Abstract
A VIS/NIR hyperspectral imaging system was used to classify three different degrees of freeze-damage in corn seeds. Using image processing methods, the hyperspectral image of the corn seed embryo was obtained first. To find a relatively better method for later imaging visualization, four different pretreatment methods (no pretreatment, multiplicative scatter correction (MSC), standard normal variation (SNV) and 5 points and 3 times smoothing (5-3 smoothing)), four wavelength selection algorithms (successive projection algorithm (SPA), principal component analysis (PCA), X-loading and full-band method) and three different classification modeling methods (partial least squares-discriminant analysis (PLS-DA), K-nearest neighbor (KNN) and support vector machine (SVM)) were applied to make a comparison. Next, the visualization images according to a mean spectrum to mean spectrum (M2M) and a mean spectrum to pixel spectrum (M2P) were compared in order to better represent the freeze damage to the seed embryos. It was concluded that the 5-3 smoothing method and SPA wavelength selection method applied to the modeling can improve the signal-to-noise ratio, classification accuracy of the model (more than 90%). The final classification results of the method M2P were better than the method M2M, which had fewer numbers of misclassified corn seed samples and the samples could be visualized well.
Highlights
Corn (Zea mays L.), one of the world’s three major food crops, is currently one of the most grown food crops in several parts of the world [1]
The objectives of this study were to: (1) conduct an electrical conductivity test on corn seeds to consider if the seed is damaged or not; (2) obtain the corn seed embryo hyperspectral image, and assess the potential of applying hyperspectral imaging technology for the classification of different degrees of freeze damage to the corn seeds; (3) evaluate the models established by different spectral pretreatment methods, wavelength selection methods and modeling methods, and compare and identify the optimal model among them; (4) visualize the classification results of two different methods (M2M and M2P), and to identify the optimal method
−10 ◦ C, for 5 h while the lowest is at the normal condition. It indicates that during the freeze-damage process, the membrane integrity of the corn seed deteriorated, and the leakage of the cell contents was serious after the seeds absorbing water, a higher conductivity was obtained
Summary
Corn (Zea mays L.), one of the world’s three major food crops, is currently one of the most grown food crops in several parts of the world [1]. As the world’s second-largest corn producing and consuming country, China has most of its corn growing areas located in the north. In these regions, the corn seed is often damaged due to low temperatures and high seed moisture content before harvest or dehydration, which is an agricultural disaster. If damage takes place in this part, it must have great impact on subsequent growth. After suffering from low-temperature freeze damage, the seed quality declines, and it is easy for mildew to grow when the seeds are stored at later stage. The internal components of the seed will change, which results in a great impact on the subsequent germination, root growth and development. To investigate the vigor change in seed and how it changes, the International Seed Testing Association (ISTA) recommended two kinds of seed viability measurement methods in 1995 [2], the electrical conductivity test could be conveniently conducted due to its simplicity and low cost [3,4]
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