尋找局部最大值

peak_local_max 函數會傳回影像中局部峰值（最大值）的座標。在內部，會使用最大值濾波器來尋找局部最大值。此操作會擴張原始影像，並合併比擴張大小更近的相鄰局部最大值。原始影像等於擴張影像的位置會被視為局部最大值傳回。

from scipy import ndimage as ndi
import matplotlib.pyplot as plt
from skimage.feature import peak_local_max
from skimage import data, img_as_float

im = img_as_float(data.coins())

# image_max is the dilation of im with a 20*20 structuring element
# It is used within peak_local_max function
image_max = ndi.maximum_filter(im, size=20, mode='constant')

# Comparison between image_max and im to find the coordinates of local maxima
coordinates = peak_local_max(im, min_distance=20)

# display results
fig, axes = plt.subplots(1, 3, figsize=(8, 3), sharex=True, sharey=True)
ax = axes.ravel()
ax[0].imshow(im, cmap=plt.cm.gray)
ax[0].axis('off')
ax[0].set_title('Original')

ax[1].imshow(image_max, cmap=plt.cm.gray)
ax[1].axis('off')
ax[1].set_title('Maximum filter')

ax[2].imshow(im, cmap=plt.cm.gray)
ax[2].autoscale(False)
ax[2].plot(coordinates[:, 1], coordinates[:, 0], 'r.')
ax[2].axis('off')
ax[2].set_title('Peak local max')

fig.tight_layout()

plt.show()