1. A method for adaptive frame averaging, comprising: dividing a current frame image into a plurality of sub-blocks; obtaining a characteristic for each of the plurality of sub-blocks to obtain a characteristic image of the current frame image; determining a frame averaging coefficient for each of the plurality of sub-blocks based on the characteristic image of the current frame image and a characteristic image of a previous frame image; and frame-averaging a resultant frame-averaged image of the previous frame image and the current frame image by using the frame averaging coefficient of each of the plurality of sub-blocks to obtain a resultant frame-averaged image of the current frame image.