[FFmpeg-trac] #9068(documentation:new): Smartblur filter: inccorct naming variance vs. standard deviation

[FFmpeg]

#9068: Smartblur filter: inccorct naming variance vs. standard deviation
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             Reporter:  simgro       |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  documentation                      |  unspecified
             Keywords:  smartblur,   |               Blocked By:
  gaussian, variance                 |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 Summary:
 The Documentation for smartblur filter  states (https://ffmpeg.org/ffmpeg-
 filters.html#smartblur-1):
 luma_radius, lr: ... specifies the variance of the gaussian filter used to
 blur the image.

 This is not correct. From how the parameter is used, it is not the
 variance but the standard deviation of the gaussian filter (variance=std-
 deviation^2).

 As far as i can see, the naming error is actually inside the used function
 sws_getGaussianVec (https://svn.ffmpeg.org/doxygen/0.8
 /libswscale_2utils_8c-source.html#l01272 ) which has an input called
 'variance' which is used as if it was the 'standard deviation' in line
 01284:
 vec->coeff[i]= exp(-dist*dist/(2*variance*variance)) /
 sqrt(2*variance*M_PI);
 For reference, see e.g., https://en.wikipedia.org/wiki/Gaussian_function

 Possible solution:
 It might be best to change the documentation such that it correctly ready
 'standard deviation'. To avoid confusion, also replace the name of the
 variable in the sws_getGaussianVec function. The documentation potentially
 has this error whenever the sws_getGaussianVec function is valled by some
 filter.

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Ticket URL: <https://trac.ffmpeg.org/ticket/9068>
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