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