An electronic device is provided and includes an image sensor including a first unit pixel including a first micro-lens and a plurality of first photodiodes facing each other with a first color filter interposed between the plurality of first photodiodes, and a second unit pixel including a second micro-lens and a plurality of second photodiodes facing each other with a second color filter interposed between the plurality of second photodiodes, a camera module including the image sensor, and a processor operatively connected with the image sensor. The first unit pixel includes a first photodiode, a second photodiode, a third photodiode, and a fourth photodiode, which are disposed in a square shape such that a horizontal number of photodiodes is identical to a vertical number of photodiodes. The second unit pixel includes a fifth photodiode, a sixth photodiode, a seventh photodiode, and an eighth photodiode, which are disposed in a square shape such that a horizontal number of photodiodes is identical to a vertical number of photodiodes. The image sensor identifies an operation setting and an external environmental condition of the camera module and, upon identifying that the operation setting is a preview mode and the external environmental condition is a high luminous environment, identifies a first area signal corresponding to a signal of the first photodiode and the second photodiode, which are concatenated with each other and included in the first unit pixel, and identifies a second area signal that corresponds to a signal of the fifth photodiode, included in the second unit pixel, corresponding to a location of the first photodiode and the sixth photodiode, included in the second unit pixel, corresponding to a location of the second photodiode, and forms first auto focus (AF) information based on the first area signal and the second area signal.