Post- and pre-processing in coding of image sequences using filters with motion compensated history

To increase the performance of image coding of sequences it is beneficial to apply temporal prefiltering before coding to increase redundancy. To reduce the subjective impact of coding artifacts also temporal postfiltering can be applied after decoding. A problem with both of these techniques however (and of the more general techniques of image sequence enhancement using temporal filters) is that severe distortion may appear in moving objects. The author presents a method to avoid these artifacts of temporal filtering by introducing movement compensated temporal filtering. This technique yields an anisotropic, non-stationary 3-dimensional transfer function, which locally `tracks´ moving objects. The effect is that the problem of unsharp moving objects is significantly reduced, which allows for much lower cut-off frequencies than stationary filters do. The approach works both with FIR- and IIR-type filters. If a linear phase FIR filter is used for postfiltering, combined with a sampling rate increase, it can be seen as a motion compensated interpolator