Python实现高斯边缘检测的拉普拉斯
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21-12-2019 - |
题
我正在寻找高斯边缘检测Laplacian的等效实施。
在matlab中,我们使用以下功能
[BW,threshold] = edge(I,'log',...)
.
在Python中,存在用于计算高斯拉普拉斯的功能。它绝对不是给边缘。
scipy.ndimage.filters.gaussian_laplace
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任何指向在线实现的指针或代码
感谢
解决方案
matlab边缘()应该是
- 计算日志
- 计算日志中的零交叉口
- 计算本地日志差异 的阈值
- 边缘像素=零交叉&&局部差异>阈值
SCIPY的日志过滤器仅执行上面的步骤1。 我实施了以下代码段以模仿步骤2〜4以上:
import scipy as sp
import numpy as np
import scipy.ndimage as nd
import matplotlib.pyplot as plt
from skimage import data
# lena = sp.misc.lena() this function was deprecated in version 0.17
img = data.camera() # use a standard image from skimage instead
LoG = nd.gaussian_laplace(img , 2)
thres = np.absolute(LoG).mean() * 0.75
output = sp.zeros(LoG.shape)
w = output.shape[1]
h = output.shape[0]
for y in range(1, h - 1):
for x in range(1, w - 1):
patch = LoG[y-1:y+2, x-1:x+2]
p = LoG[y, x]
maxP = patch.max()
minP = patch.min()
if (p > 0):
zeroCross = True if minP < 0 else False
else:
zeroCross = True if maxP > 0 else False
if ((maxP - minP) > thres) and zeroCross:
output[y, x] = 1
plt.imshow(output)
plt.show()
.
这当然是慢,可能不是惯用的,因为我也是python的新手,但应该展示这个想法。关于如何改善它的任何建议也受到欢迎。
其他提示
我用ycyeh的代码播放了一点(谢谢你提供它)。在我的应用程序中,我可以使用与min-max范围比例的输出值比仅仅是二进制0s和1s成比例的更好的结果。(然后我也不需要阈值,但是一个人可以轻松地应用于结果。)我还将循环更改为Numpy数组操作,以便更快地执行。
import numpy as np
import scipy.misc
import cv2 # using opencv as I am not too familiar w/ scipy yet, sorry
def laplace_of_gaussian(gray_img, sigma=1., kappa=0.75, pad=False):
"""
Applies Laplacian of Gaussians to grayscale image.
:param gray_img: image to apply LoG to
:param sigma: Gauss sigma of Gaussian applied to image, <= 0. for none
:param kappa: difference threshold as factor to mean of image values, <= 0 for none
:param pad: flag to pad output w/ zero border, keeping input image size
"""
assert len(gray_img.shape) == 2
img = cv2.GaussianBlur(gray_img, (0, 0), sigma) if 0. < sigma else gray_img
img = cv2.Laplacian(img, cv2.CV_64F)
rows, cols = img.shape[:2]
# min/max of 3x3-neighbourhoods
min_map = np.minimum.reduce(list(img[r:rows-2+r, c:cols-2+c]
for r in range(3) for c in range(3)))
max_map = np.maximum.reduce(list(img[r:rows-2+r, c:cols-2+c]
for r in range(3) for c in range(3)))
# bool matrix for image value positiv (w/out border pixels)
pos_img = 0 < img[1:rows-1, 1:cols-1]
# bool matrix for min < 0 and 0 < image pixel
neg_min = min_map < 0
neg_min[1 - pos_img] = 0
# bool matrix for 0 < max and image pixel < 0
pos_max = 0 < max_map
pos_max[pos_img] = 0
# sign change at pixel?
zero_cross = neg_min + pos_max
# values: max - min, scaled to 0--255; set to 0 for no sign change
value_scale = 255. / max(1., img.max() - img.min())
values = value_scale * (max_map - min_map)
values[1 - zero_cross] = 0.
# optional thresholding
if 0. <= kappa:
thresh = float(np.absolute(img).mean()) * kappa
values[values < thresh] = 0.
log_img = values.astype(np.uint8)
if pad:
log_img = np.pad(log_img, pad_width=1, mode='constant', constant_values=0)
return log_img
def _main():
"""Test routine"""
# load grayscale image
img = scipy.misc.face() # lena removed from newer scipy versions
img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
# apply LoG
log = laplace_of_gaussian(img)
# display
cv2.imshow('LoG', log)
cv2.waitKey(0)
if __name__ == '__main__':
_main()
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