Interface hangs while running while using from kivy.app

I'm studying image processing using Python.

I made an interface with Kivy.app , but it is crashing when it runs while . I'm using the code below to fill an array with "0" or "1", making the image binarized .

Any tips on how to resolve the non-crash issue?

Obs. In Python's IDLE it runs perfectly.

Code:

i = 0
        while i < (hs-1):
              j=0
              while j < (ws-1):
                    j = j+1
              if (lum_img2[i,j]) <= threshold2:
                      lum_img2[i,j] = 0
              else:
                      lum_img2[i,j]= 1
        i = i + 1
        i = 0