Difference of Gaussian (Dog) Filter. Adapted from code by Serge Belongie. Takes a "difference of Gaussian" - all centered on the same point but with different values for sigma. INPUTS r - Final filter will be 2*r+1 on each side sig - standard deviation of central Gaussian order - should be either 1 or 2 show - [optional] figure to use for display (no display if == 0) OUTPUTS G - final filter EXAMPLE G = filter_DOG_2D( 6, 3, 1, 1 ); DATESTAMP 29-Sep-2005 2:00pm See also FILTER_DOOG_2D