/// Get the centre of a kernel. Determines the pixel to be
/// modified as a window is moved over an image
pubfnkernel_centre(rows:usize, cols:usize)->(usize, usize){let row_offset = rows /2-((rows %2==0)asusize);let col_offset = cols /2-((cols %2==0)asusize);(row_offset, col_offset)}