Noise suppression in image signals

A multilevel nonlinear filter in a HD-MAC decoder, for performing intra-frame filtering corresponding to a post processing, and for performing a progressive scan conversion using edge information includes a delay unit for delaying an input image signal and providing both 1H- and 2H-delayed signals, an edge level estimation signal generating unit for generating first and second window mask data from the input image signal and the delayed signals, and performing a high-speed bubble sort for the generated first and second window mask data, thereby providing first and second estimation signals, an absolute difference signal generating unit for generating an absolute difference signal, an edge detection unit for comparing the output absolute difference signal with a predetermined threshold value, thereby producing edge detection information on a current pixel, and a noise suppression unit for median-filtering the first and second estimation signals and the information on the current pixel in case of edge detection information, and averaging-filtering the first and second estimation signals in case of non-edge detection information, thereby providing a filtered signal.