[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
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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 |
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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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