Median Stokes Q and U images with different levels of IP corrections for HD 135344B Ks-band observations. From top to bottom: Q⁺ and U⁺ components after equalising the ordinary and extra-ordinary fluxes, Q and U resulting from the double-difference method, Q_IPS and U_IPS after subtracting the median IP within an annulus, and the crosstalk-corrected Q_CTC and U_CTC components where the reduced Stokes U efficiency is accounted for. The characteristic butterfly pattern is visible in each panel, and the compasses show the orientation of the detector and the sky.