the military software training scenario. Otherwise any bright green areas would have disappeared like the invisible man.
Watch for reflections on shiny objects that may pick up your chromakey blue or green and, again, disappear. Wispy hair can also be a problem.
Remember that your actor or presenter can only move within the area which you have lit; this can be quite restricting, especially on location. Also the camera has to remain static unless you have very sophisticated motion control and post production to sync the background to the action.
If possible, test the keying on the spot, so you know it will work and the result will look natural. In a tv studio, like the one at Edge Hill University which we used, we could see the chromakey effect instantly. We had prepared a variety of background images, so were able to chose the most suitable and also position and size the actors to match objects in the background image. But we have done successful location green screen shoots, where keying had to be done in post production, although this is more of a challenge.