An image sensor including: a pixel array having a plurality of pixels connected to a plurality of row lines and a plurality of column lines; a plurality of ramp buffers configured to output a ramp voltage generated by a ramp voltage generator; a sampling circuit including a plurality of samplers, each of the plurality of samplers having a first input terminal for receiving the ramp voltage and a second input terminal connected to one of the plurality of column lines; and a switching circuit configured to connect the first input terminals of the samplers to each other or disconnect the first input terminals of the samplers from each other.