A method of estimating depths on a monocular image displayed on a display is utilized for improving correctness of depths shown on the display. Feature vectors are calculated for each patch on the monocular image for determining an intermediate depth map of the monocular image in advance. For improving the correctness of the intermediate depth map, an energy function in forms of vectors is minimized for calculating a best solution of the depth map of the monocular image. Therefore, the display may display the monocular image according to a calculated output depth map for having an observer of the display to correctly perceive depths on the monocular image.