postfiltering

Postfiltering is a processing step applied after an initial estimation, reconstruction, or encoding stage to reduce residual artifacts and improve the quality of the final signal or image. It relies on models of the likely true signal and of the residual distortion to selectively attenuate unwanted components while preserving essential information. Postfiltering is widely used across domains where early processing can introduce artifacts, such as audio, image and video, and communications systems.

In audio and speech processing, a postfilter may follow a decoder or vocoder to suppress residual noise, reduce spectral artifacts, and emphasize perceptually important features such as formants. In image and video processing, postfilters are used after compression or rendering to reduce blocking, ringing, and other artifacts; common examples include deblocking and deringing filters, as well as edge-preserving smoothing. In communications and signal estimation, postfiltering can refine a reconstructed signal by adapting to estimated noise statistics or by enforcing known signal constraints.

Common approaches include adaptive filtering, spectral shaping, non-linear masking, and Wiener-like or maximum-a-posteriori methods that weigh suppression against signal preservation. The design balances artifact removal with fidelity and introduces latency and computational cost, making real-time or low-power applications a key concern. The effectiveness of postfiltering depends on accurate models of the signal and noise, as well as on the degree to which artifacts remain after the initial stage.