The cross correlation between column indexes for each lane. To correct for band distortion within a lane, e.g., smiling, the GELect algorithm calculates correlation of pixel intensities across the lane. The pixel offset for each column of one pixel width can be detected and corrected for. In the example plot shown, a lane of 15 pixels width contains bands with a frowning pattern. It can be seen that the peak correlation values plotted as pairwise correlations shift along the vertical lane axis (see inset).