[FFmpeg-trac] #8590(undetermined:closed): 'telecine=pattern' error for p24, soft telecined sources

FFmpeg trac at avcodec.org
Mon Apr 6 04:36:09 EEST 2020


#8590: 'telecine=pattern' error for p24, soft telecined sources
-------------------------------------+-------------------------------------
             Reporter:  markfilipak  |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:  invalid
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by markfilipak):

 Replying to [comment:38 pdr0]:
 > Replying to [comment:37 markfilipak]:
 > >
 > >
 > > > It's aliasing artifacts, when viewed in motion. It boils down to
 undersampling.
 > >
 > > Well, undersampling should produce image fade (amplitude loss due to
 insufficent energy transfer), not aliasing.
 > >
 >
 > It's undersampling in the most simple sense.  That is what interlace is:
 Spatial undersampling, ...

 I hesitate to take more of your time, but you seem to want to continue and
 that's fine with me. Exploration is fun, and we seem to have a private
 channel in this closed ticket.

 Undersampling is really a vague term, isn't it? Is sampling film at a
 lower resolution than half the size of a silver halide grain
 undersampling? Or is undersampling resampling a digital image (or audio
 stream) at less than twice the frequency (or half the area) of the
 original samples. Dr. Nyquist would say that they are both "undersampled".

 Answer for yourself: Is dividing a picture into 2 half-pictures really
 undersampling? Is it really sampling at all?

 >... but full temporal sampling. ...

 Full temporal sampling? Life doesn't pass in 1/24th second increments.
 Film and video both undersample life. But of course that's not what you
 mean. :)

 What you mean is that transcoding a 24fps stream to anything less than
 48fps is temporal subsampling, and in that, Dr. Nyquist and I would both
 agree with you.

 When you say that that transcoding 24fps to 24fps is not subsampling but
 merely dividing a picture into half-pictures is subsampling, are you being
 consistent?

 >... Each field has half the spatial information of a full progressive
 frame. ...

 Does that make it subsampling?

 Before CCDs, when a 35mm Academy format film frame was sampled, it was
 'snapped' through a flying spot apperture
  29x27 µm for 576-line SD
  29x33 µm for 480-line SD
  14.5x14.5 µm for HD (2K)
 Merely dividing those samples into odd and even numbered lines of pixels
 without changing the area of the samples (µm)... Is that really
 subsampling?

 >...  A straight line becomes jagged dotted line when deinterlaced,
 because that field is resized to a full sized frame and only 50% the line
 samples are present. ...

 Now, I'm sure you know that fields -- I prefer to call them "half-
 pictures" -- aren't converted to frames without first reinterlacing -- I
 prefer to call it "reweaving" -- the half-picture-pairs to reconstruct the
 original pictures. And I'm sure you know that the only way a reconstructed
 picture has a jagged line is if the original film frame had a jagged line.

 So I assume that what you are describing is bobbing. But bobbing isn't
 undersampling either. If anything, bobbing is underdisplaying, don't you
 agree?

 >... That line information is undersampled.  In motion, those lines appear
 to "twitter". Higher quality deinterlacing algorithms attempt to
 adaptively fill in the gaps and smooth everything over, so it appears as
 if it was a true progressive frame.

 My opinion is that deinterlacing algorithms should reweave the half-
 picture lines and nothing more. A user can insert more filters if more
 processing is desired, but trying to work around 'mystery' behavior of
 filters that do more than you think they do is crazy making.

 > As motioned earlier, there are other causes, but low quality
 deinterlacing is the most common.  Other common ones are pixel binning ...

 You know, I've run across that term maybe once or twice... I don't know
 what it means.

 >... or sampling every nth pixel. Eg. large sensor DSLR's when shooting
 video mode.

 Is that undersampling or simply insufficient resolution?

 You see, a word like "undersampling" can become so broad that it's utility
 as a word is lost.



 I will continue my responses, but I have to reboot now because the
 javascript at the Johns Hospital COVID-19 site is causing problems with my
 browser. I'm surprised this window survived.

 By the way, if you exclude COVID-19 cases that are on-going and consider
 only cases that have been resolved (recovered plus fatal), over 20% of the
 people who get COVID-19 die.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8590#comment:39>
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