postfilters

Postfilters are filters applied after a primary processing stage to improve perceived quality by reducing artifacts, noise, or distortion that remain after encoding, transformation, or decoding. They are used across audio, video, and image pipelines to enhance clarity without redoing core processing.

In audio and speech processing, postfilters are often integrated into decoders to suppress residual noise, emphasize important spectral bands, and mitigate artifacts introduced by compression. They may be adaptive, leveraging estimates of the signal and noise spectra to balance noise reduction with preservation of intelligibility and transients. Some postfilters operate in the spectral domain, while others use time-domain smoothing or a combination of both.

In video and image processing, post-filtering follows the main decoding or reconstruction step to reduce blocking, ringing, and other compression artifacts. Techniques include deblocking and deringing filters, as well as edge-preserving spatial filters and temporal smoothing that minimize flicker across frames. Postfilters may be tailored to specific codecs or display pipelines and can be designed to preserve details while suppressing artifacts.

Common design characteristics include adaptivity to local signal statistics, a balance between artifact suppression and detail preservation, and manageable computational cost for real-time applications. Latency and potential over-smoothing are key considerations, as overzealous filtering can blur important features or transient details.

Overall, postfilters complement core processing by targeting residual imperfections, contributing to higher perceived quality without requiring changes to the primary encoding or reconstruction strategies. See also deblocking, denoising, and artifact reduction.