1. A method of estimating depths on a monocular image displayed on a display, comprising: transforming grey levels of a monocular image from a first color field to a second color field, which is indicated by an intensity channel and two color channels; segmenting the monocular image into a plurality of patches; calculating a feature vector for each of the plurality of patches according to a serial of filters whose output combined with their square energies form the feature vector; determining an intermediate depth map of the monocular image according to the calculated feature vector of each of the plurality of patches; and determining an output depth map according to an equation (L+λU)d=λd p ; wherein λ is a normalized parameter, U indicates an identity matrix, d p indicates the intermediate depth map, d indicates the output depth map, and L is a matting Laplacian matrix.