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Image Processing

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Stereo Prism

In 1838, Charles Wheatstone, a British scientist, discovered that the horizontal separation between our two eyes is what allows us to perceive depth (how far objects are from us) [1]. One eye sees what the other eye does, but from a slightly different viewpoint. In these two images, an object will appear in different locations, and the relative shift between these locations depends on how far the object is. The closer the object is, the greater the shift. The brain uses the two images to estimate the depths of objects in the scene. Therefore, if the two eyes are presented two different views (called a stereo pair) of the same scene, the brain is able to perceive depth. This technique is known as stereoscopy.

An anaglyph image [2] is a special kind of stereo pair where the red color from the first image is combined with the blue and green colors of the second image. Since objects are shifted in the two images, an anaglyph image looks blurry when viewed normally. To experience 3D perception, one must view the anaglyph using red-cyan tinted glasses − with the red-tinted glass on one eye and the cyan-tinted on the other. The red-tinted eye sees only the red component of the first image and the cyan-tinted eye sees only the blue-green component of the second image in the anaglyph. Our brain then combines these two views to perceive depth.

Figure 5: Stereo (3D) image formation with a biprism

Traditionally, stereo pairs are captured using two cameras placed side-by-side. However, Bigshot captures the stereo pair with a simple biprism [3][4]. The demo in Figure 5 shows how a biprism captures the two perspectives. If the prism were absent (move the slider to the left to make the prism a flat sheet), then the captured image is exactly the one produced by just the imaging lens. On introducing the biprism (move the slider to the middle), the FOV of the primary lens is split into two halves, shown by the red and blue rectangles. The two views are effectively two side-by-side perspectives of the scene, but are captured on the same image sensor. When this stereo pair is downloaded from the camera, Bigshot's software processes it to produce an anaglyph. When you view the anaglyph through red-cyan tinted glasses, you will be able to experience your photo in 3D.



[1] "Charles Wheatstone," Oct 2, 2009. [Online]. Available: http://en.wikipedia.org/wiki/Charles_Wheatstone. [Accessed: Oct 4, 2009].
[2] "Anaglyph Image," Oct 2, 2009. [Online]. Available: http://en.wikipedia.org/wiki/Anaglyph_image. [Accessed: Oct 4, 2009].
[3] Kazuo Sayanagi, Stereoscopic photograph system using a stereoscopic attachment to a camera. US Patent #3674339. July 4, 1972.
[4] D-H. Lee, I. S. Kweon, and R. Cipolla. A Biprism-Stereo Camera System. IEEE Conference on Computer Vision and Pattern Recognition, Volume 1, June 1999.