Average horizontal flow speed as a function of the elapsed time. The maps were computed using a Gaussian sampling window with an FWHM = 1200 km and time cadence Δt = 60 s. Before computing the cross-correlations, the images were convolved with a Gaussian kernel FWHM = 40–320 km to degrade the spatial resolution of the images. The increasing FWHM values are presented as progressively lighter shades of gray. The dash-dotted and dashed lines represents values above and below optimal parameter (FWHM = 160 km), respectively. The black solid line is used to depict result for the FWHM = 160 km, which is the typical spatial resolution of most Hinode G-band images (see Verma & Denker 2011).