A method for depth map generation is disclosed, capable of generating a depth map corresponding an image signal, for the application of a 2D to 3D image transformation system. In the depth map generated by the disclosed method, each of the plural image regions of the image signal is assigned with a depth value. Besides, by means of comparing the depth map with another depth map of the earlier time point, the disclosed method can generate a modulated depth map, for assigning a depth value to each of the plural image regions of the image signal more precisely. Thus, the transformation performance and efficiency of the 2D to 3D image transformation system are hereby improved.