1. A method for reducing metal artifacts in computed tomography (CT), comprising: a) obtaining a sinogram reduced in size from an original sinogram; b) setting up a linear algebraic equation according to remaining data excluding data damaged by a metal based on the obtained sinogram; c) restoring a low-resolution image based on the set up linear algebraic equation; d) calculating a sinogram from the restored low-resolution image; e) restoring a sinogram by disposing the calculated sinogram data in the original sinogram and by utilizing the calculated sinogram data as pre-information; and f) restoring a final CT image from the restored sinogram.