Changes between Initial Version and Version 1 of Postprocessing


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Timestamp:
Jan 11, 2015, 7:40:19 PM (4 years ago)
Author:
arwa
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  • Postprocessing

    v1 v1  
     1Post-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.
     2
     3Following sections contain various post-processing filters which are part of the FFmpeg project.
     4
     5== '''SPP - Simple Postprocessing''' ==
     6
     7Simple Post-proceesing filter compresses and decompresses the image at several (or - in the case of quality level 6 - all) shifts and average the results. The options available are -
     8
     9=== Quality ===
     10
     11This option defines the number of levels for averaging. It accepts an integer in the range 0-6. If set to 0, the filter will have no effect. A value of 6 represents highest quality. For each increment of that value the speed drops by a factor of approximately 2. Default value is 3.
     12
     13The filter basically smooths away blocking and other artifacts from low quality sources. The further you increment the value of quality, the more intensely it smooths away detail.
     14
     15=== QP ===
     16
     17Force a constant quantization parameter. It accepts an integer in range 0-63. If not set, the filter will use the QP from the video stream (if available).
     18
     19In 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. So, if you want to lower bit rate, you can do so by lowering QP at a cost of increased distortion.
     20
     21=== Mode ===
     22
     23To set the thresholding mode. Available modes are:
     24
     25==== ‘hard’ ====
     26For hard thresholding - default.
     27
     28==== ‘soft’ ====
     29For soft thresholding - better de-ringing effect but the results are blurrier when compared to the default mode.
     30
     31
     32=== use_bframe_qp ===
     33Enable the use of the QP from the B-Frames if set to 1. Using this option may cause flicker since the B-Frames have often larger QP. Default is 0 (not enabled).
     34
     35Let's consider the example of test sequence called "Foreman"(frame 155, compressed using Xvid with bitrate option 50, 75, 100kbs):
     36
     37[[Image(spp.png)]]
     38
     39
     40== '''USPP - Ultra Simple/Slow Postprocessing''' ==
     41
     42Ultra slow/simple postprocessing filter compresses and decompresses the image at several (or - in the case of quality level 8 - all) shifts and average the results.
     43
     44The way this differs from the behavior of spp is that uspp actually encodes & decodes each case with libavcodec Snow, whereas spp uses a simplified intra only 8x8 DCT similar to MJPEG. So, you should use USPP if and only if your CPU is powerful.
     45
     46The filter accepts the following options:
     47
     48=== Quality ===
     49
     50This option defines the number of levels for averaging. It accepts an integer in the range 0-8. If set to 0, the filter will have no effect. A value of 8 represents highest quality. For each increment of that value the speed drops by a factor of approximately 2. Default value is 3.
     51
     52The filter basically smooths away blocking and other artifacts from low quality sources. The further you increment the value of quality, the more intensely it smooths away detail.
     53
     54=== QP ===
     55
     56Force a constant quantization parameter. It accepts an integer in range 0-63. If not set, the filter will use the QP from the video stream (if available).
     57
     58In 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. So, if you want to lower bit rate, you can do so by lowering QP at a cost of increased distortion.
     59
     60
     61--------------------------Images-------------------------
     62
     63
     64== '''FSPP - Fast Simple Postprocessing''' ==
     65
     66FSPP is a faster version of SPP. The processing is performed on groups of pixels, instead of individual pixels, making computation faster. The filter accepts the following options:
     67
     68=== Quality ===
     69
     70This option defines the number of levels for averaging. It accepts an integer in the range 4-5. Default value is 4.
     71
     72The filter basically smooths away blocking and other artifacts from low quality sources. The further you increment the value of quality, the more intensely it smooths away detail.
     73
     74=== QP ===
     75
     76Force a constant quantization parameter. It accepts an integer in range 0-63. If not set, the filter will use the QP from the video stream (if available).
     77
     78In 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. So, if you want to lower bit rate, you can do so by lowering QP at a cost of increased distortion.
     79
     80
     81=== Strength ===
     82
     83To set the filter strength. It accepts an integer in range -15 to 32. Lower values mean more details but also more artifacts, while higher values make the image smoother but also blurrier. Default value is 0 (PSNR optimal).
     84
     85=== use_bframe_qp ===
     86
     87Enable the use of the QP from the B-Frames if set to 1. Using this option may cause flicker since the B-Frames have often larger QP. Default is 0 (not enabled).
     88
     89Let's consider the example of test sequence called "Foreman"(frame 155, compressed using Xvid with bitrate option 50, 75, 100kbs):
     90
     91[[Image(fspp.png)]]
     92
     93
     94
     95== '''PP7 - Postprocessing 7''' ==
     96
     97PP7 is variant of the SPP filter. It is similar to SPP = 6 with 7 point DCT, where only the center sample is used after IDCT.
     98
     99The filter accepts the following options:
     100
     101=== QP ===
     102
     103Force a constant quantization parameter. It accepts an integer in range 0-63. If not set, the filter will use the QP from the video stream (if available).
     104
     105In 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. So, if you want to lower bit rate, you can do so by lowering QP at a cost of increased distortion.
     106
     107=== Mode ===
     108
     109To set the thresholding mode. Available modes are:
     110
     111==== ‘hard’ ====
     112For hard thresholding.
     113
     114==== ‘soft’ ====
     115For soft thresholding - better de-ringing effect but the results are blurrier when compared to the default mode.
     116
     117==== ‘medium' ====
     118For medium thresholding. Gives good results. This is the default mode.
     119
     120Let's consider the example of test sequence called "Foreman"(frame 155, compressed using Xvid with bitrate option 50, 75, 100kbs):
     121
     122[[Image(pp7.png)]]