An image sensor, including a pixel array including a plurality of pixels connected to row lines extending in a first direction and column lines extending in a second direction intersecting the first direction; a ramp voltage generator configured to output a ramp voltage; a sampling circuit including a plurality of comparators, each comparator of the plurality of comparators having a first input terminal connected to a column of the column lines and a second input terminal configured to receive the ramp voltage; and an analog-to-digital converter configured to convert an output of the plurality of comparators to a digital signal, wherein the plurality of comparators include a first comparator connected to a first column line, and a second comparator connected to a second column line adjacent to the first column line in the first direction, wherein each of the first comparator and the second comparator includes a first transistor and a second transistor disposed sequentially in the second direction, and wherein a gap between the first transistor of the first comparator and the second transistor of the first comparator is different from a gap between the first transistor of the second comparator and the second transistor of the second comparator.