Adaptive filtering

A device for determining an adaptive filter having multiple filter parameters in the form of multiple filter taps and an optional scaling factor, said device comprising:

• a filter parameter definer configured to define at least one filter parameter of said multiple filter parameters as having a coarse level of adaptivity, for which a filter parameter value can be selected amen a first set of allowable filter parameter values, and configured to define at least one other filter parameter of said multiple filter parameters as having a fine level of adaptivity, for which a filter parameter value can be selected among a second set of allowable filter parameters, the first set of allowable filter parameter values being smaller than the second set of allowable filter parameter values;
• a first parameter determiner configured to determine a filter parameter value for said at least one filter parameter having the coarse level of adaptivity among the first set of allowable filter parameter values based on optimization of a first optimization criterion selected from the group of:
• i) minimizing complexity of a filtering operation with the adaptive filter by selecting the filter parameter value among the first set of allowable filter parameter values to limit the filtering operation to additions and/or shifts,
• ii) optimizing a frequency shape of the adaptive filter to achieve a desired lowpass filtering characteristic of the adaptive filter by selecting an adaptive scaling factor for the adaptive filter among the first set of allowable filter parameter values, and
• iii) optimizing pixel value scaling by selecting an adaptive scaling factor for the adaptive filter to be equal to a difference in or a quotient between an average value of at least one original pixel block in a current frame of an image or video sequence and an average value of at least one reference pixel block in a reference frame of the image or video sequence;
• wherein optimizing the first optimization criterion includes selecting the filter parameter value for the at least one filter parameter from the first set of allowable filter parameter values that optimizes the first optimization criterion;
• and
• a second filter parameter determiner for determining configured to determine a filter parameter value for said at least one filter tap having the fine level of adaptivity among the second set of allowable filter parameter values, based on optimization of a second, different optimization criterion that minimizes a prediction error between an original pixel block of the current frame and the at least one reference block of the reference frame filtered with the adaptive filter;
• wherein optimizing the second optimization criterion involves selecting the filter parameter value for the at least one filter parameter from the second set of allowable filter parameter values that optimizes the second optimization criterion.