In a real-time quality inspection of printed matter based on machine vision, artifacts are induced by commonly used image difference methods, making the identification of defects difficult. Thus, to eliminate artifacts and improve detection rate of printing defects, this study proposed a method that combines grayscale and gradient differences. First, the grayscale difference between template image and inspected image was performed to determine the defect in the nonedge region according to the grayscale difference threshold of non-weighted neighborhood. Then, the gradient difference between the template image and inspected image was employed to determine the edge defect according to the grayscale difference threshold of weighted neighborhood. Finally, the difference artifacts were effectively eliminated by the two different image fusions and the real defects were retained. Experiments were conducted to compare the defect detection rate of printed image by using the traditional and proposed methods. Results demonstrate that for the most common dot defects the detection rate of the proposed methods is significantly higher than that of the traditional difference method due to the effective elimination of artifacts. The parallel acceleration based on compute unified device architecture (CUDA) enables the algorithm to speed up the defect detection of large print images by more than 60 times. The study provides significantly references for industrial inspection based on machine vision.

The dielectric barrier discharge (DBD) in the glow regime in neon has been investigated by experiment and two-dimensional (2D) fluid modeling. The discharge was carried out in a planar DBD system with segmented-electrodes driven by square-wave voltage. The results show that the glow DBD originates in the center of the electrode and expands outward to the electrode edge during each half cycle of the voltage, forming a radial structure. The discharge decays firstly in the inner area but sustains longer in the edge area, showing a reversed discharge area. The discharge cannot completely cover the entire electrode surface, but remains a border of non-or weak discharge. The fluid modeling shows a similar result in agreement with the experiments. The simulations indicate that the electric field in the edge area is distorted due to the boundary effect so that the electric field and charge distribution are different from that in the inner part. The distorted field reduces the longitudinal component near the edge and causes the local field to be lower than that in the center, and hence makes the discharge behindhand. It also induces a transverse field that makes the discharge extend radially outward to the edge. The boundary effect plays an important role in the glow DBD structure.