The modified alpha value and the modified color of a pixel are determined as {TAIL ~ a function} of {HEAD ~ the amount} of gray in the original color of the pixel 
The modified alpha value and the modified color of a pixel are determined as { TAIL ~ a function } of { HEAD ~ the amount } of gray in the original color of the pixel
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH