Cleaning of horizontal stripes (systematic readout noise). Upper left: detail of August 2012 K_s-band image. Lower left: as upper left, but cleaned. Upper right: detail of deep, mean combined K_s-band image when the input images have not been cleaned. Lower right: detail of deep, mean combined K_s-band image after cleaning of the input images. The displayed field is located about 12.0′′ and 1.7′′ north of Sgr A*. The colour scale is logarithmic and identical for all images.