OPTICAL DETECTION OF FOOD SAFETY AND FOOD DEFENSE HAZARDS
Location: Quality and Safety Assessment Research Unit
Title: Improved egg crack detection algorithm for modified pressure imaging system
Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: May 19, 2011
Publication Date: June 20, 2011
Citation: Yoon, S.C., Lawrence, K.C., Jones, D.R., Heitschmidt, G.W., Park, B. 2011. Improved egg crack detection algorithm for modified pressure imaging system. SPIE. Vol. 8027:U1-7.
Interpretive Summary: Detection of cracks in the egg shell is important to provide safer egg products for the consumers because cracked eggs increase the risk of bacterial contamination. USDA human graders at egg processing plants have difficulty in detecting very small hairline cracks called microcracks. Hand candling over a light source is the standard egg grading method of USDA human graders. The fatigue from extended hours in a dark room with a concentrated light source can reduce the grader’s ability to consistently assess eggs. In response to need for a more accurate method for USDA human graders to detect microcracks, the researchers at the Agricultural Research Service of the USDA developed an imaging system based on modified pressure and demonstrated over 99% of crack detection accuracy. Occasionally, the imaging system, however, miss-classified intact eggs as cracked eggs because of displacement errors between two images at atmospheric pressure and under negative pressure (vacuum). This displacement (i.e. motion) was caused mainly by movement of the top lid hinged to the vacuum egg chamber. In this paper, this motion error was fixed by motion estimation and compensation. In a test with 3000 eggs, the new image processing algorithm adopting motion estimation and compensation reduced the false positive readings from 8 eggs to zero. The new image processing algorithm did not reduce the crack detection performance. The imaging system has the potential to increase the grading accuracy of USDA graders.
Shell eggs with microcracks are often undetected during egg grading processes. In the past, a modified pressure imaging system was developed to detect eggs with microcracks without adversely affecting the quality of normal intact eggs. The basic idea of the modified pressure imaging system was to apply a short burst of vacuum within a transparent chamber in order to cause a momentary and forced opening in the egg shell with a crack and thus to utilize the changes in image intensities during this process. The intensity changes from dark to bright in the shell surface were recorded by a high-resolution digital camera and processed by an image ratio technique. The performance of the imaging system, however, was sometimes compromised by false readings due to motion of intact eggs relative to the camera. The uneven movement of the lid hinged on the chamber was considered as the main cause of motion errors. In this paper, a machine vision technique to compensate the motion errors was developed to reduce the false detection readings caused by motion of intact eggs. The developed motion compensation algorithm is based on motion estimation of individual eggs.