Color Overprint Deviation Detection Method

This paper carries out the research in the defects detecting of color printed overlapping based on computer vision technology. It presents a novel algorithm of Edge Co-occurrence conditional probability Matrix(ECM) according to the edge feature of color printed overlapping. It can be used to control the machinery positioning of printing equipment and analyze the quality of color printing offline. Firstly, this paper studies and analysis the edge detection algorithms in detail and selects one detection algorithm which is suitable for Edge Co-occurrence conditional probability Matrix(ECM). Then, it introduces the Edge Co-occurrence conditional probability Matrix(ECM) algorithm. At last, it introduces algorithm s about the extraction of image extreme point.The preface presents the background and significance of this paper. It analysis the domestic and overseas research on color printed overlapping at present, summarizes the content and the organization of whole paper. Color overlay printing is printed by several different colors to the same location repeatedly in order to get the right color. In paper color printing, it mainly uses four colors, CMYK. Most part of colors in nature can be achieved by mixing different proportions of these four colors. In fabric dyeing, it uses much more colors to printing. The color overlay is the overlap printing on the same position in the paper or fabric rather than printing after get the pre-mixed colors. Because of this, it has the problem that if different print swatches have register problem. If the color register out of the mass range, it will induce the printing patterns become blurred and cause chromatic aberration, reduce the quality of products. By now, artificial detection or other detection methods which take advantage of registration marks at the edge of registration are used both in online printing or the offline analysis of the printing quality. But manual inspection is inefficient and imprecise. The methods that use registration marks are not detect the printed overlapping of color printing directly, it need to reserve the area for the marks and cutting after completion of the printing. To solve the problems above, this paper presents a solution for defects detecting of color printed overlapping based on computer vision technology, Edge Co-occurrence conditional probability Matrix(ECM). It is an automatic detection method for image content and does not depend on the template image. The second chapter presents the image edge detection algorithms. The edge of image is the set of pixels whose gray transformation is dramatic in the image. It exists between the target and background, objectives and goals, region to region, primitive and the primitives. The classical edge detection algorithms includes the method based on the first derivative, the method based on second derivative, the edge detection method based on wavelet transform, the edge detection based on mathematical morphology, the edge detection based on Fractal Theory detection firm and so on. According to detailed analysis, this paper selects edge detection which uses Canny edge detection method to extract the color overprint deviation image. The main reason is this method can reduce the image weak edge information through two thresholds.The third chapter proposes the core algorithm of this paper, Edge Co-occurrence conditional probability Matrix(ECM). Firstly, it discusses the characteristics of color overlay images. It is a typical ghost image. In the edge image of ghost image, its corresponding edge can be considered parallel. Using this feature, this paper proposes the Edge Co-occurrence conditional probability Matrix(ECM) to statistical parameters of color overlay image of migration. It uses different angles and different scan vector to scan the Image that to be detected. When the starting point of scan vector is located on the edge of the image, the corresponding element in the Edge Co-occurrence conditional probability Matrix(ECM) will plus one. If the image to be detected has color printed overlapping, its Edge Co-occurrence conditional probability Matrix(ECM) will have one or more peak points, and this or these points will be the deviation parameter of this color overlay images. If there is no color printed overlapping exist in the image, its Edge Co-occurrence conditional probability Matrix(ECM) has no obvious peak points.The fourth chapter discussed the detection process of color printed overlapping based on the Edge Co-occurrence conditional probability Matrix(ECM). Firstly, it discusses the characteristics of color overlay defects. Then it proposed three steps for the detection of color printed overlapping:the first step is to extract the edge image, this paper selects the canny edge detection method; in the next step, calculated conditional probability of an edge matrix of symbiotic use the method that proposed in this paper; In step three, remove the background information and calculate the peak value of the matrix that get from step two.The fifth chapter discusses the setup of experiment, the procedure of experiment, and the result. The algorithm proposed in this paper is implemented by matlab. It selects different color overlay images as test images. The experiment results show that the detection method proposed in this paper is accurate and efficient.This paper presents a novel algorithm of Edge Co-occurrence conditional probability Matrix(ECM) for detecting color printed overlapping defects without the reference image and color mark using for registration. It can be used to detect the color printed overlapping defects and evaluate the shift parameter. Due to the color printed overlapping defects are usually caused by the shift of some certain printing plates, we use statistical shift information to detect the color printed overlapping defects and evaluate the shift parameter. Experiments in the paper demonstrate that the detection result can accurate to one pixel and the algorithm is effective and accuracy.