‘Stranger Danger’: the special effects

by Jeremy Cooper (Director, Editor)

See also Making the backgrounds, Movie Trivia


The special effects were made by building up layers of images, and then using “colour keying” (also called “colour separation overlay”) to make part of the image transparent.
The main colour key used nowadays is a bright green. It used to be blue, but people’s eyes and clothes tended to stop that working properly. So everyone switched to using a shade of green which is seldom found in clothes, eyes, food …
But you can actually use any bright colour which is not in the scene you are shooting.

(Geek note: the edit used Adobe Premier Pro CC on an Apple iMac computer)


This was the basic shooting setup for the sticks house interior shots

This is what the camera saw – the actor, furniture and props in front of the
green-screen stretched behind.
(The green was really much brighter than it appears here – see the Wolf-at-the-door example, below)

The editing computer has turned (‘keyed’) the green to black –
the black is, in effect, transparent.

We add the background image, and can see it through the transparent black.

The image of the stickers is now superimposed on the computer screen.
That’s the final shot!

This is the editing ‘timeline’ – you can see the different tracks (layers) that make up the shot:

  • the blue track ‘00047.MTS’ is the main camera shot of the actor, the chairs, the table, the tea things and the computer all in front of the green-screen.
  • the pink ‘sticks3.png’ track is the sticks house background (see Making the Backgrounds for how I did that).
  • the pink ‘Black Video’ track is to hide the Acer trademark sign on the computer!
  • the pink ‘stickers4.png’ track is the image of the stickers. I could move that around and angle it to keep it on the back of the computer, whatever angle that was at.
  • the green and darker blue tracks at the bottom are the sound.

The ‘outside’ scenes were a bit trickier – I had to use two levels of colour-keying to make it possible for the house walls and door to ‘fly away’ when the wolf huffs and puffs, leaving the countryside behind.

This was the basic shooting setup for the wolf-at-the-door scenes.This is what the camera saw.The green has been keyed to transparent black.Through the black we can see the image of the sticks wall, with a blue background to fill the rest of that image frame.Now the blue has also been ‘keyed’ to transparent black.

Finally we see through the two layers of transparent black to the image of the countryside.

This is the timeline:

  • the blue track, ‘00152.MTS’ is the camera shot.
  • the pink ‘stick door copy.png’ track is the sticks wall.
  • the pink ‘13496086_m.jpg’ track is the countryside background.

the darker blue track at the bottom is sound.


See also Making the backgrounds, Movie Trivia