3x3 Moving Window

Hi guys,
I have searched for a sample code about 3x3 moving window which will be used to change the pixel values using the surrounding 8 cells in vb .net. It will start manipulating from (0,0) or top left corner pixel of the image and end the process after the last cell which is bottom right pixel.

For example, lets say 3x3 window starts from the pixel (0,0). The surrounding pixel values will be added and the total value will be assigned to the pixel (0,0). Then the 3x3 window moves to the next pixel which is located at (0,1) or (row 0, column 1) and again its surrounding 8 pixels values are added and the total value will be assigned to the pixel in effect which is (0,1). The 3x3 moving window moves one pixel again etc...

I would appreciate it if you could provide me some sample code to manage this. I also googled about this but could not find any sample code in VB .NET.

Thanks in advance.