d the location
 of each mask is either 1/4 or 3/4 of siz(d) and likewise if M=3 that mask
 is at 1/6,3/6, or 5/6 of siz(d). For higher M the locations are:
 1/2M,3/2M,...,M-1/2M. See examples below to visualize the masks.

 The std of each gaussian is set to be equal to the spacing between two
 adjacent masks multiplied by width.  Reducing the widths of the gaussians
 causes there to be less overlap between masks, but if the width is
 reduced too far certain pixels in between masks receive very litt