Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/20/2008
Publication Date: 5/9/2009
Publication URL: hdl.handle.net/10113/34461
Citation: Reese, D., Lefcourt, A.M., Kim, M.S., Lo, M.Y. 2009. Using parabolic mirrors for complete imaging of apple surfaces. Bioresource Technology. 100(19):4499-4506. Interpretive Summary: The use of automated systems to inspect fruit during processing offers the potential to increase the safety of food consumed by the public. Such systems use cameras to take pictures of the fruit and computer software to determine if the fruit is contaminated, or if they are damaged or diseased. For apples and similarly shaped fruit, imaging 100% of the surface is difficult because the stem and calyx regions are concave. It is difficult to set up a visioning systems that is guaranteed to be able to see inside these regions for any random positioning of a fruit. This study examined the use of a single camera and 2, 4 or 6 parabolic mirrors to imagine apples with known locations of the stem and calyx and with random, i.e. unknown, locations. Results suggest that concave parabolic mirrors are superior to normal flat mirrors for this type of imaging because they magnify the reflected images and improve image contrast. Both the 4 and 6 mirror configurations showed minor failures where a small portion of the stem or calyx regions could not be seen for a small percentage of possible apple positions. An alternative configuration using 2 opposed mirrors and additional images as the apple rolled through the imaging field also proved viable. In practice, these configurations could be used to image almost 100% of the surface of all apples regardless of apple positioning. These results suggest that consideration for using parabolic mirrors for commercial apple inspection is warranted. This work will be of interest to scientists, regulators, producers, and equipment manufacturers.
Technical Abstract: Automated imaging systems offer the potential to inspect the quality and safety of fruits consumed by the public. One problem that has hindered adoption of automated technologies has been the inability to image 100% of the surface of an individual fruit. A particular problem is that both the stem and calyx are concave structures. The goal of this project was to examine tradeoffs for using multiple mirrors to image the surface of apples. For testing, individual apples were suspended using two thin wires, mirrors were placed around an apple, and movies were captured at 90 images per sec. Apples were rotated in all dimensions to examine the efficacy of different mirror configurations. It was determined that specific configurations of two, four, or six parabolic concave mirrors could image an entire surface. A configuration using two mirrors and multiple images acquired as apples roll by was also found to be viable.