A first image and a second image of an object taken with different viewing directions are received. The first image and the second image are downscaled in a ratio of a downscale factor DF to generate a first downscaled image and a second downscaled image, respectively. An edge map is generated by detecting an edge pixel from the first downscaled image. An initial cost volume matrix is generated from the first downscaled image and the second downscaled image according to the edge map. An initial disparity estimate is generated from the initial cost volume matrix. The initial disparity estimate is refined using the initial disparity estimate to generate a final disparity set. A depth map is generated from the first image and the second image using the final disparity set.