The present invention relates to an image sensor system. The invention further relates to an X-ray imaging system comprising such an image sensor system. More in particular, the present invention is related to image sensor systems that use a relatively small pixel width.According to the present invention, the conversion unit comprises, for each column of pixels, a load that comprises a toggling unit configured for toggling a predefined number of bits in response to the clock signal. Furthermore, the load and binary counter are operable in a counting mode, in which mode the binary counter increases the binary count value in dependence of the clock signal and the load does not toggle, and in a non-counting mode, in which mode the binary counter has stopped counting and the load toggles said predefined number of bits in dependence of the clock signal. The predefined number corresponds to the average number of bits that toggle in the binary counter per counting step while the binary counter is in the counting mode.