Provided is an operation method of an image sensor including a plurality of pixels, the operation method including transmitting a first output voltage of a first pixel to a first amplifier, transmitting the first output voltage to a second amplifier by controlling a first switch connected to the first pixel, transmitting a second output voltage of a second pixel to be binned with the first pixel to the second amplifier by controlling a second switch connected to the second pixel, and outputting selectively one of a first output of the first amplifier and a second output of the second amplifier based on an illuminance of an environment in which the image sensor operates.