You have everything to do that. Instead of
My.Computer.Screen.Bounds
use some greater values of
sourceX
and
sourceY
which will define offsets from the top and left bounds of the screen and reduce size to required size. In this way, you will copy a smaller source rectangle representing a subset of the screen pixels.
See
http://msdn.microsoft.com/en-us/library/cdcw1c3b.aspx[
^].
—SA