【正文】 ifference operator to look for edge. Its effect is the best for the image with steep low noise. But the borderline of the extracted image is quite thick using the Robots operator, so the edge location is not very accurate.Robots operator is defined as: (4)But absolute deviation algorithm is usually used to predigest the equation (4) in practice. The following equations (5) and (6) are the process of reduction. (5) (6)The template of the Robots operator is shown in Fig. 3Fig. 3 Roberts operator(2)Sobel and Prewitt operatorTo reduce the influence of noise when detecting edge, the Prewitt operator enlarges edge detection operator template from two by two to three by three to pute difference operator. Using the Prewitt operator can not only detect edge points, but also restrain the noise. The Sobel operator has the similar function as the Prewitt operator, but the edge detected by the Sobel operator is wider.Suppose that the pixel number in the3x3 subdomain of image is as follows:We order that X=(A0+A1+A2)( A 4+ A 5 +A 6) and Y=(A0+A7+A6)( A2+ A 3+A 4)Then Prcwitt operator is as follows: (7)Or (8)Prewitt operator is said in in the form 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。 of pixels and extract the set of edge points through setting threshold. But the borderline detected may produce interruption as a result of existing noise and image dark. Thus edge detection contains the following two parts:1)Using edge operators the edge points set are extracted. 2)Some edge points in the edge points set are removed and a number of edge points are filled in the edge points set. Then the obtained are connected to be a line.The mon used operators are the Differential, Log, Canny operators and Binary morphology, etc.A. Differential operatorDifferential operator can outstand grey change. There are some points where grey change is bigger. And the value calculated in those points is higher applying derivative operator. So these differential values may be regarded as relevant `edge intensity39。當(dāng)圖像受到投影，混合和噪聲等因素的影響時(shí)，圖像特征會(huì)變得模糊和失真，使得圖像特征的提取變得困難。二．圖像去噪實(shí)際情況中的圖像在采集、傳輸、接收和處理的過程中含有噪聲疊加的過程。 小波去噪的Matlab仿真結(jié)果如圖2所示 ： 帶噪聲的原始圖像 中值濾波圖像 小波去噪圖像圖2 兩種去噪方法比較與傳統(tǒng)的匹配濾波器相比，小波變換去噪不損壞圖像的高頻部分。微分算子可以突出邊緣灰度的變化。 羅伯茨算子的定義是： (4)但在實(shí)際中絕對(duì)偏差算法通常采用方程(4)的簡化形式，如方程(5)和(6)?？傊?，Sobel和Prewitt算子有較好的效果，例如圖像灰度的逐步改變。C. Canny算子Canny算子是一種新的邊緣檢測算子。從定位準(zhǔn)確性的角度來看，Canny算子優(yōu)于其他算子。可以很容易地確定物體的圖像背景。構(gòu)建的結(jié)構(gòu)元素越大，獲得的邊緣越寬闊。因此，我們將介紹一種通過像素梯度的大小和方向進(jìn)行邊緣跟蹤的方法。五．結(jié)論這些邊緣檢測算子在邊緣明顯和低噪聲的情況下，有較好的邊緣