An image sensor operates in a base mode according to a first sampling rate and a first pixel exposure time and includes a light condition detector that extracts illuminance information from a pixel signal received from pixels in a pixel array, and generates a low-illuminance information signal upon detecting that a value of the illuminance information falls within a first range, a sampling controller that changes the first sampling rate to a second sampling rate in response to the low-illuminance information signal, and an exposure time controller that changes the first pixel exposure time to a second pixel exposure time in response to the low-illuminance information signal.