Threshold is based on a small number of component sequences. It begins with abstract colour fields filling the whole screen then develops through other simple abstract images created by accidental exposure of film stock - edge fogging. The main image of the film is of border guards at a frontier post.
The film explores a range of film printing techniques using colour filtering, mattes and multiple superimpositions. It also includes a short section of computer generated abstract animation made at the Government Atomic Energy Laboratory in Britain in 1969.
The title is intended to imply various forms of threshold or edge when significant transformations occur or are inhibited - the border of a state, the perceptual points when one optical experience transforms to another the point at which an image becomes an abstraction of its shape or movement.
The performance version of the film is an improvisation - moving the projectors and superimposing the image as the projection takes place.