Issue 30

W. Tao et alii, Frattura ed Integrità Strutturale, 30 (2014) 537-544; DOI: 10.3221/IGF-ESIS.30.64 539 an image. The spatial correlation between the neighbor pixels of the image is high. But the noise is relatively independent. Non-weighted average is the simplest and most commonly applied neighborhood average method. (1) Set one image   , f x y . Then express the gray value of a pixel in the image as   , g x y , which is the square windows of field S n n   . The total number of points is set to be M . Thus the gray value of this point after smoothness is: , 1 ( , ) ( , ) i j S g x y f i j M    We can use formation templates to describe the non-weighted average neighborhood law. That is, we need to move the filtering template point-by-point and get the sum of products. When applying neighbor pixels defined in the image template on template operation, the coefficient   0, 0  of template corresponds with the   , x y in the image. Set the template size to be 33  . The application of this template can produce a result as follows: 1 1 1 1 ( , ) ( , ) m n R m n f x m y n         (2) Set the gray value of point   , x y in the neighborhood of n n  . The gradient inverse   , W i j is defined as:       1 , 1, 1 , W i j f x y f x y     Gray-level threshold segmentation The threshold segmentation produces a binary image. The position of the pixels is represented in the image through a grayscale image   , f x y and the coordinates   yx , . T is the threshold and the binary images are represented through using   , B x y after the threshold. The expression is as follows:       1, , , 0, , f x y T B x y f x y T       (3) We can know from the above that the appropriate threshold is concerned with gray closed segmentation. This article uses the iterative method to auto-select thresholds according to the following steps: 1) Calculate the maximum max T and minimum min T gray value of the entire image. Both average values are just about the initial threshold 0 T .   2 min max 0 T T T   ; 2) Segment the image based on h T and respectively solve the average gray level of foreground 1 G and background 2 G ; 3) Solve the new threshold value   1 1 2 2 h T G G    ; 4) Take a new threshold. Repeat steps 2 to 4 until 1 h h T T   in subsequent iterations remains basically unchanged. An iterative method is used to make the grayscale threshold segmentation up to a gray level image, as shown in Fig. 3. (a) (b) Figure 3 : (a) Grayscale image; (b) Image after iterative segmentation.