1. A focus enhancing method for a portrait in a digital image, comprising: a foreground definition procedure, for computing a face position in the digital image by using a face detection technique, locating a position of a face feature according to the face position by using a feature detection, correcting the face feature according to the detected skin color by using a skin detection technique to define a head region, computing a portrait including the head region and a body region by using a dimension scale of the body region and the head region, and using the portrait as a foreground of the digital image; a foreground and background segmentation procedure, for cutting an image other than the foreground from the digital image by using a graph cutting technique, and using the result as a background of the digital image; and a foreground and background blending procedure, for blurring the background, feathering a transition region that couples the foreground and the background, such that the transition region has a smoother and more natural image, and blending the foreground, the transition region and the background to form a new digital image with a prominent portrait.