If the four corner cells shape data is added to the data from the border cells, each in a known location where alignment is determined and added to the skew found from looking at the four corners, {HEAD ~ the combined information} provides {TAIL ~ a more accurate picture} of non balanced skew such as lens barreling where the middle of the symbols four sides rounds outward and trapezoidal problems where the lens is not square with the symbol which is not seen or corrected by just looking at the corners points themselves 
If the four corner cells shape data is added to the data from the border cells , each in a known location where alignment is determined and added to the skew found from looking at the four corners , { HEAD ~ the combined information } provides { TAIL ~ a more accurate picture } of non balanced skew such as lens barreling where the middle of the symbols four sides rounds outward and trapezoidal problems where the lens is not square with the symbol which is not seen or corrected by just looking at the corners points themselves
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