An image sensor including: a pixel array including a plurality of pixels connected to a plurality of row lines and a plurality of column lines, each of the plurality of pixels including a photodiode for generating an electric charge in response to light, and a pixel circuit having a floating diffusion for storing the electric charge; and a controller configured to adjust a capacitance of the floating diffusion to a first value and obtain a first pixel signal from the pixel circuit during a first time period, adjust the capacitance of the floating diffusion to a second value greater than the first value and obtain a second pixel signal from the pixel circuit during a second time period subsequent to the first time period, and generate a result image using the first pixel signal and the second pixel signal.