*读取图片
read_image (Image, 'fabrik') *提取边缘
roberts (Image, ImageRoberts, 'roberts_max')
*二值化 threshold (ImageRoberts, Region, 9, 255) *提取骨架
skeleton (Region, Skeleton) dev_display (Image) dev_set_color ('red') dev_display (Skeleton)
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Roberts算子，又称罗伯茨算子，是一种最简单的算子，是一种利用局部差分算子寻找边缘的算子。
他采用对角线方向相邻两象素之差近似梯度幅值检测边缘。
检测垂直边缘的效果好于斜向边缘，定位精度高，对噪声敏感,无法抑制噪声的影响。
roberts(Image : ImageRoberts : FilterType : )
Description
roberts calculates the first derivative of an image and is used as an edge operator. If the following mask describes a part of the image,
A B
C D
the different filter types are defined as follows:
'roberts_max' max(| A - D |,| B - C |)
'gradient_max' max(| A + B - (C + D)|,| A + C - (B + D)|)
'gradient_sum' |A + B - (C + D)| + |A + C - (B + D)|
If an overflow occurs the result is clipped. The result of the operator is stored at the pixel with the coordinates of "D".