Image sensors and methods of operating the image sensors are provided. The image sensors may include a pixel configured to generate an image signal in response to light incident on the pixel. The pixel may include a charge collection circuit configured to collect charges, which are produced by the light incident on the pixel, during a sensing period and a floating diffusion region. The image sensor may further include a storage unit configured to store the charges and, during a transfer period after the sensing period, configured to transfer at least a portion of the charges to the floating diffusion region. An amount of charges that is transferred from the storage unit to the floating diffusion region may be controlled by a voltage level of a storage control signal that is applied to a storage control terminal of the storage unit.