[FFmpeg-trac] #4304(avfilter:new): Add Spatial Information (SI) / Temporal Informatilon (SI) filter according to ITU-T P.910

[FFmpeg]

#4304: Add Spatial Information (SI) / Temporal Informatilon (SI) filter according
to ITU-T P.910
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             Reporter:  slhck     |                     Type:  enhancement
               Status:  new       |                 Priority:  wish
            Component:  avfilter  |                  Version:  unspecified
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 ITU-T P.910 ("Subjective video quality assessment methods for multimedia
 applications") specifies two metrics that can be used to classify content:

 == Spatial information ==

 According to P.910:

   The spatial perceptual information (SI) is based on the Sobel filter.
 Each video frame (luminance plane) at time n (Fn) is first filtered with
 the Sobel filter [Sobel(Fn)]. The standard deviation over the pixels
 (stdspace) in each Sobel-filtered frame is then computed. This operation
 is repeated for each frame in the video sequence and results in a time
 series of spatial information of the scene. The maximum value in the time
 series (maxtime) is chosen to represent the spatial information content of
 the scene.

 == Temporal information ==

 According to P.910:

  The temporal perceptual information (TI) is based upon the motion
 difference feature, Mn(i, j), which is the difference between the pixel
 values (of the luminance plane) at the same location in space but at
 successive times or frames. Mn(i, j) as a function of time (n) is defined
 as:

  [[Image(http://i.imgur.com/MRsJtdT.png)]]

  here Fn(i, j) is the pixel at the ith row and jth column of nth frame in
 time.
  The measure of temporal information (TI) is computed as the maximum over
 time (maxtime) of the standard deviation over space (stdspace) of Mn(i, j)
 over all i and j.

  [[Image(http://i.imgur.com/zRXcVJO.png)]]

  More motion in adjacent frames will result in higher values of TI.


 == What should be implemented ==

 There should be a `siti` filter which outputs:

 * The SI value for each frame
 * Summary SI statistics (mean, min, max, median) for the sequence
 * The TI value for the sequence

 It requires no output video and would just print to the console.

 (This feature request serves as a reference for me and others; I might
 implement it some day, maybe when filter kernels are implemented.)

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Ticket URL: <https://trac.ffmpeg.org/ticket/4304>
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