Daniel E. Smalley and Dr. Richard H. Selfridge, Electrical and Computer Engineering
The goal of this creative works project was to build an inexpensive Stereogram printer capable of producing three-dimensional images from a series of two-dimensional pictures. This type of printer is very useful for making hologram-like images of objects and scenes that would be impossible to ‘holograph’ by traditional, optical methods. Though several printers of this type have already been built, they generally cost several thousands of dollars to develop. The author built the following small-scale printer primarily from a $200 LCD television and a $10 scanner. (However, it should be noted that this piece of equipment had to be run on an expensive optics table.)
To make a Stereogram, a perspective view of an object–we’ll say our object is a piano–is displayed on a LCD screen. The LCD screen’s image is then recorded holographically onto a strip of film just behind a slit in an opaque aperture. This aperture is moveable and can be incremented as needed over the length of the film. After the first exposure is made the aperture is moved slightly to uncover a region of film adjacent to the region of film just exposed. A new image with a slightly shifted perspective view of the piano is displayed on the LCD screen and the uncovered region of film is exposed to the laser-lit LCD image. The aperture is again moved, a slightly modified image is displayed on the LCD and the next region of film is exposed. This cycle continues until 24 or more adjacent exposures have been made.
More has to be done in order to make the film into a finished Stereogram, but to give a complete explanation would require a discussion of holographic theory and technique. Such a discussion is beyond the scope of this paper (see “Practical Holography” referenced below). Let it suffice to say that the 24 exposed regions on the film become the 24 different images that a viewer will see when she looks at the final Stereogram. Each of the images recorded will appear only when viewed from a particular angle. The disparity that occurs when the viewer’s eyes see two slightly different perspectives of the same piano cause the viewer to perceive a three-dimensional piano.
These photographs were taken of the first Stereogram produced on the Stereogram printer created for this project. The gaps or bands that run vertical across the image are artifacts caused by the fact that the exposures made in the printing process described above were not made perfectly adjacent to one another. This artifact gives the viewer the feeling that she is looking through vertical blinds at the image. Notice that the piano’s front leg is occluded in the left-eye view but unobstructed in the right-eye view.
The final Stereogram was successful in some significant ways. The Stereogram was clear and had sufficient brightness to be seen without difficulty. Multiple stereo pairs played back from the Stereogram giving a realistic three-dimensional image. As the viewer’s eyes move from one view to another the new images register well and there is very little vertical ‘jumpiness.’ Considering the fact that this was the first print made on the hologram printer, the final product was satisfying.
Despite the general success of this first test, there remain several problems to fix and several improvements to be made. First, the images were exposed in reversed order, so the left eye and right eye views were actually switched in every stereo pair that the Stereogram displayed. This caused a reversed-depth or “pseudoscopic” effect. Also the movement of the shutter was supposed to be computer controlled. Because of complications in the aperture driving mechanism this first test was made by manually incrementing the slit. Additionally, the vertical lines could be eliminated by a more accurate incrementing of the aperture during the exposure cycle. Finally, the Stereogram could be made white light viewable instead of only laser viewable.
References and Acknowledgments
- Saxby, Graham, 1988 “Practical Holography”, Prentice Hall.
- Thanks to Elroy Pearson, Oliver Cossairt, Rob Kotredes, Steve Smith, Julie Black and all those at the MIT Spatial Imaging Group who contributed time and ideas to this project.