An exemplary auto white balance system for an image sensor includes a global positioning system (GPS) receiver, a memory, a setting determining unit, and a white balance unit. The GPS receiver is configured for receiving signals from a satellite, and calculating its position and local time using signals received from at least four satellites. The memory is configured for storing a number of white balance settings. The setting determining unit is configured for determining which one of the white balance settings is suitable for the current ambient light conditions based on the received signal of the global positioning system receiver. The white balance unit is configured for adjusting the color temperature of a current image captured by the image sensor using the determined white balance setting.