ARS | Publication request: Use of concave mirrors and a single camera to acquire full surface information of randomly oriented apples

Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: June 9, 2008
Publication Date: July 2, 2008
Citation: Lefcourt, A.M., Reese, D., Kim, M.S., Lo, Y. 2008. Use of concave mirrors and a single camera to acquire full surface information of randomly oriented apples. ASABE Annual International Meeting, June 29 - July 2, 2008, Providence, RI.

Technical Abstract: Using machine vision to fully inspect fruit for contamination requires imaging as much of the surface of each fruit as is possible. For apples, the concave nature of the stem and calyx regions present a particular problem. These regions are more likely to harbor contamination and full visualization of these regions requires the use of multiple imaging perspectives if apples are randomly oriented. A cost-effective imaging system was previously developed using a single camera and two parabolic concave mirrors to capture nearly 100% of the surface of apples when they were specifically oriented so that the stem faced one mirror, the calyx faced the other mirror, and images were acquired using a camera mounted above. However, this system could not capture full information about these regions if the apple was oriented with the stem/calyx axis at a steep angle relative to the mirror axis. In addition, even when apples were oriented as specified, the quality of image information was not uniform. The major problem was that the very top and bottom areas of the apple, which were perpendicular to the stem/calyx axis and parallel to the plane of the camera, only appear at edges in the image. Detection of contamination near edges is hindered as areas near edges commonly exhibit more distortion and less contrast, and a single contamination site can be appear as multiple, smaller, contamination sites in disconnected areas of the image. To allow full imaging of randomly oriented apples, and to add additional perspectives so that there was no need to consider areas near edges, four additional concave parabolic mirrors were added to the imaging system. The objective of this study was to examine the relationship between mirror placement and information content of images. The only constraints were that images were acquired by a single camera and mirrors did not block the theoretical path by which the apples moved into and out of the imaging area.