In order to improve image resolution, any interpolation has to be applied. However, in general, interpolation generates smooth connections between adjacent sampling points and yields blurred edges in the interpolated image. To suppress such a blur in edges, it is desired to include any sharpening effect in the interpolating process. In this paper, we propose a sharpening method using cubic operations of the differences of pixel values. Experimental results show that this method produces sharp high resolution image which is more similar to a target image than that by any other method.