We employ two equivalent subscripting schemes for referring to an element of the two-dimensional image, . Firstly, with two subscripts, bpx,py refers to the element that lies px increments along the x-axis, and py increments along the y-axis. Ranges of pxand py are given by , and respectively. Helical coordinates suggest an alternative subscripting scheme: We can use a single subscript, ph=px + py Nx, such that bpx,py = bph and the range of ph is given by .Moreover, if we impose helical boundary conditions, we can treat as a one-dimensional function of subscript ph.