wiki:

Postprocessing


Version 6 (modified by arwa, 5 years ago) (diff)

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Post-processing filters are used in videos for quality-improvement. These filters are intended for recovering quality of videos ripped from DVD, VideoCD or after decompressing.

Following are the post-processing filters which are part of the FFmpeg project:

  1. SPP - Simple Postprocessing
  2. USPP - Ultra Simple or Slow Postprocessing
  3. FSPP - Fast Simple Postprocessing
  4. PP7 - Postprocessing 7
  5. libpostproc

These filters basically smooth away blocking and other artifacts from low quality sources.The parameter QP is chosen by the encoder used to create the video, VCD, DVD, etc. Lower QP for the encoder results in higher bitrate and higher quality encoding. If no "QP" parameter is specified by the user to the Postprocessing filter then it uses the one that is stored in the encoded file for the specific area. In particular, the quantization parameter QP regulates how much spatial detail is saved. When QP is very small, almost all that detail is retained. As QP is increased, some of that detail is aggregated so that the bit rate drops – but at the price of some increase in distortion and some loss of quality.

USPP uses an encoder, hence, should be used only when one has a powerful CPU. Also, USPP is very slow as compared to other filters. Therefore, for processing large amount of data, FSPP is a good option (It gives good results if parameters are chosen wisely).

Let's consider the example of

  1. Test sequence called "Foreman"(frame 155, compressed using Xvid with bitrate option 50, 75, 100kbs):
Query Image
benchmark1 for comparing the post-processing filters
spp=4:10 spp=6:20 spp=6:44:1
spp=4:10 spp=6:20 spp=6:44:1
fspp=4:10 fspp=4:10:5 fspp=5:44:10
fspp=4:10 fspp=4:10:5 fspp=5:44:10
pp7=10:0 pp7=20:1 pp7=42
PP7=10:0 PP7=20:1 fspp=5:44:10
  1. The standard lena 256×256 image which is saved by gimp to 10% quality.
Query Image
benchmark2 for comparing the post-processing filters
spp=5:10:0:1 spp=5:20 spp=5:40:0:1
spp=5:10:0:1 spp=5:20 spp=5:40:0:1
fspp=4:10 fspp=4:10:10 fspp=5:20
fspp=4:10 fspp=4:10:10 fspp=5:20
pp7=10:0 pp7=10:1 pp7=20
PP7=10:0 PP7=10:1 PP7=20

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