calculate how many regions of white pixels that are surrounded by black pixels?

Hello,
I have an image that I converted into a 30x30 matrix of 0's and1's. The value 0 represents a white pixel and the value 1 represents a black pixel. A region of white pixels is a circle if it is surrounded by a ring of black pixels that are connected to each other. I am trying to calculate how many circles there are in the matrix. Any idea on how to start this? ( I am not looking for full answer just a idea or guidance on how to start me off).

Thanks very much in advance