8. The method of claim 1 , wherein step (d) includes the steps of: computing an average and a standard deviation by computing the average and the standard deviation of those vertical projections being greater than 0, respectively; computing a first threshold being the sum of the average and a first threshold coefficient multiplying the standard deviation; selecting a plurality of peak coordinates, the vertical projections of which are greater than the first threshold; and selecting the first coordinate and the second coordinate from the peak coordinates.
8. The method of claim 1 , wherein step (d) includes the steps of: computing an average and a standard deviation by computing the average and the standard deviation of those vertical projections being greater than 0, respectively; computing a first threshold being the sum of the average and a first threshold coefficient multiplying the standard deviation; selecting a plurality of peak coordinates, the vertical projections of which are greater than the first threshold; and selecting the first coordinate and the second coordinate from the peak coordinates. 9. The method of claim 8 further comprising the step of counting the number of the peak coordinates.