```
class Solution(object):
def findLonelyPixel(self, picture):
"""
:type picture: List[List[str]]
:rtype: int
"""
if not picture:
return 0
bpos = []
for row in picture:
idx = [i for i in range(len(row)) if row[i] == 'B']
bpos.append(idx)
cnt = 0
bposFlat = sum(bpos, [])
for row in bpos:
if len(row) == 1 and bposFlat.count(row[0]) == 1:
cnt += 1
return cnt
```