Disclosed is an image sensor. The image sensor according to an embodiment of the invention comprises: at least one active pixel and at least one line-optical black (L-OB) pixel arranged in a matrix formation including first through n^th rows and first through m^th columns; a pixel array which outputs pixel signals and dark level offset signals for columns during a readout process on at least one of the first through n^th rows; a row driver which outputs a selection control signal for the first through n^th rows; and an analog to digital converter (ADC) block which converts the pixel signal and the dark level offset signal to a digital format, wherein the pixel array simultaneously outputs dark level offset signals for L-OB pixels included in another row during the readout process on at least one of the first through n^th rows, and n and m are integers greater than or equal to two. By using the image sensor according to an embodiment of the invention, the number of L-OB pixels contributing to the readout process on one of the rows is boosted without increase of the size of a pixel array, such that pixel specific noises are efficiently reduced.
