How to find the diameter of objects using image processing in Python?

Question

Given an image with some irregular objects in it, I want to find their individual diameter.

Thanks to this answer, I know how to identify the objects. Howeve

Answer 1

You could use skimage.measure.regionprops to determine the bounding box of all the regions in your image. For roughly circular blobs the diameter of the minimum enclosing circle can be approximated by the largest side of the bounding box. To do so you just need to add the following snippet at the end of your script:

from skimage.measure import regionprops

properties = regionprops(labels)
print 'Label \tLargest side'
for p in properties:
    min_row, min_col, max_row, max_col = p.bbox
    print '%5d %14.3f' % (p.label, max(max_row - min_row, max_col - min_col))

fig = plt.figure()
ax = fig.add_subplot(111)    
ax.imshow(np.ma.masked_array(labels, ~blobs), cmap=plt.cm.gist_rainbow) 
ax.set_title('Labeled objects')
plt.xticks([])
plt.yticks([])
for ri, ci, li in zip(r, c, range(1, nlabels+1)):
    ax.annotate(li, xy=(ci, ri), fontsize=24)
plt.show()

And this is the output you get:

Label   Largest side
    1        106.000
    2         75.000
    3         79.000
    4         56.000
    5        161.000
    6         35.000
    7         47.000