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The Many Colors of Fruit

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Brent D. Johnson, Senior News Editor

Two major problems with cherries are cracking and bruising. Cracking can occur when it rains near a harvest time, causing the cherry to grow too fast and bursting the skin. Photonics technology offers one way to prevent this damaged fruit from reaching the market.

Multispectral imaging can help fruit growers and food regulators sort commodities for sale.

Daniel Guyer, an associate professor of agricultural engineering at Michigan State University, has been analyzing sweet cherries with multispectral imaging for two years.

He said that other researchers have used spectral radiometers to study and differentiate fruit tissue characteristics. Imaging systems, based primarily in the visible and very near infrared regions, are helping sort commodities in emerging commercial applications. However, his team's work seeks to couple imaging with visible and slightly extended IR multispectral information to identify defects in the fruit.

Two approaches are possible, Guyer said. The first casts broadband light on the object and uses filters to separate specific wavelengths. The second casts different spectra onto the object and uses a broadly sensitive camera to capture an image.

A key element of both methods, said Michael McMinn, president of systems integrator Zedec Technologies Inc., is the C2741 near-IR camera from Hamamatsu. The camera uses a lead sulfide vidicon to capture multispectral images in the 400- to 2000-nm range. He said he chose the camera because he does not know of another that can capture that range.

The drawback of the multispectral imaging technique is light delivery. Guyer's group sends light through an optical fiber, producing a 2- to 3-in.-diameter circle of light on the object. This is sufficient for small fruit such as cherries, but the field of view is not large enough for apples. The researchers are working to improve this and are brainstorming on ways to adapt the device to detect insect infestation.

McMinn said quality control for fruit is becoming more important because of foreign trade issues.

Photonics Spectra
Sep 2001
Accent on ApplicationsApplications

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