Inverted greyscale of our XXL-S Pilot Survey mosaic at 2.1 GHz. The greyscale colourbar in units of mJy/beam is shown at the top. Overlaid are histograms of pixel flux distributions for different regions of the mosaic. The standard deviation for each region is indicated in each panel (in units of μJy/beam). The x-axis of the histograms shows flux density in μJy/beam and the y-axis shows counts. The outer 500 pixels of the map have been excluded here since they are not considered in the source-finding process.