Amazing 3D pictures: World Trade Center attack

William Seger

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Mon Sep-25-06 09:29 AM
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Amazing 3D pictures: World Trade Center attack

As United flight 175 flew toward the World Trade Center south tower, Carmen Taylor took a photo from the Ellis Island ferry, docked at Battery Park. At the same time, someone identified as Michael Hezarkhani was taking a video of the same scene, apparently somewhere very near Taylor, but I haven't been able to find any more info about the video except that it was included on a CNN DVD. A second or two later, Taylor took a another shot just as the fireballs were erupting from the tower. From Hezarkhani's video, it's possible to extract the two frames that were taken at approximately the same time as Taylor's snapshots. You may have seen these pictures before, but I doubt that you've seen them in 3D, and the effect is chilling. NOTE: This is NOT a "9/11 conspiracy theory" post, so I will beg people on both sides of that to please not treat it as such and get this post banished! (There's already a thread on the September 11 forum for that; drop by if you like.) But I believe these pictures are just so astonishing, I wanted to share them with people who do not visit that board, so I hope the moderators will allow it to stay.

Two pictures of the same scene taken from two slightly different angles happens to be the basis of "stereo" or 3D photography -- e.g. like the antique stereoscope invented in the mid-1800s and the View-Master invented in the mid-1900s. Each eye sees a slightly different perspective of the scene, and our brain's vision processing system interprets differences in angles for different objects as differences in distance.

I have taken those two pairs of pictures and run them through a great freeware program called StereoPhoto Maker. This program uses an algorithm called SIFT to identify common points in a poorly aligned "stereo pair" of pictures and do any necessary resizing, rotating, perspective correction, and horizontal and vertical shifting to make a properly aligned stereo pair. (I should note that this is simply a convenience; the same alignment can be done manually if you have the patience. The program is not "synthesizing" the 3D; that's already in the pictures because they were taken from two slightly different locations.) Below are the very interesting results. These pairs turn out to have a "hyper-stereo" effect, which is caused by the two cameras being farther apart than your eyes, which causes an exaggeration of the 3D effect. (Because of this exaggeration, hyper-stereos tend to look like pictures of small-scale models. Hyper-stereos cannot be taken with standard two-lens stereographic cameras because they require a greater separation than that.)

These first sets of three pictures in a row are "left-right-left" sets: The first and second picture in each set form a "parallel view" pair, while the second and third form a "cross-eyed" pair. That is, the first-plus-second pair can be viewed in 3D by relaxing your eyes as if looking far into the distance until those two images overlap. The second-plus-third pair can be viewed by crossing your eyes as if looking at something close until the two images overlap. (You may find this method easier if you start by looking at your fingertip placed about half-way between your eyes and the picture pair, then move it back and forth until the images beyond appear to be about overlapped, then shift your focus directly to the pictures without changing the angle of your eyes.) In either case, if you can get the pictures to overlap fairly closely, your brain should take over and fit them the rest of the way together so that you see a 3D view.

These are larger versions of the parallel views, for any of you who happen to have a stereo viewer. (Stereo photography is a great hobby, by the way.)

Here are "color anaglyphs" of the pictures, which can be viewed with the type of 3D glasses that have red-and-cyan (blue/green) lenses. (These are the type of glasses used for the Spy Kids and certain other movies, if you have those DVDs. The photos above look much better if you can manage the freeviewing, but in case you can't but have the glasses):

Finally, here are analglyphs for the older style red-and-blue 3D glasses (like the old comic books):