The protein arrays contain null results that include marker dots and dots that do not produce any signal, hereby referred to as blank dots. Each cell can have up to 2 pairs of blank dots that should be excluded from subsequent statistical analyses. Marker dots were removed based on previously known positions whereas blank dots were removed based on divergence of the pixel intensity field. Dots with signals form sinks in the divergence field. Figure shows the position of the blank dots and marker dots throughout the entire array.