In comp.sys.raspberry-pi, Ahem A Rivet's Shot   wrote:
> Axel Berger  wrote:
>> Exactly. And there is another thing. Originally video had to be fast,
>> for the eye needed at least 70 Hz not to see annnoying flicker. Those
>  That number seems to have been creeping up all my life - 24FPS was
> once considered good enough for movie cameras.

Possibly, but probably not. Thomas Edison believed 48 FPS was minimum
quality projection. Is that during your life? Film was recorded at 24
FPS, yes, but projected so that each frame was shown two or three
times, 48 to 72 FPS.

At around 16 FPS the motion stops looking jerky, but there's still a
visible flicker and some eyestrain. Faster playback rates (with
duplicated frames) removes the flicker, but depending on the duplication
method can introduce other artifacts. 24FPS source shown on a
television, for example.

Televisions used AC frequency as a reference, so preferred 50 FPS in
50Hz parts of the world and 60 FPS in 60 Hz areas for projection and
half that for recording. Stuff recorded at other frame rates get extra
frame duplication to keep pace.

25FPS source     ABCDEFGHIJKLMNOPQRSTUVWXY
yeilds by simple doubling:
50FPS display    AABBCCDDEEFFGGHHIIJJKKLLMMNNOOPPQQRRSSTTUUVVWWXXYY

24FPS source     ABCDEFGHIJKLMNOPQRSTUVWX
yeilds by mostly doubling but also padding:
50FPS display    AAAABBCCDDEEFFGGHHIIJJKKLLMMNNOOPPQQRRSSTTUUVVWWXX

Theoretically you could do something like:
                 AAABBCCDDEEFFGGHHIIJJKKLLMMMNNOOPPQQRRSSTTUUVVWWXX
but I think TV signal pipeline is designed around 25 FPS input.

24FPS to 60FPS works similarly, but has more doubled doubles.

As technology has improved, so have standards, though. Artifacts of
a slower displays were previously tolerated, but now a effort is made
to avoid those problems. Now you can more easily accomodate that
AAABBCCDDEEFFGGHHIIJJKKLLMMMNNOOPPQQRRSSTTUUVVWWXX version, for example.

Totally as an aside:

One interesting trick I've seen done is mixing "frame" rates to make
things look jerky. In the _Lego Movie_ the camera and backgrounds
update at 24FPS, but the characters in the foreground update at 12FPS.
It gives the film a much more hand animated look.

I've got a slowed down sample from a since removed Youtube clip that I
made in 2014:

https://qaz.wtf/C/lego-sample.gif

Note that the character spinning in the background on the left animates
every frame, while the walking hero front and center animates every
other frame.

Elijah
------
severely compressed the colors in the gif to get the file size down

--- SoupGate-Win32 v1.05