Figure 1

Area 1:

      1  2  3
      4  5  6
      7  8  9

     Output of homogeneity edge detector is:
     max of {
         | 5 - 1 |      | 5 - 2 |      | 5 - 3 |

         | 5 - 4 |      | 5 - 6 |      | 5 - 7 |

         | 5 - 8 |      | 5 - 9 |
     } = 4


Area 2:

     10  10  10
     10  10  10
     10  10   1

     Output of homogeneity edge detector is:
     max of {
         | 10 - 10 |   | 10 - 10 |   | 10 - 10 |

         | 10 - 10 |   | 10 - 10 |   | 10 - 10 |

         | 10 - 10 |   | 10 - 1  |
     } = 9


Area 3:

     10  5  3
     10  5  3
     10  5  3

      Output of homogeneity edge detector is:
      max of {
          | 5 - 10 |     | 5 - 5 |     | 5 - 3  |

          | 5 - 10 |     | 5 - 3 |     | 5 - 10 |

          | 5 - 5  |     | 5 - 3 |
      } = 5