When we were approached to do a music video for the electronic band Violet Sands, we wanted to create a visual effect that played off the distorted and chopped up feel of their music. After researching multiple distortion techniques, we discovered slit scanning. We were immediately mesmerized by the twisting and warping nature of the effect. Particularly captivating was the way it distorted images; bodies, objects, and faces would melt in time and become abstract liquid forms.
In contrast to other distortion effects like pixel moshing, slit scanning remains very organic and that might have to do with its origins. The effect was first used in still photography, and then in film by Douglas Trumbull to create the “Star Gate” sequence in 2001: A Space Odyssey. The original process of slit scanning was incredibly time consuming and painstaking, so we had to figure out the best way to replicate it with digital tools.
The best digital technique to generate a slit scan-like effect is time displacement in Adobe AE. The time displacement effect uses a displacement map (or gradient map), and it bases the movement of pixels in the layer on luminance values in the map. Pixels in the layer that correspond to bright areas in the displacement map are replaced by pixels in the same position, but at a specified number of seconds forward in time.
Likewise, pixels in the layer that correspond to dark areas in the displacement map are replaced by pixels at a specified number of seconds backward in time. Any layer can potentially be used as a displacement map, though using a grayscale image makes it easier to see brightness levels and predict how pixels will be displaced. You might want to start with this very useful tutorial from FilmmakerIQ.
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