Detecting Cracks Of Preserved Egg Using Optical Technology

Pidan or century egg also known as preserved egg is one of the most traditional and popular preserved egg products in China. Pidan is widely adopted into the local cuisine as an appetizer, its nutritional value and a pleasant fragrant taste that is preferred by most people in Southeast Asian countries. The traditional detecting crack of pickled egg was based on manual work in many factories. On the basis of analyzing relevant researches, This dissertation presented a method of detecting preserved eggshell cracks automatically based on image processing techniques and polarized optical technology in the experiment. The main contents are as follows:(1) Set-up image acquisition system on ordinary source, a series of image processing foundational algorithms, such as image denoising, image inhancenment, edge detection operators and morphology calculus, were analyzed in this work. It is configured in these ways by selecting different image processing algorithms in each stage. According to experiments and desired results obtained from this experiment, it was found that morphology calculus algorithms was the most effective way to detect cracks on preserved eggshell.(2) Some shape feature parameters and texture parameters were extracted after the image processing with morphology calculus algorithms. The four characteristic parameters were the crack length L, the crack degree coefficient K, the maximum between horizontal and vertical gray Tmax, the angler points. The inact and cracked preserved eggs was classified with SVM model. A comparison study of the classification capacibility of different kernel function of SVM model, training sample size and test smple size, it was found that the SVM model with RBF kernel function procided the best classification performance and the classification accuracy was up to94%.(3) For the different polarization degree of black spots and cracks on preserved eggshell, a polarization optical system was designed in this work. It accepted the Stokes Vector method to describe polarization image. Using the polarization optical system acquired different polarization angles images, including degree of zero, degree of forty five, degree of negative forty five and degree of nintey. It detailed introduced the hardware and software design of the polarization optical system. The image of different polarization angles was acquired by analyzer rotating automatically, while the analyzer was controlled by stepper motor. Every angle of analyzer rotating was obtained automatically by computer controlling the stepper motor using DLL (dynamic link library) and instructions.(4) According to different depolarization mechanism for black spots and cracks on preserved eggshell, it can distinguish black spots and cracks on polarization image. The polarization image after pretreated processing, it took the most connected area of high gray value as center to cut an image about100*100pixel area. Four characteristic parameters was extracted to distinguish the cracks on preserved eggshell, including the length of the crack as L, mean variance ratio as R, skewness as α and kurtosis as β. We put forward four characteristic parameters and use cluster analysis to detect cracks. This paper employed Info-Kmeans clustering algorithm, and the clustering of high-dimensional sparse data extract from images. The result showed that all preserved eggs were classified into intact and cracked groups with the Info-Kmeans clustering algorithm, and the accuracy was up to93%.(5) Comparing two different identification methods on the same samples, a fusion based on multi-recognition technology and multi-feature method was proposed. The results showed that the total classification accuracy rate was up to96%.It showed that image processing techniques and polarized optical technology distinguished intact and cracked preserved eggs efficiently, and these results could provide a theoretical basis for detecting cracks of preserved egg on product lines.