An image sensor is provided. The image sensor includes a counting code generator configured to generate a counting code, a pixel array including at least one pixel, a correlated double sampling (CDS) circuit configured to compare a magnitude of a pixel signal output from the at least one pixel with a magnitude of a ramp signal and to output a corresponding comparison signal, a pulse generator configured to generate a pulse signal synchronized with a first clock signal based on the comparison signal, and a counter circuit configured to latch a value of the counting code to correspond to a transition of a level of the comparison signal based on the pulse signal.