A method, apparatus, and article of manufacture for restoring a deteriorated signal to an undeteriorated signal. A deteriorated signal consists of a plurality of deteriorated and undeteriorated data points. For each deteriorated data point, a plurality of class types is created based upon characteristics of the area containing the deteriorated data point. The data point is classified with respect to one of the plurality of class types and assigned a corresponding input signal class. The undeteriorated signal is generated by adaptively filtering the deteriorated input signal in accordance with the input signal classification result. More than one classification method is used to create the plurality of class types. The deteriorated input signal is modified by preprocessing peripheral erroneous data.