Time For Space Wiggle A Surprise Hit on the Web
by Jim Gasperini
from OCC Panoram August 2003

A year or so ago I began experimenting with a way to present stereo images on a computer using a simple two-frame animation technique. Over the summer, to my surprise, the technique I dubbed "time for space wiggle" was discovered by a network of hip bloggers, starting with a site called Metafilter. During the brief time it took for this internet wave to swell, crest and pass on, stereo photography enjoyed an ephemeral place in the underground Internet spotlight, with links appearing at dozens of sites and my inbox flooded with requests for an explanation of how to do it.

"Time for space" describes the what happens when you use the two halves of a stereo pair as frames in an animation, so that you see them sequentially in time rather than arranged in space. The human brain, struggling to make sense of the images put before it, tends to perceive depth in a manner quite similar to the effect of a stereo photograph. The elements that differ spatially between the two parts of a pair will seem to "wiggle" when presented in time.

How to: Animated .gif vs. Flash

My first efforts in wiggling stereo for the web took the form of animated .gif files. Various tools have the ability to export these, including freeware specifically designed for it, but I used Adobe ImageReady. I have since switched to Macromedia Flash, which offers several advantages including file size (the versions below of Tall Tales - Le Baise Main are 106K as a .gif and 55K in Flash, even though the Flash is larger and compression quality settings have set very high to minimize banding effects that appear in this particular image.)


Animated .gif made with Adobe ImageReady, 106k

Macromedia Flash 5, 55k

Either way, I do most of the preparation in Adobe Photoshop. A crucial step, illustrated below, is to place the two images in different layers and superimpose them, reducing the opacity of the of the top layer in order to adjust how key elements line up. The effect works best when important figures, usually in the middleground, are superimposed as closely as possible. These will appear to "wiggle" less, or not at all, while elements in front and behind swing back and forth to give the illusion of depth.

A step in the process of creating a "time for space wiggle" stereo animation of Tall Tales - Le Baise-Main.

Left and right images are superimposed in Photoshop, with one made partly transparent, to align the central figures and correct a vertical tilt problem by rotating one image clockwise. If "wiggling" stereo images are not well aligned horizontally, the image will seem to rock back and forth in addition to wiggling.

Not all stereo images work well with this technique. Very dramatic parallax can cause objects to wiggle so widely that the effect is disconcerting. Also, slight alignment errors that pass without notice even in projection become distressingly obvious. In the example, the original handheld Realist shot was not quite level, making the figures and bridge seem to not only wiggle but rock back and forth. In the screen capture I am correcting by rotating the left image to match the alignment of the right. The next steps are to crop away elements of each image not matched in the other, sharpen as necessary and move to Flash or ImageReady. Iíve experimented with varying the frame rate and 12 frames per second, which is the generally recommended frame rate for the web, seems to work well. A finished version of this animation can be found at http://www.cockeyedcreations.com.

Depth Effect Without Stereo Vision

Surprisingly, when viewing images presented this way one does not have to actually use stereo vision to get a "stereo" effect. A web browser from Australia first alerted me to this phenomenon, writing with excitement that he was seeing depth for the first time since a cataract operation 30 years ago left him without the ability to coordinate his eyes. Viewed with one eye closed, the effect is pretty much the same. Apparently it works much like Ďretinal rivalry,í in that the when confronted by an odd visual effect the brain tries to make sense of it. Confronted by rapidly alternating images that appear to inhabit the same space, the brain switches from seeing them as displaced in time to perceivingthe differences between the images as depth.

Despite the various kudos that people new to stereo have been sending my way, I am apparently far from the first to use this technique. Iím told it was even briefly experimented with years ago as a technique for creating 3D movies. The effect viewed at length proved too disconcerting (some people find even single images presented this way hard to take) and the experiment was abandoned.

Wiggle While You Web

More of my wiggling images can be found at
http://www.well.com/user/jimg/
http://www.burningmanopera.org/2002/2002_stereo_wiggle1.html
http://www.burningmanopera.org/2003/2003_stereo.html

Discussion of the technique can be found at
http://www.metafilter.com/mefi/27391
http://www.meish.org/archives/20030802_stereoereoereo.php

A list of various citations on blogs etc.:
http://www.popdex.com/citations.php?id=1481452&start=0



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