US Patent 7254277 Image processing with minimization of ringing artifacts and noise

A method of reducing ringing artifacts in image data that has been filtered with a high frequency emphasis filter. For each filtered data value, a local variance is calculated from data values at neighboring filter taps. This variance is compared to a threshold, and if the threshold is exceeded, the filtered data value is limited between local minimum and maximum values. A method of reducing noise, also using the local variance, is also described.