A method and apparatus is provided for interpolating a digital image in response to a requested degree of sharpness. An adjusting signal representing the requested degree of sharpness will then be generated. The interpolated pixel data are computed based on a 3 order or 4 order interpolation function for three sampling input pixels with an adjustable weight coefficient representing the selected degree of sharpness. The apparatus of the present invention mainly includes: a control interface, a control unit, a vertical interpolation computation module, and a horizontal interpolation module. The vertical interpolation computation module and the horizontal interpolation module are implemented according to an interpolation function derived by the present invention. The control unit comprises a lookup table built according to a scaling function of the present invention. The vertical scaling factor and the horizontal scaling factor required for the interpolation function can be obtained by looking up the lookup table according to the adjusting signal, and the position of the interpolated pixel. Accordingly, the present invention can control the degree of sharpness without having to implement an additional sharp control circuit.