Hyperspectral system picks pickles

Nov. 27, 2006
Light-based methods for detecting vegetable quality have been developed but are not useful on an assembly line because of the execution time required. To speed inspection, researchers at Michigan State University (East Lansing, MI, USA; www.msu.edu) are developing a hyperspectral imaging system to check the quality of pickling cucumbers.

The pickle, made from a cucumber, is a popular vegetable, but consumers require pickles with consistent quality and no internal cavities or damage that might result from harvesting or shipping. Light-based methods for detecting vegetable quality have been developed but are not useful on an assembly line because of the execution time required. To speed inspection, researchers at Michigan State University (East Lansing, MI, USA; www.msu.edu) are developing a hyperspectral imaging system to check the quality of pickling cucumbers. They have experimented with different wavelength ranges and image-processing algorithms to find the best approach.

In one version, a visible and near-IR transmittance imager covers the 450-1000-nm region; it includes a high-performance back-illuminated CCD and control unit from Hamamatsu (Bridgewater, NJ, USA; www.hamamatsu.com), a zoom lens, an imaging spectrograph from Spectral Imaging (Oulu, Finland; www.specim.fi), and a tungsten halogen fiberoptic light source from Fiberoptics Technology (Pomfret, CT, USA; www.fiberoptix.com). A second setup, which captures hyperspectral images in the 900--1700-nm range, operates in reflection mode and includes an InGaAs-based camera from SUI, Goodrich Corp. (Princeton, NJ, USA; www.sensorsinc.com). Two classification algorithms were tested: partial-least-squares discriminant analysis and hyperspectral image thresholding. Both were run in Matlab from The MathWorks (Natick, MA, USA; www.mathworks.com), along with a Matlab plug-in partial-least-squares program from Eigenvector Research (Wenatchee, WA, USA; www.eigenvector.com).

The average reflectance of bruised areas was lower than that of normal areas over all but the 1400--1550-nm portion of the test spectral region; the difference was the highest in the 950--1350-nm region. This spectral difference decreased over time, with the differences sometimes disappearing after six days-showing the need for prompt testing.

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