True Spherical Camera

Wide angle imaging has had a history of over a century. While many of the existing wide angle imaging systems can capture the complete spherical field of view, we are yet to see a true spherical camera. A true spherical camera may be defined as one that has the following three properties: (i) A 4π field of view that enables it to “see” in all directions; (ii) a single center of projection to avoid parallax within the field of view; and (iii) a uniform spatial and angular resolution in order to achieve a uniform sampling of the field of view. The design consists of a spherical (ball) lens encased within a spherical detector shell. The detector shell has a uniform distribution of sensing elements, but with free space between neighboring elements, thereby making the detector partly transparent to light. We determine the optimal dimensions of the sensing elements and the diameter of the detector shell that produce the most compact point spread function. The image captured with such a camera has minimal blur and can be deblurred using spherical deconvolution. Current solid state technologies do not permit the fabrication of a high resolution spherical detector array. Therefore, in order to verify our design, we have built a prototype spherical camera with a single sensing element, which can scan a spherical image one pixel at a time.

Publications

"Towards A True Spherical Camera,"
G. Krishnan and S.K. Nayar,
SPIE Human Vision and Electronic Imaging,
Jan, 2009.
[PDF] [bib] [©]

Images

  The Design:

This figure shows the conceptual design of a true sperical camera. It is well known that a spherical ball lens, due to significant optical aberrations, cannot produce a sharp image. However, a cylindrical baffle placed around a sensing element (pixel) can block a significant amount of stray light that contribute to the blurring. By evenly distributing these sensing units around a ball lens, but with free space between neighboring units, we can capture a full spherical FOV with a single center of projection.

     
  Proof-of-concept:

Since current solid state technologies do not permit the fabrication of a high resolution spherical detector array, in order to verify our design, we have built a prototype spherical camera with a single sensing element, which can scan a spherical image one pixel at a time.

     
  Initial Results:

This figure shows an image captured using the proof-of-concept spherical camera. The image represents a horizontal field of view of 12° and was captured one pixel at a time.

     
  Optimal Design Parameters:

This table provides the optimal design parameters for building a spherical camera using a ball lens of unit diameter and known refractive index. These parameters simply scale with the diameter of the lens used for building a spherical camera.

     

Videos

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  True Spherical Camera Principle:

This video shows the evolution of a true sperical camera from a spherical (ball) lens.

     
  True Spherical Capture and Display:

This video shows a simulation of a simple and intuitive device to envision the formation of image by a spherical camera. Here, the detector units (pixels) are replaced by diffusers (transclucent material). Hence, the image focused by the lens is visible through the translucent pixels.

     
  Image Capture Session with Prototype:

This video shows a sample capture session with the proof-of-concept imaging device for capturing true spherical images.

     

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