“…During the past few decades, many intelligent methods have been proposed to improve single-image denoising performance. From pixel level filtering methods, such as Gaussian filtering [1], bilateral filtering, and total variation regularization [2], to patch based filtering methods, such as non-local means [3], block-matching 3D filtering (BM3D) [4], and sparse representation [5], single-image based denoising performance has been greatly improved, with image details well recovered when the image is slightly noisy. As such filtering methods are widely used in computer vision, work has considered how to speed them up, e.g., for the bilateral filter [6] and weighted median [7].…”