【文章內(nèi)容簡介】 m of the template.Fig. 4 Prewitt operator Sobel operator can process noises and gray gradient those images with lots of well. We order that X=(A0+2A1+A2)( A 4+ 2A 5 +A 6) andY=(A0+2A7+A6)( A2+ 2A 3+A 4).Then Sobel operator is as follows: (9)Or (10) The template of the Sobel operator is shown in . Sobel operatorThe original image of cable insulation layer and the edge detection drawing of Sobel operator gained using MatLab simulation are shown in Fig. 6 and Fig. 7. the original imageFig. 7 the edge detection drawing of Sobel operatorFrom the simulation drawing Fig. 7, we can know that the edge position is very accurate. And the effect of Sobel edge detection is very satisfying. In a word, the Sobel and Prewitt operators have a better effect for such images with grey level changing gradually and more noses.B. Log operatorThe Log operator is a linear and timeinvariant operator. It detects edge points through searching for spots which twoorder differential coefficient is zero in the image grey levels. For a continuous function ，the Log operator is defined as at point (x,y): (11)The Log operator is the process of filtering and counting differential coefficient for the image. It determines the zero overlapping position of filter output using convolution of revolving symmetrical Log template and the image. The Log operator39。s template is shown in Fig. 8.Fig. 8 Log operatorIn the detection process of the Log operator, we firstly presmooth the image with Gauss lowpass filter, and then find the steep edge in the image making use of the Log operator. Finally we carry on Binarization with zero grey level to give birth to closed, connected outline and eliminate all internal spots. But double pixels boundary usually appears using the Log operator to detect edge, and the operator is very sensitive to noise. So the Log operator is often employed to judge that edge pixels lie in either bright section or dark section of the image.C. Canny operatorThe Canny operator is a sort of new edge detection operator. It has good performance of detecting edge, which has a wide application. The Canny operator edge detection is to search for the partial maximum value of image gradient. The gradient is counted by the derivative of Gauss filter. The Canny operator uses two thresholds to detect strong edge and weak edge respectively. And only when strong edge is connected with weak edge, weak edge will be contained in the output value. The theory basis of canny operator is shown in equations (12)(15).Gauss: (12)Edgenormals: (13)Edge strengths: (14)Maximal strengths: (15)For twodimensional image,canny operator can produce two information including the border gradient direction and operator is actually using templates of different directions to do convolution to the image respectively. Then the mostly direction is taken. From the viewpoint of positioning accuracy, canny operator is better than the other operators.Therefore, this method is not easily disturbed by noise and can keep the good balance between noise and edge detection. It can detect the true weak edge.D. Binary morphologyMathematical morphology is a new method applied in image processing. The basic idea is to measure and extract the corresponding shape from image with structural elements having stated form. So that the image processing and analyzing can be pleted.Using mathematical morphology to detect the edge is better than using differential treatment. Because it is not sensitive to noise, and the edge extracted is relatively smooth. Binary image is also known as blackandwhite image. The object can be easily identified from the image background. So we adopt the bination of binary image and mathematical morphology to detect edge. It is called Binary morphology.Suppose that the re