The locality of a dot is defined as the sample of dots contained within a radius of 4 dots from the dot of interest, similar to a moving window. Selection of radius size takes into account of competing factors. A small radius will have a higher homogeneity of pixel gain but suffers from statistically unreliable small samples. A 3-dot radius completely covers the area of one cell with 29 dots. At the worst case, only 4 dots lie outside of the cell. As such, a 3-dot radius locality can be susceptible to errors within a cell. A 4-dot radius yields 49 dots which includes 24 dots outside of the cell at worst. As such, the 4-dot radius is used in our analysis. Figure shows the comparison between a 3-dot and 4-dot radius locality.