The images are being projected by the light source, they are not being produced by the film itself via the sound generator.
The frequencies alter the opacity and reflective properties at various points on the surface, so you might be able to have an almost opaque block of color next to an almost transparent section.
It's not a 700nm "screen" like your monitor. It's a 700nm "screen" like you might have for a projector (but with some other cool properties).
