import cv2
from skimage import data,color
import matplotlib.pyplot as plt
from skimage.morphology import disk
import skimage.filters.rank as sfr
img=cv2.imread('C:/Users/xpp/Desktop/Lena.png')#读取图像
cv2.imshow('original',img)
grayImage=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
dst=sfr.gradient(grayImage,disk(5))#半径为5的圆形滤波器
cv2.imshow("result",dst)
cv2.waitKey(0)
cv2.destroyAllWindows()
算法：gradient滤波是通过图像的局部梯度值（如：最大值-最小值）替换区域内所有像素值。结构元素可选择，圆、矩形、椭圆、区域多边形、区域点等操作符生成。
书籍：《微分几何讲义》
论文：Harrigan, M. E. . (1992). Gradient filter. US.
Yang, L. , Hwang, S. M. , Zhuang, Q. , Lu, J. , & Chang, S. L. . (2010). Using conjugate gradient method to calculate filter coefficient for time domain equalizer.[1]Geerten W Vuister and Jesús Ruff-Cabello and Peter C.M van Zijl. (1992). Gradient-enhanced multiple-quantum filter (ge-mqf). a simple way to obtain single-scan phase-sensitive hmqc spectra. Journal of Magnetic Resonance (1969).
Zhou, X. , Baird, J. P. , & Arnold, J. F. . (1999). Fringe-orientation estimation by use of a gaussian gradient filter and neighboring-direction averaging. Applied Optics, 38(5), 795-804.
Goss, M. E. . (1994). An adjustable gradient filter for volume visualization image enhancement. Cell Death & Differentiation.
Lax, I. , & Brahme, A. . (1982). Rotation therapy using a novel high-gradient filter. Radiology, 145(2), 473-478.
Pei, B. , & Li, C. . (1997). Adaptive exponent smoothing gradient algorithm. Transactions of Nanjing University of Aeronautics and Astronautics, 14(1)
崇元, 艾葳, & 徐冠雷. (2020). 基于局部梯度极值点的经验模式分解图像增强. 兵工自动化, v.39;No.257(03), 31-34.
赵前进, 胡敏, & 檀结庆. (2006). 基于局部梯度特征的自适应多结点样条图像插值. 计算机研究与发展(09), 1537-1542.
