```
class Solution(object):
def findBlackPixel(self, picture, N):
"""
:type picture: List[List[str]]
:type N: int
:rtype: int
"""
r_no = len(picture)
c_no = len(picture[0])
search_r = [i for i in range(r_no) if picture[i].count('B')==N]
search_c = [i for i in range(c_no) if [j[i] for j in picture].count('B')==N]
count = 0
for r in search_r:
for c in search_c:
if picture[r][c] == 'B':
cur_row = picture[r]
sibs = filter(lambda x:x[c]=='B', picture)
if all([s==cur_row for s in sibs]):
count += 1
return count
```