针对复杂背景及目标的分形特性差异, 提取图像四个方向的灰度梯度, 选择最小梯度大于阈值的区域进行平滑滤波, 最后对分维参数进行分段线性拉伸-Extraction of image in four directions of the gray gradient, minimum gradient is greater than the threshold area smoothing filter, the last on the fractal dimension parameters of piecewise linear stretch