An image sensor includes a photosensitive element that generates an electrical signal corresponding to light incident thereon and a ramp signal generator that generates a ramp signal. Generation of the ramp signal is initiated in response to activation of a ramp enable signal. An offset adjusting circuit generates a counter enable signal after activation of the ramp enable signal and after initiating generation of the ramp signal. A counter initiates counting responsive to generation of the counter enable signal. A latch latches a counter output responsive to a comparison of the ramp signal and the electrical signal corresponding to light incident on the photosensitive element. Related methods are also discussed.