I am still coding a fingerprint image preprocessor on Python. I see in MATLAB there is a special function to remove H breaks and spurs:
bwmorph(a , 'hbreak') bwmorph(a , 'spur') I have searched scikit, OpenCV and others but couldn't find an equivalent for these two use of bwmorph. Can anybody point me to right direction or do i have to implement my own?
You will have to implement those on your own since they aren't present in OpenCV or skimage as far as I know. However, it should be straightforward to check MATLAB's code on how it works and write your own version in Python/NumPy.
Here is a guide describing in detail NumPy functions exclusively for MATLAB users, with hints on equivalent functions in MATLAB and NumPy: http://wiki.scipy.org/NumPy_for_Matlab_Users
Edit October 2017
the skimage module now has at least 2 options: skeletonize and thin
Example with comparison
from skimage.morphology import thin, skeletonize import numpy as np import matplotlib.pyplot as plt square = np.zeros((7, 7), dtype=np.uint8) square[1:-1, 2:-2] = 1 square[0, 1] = 1 thinned = thin(square) skel = skeletonize(square) f, ax = plt.subplots(2, 2) ax[0,0].imshow(square) ax[0,0].set_title('original') ax[0,0].get_xaxis().set_visible(False) ax[0,1].axis('off') ax[1,0].imshow(thinned) ax[1,0].set_title('morphology.thin') ax[1,1].imshow(skel) ax[1,1].set_title('morphology.skeletonize') plt.show() 
Original post
I have found this solution by joefutrelle on github.
It seems (visually) to give similar results as the Matlab version.
Hope that helps!
Edit:
As it was pointed out in the comments, I'll extend my initial post as the mentioned link might change:
Looking for a substitute in Python for bwmorph from Matlab I stumbled upon the following code from joefutrelle on Github (at the end of this post as it's very long).
I have figured out two ways to implement this into my script (I'm a beginner and I'm sure there are better ways!):
1) copy the whole code into your script and then call the function (but this makes the script harder to read)
2) copy the code it in a new python file 'foo' and save it. Now copy it in the Python\Lib (eg. C:\Program Files\Python35\Lib) folder. In your original script you can call the function by writing:
from foo import bwmorph_thin
Then you'll feed the function with your binary image:
skeleton = bwmorph_thin(foo_image, n_iter = math.inf) 
import numpy as np from scipy import ndimage as ndi # lookup tables for bwmorph_thin G123_LUT = np.array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0], dtype=np.bool) G123P_LUT = np.array([0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], dtype=np.bool) def bwmorph_thin(image, n_iter=None): """ Perform morphological thinning of a binary image Parameters ---------- image : binary (M, N) ndarray The image to be thinned. n_iter : int, number of iterations, optional Regardless of the value of this parameter, the thinned image is returned immediately if an iteration produces no change. If this parameter is specified it thus sets an upper bound on the number of iterations performed. Returns ------- out : ndarray of bools Thinned image. See also -------- skeletonize Notes ----- This algorithm [1]_ works by making multiple passes over the image, removing pixels matching a set of criteria designed to thin connected regions while preserving eight-connected components and 2 x 2 squares [2]_. In each of the two sub-iterations the algorithm correlates the intermediate skeleton image with a neighborhood mask, then looks up each neighborhood in a lookup table indicating whether the central pixel should be deleted in that sub-iteration. References ---------- .. [1] Z. Guo and R. W. Hall, "Parallel thinning with two-subiteration algorithms," Comm. ACM, vol. 32, no. 3, pp. 359-373, 1989. .. [2] Lam, L., Seong-Whan Lee, and Ching Y. Suen, "Thinning Methodologies-A Comprehensive Survey," IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol 14, No. 9, September 1992, p. 879 Examples -------- >>> square = np.zeros((7, 7), dtype=np.uint8) >>> square[1:-1, 2:-2] = 1 >>> square[0,1] = 1 >>> square array([[0, 1, 0, 0, 0, 0, 0], [0, 0, 1, 1, 1, 0, 0], [0, 0, 1, 1, 1, 0, 0], [0, 0, 1, 1, 1, 0, 0], [0, 0, 1, 1, 1, 0, 0], [0, 0, 1, 1, 1, 0, 0], [0, 0, 0, 0, 0, 0, 0]], dtype=uint8) >>> skel = bwmorph_thin(square) >>> skel.astype(np.uint8) array([[0, 1, 0, 0, 0, 0, 0], [0, 0, 1, 0, 0, 0, 0], [0, 0, 0, 1, 0, 0, 0], [0, 0, 0, 1, 0, 0, 0], [0, 0, 0, 1, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0]], dtype=uint8) """ # check parameters if n_iter is None: n = -1 elif n_iter <= 0: raise ValueError('n_iter must be > 0') else: n = n_iter # check that we have a 2d binary image, and convert it # to uint8 skel = np.array(image).astype(np.uint8) if skel.ndim != 2: raise ValueError('2D array required') if not np.all(np.in1d(image.flat,(0,1))): raise ValueError('Image contains values other than 0 and 1') # neighborhood mask mask = np.array([[ 8, 4, 2], [16, 0, 1], [32, 64,128]],dtype=np.uint8) # iterate either 1) indefinitely or 2) up to iteration limit while n != 0: before = np.sum(skel) # count points before thinning # for each subiteration for lut in [G123_LUT, G123P_LUT]: # correlate image with neighborhood mask N = ndi.correlate(skel, mask, mode='constant') # take deletion decision from this subiteration's LUT D = np.take(lut, N) # perform deletion skel[D] = 0 after = np.sum(skel) # coint points after thinning if before == after: # iteration had no effect: finish break # count down to iteration limit (or endlessly negative) n -= 1 return skel.astype(np.bool) """ # here's how to make the LUTs def nabe(n): return np.array([n>>i&1 for i in range(0,9)]).astype(np.bool) def hood(n): return np.take(nabe(n), np.array([[3, 2, 1], [4, 8, 0], [5, 6, 7]])) def G1(n): s = 0 bits = nabe(n) for i in (0,2,4,6): if not(bits[i]) and (bits[i+1] or bits[(i+2) % 8]): s += 1 return s==1 g1_lut = np.array([G1(n) for n in range(256)]) def G2(n): n1, n2 = 0, 0 bits = nabe(n) for k in (1,3,5,7): if bits[k] or bits[k-1]: n1 += 1 if bits[k] or bits[(k+1) % 8]: n2 += 1 return min(n1,n2) in [2,3] g2_lut = np.array([G2(n) for n in range(256)]) g12_lut = g1_lut & g2_lut def G3(n): bits = nabe(n) return not((bits[1] or bits[2] or not(bits[7])) and bits[0]) def G3p(n): bits = nabe(n) return not((bits[5] or bits[6] or not(bits[3])) and bits[4]) g3_lut = np.array([G3(n) for n in range(256)]) g3p_lut = np.array([G3p(n) for n in range(256)]) g123_lut = g12_lut & g3_lut g123p_lut = g12_lut & g3p_lut """`