Image sensors including pixel groups and electronic devices including image sensors

An image sensor includes first photodiodes sharing a first node that is connected to a first capacitor, second photodiodes sharing a second node that is connected to a second capacitor, a common transistor configured to selectively connect a third node to a pixel voltage node, the third node connected to a third capacitor, a first reset transistor that may selectively connect the first node to the third node, and a second reset transistor that may selectively connect the second node to the third node. The first reset transistor and the second reset transistor may electrically connect the first node, the second node, and the third node to each other according to an operation of the first reset transistor and the second reset transistor. The common transistor is configured to reset the third node to the pixel voltage according to an operation of the common transistor.