Techniques for removing ringing artifacts from video data. A deringing
filter in accordance with the present invention preserves real image edges in a
video frame, while smoothing out the interiors of objects. In one aspect, a 9-tap
low-pass filter is applied to an adaptive processing window. The filter window
is initialized with the values in a 33 mask centered on the position whose
output is computed. Then all values that are very different from the central one
are replaced with the central value. The deringing filter varies between 33
low-pass and identity, depending on how much the central value differs from its
surrounding ones. A deblocking filter in accordance may also be suitably used in
conjunction with the deringing filter.