1. An image enhancing system, comprising: an image-signal-obtaining unit, for obtaining nine pieces of image signals from three lines of image signals that are inputted continuously; a first-signal-group processing unit connecting with the image-signal-obtaining unit, for processing the nine pieces of image signals into a first-group image signals; a high-pass/low-pass-image obtaining unit connecting with the first-signal-group processing unit, for obtaining a high-frequency image signal and a low-frequency image signal via a filter that is composed of high-pass filters and low-pass filters; a brightness-adjusting unit connecting with the high-pass/low-pass-image obtaining unit, for adjusting the brightness of the low-frequency image signal; a threshold unit connecting with the high-pass/low-pass-image obtaining unit, for processing the noise of the high-frequency image signal; an amplifying unit connecting with the threshold unit, for amplifying the high-frequency image signal; an adder connecting with the amplifying unit and the brightness-adjusting unit, for adding the high-frequency image signal and the low-frequency image signal that has been processed; and a normalizing unit connecting with the adder, for normalizing the results of the adder to obtain an enhanced image.