# How is this weird background / foreground angle shift achieved?

This video is a pretty crude rap music video, so I'll warn: NSFW. That being said, I noticed a pretty interesting image perspective change effect used throughout it, and I'm curious to know how the effect is done.

It's as if they're capturing the background and foreground separately, then shifting the background, but in this effect it appears that the background connects to the foreground. Its hard to describe, you'll have to see for yourself.

How is this done?

That looks pretty simple to me, they just took a picture of the same scene from slightly different angles (like move the camera a few inches to the left or right for each image) and then glued the images together to form a sequence (like an animated gif). Depending on how far the background is away from the camera, this will of course make the background dramatically shake because of the laws of perspective.

Obviously they kept the main object (the people) in the center of the frame, so that means if you move the camera to the left, the background will also move to the left in the final image. Try it for yourself by taking 2 photos of the same thing from slightly different angles.

EDIT: here's a quick diagram of what I mean, pretty crappy because I made it on my smartphone, but hopefully understandable. http://i.imgur.com/4RvBDDE.png

On choosing the strength of the effect: If the background is twice as far away from the camera as the object that you're keeping in the center of your image, the background will seem to move to the left twice the distance that you moved the camera to the left.

You can play with and tweak this effect by choosing the distance of your camera of course. Moving the camera further away and then zooming in the right amount, will keep the main object the same size, but will change the aparrent size of things in the background and also the strength of the effect above, if applied.

The effect is called wiggle stereoscopy or wiggle 3D. The image produced is wiggle stereogram.

It is produced by taking the two images of the same subject/scene, from a slightly different viewpoint (say, 2-6 inches apart). Instead of projecting those images to different eyes to produce "normal" 3D images (e.g., like a ViewMaster), the images are looped in an animated GIF.