1. A method of displaying a preview image comprising: acquiring frames of image data by an optical sensor when there is a need to display a preview image; weighting and processing by a processor, a frame of image data currently acquired and frames of image data acquired recently for a number M of times to obtain the preview image, wherein M is a positive integer; and wherein the weighting and processing by the processor, of the frame of image data currently acquired and the frames of image data acquired recently for a number M of times to obtain the preview image comprises: determining via the processor, weights corresponding to the frame of image data currently acquired and the frames of image data acquired recently for a number M of times respectively according to a correspondence relationship between acquisition instances of time and weights; weighting and processing each frame of image data by a weight corresponding to the frame of image data; and determining the preview image according to weighted and processed frames of image data; and displaying the determined preview image on a display screen.