Finding matching submatrices inside a matrix

Question

I have a 100x200 2D array expressed as a numpy array consisting of black (0) and white (255) cells. It is a bitmap file. I then have 2D shapes (it\'s easiest to think of them as

Answer 1

Here is a method you may be able to use, or adapt, depending upon the details of your requirements. It uses ndimage.label and ndimage.find_objects:

1. label the image using ndimage.label this finds all blobs in the array and labels them to integers.
2. Get the slices of these blobs using ndimage.find_objects
3. Then use set intersection to see if the found blobs correspond with your wanted blobs

Code for 1. and 2.:

import scipy
from scipy import ndimage
import matplotlib.pyplot as plt

#flatten to ensure greyscale.
im = scipy.misc.imread('letters.png',flatten=1)
objects, number_of_objects = ndimage.label(im)
letters = ndimage.find_objects(objects)

#to save the images for illustrative purposes only:
plt.imsave('ob.png',objects)
for i,j in enumerate(letters):
    plt.imsave('ob'+str(i)+'.png',objects[j])

example input:

labelled:

isolated blobs to test against: