Stereo imaging requires two different perspectives of the same object and, traditionally, a pair of side-by-side cameras would be used but are not feasible for something as tiny as a less than 4-mm-diameter endoscope that could be used for minimally invasive surgeries or geo-exploration through tiny fissures or bores. The proposed solution here is to employ a single lens, and a pair of conjugated, multiple-bandpass filters (CMBFs) to separate stereo images. When a CMBF is placed in front of each of the stereo channels, only one wave-length of the visible spectrum that falls within the passbands of the CMBF is transmitted through at a time when illuminated. Because the passbands are conjugated, only one of the two channels will see a particular wavelength. These time-multiplexed images are then mixed and reconstructed to display as stereo images.

Schematic showing the principle of the Stereo Imaging Endoscope using CMBFs. (a) The first illumination band passes through the left CMBF to cast an image at the focal plane, but is blocked by the right CMBF. (b) The second illumination band passes through the right CMBF to cast an image at the focal plane, but is blocked by the left CMBF.
The basic principle of stereo imaging involves an object that is illuminated at specific wavelengths, and a range of illumination wavelengths is time multiplexed. The light reflected from the object selectively passes through one of the two CMBFs integrated with two pupils separated by a baseline distance, and is focused onto the imaging plane through an objective lens. The passband range of CMBFs and the illumination wavelengths are synchronized such that each of the CMBFs allows transmission of only the alternate illumination wavelength bands. And the transmission bandwidths of CMBFs are complementary to each other, so that when one transmits, the other one blocks.

This can be clearly understood if the wavelength bands are divided broadly into red, green, and blue, then the illumination wavelengths contain two bands in red (R1, R2), two bands in green (G1, G2), and two bands in blue (B1, B2). Therefore, when the objective is illuminated by R1, the reflected light enters through only the left-CMBF as the R1 band corresponds to the transmission window of the left CMBF at the left pupil. This is blocked by the right CMBF. The transmitted band is focused on the focal plane array (FPA). Here, the FPA does not include color filter array (black and white); hence, the image sensors only measure light intensities. Similarly, when the object is illuminated by R2, it is transmitted only through the right-CMBF and is blocked by the left-CMBF. This continues over other wavelength bands as well.

So, it can be seen that the image sensors at the focal plane are measuring light intensities of alternately transmitted light from the two CMBFs. At the end of one complete illumination cycle, six images will have been collected. Then the images from R1, G1, and B1 become the primary colors for the left side of the stereo image, and R2, G2, and B2 become that of the right side of the stereo image. Two stereo images have been time-multiplexed on the same imaging chip. This intensity data is stored as an array from which the 3D stereoscopic color image is constructed by applying processing and reconstruction algorithms.

This work was done by Youngsam Bae, Harish Manohara, Victor E. White, and Kirill V. Shcheglov of Caltech and Hrayr Shahinian of Skull Base Institute for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management JPL Mail Stop 202-233 4800 Oak Grove Drive

Pasadena, CA 91109-8099 E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-47420, volume and number of this NASA Tech Briefs issue, and the page number.

This Brief includes a Technical Support Package (TSP).
Stereo Imaging Miniature Endoscope

(reference NPO-47420) is currently available for download from the TSP library.

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