subtracting the integrated normalized ambient image from {TAIL ~ both the integrated first gate image} and the integrated second gate image, to yield {HEAD ~ a first and second frame integration} 
subtracting the integrated normalized ambient image from { TAIL ~ both the integrated first gate image } and the integrated second gate image , to yield { HEAD ~ a first and second frame integration }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD