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Title: Multispectral imaging system with interchangeable filter design

item KISE, MICHIO - John Deere Technical Center
item Park, Bosoon
item Heitschmidt, Gerald - Jerry
item Lawrence, Kurt
item Windham, William

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2010
Publication Date: 3/29/2010
Citation: Kise, M., Park, B., Heitschmidt, G.W., Lawrence, K.C., Windham, W.R. 2010. Multispectral imaging system with interchangeable filter design. Computers and Electronics in Agriculture. 72(2):61-68.

Interpretive Summary: This paper reports the optical design of a multispectral camera system, the calibration algorithm that compensates optical misalignment, and an evaluation of the imaging system as an instrument. Spectral imaging is to acquire the image of specific bands for measuring spectral characteristics of an object in a non-destructive manner. Typical applications for visible and near-infrared region, with emphasis on agriculture, can be found in remote sensing, fruit maturity measurement and mineral inclusion analysis. Three-band multispectral imaging system is able to acquire predetermined spectral images simultaneously which enable multispectral imaging system to be suitable for real-time applications. The objective of this study is to develop a compact, cost effective, and spectrally flexible multispectral camera system that can measure two visible and one near-infrared images simultaneously. This system can be retrofitted for a variety of applications, such as food safety and quality inspection as well as airborne remote sensing.

Technical Abstract: The design and calibration of a three-band image acquisition system was reported. The prototype system developed was a three-band spectral imaging system that acquired two visible images and a NIR image simultaneously. This was accomplished by using a three-port imaging system that consisted of three identical monochrome cameras, optical components, and three interchangeable optical filters. Spectral reflectance from an object was collimated by a front lens, and split into three ways by a cold mirror and a beam-splitter. A cold mirror reflects 90% visible light and transmits 80% NIR light. The visible light was again split identically into two directions by an additional beam-splitter. Focusing lenses then projected each image onto its corresponding detector. By incorporating an interchangeable filter design, the imaging system can measure any two visible spectral bands (400-700 nm) and one NIR band (700-1000 nm) without any complicated manufacturing process. In order to co-register three-band images, a system-specific calibration algorithm was developed that compensates lens-sensor geometric misalignments. The prototype imaging system and the system calibration algorithm were tested and evaluated for image registration accuracy. The imaging system acquired three-band images of 3D object with less than 0.4 pixel registration error.