Image sensor and operating method thereof

An image sensor includes a pixel array including a plurality of pixels arranged in a matrix, each of the pixels including a microlens, a first photoelectric conversion element, and a second photoelectric conversion element, the first and second photoelectric conversion elements being arranged parallel with each other in a first direction below the microlens; and a row decoder configured to control a first image signal generated by the first photoelectric conversion element and a sum image signal generated by the first and second photoelectric conversion elements to be sequentially output from a first pixel in a first row of the pixel array during a first readout period, and to control a second image signal generated by the second photoelectric conversion element and the sum image signal to be sequentially output from a second pixel in a second row of the pixel array during a second readout period.