1. A digital halftoning method, the method comprising steps of: (a1) dividing an original image into non-overlapping blocks; (a2) comparing at least a training image and a halftone result corresponding to the training image to obtain diffused weightings of a diffused area; (a3) optimizing a class matrix with the diffused weightings of the diffused area to obtain an optimized class matrix; and (a4) processing the non-overlapping blocks by performing a dot diffusion procedure with the optimized class matrix and the diffused weightings to generate a halftone image corresponding to the original image.