Use of a cold mirror system for citrus fruit identification

This paper presents a portable multispectral data acquisition system for extending part of citrus fruit imaging and measurement purpose. An economic mechanic based fixture has been made to position and align a classical cold mirror and two CCD cameras in relative kinematic position. With optocoupler interface, two cameras have been synchronized to capture the images at the same view to acquire certain spectral area from the visible to the near infrared area based on the cold mirror function. To register both images from two cameras, the software based self calibration has been done to estimate the precision of two cameras position relative to the 3D object pattern frame via the cold mirror. The issues regarding the calibration and the distortion produced by the lens on real images have been discussed. The calibration result from the bi-camera system achieved averagely no more than 2 pixels misalignment error corresponding to less than 8 micrometer with non-uniform error distribution on the whole image. The real time fruit citrus images from both cameras have been segmented to estimate the misalignment error to select the well aligned images for the study.