A digital image processing system (134) receives a signal S(x,y,t,c) where (x,y) are pixel coordinates, t is time, and c is a color component. The system generates the signal S*(x,y,t,c) as a function of a linear combination of the values S(x',y',t',c) over a set A of points (x',y',t') with plural values (x',y') and plural values t', wherein each value S(x',y',t',c) in the linear combination is multiplied by a coefficient which is a function of the difference S(x,y,t,c)-S(x',y',t',c). In some embodiments, one or more of the values S(x',y',t',c) are replaced with previously calculated values S*(x',y',t',c) to save memory.