difference of gaussians example in python

dog_ex.py

from skimage import data, feature, color, filters, img_as_float
from matplotlib import pyplot as plt


original_image = img_as_float(data.chelsea())
img = color.rgb2gray(original_image)

k = 1.6

plt.subplot(2,3,1)
plt.imshow(original_image)
plt.title('Original Image')

for idx,sigma in enumerate([4.0,8.0,16.0,32.0]):
    s1 = filters.gaussian(img,k*sigma)
    s2 = filters.gaussian(img,sigma)

    # multiply by sigma to get scale invariance
    dog = s1 - s2
    plt.subplot(2,3,idx+2)
    print(dog.min(),dog.max())
    plt.imshow(dog,cmap='RdBu')
    plt.title('DoG with sigma=' + str(sigma) + ', k=' + str(k))

ax = plt.subplot(2,3,6)
blobs_dog = [(x[0],x[1],x[2]) for x in feature.blob_dog(img, min_sigma=4, max_sigma=32,threshold=0.5,overlap=1.0)]
# skimage has a bug in my version where only maxima were returned by the above
blobs_dog += [(x[0],x[1],x[2]) for x in feature.blob_dog(-img, min_sigma=4, max_sigma=32,threshold=0.5,overlap=1.0)]

#remove duplicates
blobs_dog = set(blobs_dog)

img_blobs = color.gray2rgb(img)
for blob in blobs_dog:
    y, x, r = blob
    c = plt.Circle((x, y), r, color='red', linewidth=2, fill=False)
    ax.add_patch(c)
plt.imshow(img_blobs)
plt.title('Detected DoG Maxima')

plt.show()