1. A method of shoot suppression of an image signal, comprising: reducing edge transition time of an original image signal to form a transient-improved image signal; determining whether each edge of the transient-improved image signal is locally an overshoot or an undershoot; and filtering an overshoot or an undershoot at an edge of the transient-improved image signal by using a local maximum or minimum value around an edge of the original image as a local maximum or minimum value of the original image when it is determined that an edge of the transient-improved image signal is locally an overshoot or an undershoot.