An image sensor operating in multiple resolution modes including a low resolution mode and a high resolution mode includes a pixel array including a plurality of pixels, wherein each pixel in the plurality of pixels comprises a micro-lens, a first subpixel including a first photodiode, a second subpixel including a second photodiode, and the first subpixel and the second subpixel are adjacently disposed and share a floating diffusion region. The image sensor also includes a row driver providing control signals to the pixel array to control performing of an auto focus (AF) function, such that performing the AF function includes performing the AF function according to pixel units in the high resolution mode and performing the AF function according to pixel group units in the low resolution mode. A resolution corresponding to the low resolution mode is equal to or less than ¼ times a resolution corresponding to the high resolution mode.