finding longest length

Hi ,I have a matrix as follows I =

     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     1     0     0     0     0     0
     0     0     1     0     1     0     0     0     1     0
     0     1     0     1     1     0     1     0     0     1
     1     0     0     0     1     0     1     1     0     0
     0     0     0     0     1     0     1     0     0     0
     0     1     1     1     0     1     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0

I need the output as follows:

I =

     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     1     0     0     0     0     0     1     0
     0     1     0     1     0     0     0     0     0     1
     1     0     0     0     0     0     0     1     0     0
     0     0     0     0     1     0     1     0     0     0
     0     0     0     0     0     1     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0

i.e only the longest length of pixel that touches two opposite boundary.can any body help please?Thanks