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Multispectral imaging with optical bandpass filters: tilt angle and position estimationFormat | Member Price | Non-Member Price |
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Paper Abstract
Optical bandpass filters play a decisive role in multispectral imaging. Various multispectral cameras use this
type of color filter for the sequential acquisition of different spectral bands. Practically unavoidable, small tilt
angles of the filters with respect to the optical axis influence the imaging process: First, by tilting the filter,
the center wavelength of the filter is shifted, causing color variations. Second, due to refractions of the filter,
the image is distorted geometrically depending on the tilt angle. Third, reflections between sensor and filter
glass may cause ghosting, i.e., a weak and shifted copy of the image, which also depends on the filter angle. A
method to measure the filter position parameters from multispectral color components is thus highly desirable.
We propose a method to determine the angle and position of an optical filter brought into the optical path
in, e.g., filter-wheel multispectral cameras, with respect to the camera coordinate system. We determine the
position and angle of the filter by presenting a calibration chart to the camera, which is always partly reflected
by the highly reflective optical bandpass filter. The extrinsic parameters of the original and mirrored chart can
then be estimated. We derive the angle and position of the filter from the coordinates of the charts. We compare
the results of the angle measurements to a ground truth obtained from the settings of a high-precision rotation
table and thus validate our measurement method. Furthermore, we simulate the refraction effect of the optical
filter and show that the results match quite well with the reality, thus also confirming our method.
Paper Details
Date Published: 19 January 2009
PDF: 9 pages
Proc. SPIE 7241, Color Imaging XIV: Displaying, Processing, Hardcopy, and Applications, 72410Z (19 January 2009); doi: 10.1117/12.804985
Published in SPIE Proceedings Vol. 7241:
Color Imaging XIV: Displaying, Processing, Hardcopy, and Applications
Reiner Eschbach; Gabriel G. Marcu; Shoji Tominaga; Alessandro Rizzi, Editor(s)
PDF: 9 pages
Proc. SPIE 7241, Color Imaging XIV: Displaying, Processing, Hardcopy, and Applications, 72410Z (19 January 2009); doi: 10.1117/12.804985
Show Author Affiliations
Johannes Brauers, RWTH Aachen Univ. (Germany)
Til Aach, RWTH Aachen Univ. (Germany)
Published in SPIE Proceedings Vol. 7241:
Color Imaging XIV: Displaying, Processing, Hardcopy, and Applications
Reiner Eschbach; Gabriel G. Marcu; Shoji Tominaga; Alessandro Rizzi, Editor(s)
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