An image sensor includes: a pixel of a first tab; a pixel of a second tab; an operation amplifier suitable for comparing, in a comparison operation, a pixel signal of the first tab and a pixel signal of the second tab with each other to produce a comparison result, receiving, in an auto-zeroing operation, a ramp voltage and a selected pixel signal which is selected based on the comparison result between the pixel signal of the first tab and the pixel signal of the second tab, and receiving, in an analog-to-digital conversion operation, the ramp voltage and an unselected pixel signal which is not selected from the pixel signal of the first tab and the second pixel signal of the second tab; and a counter circuit suitable for generating a digital code based on an output of the operation amplifier.