An image sensor includes a pixel array that includes a first pixel group and a second pixel group, each including a plurality of image pixels to generate image data. The first pixel group includes a first phase detection pixel pair including first phase detection pixels arranged adjacent to each other in a first direction and having at least one first microlens thereon, and the second pixel group includes a second phase detection pixel pair including second phase detection pixels arranged adjacent to each other in a second direction different from the first direction and having at least one second microlens thereon. The sensitivity of the first phase detection pixels is different from the sensitivity of the second phase detection pixels.