1. A digital image processing device comprising: an image storage device for storing an interested pixel and its plural neighboring pixels; and a processor electrically coupled with the image storage device for processing the interested pixel and its plural neighboring pixels, wherein the digital image processing device uses the processor to: calculate a first gradient value of a first direction of the interested pixel and its plural neighboring pixels and a second gradient value of a second direction of the interested pixel and its plural neighboring pixels, wherein the first direction is orthogonal to the second direction; determine whether an absolute value of a difference between the first gradient value of the first direction and the second gradient value of the second direction is larger than a first pre-determined threshold value; if so, it means that the interested pixel has an obvious image border, then execute a sharpness adjustment to the interested pixel along the direction which has larger gradient value; and execute a smoothing adjustment along the direction which has smaller gradient value.