A digital double sampling method, a related complementary metal oxide semiconductor (CMOS) image sensor, and a digital camera comprising the CMOS image sensor are disclosed. The method includes generating first digital data corresponding to an initial voltage level apparent in a pixel in response to a reset signal, inverting the first digital data, outputting a detection voltage corresponding to image data received from outside of the CMOS image sensor, and counting in synchronization with a clock signal, starting from an initial value equal to the inverted first digital data, and for an amount of time responsive to a voltage level of the detection voltage.