array = np.random.randint(0, 3, size=(200, 200))
label, num_label = ndimage.label(array == 0)
size = np.bincount(label.ravel())
biggest_label = size[1:].argmax() + 1
clump_mask = label == biggest_label
Python - Efficient way to find the largest area of a specific value in a 2D numpy array