Changes between Version 6 and Version 7 of Postprocessing


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Timestamp:
Jan 20, 2015, 10:46:12 AM (12 years ago)
Author:
Stefano Sabatini
Comment:

apply misc edits, extend and clarify

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  • Postprocessing

    v6 v7  
    1 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.
     1Post-processing filters are used in videos for quality-improvement. They are especially relevant for filtering video material encoded with low-quality, as they allow to remove the more common encoding artifacts (e.g. blocking and ringing).
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    3 Following are the post-processing filters which are part of the FFmpeg project:
     3These filters are intended for recovering quality of videos ripped from DVD, VideoCD or after decompressing.
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    5 1. SPP - Simple Postprocessing
    6 2. USPP - Ultra Simple or Slow Postprocessing
    7 3. FSPP - Fast Simple Postprocessing
    8 4. PP7 - Postprocessing 7
    9 5. libpostproc
     5FFmpeg includes the following post-processing filters:
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    11 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.
     7* {{{spp}}} - Simple Postprocessing
     8* {{{uspp}}} - Ultra Simple or Slow Postprocessing
     9* {{{fspp}}} - Fast Simple Postprocessing
     10* {{{pp7}}} - Postprocessing 7
     11* {{{pp}}} - libpostproc wrapper
    1212
    13 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).
     13These filters basically smooth away blocking and other artifacts from low quality sources. The QP parameter 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 postprocessing filter 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 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.
     14
     15{{{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).
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     17Postprocessing filters can be used on the {{{ffmpeg}}} commandline like this:
     18{{{
     19ffmpeg -i INPUT ... -vf PP OUTPUT
     20}}}
     21
     22or can be used to playback the input with {{{ffplay}}} like this:
     23{{{
     24ffplay INPUT -vf PP
     25}}}
     26
     27where PP is the postprocessing filter with its parameters.
     28
     29When using postprocessing filters before encoding, keep in mind that even if encoding artifacts will be removed by the filter, new artifacts will be added by the new encoding. In some cases the postprocessing filters though will increase the visual quality (or even reduce the encoding output size).
    1430
    1531Let's consider the example of
    … …  
    17331. Test sequence called "Foreman"(frame 155, compressed using Xvid with bitrate option 50, 75, 100kbs):
    1834
    19 || ||= Query Image =|| ||
     35|| ||= Reference Image =|| ||
    2036|| || [[Image(0.jpg)]] || ||
    2137||= spp=4:10 =||= spp=6:20 =||= spp=6:44:1 =||
    … …  
    28442. The standard lena 256×256 image which is saved by gimp to 10% quality.
    2945
    30 || ||= Query Image =|| ||
     46|| ||= Reference Image =|| ||
    3147|| || [[Image(lena.jpg)]] || ||
    3248||= spp=5:10:0:1 =||= spp=5:20 =||= spp=5:40:0:1 =||
    … …  
    3652||= pp7=10:0 =||= pp7=10:1 =||= pp7=20 =||
    3753|| [[Image(lena_41.jpg)]] || [[Image(lena_42.jpg)]] || [[Image(lena_43.jpg)]] ||
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