An image sensor includes a pixel array including a plurality of pixels which are arranged in a matrix of a plurality of rows and columns and each of the plurality of pixels being configured to convert intensity of incident light into an electrical image signal; and an extended counting analog-to-digital converter configured to perform a first analog-to-digital conversion to provide a digital signal from an output signal of the pixel array, to obtain a residue using the output signal of the pixel array and the digital signal, and to perform a second analog-to-digital conversion using the residue.