Computers and Electronics in Agriculture 33 (2002) 121–137 www.elsevier.com/locate/compag Multispectral inspection of citrus in real-time using machine vision and digital signal processors N. Aleixos a , J. Blasco b , F. Navarro ´n c , E. Molto ´ b, * a UJI, Uniersitat Jaume I, Campus de Riu Sec E-12071, Castellon, Spain b IVIA, Cra. Moncada -Na ´quera Km 5, 46113 Moncada, Valencia, Spain c Food Machinery Espan ˜ola SA, Jesu ´s Morante Borra ´s 24, 46012 Valencia, Spain Received 8 May 2001; received in revised form 24 October 2001; accepted 17 December 2001 Abstract Citrus are one of the major fruits produced in Spain. Most of this production is exported to Europe for fresh consumption, where consumers increasingly demand best quality. Nowadays, Spanish producers have to compete with other countries with lower production costs. Moreover, inspection and classification tasks in these countries are made manually, which is subjective and varies among different experts or along the day. For these reasons, automatic inspection means, as machine vision, are a priority in Spain, in order to ensure products with an excellent quality. Current commercial sorters based on machine vision only solve the problems that require less computing time, as for instance, sizing or classification in colours. Sometimes they work with low resolution images, in order to achieve high processing speeds. However, this approach reduces the accuracy of the system when estimating the size of the fruit. Another important fact that needs consideration is the possibility of detecting defects on the skin surface using wavelengths that are outside the visible spectrum. This work includes the development of a multispectral camera, which is able to acquire visible and near infrared images from the same scene; the design of specific algorithms and their implementation on a specific board based on two DSPs that work in parallel, which allows to divide the inspection tasks in the different processors, saving processing time. The machine vision system was mounted on a commercial conveyor, and it is able to inspect the size, colour and presence of defects in citrus at a minimum rate of 5 * Corresponding author. Tel.: +34-961-391-000; fax: +34-961-390-240. E-mail addresses: naleixos@tec.uji.es (N. Aleixos), jblasco@ivia.es (J. Blasco), emolto@ivia.es (E. Molto ´). 0168-1699/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0168-1699(01)00002-9