[FFmpeg-trac] #8590(undetermined:closed): 'telecine=pattern' error for p24, soft telecined sources
FFmpeg
trac at avcodec.org
Sun Apr 5 08:31:44 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:36 pdr0]:
> Replying to [comment:35 markfilipak]:
> > I do some technical writing. I'd appreciate your opinion of the
following
> >
> > "Twitter is when finely textured areas such as ventilation grates,
brick walls, and textured paper appear to rapidly flash on-off-on-off or
to flash changing colors. Twitter can make an actor's face appear to
pulsate during close-ups. Twitter is actually a milder case of combing,
but over an area. For uniformly patterned surfaces, twitter can produce
moire."
> >
> > I'm not sure that twitter applies to faces appearing to pulsate.
>
> The face part isn't a good example, because faces are more organic and
have curved lines and tend to hide those types of artifacts with the
exception of the eyelids (straight line).
>
> Twitter can be described in terms of sampling theory and nyquist
theorem.
I'm familiar with Dr. Nyquist: Gausian transfer of energy (analog
impulsive response) requiring 2x sampling in the digital (z-plane) domain,
etc. It's sort of the frequency analog of complex (aka imaginary) power
when sinusoidal voltage and current are out of phase due to reactive
(inductive and/or capacitive) components (which is real, so I don't use
the word "imaginary").
> 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.
> Essentially gaps in information, which are more easily identified in
things such as straight lines , and that's what twitter usually refers to
(lines, edges). In layman' s terms it looks likes jaggy buzzing lines.
(Of course you can get "jaggy buzzing lines" from other things too, such
as compression artifacts, but twitter has a characteristic look)
I believe that, except for compression artifacts, what you describe is
combing, which is a temporal artifact of the clash of interlaced field
lines from differing sample frames/times.
> > Meaning: The 24fps video you made, right? That's a good source for
testing aspects of transcoding animations, but I wonder how applicable it
is to analog movies. 5-5-5-5 seems to work wonderfully for movies. This
brings up a bushel basket of issues.
>
> Yes, it's a synthetic high contrast test, but it's still predictive of
the issues you see on real content. Real content will typically also have
motion blur, so the effect can be reduced somewhat
Well, motion blur is the human response to combing of motion objects,
especially if smoothing is applied as most TVs apply smoothing. That's the
first thing I turn off in TV setups. The second is "image enhancement"
(i.e., sharpening and contrast enhancement or active contrast or motion
enhancement, etc., whatever they call it). Basically, I flatten everything
and desaturate the picture until it portrays scenes naturally, like in a
movie theater. Then I put up a test picture and compare it with the
photograph used to make the test picture and adjust gamma & RGB gain.
> Go test it out. I can see the combing when on trying this on a BD. Yes,
certain scenes and types of content hide it well. On others it sticks out
like a sore thumb. You have a nice high quality progressive BD, and now
there is combing artifacts, sometimes everywhere, ...
Indeed, it would be everywhere in panning shots.
>... across the whole screen, not just limited to a tiny "text" area. But
it's there and you can see it. It's terrible in my opinion, even worse
than blends. It's so distracting that it ruins the viewing experience -
not a hyperbole.
>
> Some types of displays might have additional processing and decomb it,
so you might not see it. My living room TV is 120Hz, but the computer
monitor I'm testing this on is 60Hz and I have everything set to to play
progressive, no processing. It looks bad. You said you hated the judder,
so maybe it's an acceptable compromise for you
>
> > I'd like to contribute but have been frustrated.
>
> Same. Frustrated at times too...
>
> 1) Often programmers seem like a different breed...
Before I retired, I lived in/around San Jose, California for 25 years. All
my friends were programmers. To a man, they thought that ordinary people
(i.e., non-programmers) were uniformly unimaginative/stupid. To a man,
they thought that the world would be a better place if only they ruled.
Combine ego and naivity and that's what you get. Bad as the current U.S.
president is, they would be worse. I got along fine with them of course,
and we had fun, but I smiled a lot.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/8590#comment:37>
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