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Exploring methods of three-dimensional documentation (1)

Source: method to record the spatial appearance of a scene or object is nearly as old as photography itself: already in the age of daguerrotypy, pairs of stereo images were made. This method is based on the principle of human perception: when we look at an object, each eye perceives it from a slighty different perspective. In our brain, the two different images are fused; the spatial characteristics of the scene are reconstructed from the difference between the left and the right picture.

Stereo pairs are either made by a set of two cameras (or one camera with two lenses), or by making two pictures with one camera: after the first shot, the camera is shifted horizontally, then the second picture is made. This last method only functions, of course, when the scene does not move. Since art works stand still, the method can be applied for making stereo pairs of sculptures. To enjoy the stereographic effect of such image pairs, we have to make sure the left and the right eye only see "their" image. 

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Source: Dan Shelley

This can be accomplished by a simple device composed of two small slide viewers, or by projection with polarized light. Each projection beam passes a polarization filter: one vertically directed, one horizontally. With a special pair of polarized glasses, the public can enjoy stereographic slide or even movie projections. Since computer screens cannot transmit polarized light, in the Internet most stereographic images are presented as red and blue pairs. From the left picture, the blue colour part is subtracted, from the right picture the red part. Then both pictures are fused, using Photoshop or another imaging software. If we look at the combined picture with red-and-blue glasses, the stereoscopic effect can be perceived. 
Such picture pairs are called anaglyph stereo pairs. To avoid retinal rivalry, this method works best with black-and-white pictures.



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Last update of this page: 15.08.2002