A pixel array in an image sensor includes a first pixel group. The first pixel group includes unit pixels that include photoelectric conversion units and a first signal generation unit shared by the photoelectric conversion units. The first signal generation unit includes transfer transistors connected to the photoelectric conversion units, respectively, a first floating diffusion node connected to the transfer transistors, a plurality of driving transistors connected to the first floating diffusion node and connected in parallel with one another, and a plurality of selection transistors connected in parallel between a first output terminal and the plurality of driving transistors. The first output terminal outputs pixel signals that correspond to photo charges collected by the photoelectric conversion units, respectively. A number of the plurality of selection transistors is equal to a number of the plurality of driving transistors.